A simulation study on the effect of bifurcation angles on the temperature characteristics in bifurcated tunnel fires

A simulation study on the effect of bifurcation angles on the temperature characteristics in bifurcated tunnel fires | 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 A simulation study on the effect of bifurcation angles on the temperature characteristics in bifurcated tunnel fires Rong Han, Jianlong Zhao, Xueyou Zhang, Fangfang Gao, Tingting Yan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9262630/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 13 You are reading this latest preprint version Abstract The fire safety design of bifurcated tunnels poses unique challenges, mainly due to complex smoke dynamics. These tunnels are common in modern urban underground traffic networks. This study presents a comprehensive numerical investigation into how the bifurcation angle ( θ ) influences the maximum gas temperature rise ( ΔT max ) beneath the ceiling and its longitudinal decay in naturally ventilated bifurcated tunnel fires. We used the Fire Dynamics Simulator (FDS) to conduct high-fidelity simulations. The bifurcation angle (30°, 45°, 60°, 90°) and the heat release rate (5–30 MW) were systematically varied. Dimensional analysis and simulation data reveal that the classic dimensionless relationship ΔT max /ΔT 0 ∝ kQ * 2/3 remains valid, but the proportionality constant k is strongly geometry-dependent. We established a generalized empirical model: ΔT max /ΔT 0 = (5.855 + 1.921 sinθ ) Q * 2/3 . This model shows that ΔT max increases with the bifurcation angle for a given fire size. Furthermore, we analyze the longitudinal temperature distribution. In the main tunnel upstream and downstream of the fire, temperature decay follows a double-exponential model. In the branch tunnel, the decay characteristics are significantly modulated by θ . We provide predictive correlations for all key decay parameters as functions of sin θ . This work provides fundamental insights and practical, quantitative tools for performance-based fire-safety design. Physical sciences/Engineering Physical sciences/Mathematics and computing Physical sciences/Physics Bifurcated tunnel fire Bifurcation angle Fire Dynamics Simulator Maximum temperature rise Longitudinal temperature decay Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 11 May, 2026 Reviews received at journal 01 May, 2026 Reviewers agreed at journal 28 Apr, 2026 Reviews received at journal 27 Apr, 2026 Reviewers agreed at journal 26 Apr, 2026 Reviewers agreed at journal 23 Apr, 2026 Reviewers agreed at journal 23 Apr, 2026 Reviewers agreed at journal 12 Apr, 2026 Reviewers invited by journal 10 Apr, 2026 Editor assigned by journal 10 Apr, 2026 Editor invited by journal 10 Apr, 2026 Submission checks completed at journal 06 Apr, 2026 First submitted to journal 06 Apr, 2026 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-9262630","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":622063588,"identity":"339b82f5-778c-4f39-bdf6-44f0a72329ac","order_by":0,"name":"Rong Han","email":"","orcid":"","institution":"Shanxi Vocational University of Engineering Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Rong","middleName":"","lastName":"Han","suffix":""},{"id":622063589,"identity":"785bd794-f2b6-4be5-bd16-93a343702d9c","order_by":1,"name":"Jianlong Zhao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFUlEQVRIiWNgGAWjYDACCRA2YGDgA3E+gAUSGBh4iNHCBqQZZxCtBQRAWph5iNEiP7v54QOLArs8Nvbew69t/hy2m9mewPjgbRuDvDkOLYxzjhkbSBgkF7PxnEuzzm1LS57N84DZcG4bg+HOBuxamCUSzCQkDJgT2yRyzIxzG2yS5SQS2KR52xgSDA5g18Imkf4NqKUeosXijwRIC/tvfFp4gCqBWg6DtBg/ZmCzsZMG2sKMT4uERE4x0C/HE9t4zpgx9ralJUj2PGyWnHNOwnADDi3yM9I3Ppb4U53Yz95j/OHHn8P2EseTD354U2Yjj8sWSBDA/AUkEhsYGBsYEPGFHTB+gGoF0fZ4lY6CUTAKRsGIBAAtEFIBh5M9RgAAAABJRU5ErkJggg==","orcid":"","institution":"Shanxi Vocational University of Engineering Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Jianlong","middleName":"","lastName":"Zhao","suffix":""},{"id":622063590,"identity":"9be96ee4-074d-4f57-bcb6-95b2b2cb0077","order_by":2,"name":"Xueyou Zhang","email":"","orcid":"","institution":"Shanxi Vocational University of Engineering Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Xueyou","middleName":"","lastName":"Zhang","suffix":""},{"id":622063591,"identity":"48420fee-1fb7-4897-9fa1-d3c3dbe15d2c","order_by":3,"name":"Fangfang Gao","email":"","orcid":"","institution":"Shanxi Vocational University of Engineering Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Fangfang","middleName":"","lastName":"Gao","suffix":""},{"id":622063592,"identity":"a695fdf0-0d58-4bb1-bbf8-51f891affe1b","order_by":4,"name":"Tingting Yan","email":"","orcid":"","institution":"Shanxi Vocational University of Engineering Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tingting","middleName":"","lastName":"Yan","suffix":""}],"badges":[],"createdAt":"2026-03-30 05:38:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9262630/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9262630/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107488974,"identity":"8463cf94-9446-407e-90d1-6dfb31f20e58","added_by":"auto","created_at":"2026-04-22 02:46:17","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1645109,"visible":true,"origin":"","legend":"","description":"","filename":"Manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9262630/v1_covered_f9a9b83f-8272-4c13-9d39-d44775e76357.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A simulation study on the effect of bifurcation angles on the temperature characteristics in bifurcated tunnel fires","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Bifurcated tunnel fire, Bifurcation angle, Fire Dynamics Simulator, Maximum temperature rise, Longitudinal temperature decay","lastPublishedDoi":"10.21203/rs.3.rs-9262630/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9262630/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe fire safety design of bifurcated tunnels poses unique challenges, mainly due to complex smoke dynamics. These tunnels are common in modern urban underground traffic networks. This study presents a comprehensive numerical investigation into how the bifurcation angle (\u003cem\u003eθ\u003c/em\u003e) influences the maximum gas temperature rise (\u003cem\u003eΔT\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e) beneath the ceiling and its longitudinal decay in naturally ventilated bifurcated tunnel fires. We used the Fire Dynamics Simulator (FDS) to conduct high-fidelity simulations. The bifurcation angle (30\u0026deg;, 45\u0026deg;, 60\u0026deg;, 90\u0026deg;) and the heat release rate (5\u0026ndash;30 MW) were systematically varied. Dimensional analysis and simulation data reveal that the classic dimensionless relationship \u003cem\u003eΔT\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/ΔT\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e \u0026prop; \u003cem\u003ekQ\u003c/em\u003e\u003csup\u003e\u003cem\u003e*\u003c/em\u003e2/3\u003c/sup\u003e remains valid, but the proportionality constant \u003cem\u003ek\u003c/em\u003e is strongly geometry-dependent. We established a generalized empirical model: \u003cem\u003eΔT\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/ΔT\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e = (5.855\u0026thinsp;+\u0026thinsp;1.921\u003cem\u003esinθ\u003c/em\u003e) \u003cem\u003eQ\u003c/em\u003e\u003csup\u003e\u003cem\u003e*\u003c/em\u003e2/3\u003c/sup\u003e. This model shows that \u003cem\u003eΔT\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e increases with the bifurcation angle for a given fire size. Furthermore, we analyze the longitudinal temperature distribution. In the main tunnel upstream and downstream of the fire, temperature decay follows a double-exponential model. In the branch tunnel, the decay characteristics are significantly modulated by \u003cem\u003eθ\u003c/em\u003e. We provide predictive correlations for all key decay parameters as functions of sin\u003cem\u003eθ\u003c/em\u003e. This work provides fundamental insights and practical, quantitative tools for performance-based fire-safety design.\u003c/p\u003e","manuscriptTitle":"A simulation study on the effect of bifurcation angles on the temperature characteristics in bifurcated tunnel fires","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-20 20:12:23","doi":"10.21203/rs.3.rs-9262630/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-11T10:38:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-02T00:53:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"230407617863402295495976319599688636064","date":"2026-04-29T01:12:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-27T09:30:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328370684968477662346325415110962973017","date":"2026-04-27T02:42:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"230136818073805125230697072264368790787","date":"2026-04-24T00:34:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"106525013733222374477616499663093800673","date":"2026-04-23T15:18:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"214346591389427891663501162311590453712","date":"2026-04-12T09:45:03+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-10T07:24:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-10T07:16:53+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-10T06:18:37+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-07T02:05:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-04-07T02:01:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1dc4cb8e-887f-4733-bfbd-ce6ce07d9fb9","owner":[],"postedDate":"April 20th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-11T10:38:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-02T00:53:34+00:00","index":47,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[{"id":66193611,"name":"Physical sciences/Engineering"},{"id":66193612,"name":"Physical sciences/Mathematics and computing"},{"id":66193613,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2026-05-11T10:56:02+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-20 20:12:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9262630","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9262630","identity":"rs-9262630","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}