Passive scalar transport in a cross-ventilating flow with upstream source: Wind and Water tunnel measurements

Passive scalar transport in a cross-ventilating flow with upstream source: Wind and Water tunnel measurements | 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 Passive scalar transport in a cross-ventilating flow with upstream source: Wind and Water tunnel measurements Subhajit Biswas, Paul Hayden, Matteo Carpentieri, Christina Vanderwel This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7973606/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 In urban environments, pollutant ingress from outdoor sources poses a significant challenge to indoor air quality. Cross-ventilation, while essential for passive cooling and natural airflow, can also facilitate the entry of outdoor contaminants into indoor spaces. To investigate the dynamics of outdoor-to-indoor pollutant transport, the present study employs an idealised configuration, namely a hollow cube representing a scaled-down model building with window openings in the upstream and downstream faces, subjected to an upstream passive scalar source within an atmospheric boundary layer. The experiments are conducted in two distinct facilities: a water tunnel using Rhodamine dye as the scalar, and a wind tunnel using propane gas, all performed at a specified flow Reynolds number of Re = U Ref H/ν ≈ 50, 000 for a fixed boundary layer-to-cube height ratio of about 3; here, U Ref is the streamwise velocity at cube’s height (H) measured without the cube. The scalar, released from a ground-level upstream source, is predominantly transported by a streamwise advective flux, while relatively weaker wall-normal advective and turbulent fluxes contribute to vertical dispersion and local mixing. A fraction of the oncoming scalar enters the cube intermittently, through the upstream window. Inside, a central jet-like flow carries the scalar parcels primarily by streamwise advective flux, while also interacting with the upper and lower recirculation regions, enabling scalar exchange across these zones through wall-normal advective and turbulent fluxes. While the time-averaged concentration field inside the cube is nearly uniform, suggesting effective mixing, instantaneous concentration traces exhibit strong intermittency, with sporadic peak events, highlighting the risk of transient peak exposures. The indoor concentration exponentially decays over time once the source is turned off, with a slower decay in the upper recirculation region, implying relatively prolonged exposure near the ceiling region. Both experimental setups produce closely matching values and consistent trends in the spatio-temporal dynamics of scalar concentration, and also highlight their complementary nature, with each offering distinct advantages. The present findings will deepen our understanding of pollutant ingress and mixing in buildings in cross-ventilated flows and also offer valuable insights to future modelling of pollutant exposure in urban indoor spaces. Environmental Engineering Air pollution Outdoor dispersion Indoor dispersion Indoor-outdoor exchange Cross-ventilation Transport mechanisms Full Text Additional Declarations The authors declare no competing interests. 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. 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-7973606","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":536496664,"identity":"85aaf519-ca40-4d10-94bd-5e99b679bf65","order_by":0,"name":"Subhajit Biswas","email":"","orcid":"https://orcid.org/0000-0002-0357-5796","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Subhajit","middleName":"","lastName":"Biswas","suffix":""},{"id":536496665,"identity":"29b93830-0b0e-48e0-b9de-032acd7cb35a","order_by":1,"name":"Paul Hayden","email":"","orcid":"https://orcid.org/0000-0002-0180-9851","institution":"University of Surrey","correspondingAuthor":false,"prefix":"","firstName":"Paul","middleName":"","lastName":"Hayden","suffix":""},{"id":536496666,"identity":"30e91b45-0ab1-4f19-8c9f-9e1abbfe1996","order_by":2,"name":"Matteo Carpentieri","email":"","orcid":"https://orcid.org/0000-0002-8968-9339","institution":"University of Surrey","correspondingAuthor":false,"prefix":"","firstName":"Matteo","middleName":"","lastName":"Carpentieri","suffix":""},{"id":536496667,"identity":"d2fe3063-9f1a-4f68-a13e-b063dad44c71","order_by":3,"name":"Christina Vanderwel","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/ElEQVRIiWNgGAWjYBADxgYQ+aACSUiCKC0JZxgYeEjTkthGhBb+Bu4EZp6aO7L90mcMHyTOq5OzZ+89wPCjhiFxZgN2LRIHeDcw8xx7ZjyzL8fYIHHbYWMennMJjD3HGBJn47DFgIF3A+MMtsOJG87wbpNI3HYgsUciByjYwJA4D6+Wf4cT95/h3f4jcU4dWAvjXwJaGD62AW3h4d3GkNjADNbCDLIFl8MkDvNuOPCx77DxjDP8nyUSjgH9cuaMwWGZYxLGuLzP39678UHCt8Oy/T1siR8+1NTJsbf3GD58U2MjO+MADmuYGRgwpQ4QjshRMApGwSgYBfgAAMGKWb5wNf0sAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-5114-8377","institution":"University of Southampton","correspondingAuthor":true,"prefix":"","firstName":"Christina","middleName":"","lastName":"Vanderwel","suffix":""}],"badges":[],"createdAt":"2025-10-28 20:25:57","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-7973606/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7973606/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":94730317,"identity":"5979b311-3b7e-40a9-ad68-0e10f303edfa","added_by":"auto","created_at":"2025-10-30 07:05:51","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":20671451,"visible":true,"origin":"","legend":"","description":"","filename":"BiswasVanderwelEXIF2025.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7973606/v1_covered_e157362e-abfd-4c06-a1f1-ed17093a09c1.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003ePassive scalar transport in a cross-ventilating flow with upstream source: Wind and Water tunnel measurements\u003c/p\u003e","fulltext":[],"fulltextSource":"","fullText":"","funders":[{"identity":"a0aa12de-0c92-4884-b70f-fcba676a20c0","identifier":"10.13039/100014013","name":"UK Research and Innovation","awardNumber":"MR/S015566/1","order_by":0},{"identity":"c4a79884-b99d-4240-a0bf-678d62c77935","identifier":"10.13039/501100000270","name":"Natural Environment Research Council","awardNumber":"NE/Y005376/1","order_by":1}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"University of Southampton","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"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":"Air pollution, Outdoor dispersion, Indoor dispersion, Indoor-outdoor exchange, Cross-ventilation, Transport mechanisms","lastPublishedDoi":"10.21203/rs.3.rs-7973606/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7973606/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn urban environments, pollutant ingress from outdoor sources poses a significant challenge to indoor air quality. Cross-ventilation, while essential for passive cooling and natural airflow, can also facilitate the entry of outdoor contaminants into indoor spaces. To investigate the dynamics of outdoor-to-indoor pollutant transport, the present study employs an idealised configuration, namely a hollow cube representing a scaled-down model building with window openings in the upstream and downstream faces, subjected to an upstream passive scalar source within an atmospheric boundary layer. The experiments are conducted in two distinct facilities: a water tunnel using Rhodamine dye as the scalar, and a wind tunnel using propane gas, all performed at a specified flow Reynolds number of Re = U\u003csub\u003eRef\u003c/sub\u003eH/ν ≈ 50, 000 for a fixed boundary layer-to-cube height ratio of about 3; here, U\u003csub\u003eRef\u003c/sub\u003e is the streamwise velocity at cube’s height (H) measured without the cube. The scalar, released from a ground-level upstream source, is predominantly transported by a streamwise advective flux, while relatively weaker wall-normal advective and turbulent fluxes contribute to vertical dispersion and local mixing. A fraction of the oncoming scalar enters the cube intermittently, through the upstream window. Inside, a central jet-like flow carries the scalar parcels primarily by streamwise advective flux, while also interacting with the upper and lower recirculation regions, enabling scalar exchange across these zones through wall-normal advective and turbulent fluxes. While the time-averaged concentration field inside the cube is nearly uniform, suggesting effective mixing, instantaneous concentration traces exhibit strong intermittency, with sporadic peak events, highlighting the risk of transient peak exposures. The indoor concentration exponentially decays over time once the source is turned off, with a slower decay in the upper recirculation region, implying relatively prolonged exposure near the ceiling region. Both experimental setups produce closely matching values and consistent trends in the spatio-temporal dynamics of scalar concentration, and also highlight their complementary nature, with each offering distinct advantages. The present findings will deepen our understanding of pollutant ingress and mixing in buildings in cross-ventilated flows and also offer valuable insights to future modelling of pollutant exposure in urban indoor spaces.\u003c/p\u003e","manuscriptTitle":"Passive scalar transport in a cross-ventilating flow with upstream source: Wind and Water tunnel measurements","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-30 04:56:31","doi":"10.21203/rs.3.rs-7973606/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":"b02b7ecc-d84f-4cf4-bd31-de260c2ba76f","owner":[],"postedDate":"October 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":57046630,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2025-10-30T04:56:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-30 04:56:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7973606","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7973606","identity":"rs-7973606","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}