Force and velocity fluctuations over rough foils at moderate Reynolds number

Force and velocity fluctuations over rough foils at moderate Reynolds number | 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 Research Article Force and velocity fluctuations over rough foils at moderate Reynolds number Melike Kurt, Rodrigo Vilumbrales-Garcia, Gabriel Weymouth, Bharathram Ganapathisubramani This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4847181/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Oct, 2025 Read the published version in Experiments in Fluids → Version 1 posted 3 You are reading this latest preprint version Abstract Surface roughness modifies the flow dynamics over static surfaces and can significantly affect the instantaneous generation of lift and drag. This study presents force and flow measurements on NACA0012 foils covered with simple, commercially available spherical-cap roughness elements. We varied the roughness area coverage relative to the propulsive area from 0% (smooth) to 35% (mid-rough) and 70% (full-rough). Our experiments survey an angle of attack and a Reynolds number range of $-2^\circ\leq\alpha\leq20^\circ$ and $10,000\lessapprox Re \lessapprox 55,000$, respectively. Within this parameter space, surface roughness leads to small alterations in time-averaged statistics of lift and drag. In contrast, it leads substantial changes in unsteady force and flow behavior. Specifically, surface roughness reduces lift fluctuations, up to $\sim60%$, due to decreased pressure fluctuations on the foil surface. This reduction is accompanied by a modest decrease in time-averaged lift coefficient and an increase in time-averaged drag coefficient. Drag fluctuations increase by up to $\sim30%$, except near stall, where both lift and drag fluctuations decrease. Roughness also mitigates flow separation, as indicated by reduced velocity fluctuations and a delayed stall onset in the $C_L(\alpha)$ curves. These results show that surface roughness influences not only time-averaged statistics but also the instantaneous response of lift, drag, and flow fields. Our findings offer insights into the hydrodynamic function of shark-skin-inspired surfaces and demonstrate how simple, distributed roughness can provide passive control of boundary layer behavior and flow separation. Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 09 Oct, 2025 Read the published version in Experiments in Fluids → Version 1 posted Editorial decision: Accepted 20 Sep, 2025 Submission checks completed at journal 19 Sep, 2025 First submitted to journal 18 Sep, 2025 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4847181","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":518075476,"identity":"60926552-f081-453f-a8b1-0148248f1f7c","order_by":0,"name":"Melike Kurt","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvElEQVRIiWNgGAWjYFACNhBhgyTAQ5SWhDSoVhK0HCZBi24DW5p05Y/z9vzyzcceMNTYMRicOYBfi9kBtmOSZxJuJ85sY0s3YDiWzGBwtoGQFvY2yYaE2wkGx3jMJBjYDjAYnCfgMKiWc/YQLf+I0gJ0WEPCAcYNIC2MbQeIcNhhtmTLhrRkoF/S0iQS+5J5JAl6/3ib4c0GGzt7fubDxyQ+fLOT4zuTQMBlzMicBGIichSMglEwCkYBYQAAX3o7rswOcbQAAAAASUVORK5CYII=","orcid":"","institution":"University of Southampton","correspondingAuthor":true,"prefix":"","firstName":"Melike","middleName":"","lastName":"Kurt","suffix":""},{"id":518075478,"identity":"1e1efdf9-d0e6-4421-ad49-7c8bd924fadf","order_by":1,"name":"Rodrigo Vilumbrales-Garcia","email":"","orcid":"","institution":"University of Michigan–Ann Arbor","correspondingAuthor":false,"prefix":"","firstName":"Rodrigo","middleName":"","lastName":"Vilumbrales-Garcia","suffix":""},{"id":518075479,"identity":"ba40f948-1e6f-4df0-b08f-4b2ce34e484f","order_by":2,"name":"Gabriel Weymouth","email":"","orcid":"","institution":"Delft University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Gabriel","middleName":"","lastName":"Weymouth","suffix":""},{"id":518075480,"identity":"f44e518a-c102-4d4b-a8e1-7eec3d56ad5a","order_by":3,"name":"Bharathram Ganapathisubramani","email":"","orcid":"","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Bharathram","middleName":"","lastName":"Ganapathisubramani","suffix":""}],"badges":[],"createdAt":"2024-08-02 09:12:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4847181/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4847181/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00348-025-04124-8","type":"published","date":"2025-10-09T15:57:10+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":91823424,"identity":"93995ac7-370b-4e28-8c21-141b399a2c42","added_by":"auto","created_at":"2025-09-22 07:54:28","extension":"json","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6564,"visible":true,"origin":"","legend":"","description":"","filename":"00f9738c154944638dc199a75750b086.json","url":"https://assets-eu.researchsquare.com/files/rs-4847181/v1/c9c62b514f44d055c97b61f1.json"},{"id":93419633,"identity":"915e1e6e-1039-4c0f-b456-1939aa76cd67","added_by":"auto","created_at":"2025-10-13 16:04:46","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":19885294,"visible":true,"origin":"","legend":"","description":"","filename":"R2revisedmanuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4847181/v1_covered_2fc0381b-ccf2-414a-9633-d458d0a4e5a5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Force and velocity fluctuations over rough foils at moderate Reynolds number","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"experiments-in-fluids","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"exif","sideBox":"Learn more about [Experiments in Fluids](http://link.springer.com/journal/348)","snPcode":"348","submissionUrl":"https://submission.nature.com/new-submission/348/3","title":"Experiments in Fluids","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4847181/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4847181/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Surface roughness modifies the flow dynamics over static surfaces and can significantly affect the instantaneous generation of lift and drag. This study presents force and flow measurements on NACA0012 foils covered with simple, commercially available spherical-cap roughness elements. We varied the roughness area coverage relative to the propulsive area from 0\\% (smooth) to 35\\% (mid-rough) and 70\\% (full-rough). Our experiments survey an angle of attack and a Reynolds number range of $-2^\\circ\\leq\\alpha\\leq20^\\circ$ and $10,000\\lessapprox Re \\lessapprox 55,000$, respectively. Within this parameter space, surface roughness leads to small alterations in time-averaged statistics of lift and drag. In contrast, it leads substantial changes in unsteady force and flow behavior. Specifically, surface roughness reduces lift fluctuations, up to $\\sim60\\%$, due to decreased pressure fluctuations on the foil surface. This reduction is accompanied by a modest decrease in time-averaged lift coefficient and an increase in time-averaged drag coefficient. Drag fluctuations increase by up to $\\sim30\\%$, except near stall, where both lift and drag fluctuations decrease. Roughness also mitigates flow separation, as indicated by reduced velocity fluctuations and a delayed stall onset in the $C_L(\\alpha)$ curves. These results show that surface roughness influences not only time-averaged statistics but also the instantaneous response of lift, drag, and flow fields. Our findings offer insights into the hydrodynamic function of shark-skin-inspired surfaces and demonstrate how simple, distributed roughness can provide passive control of boundary layer behavior and flow separation.","manuscriptTitle":"Force and velocity fluctuations over rough foils at moderate Reynolds number","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-22 07:54:23","doi":"10.21203/rs.3.rs-4847181/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Accepted","date":"2025-09-20T15:30:20+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-19T13:46:11+00:00","index":"","fulltext":""},{"type":"submitted","content":"Experiments in Fluids","date":"2025-09-18T13:58:18+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"experiments-in-fluids","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"exif","sideBox":"Learn more about [Experiments in Fluids](http://link.springer.com/journal/348)","snPcode":"348","submissionUrl":"https://submission.nature.com/new-submission/348/3","title":"Experiments in Fluids","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"fdc75bcc-1eff-4567-ace2-6bb6bb1a3c90","owner":[],"postedDate":"September 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-13T15:59:33+00:00","versionOfRecord":{"articleIdentity":"rs-4847181","link":"https://doi.org/10.1007/s00348-025-04124-8","journal":{"identity":"experiments-in-fluids","isVorOnly":false,"title":"Experiments in Fluids"},"publishedOn":"2025-10-09 15:57:10","publishedOnDateReadable":"October 9th, 2025"},"versionCreatedAt":"2025-09-22 07:54:23","video":"","vorDoi":"10.1007/s00348-025-04124-8","vorDoiUrl":"https://doi.org/10.1007/s00348-025-04124-8","workflowStages":[]},"version":"v1","identity":"rs-4847181","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4847181","identity":"rs-4847181","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}