Research on Aerodynamic Drag Reduction of EMU Tail Car Bogie on Combined Suction and Blowing

Research on Aerodynamic Drag Reduction of EMU Tail Car Bogie on Combined Suction and Blowing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Research on Aerodynamic Drag Reduction of EMU Tail Car Bogie on Combined Suction and Blowing Hongjiang Cui, Huaiyu Tang, Ying Guan, Di Wu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3875082/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The flow field structure in the bogie region has an important impact on the aerodynamic drag of the EMU. In order to meet the lower aerodynamic drag requirements for further speed increases of EMU trains, this paper adopts numerical simulation method to study the active control drag reduction technology of suction and blowing air combined with bogie. The results indicate that the setting of suction and blowing air holes at the front and rear end plates of the tail bogie has only a drag reduction effect on the pressure drag in the aerodynamic drag of the bogie and tail car. With the change of suction and blowing air speeds, the drag reduction rate of the tail car reaches the optimal value of 3.82% at 0.05U, and the drag reduction rate of the bogie reaches the optimal value of 4.61% at 0.2U. The study on the combined suction and blowing air drag reduction method of the bogie has important significance in breaking through the limitations of traditional bogie aerodynamic drag reduction. Physical sciences/Engineering Physical sciences/Engineering/Mechanical engineering EMU bogie combined suction and blowing aerodynamic drag reduction flow field structure flow control Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Introduction The aerodynamic characteristics of high Reynolds numbers and complex flow patterns at the bottom of the EMU's exterior structure result from its complex shape. Increasing the operating speed of EMUs remains a key goal for the development of rail transit. Additionally, components with complex shapes, such as bogies, windshields, and pantographs, are prone to flow disturbances and separations, leading to significant aerodynamic drag 1–5 . Among them, the aerodynamic drag in the bogie area is a significant contributor to the total drag on high-speed EMUs. When the train operates at a speed of 350 km/h, the aerodynamic drag in the bogie area accounts for 27.4% of the total drag 6–9 . Therefore, studying how to reduce the aerodynamic drag in the bogie area is of great significance for the design of aerodynamic drag reduction for high-speed trains. To meet the lower aerodynamic drag requirements for further speed increases of EMU trains, we apply flow control drag reduction technology to the bogie area of EMUs, drawing inspiration from fields such as aerospace, fluid machinery, and shipbuilding. Based on energy consumption and control loop methods, flow control technology can be divided into active and passive control 10 . Passive control technology does not require additional energy and can only control specific states, with control parameters that cannot be adjusted in real time. Active flow control technology requires extra energy and can adjust excitation parameters to control the flow field as needed, making it more efficient 11–12 . As an active flow control technology, suction and blowing combined flow control technology enhances the ability of the fluid near the bogie wall to resist pressure gradients by removing low-momentum fluid or introducing high-momentum fluid. This alters the surface pressure distribution in the bogie area to achieve the effect of inhibiting flow separation and increasing lift while reducing drag 13–15 . Suction/blowing air flow control technology can improve the aerodynamic performance of wind turbine airfoils by adjusting and controlling the flow field in real time 16–22 . Luo Shuai et al. 23–24 proposed a suction and blowing air combined jet drag reduction method. By optimizing the geometric and flow parameters such as the distance from the suction slot to the leading edge, the distance from the blowing air slot to the trailing edge, and the jet momentum coefficient, they studied the effects of different attack angles on the lift-drag coefficient, flow field structure, pressure coefficient, and boundary layer velocity of airfoils. The active flow control technology of suction/blowing air can effectively regulate the flow field by placing holes or slots for suction/blowing air at the separation points of the boundary layer on the head and tail cars or on the body of the high-speed train, thereby improving its aerodynamic performance 25–32 . Chen Z W et al. 33 proposed a blowing air scheme for the head and tail cars of high-speed trains. They analyzed the effects of blowing air velocity on a train aerodynamic drag and wake velocity. When the blowing air velocity is 0.1 times the train velocity, the decreases in aerodynamic drag for the head, middle, tail, and entire train are 9.18%, 12.77%, 10.90%, and 10.78%, respectively, with large proportion decreases. Cui H et al. 34 proposed an active flow control drag reduction method that combines suction and blowing air for EMU trains. By suctioning and blowing air at the tail of EMU trains, they can reduce pressure drag on the tail car. As the mass flow rate of suctioning and blowing air increases, the drag reduction rate gradually improves but the growth rate decreases. Under the same mass flow rate, the closer the suctioning and blowing air ports are to the upper and lower edges of the side windshields, the smaller the pressure drag on the tail car becomes. Additionally, more suctioning and blowing air ports lead to better drag reduction effects. In this article, suction and blowing air holes are set at the front and rear end plates of the EMU bogies. By using internal flow channels, gas transfer is achieved, which is an effective active flow control technology that can be used to reduce the aerodynamic drag of EMUs. The purpose of this article is to investigate the effects of different suction and blowing air velocities on the drag reduction effects of bogies and tail cars, analyze their influencing mechanisms and drag reduction characteristics, and provide references for the drag reduction design of the next generation of high-speed EMUs. Numerical Simulation Method Simulation Model This paper uses a certain type of CRH high-speed EMU as a prototype to establish a 1:1 scale aerodynamic model of the EMU, as shown in Fig. 1 . It consists of three groups, composed of the head car, middle car, and tail car. Due to the complexity of the computational model, in order to reduce the difficulty of grid division, the computational model used in this paper has been partially simplified based on the real model, omitting details such as the pantograph components on the roof, air conditioning equipment, and doors and windows on the body, and replacing them with curved surfaces during modeling. Considering the complexity of the structure of the bogie and the purpose of this article is to explore the effect of installing a suction and blowing device in the area of the bogie of the trailer car, we have ignored the influence of other bogies on the results as much as possible. Therefore, the computational model only retains the bogie of the trailer car and removes local details that have a small impact on the flow field on the bogie. The height H of the EMU is selected as the characteristic length, H = 3.89m. The semi-body model has a length of L = 20H, a width of W = 3.26m, the maximum cross-sectional area of A = 10.8m 2 . In the lower edges of the front and rear end plates of the tail bogie, suction and blowing air holes are set. The number of air holes at the front and rear end plates is the same (3 rows × 15), with a total of 45 suction and blowing air holes in each region. The diameter of the air holes is 80mm, and the pitch between adjacent air holes in each row is 120mm. As shown in Fig. 1 (d). In addition, in order to make the entire suction and blowing process independent of external air sources and enhance the flexibility and controllability of the entire suction and blowing system, a compressor device is installed in the flow channel between the suction and blowing air holes on both sides of the bogie end plates to achieve gas transfer, as shown in Fig. 2. In order to simplify calculations, the internal flow path can be omitted in the optimized simulation model, and both the suction hole and the blowing hole are set as velocity inlets, the speed of the inhaled gas is equal to the speed of the blown-out gas, and the rest of the boundary conditions are consistent with the original vehicle model. Calculation domain and boundary conditions To avoid interference with the surrounding environment of the EMU, a reasonable and limited size of the computational domain is selected. The geometric dimensions and boundary conditions are shown in Fig. 3 . The EMU is positioned in the middle-front of the computational domain, with the nose tip of the train located 15H away from the entrance of the computational domain to ensure that the turbulent flow field is fully developed from the entrance. The nose tip of the tail car is located 40H away from the exit of the computational domain to prevent the shedding of wake vortices from being affected by the exit. The width of the computational domain is 24H, and the height is 15H. In this article, the three-dimensional compressible Navier-Stokes equations are used to describe the flow field of the EMU. Since the general velocity inlet is not suitable for flow fields of compressible fluids, the inlet condition is set as a pressure far-field boundary, and the outlet condition is set as a pressure outlet boundary. The literature analysis shows that the surface roughness of the EMU has a small impact on the aerodynamic drag 35–36 .Therefore, this paper does not consider setting the roughness size of the surface of the EMU model, and the body is set as a no-slip fixed wall. Meshing The computational grid is generated using the ANSYS Fluent meshing module, which consists of a mix of hexahedral and polyhedral cells to ensure the transition of the body grid around the EMU. The grid is refined in key areas such as the streamlined tail and bogie to improve computational accuracy and reliability. The surface of the EMU uses a prismatic layer grid with a growth rate of 1.2 to simulate the flow within the boundary layer near the wall of the EMU. The height of the first layer of the grid is 0.8mm, which can better capture the flow details within the boundary layer, while ensuring computational efficiency and accuracy. As shown in Fig. 4 . Numerical Method This paper conducts numerical simulation research based on the Realizable k-epsilon two-equation turbulence model. The Realizable k-epsilon model can accurately predict the diffusion effect of planar and circular jets, and it can also provide accurate results for complex flows such as rotating flow, boundary layer flow with strong adverse pressure gradient, flow separation, and secondary flow 37 . In the calculation, the incoming wind speed U = 111.11m/s (400km/h), the Mach number of the flow field around the train is greater than 0.3, and the environment is compressible air with strong turbulence, so the Coupled algorithm is chosen, the numerical simulation selects the Realizable k-epsilon turbulence model, and the wall function uses the enhanced wall function method. Among them, the gradient discretization uses the cell-based Green-Gauss method, both the convection term and the dissipation term use the second-order upwind scheme for calculation; the residual terms are all set to 10 − 5 to ensure that the monitored physical quantities are stable. Mesh Independence Verification Due to the significant impact of grid density on numerical calculation results, in order to ensure the accuracy of calculations, while considering the economical and reasonable use of computational resources, improving computational efficiency and saving costs, this paper has carried out grid independence verification for three different grid densities: coarse grid, medium grid, and fine grid. Table 1 Comparison of three density grids and average y + on the vehicle body surface. Mesh density Mesh number (10 6 ) Number of encrypted areas Smallest mesh size on the surface of the vehicle body Smallest mesh size on the surface of the bogie Mean y + on the surface of the vehicle body coarse 14.30 3 15mm 5mm 98 medium 22.18 4 15mm 5mm fine 44.22 4 10mm 5mm For ease of analysis, the calculation results of aerodynamic resistance are characterized by the resistance coefficient and represented by the dimensionless coefficient C d , and its relationship is as follows: Where F d is the drag of the EMU in operation, ρ is air density, U is the speed of the EMU, and S is the cross-sectional area of the EMU. The drag reduction rate of the EMU is defined as α , the expression is as follows: Where α represents the drag reduction rate, F d(n−S−B) represents aerodynamic drag of EMU without blowing and suction, F d(S−B) represents aerodynamic drag of EMU under a certain suction-blowing condition. The comparison of the aerodynamic drag coefficients of the EMU at different grid densities is shown in Fig. 5. According to Fig. 5, the aerodynamic drag coefficients of various parts of the EMU are relatively consistent, and the calculation results of the medium grid and the coarse grid differ by only 1.73%. The difference in calculation results between the fine grid and the medium grid is also relatively small, and the error rate of the whole vehicle is only 0.518%. This indicates that after reaching the medium grid density, as the number of grids increases, the change in numerical calculation results is not significant. Therefore, the medium grid density can meet the requirements of grid independence and is suitable for numerical calculation research. Algorithm Verification In order to verify the correctness of the numerical calculation method, the modeling method and medium grid strategy described in this article are used. The model used in the wind tunnel test is a 1/8 scale model of the improved CRH380A EMU, which is divided into 3 car groups, including the head car, middle car, and tail car; the length of the model is 9.75m.This experiment was conducted at the China Aerodynamics Research and Development Center in Sichuan, with a free stream speed of 60m/s 38 , as shown in Fig. 6. Table 2 Shows the comparison of the aerodynamic drag coefficient of the whole vehicle between numerical simulation and wind tunnel test. Research method C d Error Numerical simulation 0.3183 2.39% Wind tunnel test 0.3261 — As can be seen from Table 2 and Fig. 7 , the aerodynamic resistance coefficient of the numerical simulation using the medium grid is not much different from the aerodynamic resistance coefficient of the wind tunnel test, and the error of the whole vehicle is within 3%, which meets the accuracy requirements of actual engineering. By comparing with the wind tunnel test, it is verified that the numerical calculation method and grid strategy used in this paper are correct and reliable. Numerical results Aerodynamic force In order to study the impact of suction and blowing air speed on aerodynamic resistance, the aerodynamic resistance coefficients of the whole vehicle and each car are analyzed under different suction and blowing air speed conditions (0, 0.05U, 0.1U, 0.15U, 0.2U, 0.3U) in Table 3 , where the air holes at the front-end plate of the EMU bogie are inhaled and the air holes at the rear end plate of the EMU bogie are blown. The resistance experienced by the EMU bogie is analyzed under different suction and blowing air speed conditions in Table 4. Table 3 Shows the resistance coefficients at different speeds for each position of the EMU. Position The aerodynamic resistance coefficient at different suction and blowing air speeds 0 0.05U 0.1U 0.15U 0.2U 0.3U Whole vehicle 0.2050 0.2027 0.2035 0.2047 0.2061 0.2084 Head car 0.0621 0.0621 0.0621 0.0621 0.0621 0.0621 Middle car 0.0432 0.0432 0.0432 0.0432 0.0432 0.0432 Tail car 0.0974 0.0951 0.0960 0.0971 0.0985 0.1008 Windshield 0.0023 0.0023 0.0023 0.0023 0.0023 0.0023 It can be found from Table 3 that setting up suction and blowing air holes at the front and rear end plates of the EMU bogie mainly has a greater impact on the aerodynamic resistance of the tail car, while it has a smaller impact on the aerodynamic resistance of the head car, middle car, and windshield area. Table 4 Shows the change in resistance of the EMU tail car bogie at different speeds. Suction and blowing air speed Resistance/N Drag reduction rate (%) 0 751.41 — 0.05U 750.91 0.067 0.1U 740.36 1.471 0.15U 725.80 3.409 0.2U 716.80 4.606 0.3U 746.45 0.661 According to Fig. 8, it can be seen from the change in the vehicle resistance coefficient that the suction and blowing air speed of 0.05U has the best aerodynamic drag reduction effect, with a drag reduction rate of about 1.123%. As the suction and blowing air speed increases, the resistance coefficient rises, the drag reduction effect weakens, and when the suction and blowing air speed exceeds 0.15U, it shows an increase in resistance. From the perspective of each car, the change in the resistance coefficient of the tail car is similar to that of the whole vehicle, and it also has the best aerodynamic drag reduction effect at a suction and blowing air speed of 0.05U. As the suction and blowing air speed increases, the drag reduction rate of the tail car bogie decreases, and it has the best aerodynamic drag reduction effect at a suction and blowing air speed of 0.2U, with a drag reduction rate of about 4.606%. When the suction and blowing air speed exceeds 0.2U, it also shows an increase in resistance. To further analyze the impact of different suction and blowing air speeds on the aerodynamic resistance of the EMU, the changes in frictional resistance and differential pressure resistance are compared separately, and their drag reduction contribution rates are shown in Fig. 9. According to Fig. 9, the differential pressure resistance and frictional resistance experienced by the EMU were analyzed. The results show that setting up suction and blowing air at the bogie mainly reduces the differential pressure resistance, while it does not have a significant drag reduction effect on the frictional resistance. Within the range of 0 ~ 0.05U for the suction and blowing air speed, the differential pressure drags reduction rate of the tail car and the whole vehicle gradually increases with the increase in the suction and blowing air speed, and reaches the best drag reduction effect at 0.05U. However, within the range of 0 ~ 0.2U for the suction and blowing air speed, the differential pressure drag reduction rate of the bogie gradually increases with the increase in the suction and blowing air speed, and reaches the maximum differential pressure drag reduction rate at 0.2U. This is similar to the change rule of the aerodynamic drag reduction rate. When the suction and blowing air speed is 0.1U, the differential pressure resistance of the bogie, tail car, and the whole vehicle are all reduced, and they are all in a relatively good drag reduction range. Pressure distribution Since setting up suction and blowing air at the bogie mainly reduces the differential pressure resistance, to explore the reason for the change in differential pressure resistance, Fig. 10 shows the change in pressure coefficient at different suction and blowing air speeds. When the suction and blowing air speed is in the range of 0 ~ 0.1U, the negative pressure area caused by the front end plate of the bogie inhaling has a small impact, and the blowing of the rear end plate of the bogie reduces the high pressure area there, thereby making the pressure distribution more uniform. Therefore, in the range of 0 ~ 0.1U for suction and blowing air, the differential pressure resistance of the bogie, tail car, and the whole vehicle are all reduced. As the suction and blowing air speed increases, the pressure distribution becomes more uneven, and the pressure gradient also increases accordingly. Flow field characteristics In order to observe the trajectory of the suction and blowing airflow, a velocity streamline diagram of the symmetrical cross section in the center of the bogie area was used, as shown in Fig. 11 . It can be clearly seen from the diagram that there is airflow flowing in from the blowing hole on the rear end plate and flowing out from the suction hole on the front end plate, which causes the vortex structure in the bogie area to transition from small scale to large scale, thereby reducing the aerodynamic drag of the bogie. However, as the suction and blowing speed increases, the vortex structure gradually affects the bogie, and when the suction and blowing speed exceeds 0.2U, the suction and blowing device on the bogie will change from reducing drag to increasing drag. In academic terms. This text aims to explore the effect of setting up suction and blowing devices in the area of the tail car bogie, so the relationship between the change in vorticity in the near wake region and the aerodynamic drag of the tail car is particularly crucial 39–40 . A vertical section located 42.5mm in front of the nose of the tail car was selected, and X Vorticity was extracted from it. As shown in Fig. 12 , it can be observed from the figure that the bottom vorticity exhibits a significant dissipation with the increase in suction and blowing air speed, and its transverse width is also gradually decreasing. According to the study by Oh et al. 41 , when the transverse width of the tail car vortex changes, the aerodynamic drag of the tail car will also change accordingly. Therefore, the suction and blowing devices set up at the bogie can alter the aerodynamic drag of the tail car. The suction and blowing devices set up at the bogie can alter the aerodynamic drag of the tail car. Conclusion and prospect In this article, a computational method based on the three-dimensional steady-state Realizable k-epsilon turbulence model is used to investigate the active control drag reduction technology combining suction and blowing air for EMU bogies. The aerodynamic drag reduction characteristics of a simplified EMU model at 400 km/h are analyzed. By setting suction and blowing air holes, the effects of different suction and blowing air velocities on aerodynamic drag, flow characteristics in the bogie area, and surface pressure distribution on the underbody are explored. The conclusions and prospects are summarized as follows: Inhaling at the lower edge of the front end plate of the bogie and blowing at the lower edge of the rear end plate can significantly reduce the pressure differential resistance inside the bogie cabin. Suction can remove low momentum fluid, and blowing can improve the flow field structure inside the cabin. Suitable low suction and blowing air speed have a significant aerodynamic drag reduction effect on the bogie and tail car, but too high suction and blowing air speed will reduce the drag reduction efficiency and increase energy consumption. Through the study of different suction and blowing air speeds, the drag reduction rate of the trailing vehicle reaches the best at 0.05U, with a pressure difference drag reduction rate of 3.82%. At 0.2U, the drag reduction rate of the bogie reaches the best, with an aerodynamic drag reduction rate of 4.61%. At 0.1U, good drag reduction effects can be achieved for both the bogie and the trailing vehicle. Although the simplification of the calculation model results in a smaller overall total aerodynamic resistance calculation result and a deviation in the drag reduction rate, the drag reduction method of combining suction and blowing air at the tail car bogie of the EMU can still effectively reduce the pressure differential resistance of the bogie and tail car. Subsequent research can apply the same drag reduction method to the bogie areas of other cars to further reduce the pressure differential resistance and aerodynamic resistance of the whole vehicle. Considering that different models of EMUs have different structures and performance characteristics, when setting up suction and blowing air holes, the overall aerodynamic performance and mechanical performance of the EMU need to be considered, and specific problems need to be analyzed specifically. Declarations Acknowledgements This research was funded by the Science Researching Plans of Liaoning Provincial Education Department under Grant No. LJKFZ20220203. We would like to thank the Liaoning Provincial Department of Education for providing financial support for this research. Meanwhile, we would like to thank Dalian Jiaotong University for providing the thermal engineering laboratory for this research and all the laboratory teachers for their hard work. Author Contribution H. and H. wrote the main manuscript text and H. prepared figures 1-12. All authors reviewed the manuscript. All authors contributed equally. Competing interests The authors declare no competing interests. Data availability The datasets generated and/or analysed during the current study are not publicly available due [REASON WHY DATA ARE NOT PUBLIC] but are available from the corresponding author on reasonable request. References Anderson, J. D. Fundamentals of Aerodynamics (in SI Units). (2011). Tian Hongqi. 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Effects of bogies on the wake flow of a high-speed train. Applied Sciences 9.4 (2019). Onorato, M., A. F. Costelli, and A. Garrone. Drag measurement through wake analysis. No. 840302. SAE Technical Paper , (1984). Baker, C. J. A review of train aerodynamics Part 2–Applications. The Aeronautical Journal 118.1202,345-382(2014) Oh, Sahuck, et al. Finding the optimal shape of the leading-and-trailing car of a high-speed train using design-by-morphing. Computational Mechanics 62,23-45 (2018). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3875082","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":270289686,"identity":"34459a25-9bac-4dbd-b3fa-406a44782a42","order_by":0,"name":"Hongjiang Cui","email":"","orcid":"","institution":"Dalian Jiaotong University","correspondingAuthor":false,"prefix":"","firstName":"Hongjiang","middleName":"","lastName":"Cui","suffix":""},{"id":270289687,"identity":"9c4ea77c-777e-45ae-a6b4-1a446376535e","order_by":1,"name":"Huaiyu Tang","email":"","orcid":"","institution":"Dalian Jiaotong University","correspondingAuthor":false,"prefix":"","firstName":"Huaiyu","middleName":"","lastName":"Tang","suffix":""},{"id":270289688,"identity":"347fd856-8599-4ab2-bfef-52857c99b3af","order_by":2,"name":"Ying Guan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABD0lEQVRIie2NsUrDUBSGT7xwuhya9YYOfYUrAaUoyWs4NlywSxVBCA4iNwSaxQeI0OdwTrnQLtI5oIsImTI4lQwONlHHWzsK3m87h//jA7BY/iwCwGVO1rwjdjffS/GyVHk5It9Taa2nlRoQwu/K8ExWb3T1EqgyUv5p3L8TBVs8EwSXJuWwPD/2SVQyySMlp2vkokB5QiCvjUo+PhqQ0JLxSOmLWavQ9gNFpIzKZNMpyKMkHXWKu9mpDPm0qwREi5Q5XxXcqQiqY28u9Jj3kplzv0bvQaM/mgtprmSTR15/6DDUvQqaeOn2V+lrWd8E5koBcEAAP4MlAOv+hn1b2U6dBiD8vm/NU4vFYvm3fAK96FQpxBshvwAAAABJRU5ErkJggg==","orcid":"","institution":"Dalian Jiaotong University","correspondingAuthor":true,"prefix":"","firstName":"Ying","middleName":"","lastName":"Guan","suffix":""},{"id":270289689,"identity":"e2d2198c-888b-471d-8de7-269a36c483d8","order_by":3,"name":"Di Wu","email":"","orcid":"","institution":"Dalian Jiaotong University","correspondingAuthor":false,"prefix":"","firstName":"Di","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2024-01-18 07:46:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3875082/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3875082/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":50556625,"identity":"625ad15c-e103-4872-87aa-5ff8e949cd90","added_by":"auto","created_at":"2024-02-02 12:48:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":158699,"visible":true,"origin":"","legend":"\u003cp\u003eSimplified model of EMU: (a) Simplified body model of multiple units; (b) Bogie model ; (c) Inhalation and blowing of the vent position; (d) Inhalation and blowing hole size.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/3cbe29dfaf6a5b9f85e9d78f.png"},{"id":50556172,"identity":"064eb9e5-f4ed-4a1e-9b61-d4c975e252ac","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":104997,"visible":true,"origin":"","legend":"\u003cp\u003eIs a schematic diagram of the internal flow path.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/0c32290ed395a8480481530b.png"},{"id":50556173,"identity":"52b282ba-6258-4dd2-9701-4a32d16a61a1","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":74662,"visible":true,"origin":"","legend":"\u003cp\u003eSimulation Computational Domain and Boundary Conditions.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/e59d674f1627ad8a2298c9ad.png"},{"id":50556627,"identity":"8fa50c2d-00db-44f9-b61f-f6b81c6d9fd8","added_by":"auto","created_at":"2024-02-02 12:48:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":591140,"visible":true,"origin":"","legend":"\u003cp\u003eMesh for computation:(a) The medium mesh distributions on the tail car; (b) Calculate the cross-section of the vertical axis center of the domain; (c) Mesh of the suction and blowing apertures.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/f5cf13f48fad6395b7e0f891.png"},{"id":50556628,"identity":"271b947d-1e43-43df-9035-800e4064b440","added_by":"auto","created_at":"2024-02-02 12:48:11","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":176713,"visible":true,"origin":"","legend":"\u003cp\u003eCompares the aerodynamic drag coefficient of the EMU at different grid densities.\u003c/p\u003e","description":"","filename":"image5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/41ee569d060a5f6291bc4cdf.jpg"},{"id":50556178,"identity":"830be594-6a7e-44bc-a6b8-ee62944b4bd4","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":299884,"visible":true,"origin":"","legend":"\u003cp\u003eShows the wind tunnel test device and the numerical simulation calculation domain.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/f2d16a76d87ea485fe63afd7.png"},{"id":50556626,"identity":"9e4c4432-a82f-483f-9fd6-1cb28113bc99","added_by":"auto","created_at":"2024-02-02 12:48:11","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":192814,"visible":true,"origin":"","legend":"\u003cp\u003eCompares the aerodynamic drag coefficient of numerical simulation with wind tunnel test.\u003c/p\u003e","description":"","filename":"image7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/154b21606b15d4a178f7e3c1.jpg"},{"id":50556175,"identity":"23321920-92e0-4435-b285-8ce8711bfaa8","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":108801,"visible":true,"origin":"","legend":"\u003cp\u003eShows the aerodynamic drag reduction rate at different suction and blowing air speeds.\u003c/p\u003e","description":"","filename":"image8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/8f438e2dc9639fab8a8ee74f.jpg"},{"id":50556177,"identity":"77ab5bab-df13-4f6b-b596-6a5fed55b171","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":156946,"visible":true,"origin":"","legend":"\u003cp\u003eShows the differential pressure and frictional drag reduction rates at different suction and blowing air speeds.\u003c/p\u003e","description":"","filename":"image9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/7c60c224b89e506aa9aea7d3.jpg"},{"id":50556629,"identity":"e287b22b-8425-4e8d-b8e4-03602e377c7d","added_by":"auto","created_at":"2024-02-02 12:48:11","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":322713,"visible":true,"origin":"","legend":"\u003cp\u003eThe pressure coefficient cloud diagram with various suction and blowing air speeds.: (a) V=0; (b) V=0.05U; (c) V=0.1U; (d) V=0.15U; (e) V=0.2U; (f) V=0.3U.\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/74b6f4112aea2e208aa26a2b.png"},{"id":50556181,"identity":"6ecbe58c-cfa7-4425-82d8-d02a6e226160","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":588405,"visible":true,"origin":"","legend":"\u003cp\u003eThe velocity streamline diagram of the symmetrical cross section (y=0) at the bogie area with different suction and blowing air speeds.: (a) V=0; (b) V=0.05U; (c) V=0.1U; (d) V=0.15U; (e) V=0.2U; (f) V=0.3U.\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/709f53fb57244e9fb0d98bc5.png"},{"id":50556182,"identity":"4076b8d6-4b52-44c4-8824-d6c9da3d6631","added_by":"auto","created_at":"2024-02-02 12:40:11","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":216062,"visible":true,"origin":"","legend":"\u003cp\u003eThe X Vorticity cloud diagram with various suction and blowing air speeds.: (a) V=0; (b) V=0.05U; (c) V=0.1U; (d) V=0.15U; (e) V=0.2U; (f) V=0.3U.\u003c/p\u003e","description":"","filename":"image12.png","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/573ecb7efb6c3e670a8559fb.png"},{"id":54491990,"identity":"b9146ada-bdd2-48e8-872c-3e8e8694f4a7","added_by":"auto","created_at":"2024-04-11 10:38:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3062105,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3875082/v1/6dddf1fc-359d-410f-bcff-4d68ad9d232d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Research on Aerodynamic Drag Reduction of EMU Tail Car Bogie on Combined Suction and Blowing","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe aerodynamic characteristics of high Reynolds numbers and complex flow patterns at the bottom of the EMU's exterior structure result from its complex shape. Increasing the operating speed of EMUs remains a key goal for the development of rail transit. Additionally, components with complex shapes, such as bogies, windshields, and pantographs, are prone to flow disturbances and separations, leading to significant aerodynamic drag \u003csup\u003e1\u0026ndash;5\u003c/sup\u003e. Among them, the aerodynamic drag in the bogie area is a significant contributor to the total drag on high-speed EMUs. When the train operates at a speed of 350 km/h, the aerodynamic drag in the bogie area accounts for 27.4% of the total drag \u003csup\u003e6\u0026ndash;9\u003c/sup\u003e. Therefore, studying how to reduce the aerodynamic drag in the bogie area is of great significance for the design of aerodynamic drag reduction for high-speed trains. To meet the lower aerodynamic drag requirements for further speed increases of EMU trains, we apply flow control drag reduction technology to the bogie area of EMUs, drawing inspiration from fields such as aerospace, fluid machinery, and shipbuilding. Based on energy consumption and control loop methods, flow control technology can be divided into active and passive control \u003csup\u003e10\u003c/sup\u003e. Passive control technology does not require additional energy and can only control specific states, with control parameters that cannot be adjusted in real time. Active flow control technology requires extra energy and can adjust excitation parameters to control the flow field as needed, making it more efficient \u003csup\u003e11\u0026ndash;12\u003c/sup\u003e. As an active flow control technology, suction and blowing combined flow control technology enhances the ability of the fluid near the bogie wall to resist pressure gradients by removing low-momentum fluid or introducing high-momentum fluid. This alters the surface pressure distribution in the bogie area to achieve the effect of inhibiting flow separation and increasing lift while reducing drag \u003csup\u003e13\u0026ndash;15\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eSuction/blowing air flow control technology can improve the aerodynamic performance of wind turbine airfoils by adjusting and controlling the flow field in real time \u003csup\u003e16\u0026ndash;22\u003c/sup\u003e. Luo Shuai et al. \u003csup\u003e23\u0026ndash;24\u003c/sup\u003eproposed a suction and blowing air combined jet drag reduction method. By optimizing the geometric and flow parameters such as the distance from the suction slot to the leading edge, the distance from the blowing air slot to the trailing edge, and the jet momentum coefficient, they studied the effects of different attack angles on the lift-drag coefficient, flow field structure, pressure coefficient, and boundary layer velocity of airfoils. The active flow control technology of suction/blowing air can effectively regulate the flow field by placing holes or slots for suction/blowing air at the separation points of the boundary layer on the head and tail cars or on the body of the high-speed train, thereby improving its aerodynamic performance \u003csup\u003e25\u0026ndash;32\u003c/sup\u003e. Chen Z W et al. \u003csup\u003e33\u003c/sup\u003e proposed a blowing air scheme for the head and tail cars of high-speed trains. They analyzed the effects of blowing air velocity on a train aerodynamic drag and wake velocity. When the blowing air velocity is 0.1 times the train velocity, the decreases in aerodynamic drag for the head, middle, tail, and entire train are 9.18%, 12.77%, 10.90%, and 10.78%, respectively, with large proportion decreases. Cui H et al. \u003csup\u003e34\u003c/sup\u003e proposed an active flow control drag reduction method that combines suction and blowing air for EMU trains. By suctioning and blowing air at the tail of EMU trains, they can reduce pressure drag on the tail car. As the mass flow rate of suctioning and blowing air increases, the drag reduction rate gradually improves but the growth rate decreases. Under the same mass flow rate, the closer the suctioning and blowing air ports are to the upper and lower edges of the side windshields, the smaller the pressure drag on the tail car becomes. Additionally, more suctioning and blowing air ports lead to better drag reduction effects.\u003c/p\u003e\n\u003cp\u003eIn this article, suction and blowing air holes are set at the front and rear end plates of the EMU bogies. By using internal flow channels, gas transfer is achieved, which is an effective active flow control technology that can be used to reduce the aerodynamic drag of EMUs. The purpose of this article is to investigate the effects of different suction and blowing air velocities on the drag reduction effects of bogies and tail cars, analyze their influencing mechanisms and drag reduction characteristics, and provide references for the drag reduction design of the next generation of high-speed EMUs.\u003c/p\u003e"},{"header":"Numerical Simulation Method","content":"\u003cp\u003eSimulation Model\u003c/p\u003e\n\u003cp\u003eThis paper uses a certain type of CRH high-speed EMU as a prototype to establish a 1:1 scale aerodynamic model of the EMU, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. It consists of three groups, composed of the head car, middle car, and tail car. Due to the complexity of the computational model, in order to reduce the difficulty of grid division, the computational model used in this paper has been partially simplified based on the real model, omitting details such as the pantograph components on the roof, air conditioning equipment, and doors and windows on the body, and replacing them with curved surfaces during modeling. Considering the complexity of the structure of the bogie and the purpose of this article is to explore the effect of installing a suction and blowing device in the area of the bogie of the trailer car, we have ignored the influence of other bogies on the results as much as possible. Therefore, the computational model only retains the bogie of the trailer car and removes local details that have a small impact on the flow field on the bogie. The height H of the EMU is selected as the characteristic length, \u003cem\u003eH\u003c/em\u003e = 3.89m. The semi-body model has a length of \u003cem\u003eL\u003c/em\u003e = 20H, a width of \u003cem\u003eW\u003c/em\u003e = 3.26m, the maximum cross-sectional area of \u003cem\u003eA\u003c/em\u003e = 10.8m\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eIn the lower edges of the front and rear end plates of the tail bogie, suction and blowing air holes are set. The number of air holes at the front and rear end plates is the same (3 rows × 15), with a total of 45 suction and blowing air holes in each region. The diameter of the air holes is 80mm, and the pitch between adjacent air holes in each row is 120mm. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(d).\u003c/p\u003e\n\u003cp\u003eIn addition, in order to make the entire suction and blowing process independent of external air sources and enhance the flexibility and controllability of the entire suction and blowing system, a compressor device is installed in the flow channel between the suction and blowing air holes on both sides of the bogie end plates to achieve gas transfer, as shown in Fig.\u0026nbsp;2.\u003c/p\u003e\n\u003cp\u003eIn order to simplify calculations, the internal flow path can be omitted in the optimized simulation model, and both the suction hole and the blowing hole are set as velocity inlets, the speed of the inhaled gas is equal to the speed of the blown-out gas, and the rest of the boundary conditions are consistent with the original vehicle model.\u003c/p\u003e\n\u003cp\u003eCalculation domain and boundary conditions\u003c/p\u003e\n\u003cp\u003eTo avoid interference with the surrounding environment of the EMU, a reasonable and limited size of the computational domain is selected. The geometric dimensions and boundary conditions are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The EMU is positioned in the middle-front of the computational domain, with the nose tip of the train located 15H away from the entrance of the computational domain to ensure that the turbulent flow field is fully developed from the entrance. The nose tip of the tail car is located 40H away from the exit of the computational domain to prevent the shedding of wake vortices from being affected by the exit. The width of the computational domain is 24H, and the height is 15H. In this article, the three-dimensional compressible Navier-Stokes equations are used to describe the flow field of the EMU. Since the general velocity inlet is not suitable for flow fields of compressible fluids, the inlet condition is set as a pressure far-field boundary, and the outlet condition is set as a pressure outlet boundary. The literature analysis shows that the surface roughness of the EMU has a small impact on the aerodynamic drag\u003csup\u003e35–36\u003c/sup\u003e.Therefore, this paper does not consider setting the roughness size of the surface of the EMU model, and the body is set as a no-slip fixed wall.\u003c/p\u003e\n\u003cp\u003eMeshing\u003c/p\u003e\n\u003cp\u003eThe computational grid is generated using the ANSYS Fluent meshing module, which consists of a mix of hexahedral and polyhedral cells to ensure the transition of the body grid around the EMU. The grid is refined in key areas such as the streamlined tail and bogie to improve computational accuracy and reliability. The surface of the EMU uses a prismatic layer grid with a growth rate of 1.2 to simulate the flow within the boundary layer near the wall of the EMU. The height of the first layer of the grid is 0.8mm, which can better capture the flow details within the boundary layer, while ensuring computational efficiency and accuracy. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eNumerical Method\u003c/p\u003e\n\u003cp\u003eThis paper conducts numerical simulation research based on the Realizable k-epsilon two-equation turbulence model. The Realizable k-epsilon model can accurately predict the diffusion effect of planar and circular jets, and it can also provide accurate results for complex flows such as rotating flow, boundary layer flow with strong adverse pressure gradient, flow separation, and secondary flow\u003csup\u003e37\u003c/sup\u003e. In the calculation, the incoming wind speed U = 111.11m/s (400km/h), the Mach number of the flow field around the train is greater than 0.3, and the environment is compressible air with strong turbulence, so the Coupled algorithm is chosen, the numerical simulation selects the Realizable k-epsilon turbulence model, and the wall function uses the enhanced wall function method. Among them, the gradient discretization uses the cell-based Green-Gauss method, both the convection term and the dissipation term use the second-order upwind scheme for calculation; the residual terms are all set to 10\u003csup\u003e− 5\u003c/sup\u003e to ensure that the monitored physical quantities are stable.\u003c/p\u003e\n\u003cp\u003eMesh Independence Verification\u003c/p\u003e\n\u003cp\u003eDue to the significant impact of grid density on numerical calculation results, in order to ensure the accuracy of calculations, while considering the economical and reasonable use of computational resources, improving computational efficiency and saving costs, this paper has carried out grid independence verification for three different grid densities: coarse grid, medium grid, and fine grid.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComparison of three density grids and average y\u003csup\u003e+\u003c/sup\u003e on the vehicle body surface.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMesh density\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMesh number (10\u003csup\u003e6\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNumber of encrypted areas\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSmallest mesh size on the surface of the vehicle body\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSmallest mesh size on the surface of the bogie\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean y\u003csup\u003e+\u003c/sup\u003e on the surface of the vehicle body\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ecoarse\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"3\" align=\"char\"\u003e\n \u003cp\u003e98\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003emedium\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5mm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003efine\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5mm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eFor ease of analysis, the calculation results of aerodynamic resistance are characterized by the resistance coefficient and represented by the dimensionless coefficient \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ed\u003c/em\u003e\u003c/sub\u003e, and its relationship is as follows:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"426\" height=\"73\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere \u003cem\u003eF\u003c/em\u003e\u003csub\u003e\u003cem\u003ed\u003c/em\u003e\u003c/sub\u003e is the drag of the EMU in operation, \u003cem\u003eρ\u003c/em\u003e is air density, \u003cem\u003eU\u003c/em\u003e is the speed of the EMU, and \u003cem\u003eS\u003c/em\u003e is the cross-sectional area of the EMU.\u003c/p\u003e\n\u003cp\u003eThe drag reduction rate of the EMU is defined as \u003cem\u003eα\u003c/em\u003e, the expression is as follows:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"434\" height=\"70\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eWhere \u003cem\u003eα\u003c/em\u003e represents the drag reduction rate, \u003cem\u003eF\u003c/em\u003e\u003csub\u003e\u003cem\u003ed(n−S−B)\u003c/em\u003e\u003c/sub\u003e represents aerodynamic drag of EMU without blowing and suction, \u003cem\u003eF\u003c/em\u003e\u003csub\u003e\u003cem\u003ed(S−B)\u003c/em\u003e\u003c/sub\u003e represents aerodynamic drag of EMU under a certain suction-blowing condition.\u003c/p\u003e\n\u003cp\u003eThe comparison of the aerodynamic drag coefficients of the EMU at different grid densities is shown in Fig.\u0026nbsp;5.\u003c/p\u003e\n\u003cp\u003eAccording to Fig.\u0026nbsp;5, the aerodynamic drag coefficients of various parts of the EMU are relatively consistent, and the calculation results of the medium grid and the coarse grid differ by only 1.73%. The difference in calculation results between the fine grid and the medium grid is also relatively small, and the error rate of the whole vehicle is only 0.518%. This indicates that after reaching the medium grid density, as the number of grids increases, the change in numerical calculation results is not significant. Therefore, the medium grid density can meet the requirements of grid independence and is suitable for numerical calculation research.\u003c/p\u003e\n\u003cp\u003eAlgorithm Verification\u003c/p\u003e\n\u003cp\u003eIn order to verify the correctness of the numerical calculation method, the modeling method and medium grid strategy described in this article are used. The model used in the wind tunnel test is a 1/8 scale model of the improved CRH380A EMU, which is divided into 3 car groups, including the head car, middle car, and tail car; the length of the model is 9.75m.This experiment was conducted at the China Aerodynamics Research and Development Center in Sichuan, with a free stream speed of 60m/s\u003csup\u003e38\u003c/sup\u003e, as shown in Fig.\u0026nbsp;6.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eShows the comparison of the aerodynamic drag coefficient of the whole vehicle between numerical simulation and wind tunnel test.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eResearch method\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ed\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eError\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNumerical simulation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.3183\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.39%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWind tunnel test\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.3261\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e—\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAs can be seen from Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, the aerodynamic resistance coefficient of the numerical simulation using the medium grid is not much different from the aerodynamic resistance coefficient of the wind tunnel test, and the error of the whole vehicle is within 3%, which meets the accuracy requirements of actual engineering. By comparing with the wind tunnel test, it is verified that the numerical calculation method and grid strategy used in this paper are correct and reliable.\u003c/p\u003e"},{"header":"Numerical results","content":"\u003cp\u003eAerodynamic force\u003c/p\u003e\n\u003cp\u003eIn order to study the impact of suction and blowing air speed on aerodynamic resistance, the aerodynamic resistance coefficients of the whole vehicle and each car are analyzed under different suction and blowing air speed conditions (0, 0.05U, 0.1U, 0.15U, 0.2U, 0.3U) in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, where the air holes at the front-end plate of the EMU bogie are inhaled and the air holes at the rear end plate of the EMU bogie are blown. The resistance experienced by the EMU bogie is analyzed under different suction and blowing air speed conditions in Table\u0026nbsp;4.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eShows the resistance coefficients at different speeds for each position of the EMU.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth rowspan=\"2\" align=\"left\"\u003e\n \u003cp\u003ePosition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth colspan=\"6\" align=\"left\"\u003e\n \u003cp\u003eThe aerodynamic resistance coefficient at different suction and blowing air speeds\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0.05U\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0.1U\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0.15U\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0.2U\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e0.3U\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWhole vehicle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2027\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2035\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2047\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2061\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.2084\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHead car\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0621\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0621\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0621\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0621\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0621\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0621\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMiddle car\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0432\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0432\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTail car\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0974\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0951\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0960\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0971\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0985\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1008\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWindshield\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.0023\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eIt can be found from Table 3 that setting up suction and blowing air holes at the front and rear end plates of the EMU bogie mainly has a greater impact on the aerodynamic resistance of the tail car, while it has a smaller impact on the aerodynamic resistance of the head car, middle car, and windshield area.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cp\u003eTable 4\u003c/p\u003e\n \u003cp\u003eShows the change in resistance of the EMU tail car bogie at different speeds.\u003c/p\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSuction and blowing air speed\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eResistance/N\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDrag reduction rate (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e751.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.05U\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e750.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.067\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1U\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e740.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.471\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.15U\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e725.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.409\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2U\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e716.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.606\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3U\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e746.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.661\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eAccording to Fig.\u0026nbsp;8, it can be seen from the change in the vehicle resistance coefficient that the suction and blowing air speed of 0.05U has the best aerodynamic drag reduction effect, with a drag reduction rate of about 1.123%. As the suction and blowing air speed increases, the resistance coefficient rises, the drag reduction effect weakens, and when the suction and blowing air speed exceeds 0.15U, it shows an increase in resistance. From the perspective of each car, the change in the resistance coefficient of the tail car is similar to that of the whole vehicle, and it also has the best aerodynamic drag reduction effect at a suction and blowing air speed of 0.05U. As the suction and blowing air speed increases, the drag reduction rate of the tail car bogie decreases, and it has the best aerodynamic drag reduction effect at a suction and blowing air speed of 0.2U, with a drag reduction rate of about 4.606%. When the suction and blowing air speed exceeds 0.2U, it also shows an increase in resistance.\u003c/p\u003e\n\u003cp\u003eTo further analyze the impact of different suction and blowing air speeds on the aerodynamic resistance of the EMU, the changes in frictional resistance and differential pressure resistance are compared separately, and their drag reduction contribution rates are shown in Fig.\u0026nbsp;9.\u003c/p\u003e\n\u003cp\u003eAccording to Fig.\u0026nbsp;9, the differential pressure resistance and frictional resistance experienced by the EMU were analyzed. The results show that setting up suction and blowing air at the bogie mainly reduces the differential pressure resistance, while it does not have a significant drag reduction effect on the frictional resistance. Within the range of 0\u0026thinsp;~\u0026thinsp;0.05U for the suction and blowing air speed, the differential pressure drags reduction rate of the tail car and the whole vehicle gradually increases with the increase in the suction and blowing air speed, and reaches the best drag reduction effect at 0.05U. However, within the range of 0\u0026thinsp;~\u0026thinsp;0.2U for the suction and blowing air speed, the differential pressure drag reduction rate of the bogie gradually increases with the increase in the suction and blowing air speed, and reaches the maximum differential pressure drag reduction rate at 0.2U. This is similar to the change rule of the aerodynamic drag reduction rate. When the suction and blowing air speed is 0.1U, the differential pressure resistance of the bogie, tail car, and the whole vehicle are all reduced, and they are all in a relatively good drag reduction range.\u003c/p\u003e\n\u003cp\u003ePressure distribution\u003c/p\u003e\n\u003cp\u003eSince setting up suction and blowing air at the bogie mainly reduces the differential pressure resistance, to explore the reason for the change in differential pressure resistance, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e shows the change in pressure coefficient at different suction and blowing air speeds. When the suction and blowing air speed is in the range of 0\u0026thinsp;~\u0026thinsp;0.1U, the negative pressure area caused by the front end plate of the bogie inhaling has a small impact, and the blowing of the rear end plate of the bogie reduces the high pressure area there, thereby making the pressure distribution more uniform. Therefore, in the range of 0\u0026thinsp;~\u0026thinsp;0.1U for suction and blowing air, the differential pressure resistance of the bogie, tail car, and the whole vehicle are all reduced. As the suction and blowing air speed increases, the pressure distribution becomes more uneven, and the pressure gradient also increases accordingly.\u003c/p\u003e\n\u003cp\u003eFlow field characteristics\u003c/p\u003e\n\u003cp\u003eIn order to observe the trajectory of the suction and blowing airflow, a velocity streamline diagram of the symmetrical cross section in the center of the bogie area was used, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e. It can be clearly seen from the diagram that there is airflow flowing in from the blowing hole on the rear end plate and flowing out from the suction hole on the front end plate, which causes the vortex structure in the bogie area to transition from small scale to large scale, thereby reducing the aerodynamic drag of the bogie. However, as the suction and blowing speed increases, the vortex structure gradually affects the bogie, and when the suction and blowing speed exceeds 0.2U, the suction and blowing device on the bogie will change from reducing drag to increasing drag. In academic terms.\u003c/p\u003e\n\u003cp\u003eThis text aims to explore the effect of setting up suction and blowing devices in the area of the tail car bogie, so the relationship between the change in vorticity in the near wake region and the aerodynamic drag of the tail car is particularly crucial\u003csup\u003e39\u0026ndash;40\u003c/sup\u003e. A vertical section located 42.5mm in front of the nose of the tail car was selected, and X Vorticity was extracted from it. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e, it can be observed from the figure that the bottom vorticity exhibits a significant dissipation with the increase in suction and blowing air speed, and its transverse width is also gradually decreasing. According to the study by Oh et al.\u003csup\u003e41\u003c/sup\u003e, when the transverse width of the tail car vortex changes, the aerodynamic drag of the tail car will also change accordingly. Therefore, the suction and blowing devices set up at the bogie can alter the aerodynamic drag of the tail car. The suction and blowing devices set up at the bogie can alter the aerodynamic drag of the tail car.\u003c/p\u003e"},{"header":"Conclusion and prospect","content":"\u003cp\u003eIn this article, a computational method based on the three-dimensional steady-state Realizable k-epsilon turbulence model is used to investigate the active control drag reduction technology combining suction and blowing air for EMU bogies. The aerodynamic drag reduction characteristics of a simplified EMU model at 400 km/h are analyzed. By setting suction and blowing air holes, the effects of different suction and blowing air velocities on aerodynamic drag, flow characteristics in the bogie area, and surface pressure distribution on the underbody are explored. The conclusions and prospects are summarized as follows:\u003c/p\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cp\u003eInhaling at the lower edge of the front end plate of the bogie and blowing at the lower edge of the rear end plate can significantly reduce the pressure differential resistance inside the bogie cabin. Suction can remove low momentum fluid, and blowing can improve the flow field structure inside the cabin. Suitable low suction and blowing air speed have a significant aerodynamic drag reduction effect on the bogie and tail car, but too high suction and blowing air speed will reduce the drag reduction efficiency and increase energy consumption.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThrough the study of different suction and blowing air speeds, the drag reduction rate of the trailing vehicle reaches the best at 0.05U, with a pressure difference drag reduction rate of 3.82%. At 0.2U, the drag reduction rate of the bogie reaches the best, with an aerodynamic drag reduction rate of 4.61%. At 0.1U, good drag reduction effects can be achieved for both the bogie and the trailing vehicle.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eAlthough the simplification of the calculation model results in a smaller overall total aerodynamic resistance calculation result and a deviation in the drag reduction rate, the drag reduction method of combining suction and blowing air at the tail car bogie of the EMU can still effectively reduce the pressure differential resistance of the bogie and tail car. Subsequent research can apply the same drag reduction method to the bogie areas of other cars to further reduce the pressure differential resistance and aerodynamic resistance of the whole vehicle.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eConsidering that different models of EMUs have different structures and performance characteristics, when setting up suction and blowing air holes, the overall aerodynamic performance and mechanical performance of the EMU need to be considered, and specific problems need to be analyzed specifically.\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThis research was funded by the Science Researching Plans of Liaoning Provincial Education Department under Grant No. LJKFZ20220203. We would like to thank the Liaoning Provincial Department of Education for providing financial support for this research. Meanwhile, we would like to thank Dalian Jiaotong University for providing the thermal engineering laboratory for this research and all the laboratory teachers for their hard work.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eH. and H. wrote the main manuscript text and H. prepared figures 1-12. All authors reviewed the manuscript. All authors contributed equally.\u003c/p\u003e\n\u003ch2\u003eCompeting interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003ch2\u003eData availability\u003c/h2\u003e\n\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available due [REASON WHY DATA ARE NOT PUBLIC] but are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnderson, J. D. Fundamentals of Aerodynamics (in SI Units). (2011).\u003c/li\u003e\n\u003cli\u003eTian Hongqi. 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Finding the optimal shape of the leading-and-trailing car of a high-speed train using design-by-morphing. \u003cem\u003eComputational Mechanics\u003c/em\u003e 62,23-45 (2018).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"EMU, bogie, combined suction and blowing, aerodynamic drag reduction, flow field structure, flow control","lastPublishedDoi":"10.21203/rs.3.rs-3875082/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3875082/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe flow field structure in the bogie region has an important impact on the aerodynamic drag of the EMU. In order to meet the lower aerodynamic drag requirements for further speed increases of EMU trains, this paper adopts numerical simulation method to study the active control drag reduction technology of suction and blowing air combined with bogie. The results indicate that the setting of suction and blowing air holes at the front and rear end plates of the tail bogie has only a drag reduction effect on the pressure drag in the aerodynamic drag of the bogie and tail car. With the change of suction and blowing air speeds, the drag reduction rate of the tail car reaches the optimal value of 3.82% at 0.05U, and the drag reduction rate of the bogie reaches the optimal value of 4.61% at 0.2U. The study on the combined suction and blowing air drag reduction method of the bogie has important significance in breaking through the limitations of traditional bogie aerodynamic drag reduction.\u003c/p\u003e","manuscriptTitle":"Research on Aerodynamic Drag Reduction of EMU Tail Car Bogie on Combined Suction and Blowing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-02 12:40:06","doi":"10.21203/rs.3.rs-3875082/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c798dd47-ddba-45ce-b494-4949389fed8e","owner":[],"postedDate":"February 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":28489945,"name":"Physical sciences/Engineering"},{"id":28489946,"name":"Physical sciences/Engineering/Mechanical engineering"}],"tags":[],"updatedAt":"2024-04-11T10:30:36+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-02 12:40:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3875082","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3875082","identity":"rs-3875082","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}