The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step
The importance of buoyancy relative to free-stream flow is described using an adapted Froude number $Fr' = U/f_0^{1/3}$, where $U$ is the flow speed and $f_0$ is the exhaust buoyancy flux per unit length. We varied $Fr'$ by changing the free-stream flow rate, the exhaust flow rate and the...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Cambridge University Press
2023-01-01
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| Series: | Flow |
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| Online Access: | https://www.cambridge.org/core/product/identifier/S2633425923000144/type/journal_article |
| _version_ | 1797777664457572352 |
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| author | Samuel Charlwood Daria Frank Megan Davies Wykes |
| author_facet | Samuel Charlwood Daria Frank Megan Davies Wykes |
| author_sort | Samuel Charlwood |
| collection | DOAJ |
| description | The importance of buoyancy relative to free-stream flow is described using an adapted Froude number $Fr' = U/f_0^{1/3}$, where $U$ is the flow speed and $f_0$ is the exhaust buoyancy flux per unit length. We varied $Fr'$ by changing the free-stream flow rate, the exhaust flow rate and the buoyancy of the exhaust. We have experimentally identified two flow regimes, depending on the value of $Fr'$. For high $Fr'$ (low buoyancy), dispersion is driven by inertial forces in the wake and the amount of a pollutant in the wake is independent of $Fr'$. For moderate $Fr'$, a wall plume develops up the back of the step, directly feeding the pollutant into the shear layer, but without altering the shape of the wake. This wall plume reduces the amount of pollutant trapped behind the step. We developed an analytic model to describe the quantity of pollutant trapped behind the step. The model predicts the transition from buoyancy being negligible to being the dominant transport mechanism within the wake. We have hypothesised and observed some evidence of a third regime at low $Fr'$, when the buoyancy is sufficient to distort the macrostructure of the shear layer and wake. |
| first_indexed | 2024-03-12T23:08:01Z |
| format | Article |
| id | doaj.art-d3192c38ed14448d9d78a4f1ef6d98bb |
| institution | Directory Open Access Journal |
| issn | 2633-4259 |
| language | English |
| last_indexed | 2024-03-12T23:08:01Z |
| publishDate | 2023-01-01 |
| publisher | Cambridge University Press |
| record_format | Article |
| series | Flow |
| spelling | doaj.art-d3192c38ed14448d9d78a4f1ef6d98bb2023-07-18T12:53:52ZengCambridge University PressFlow2633-42592023-01-01310.1017/flo.2023.14The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing stepSamuel Charlwood0https://orcid.org/0000-0002-9652-0080Daria Frank1https://orcid.org/0000-0001-7833-6784Megan Davies Wykes2University of Cambridge Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UKDepartment of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UKUniversity of Cambridge Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UKThe importance of buoyancy relative to free-stream flow is described using an adapted Froude number $Fr' = U/f_0^{1/3}$, where $U$ is the flow speed and $f_0$ is the exhaust buoyancy flux per unit length. We varied $Fr'$ by changing the free-stream flow rate, the exhaust flow rate and the buoyancy of the exhaust. We have experimentally identified two flow regimes, depending on the value of $Fr'$. For high $Fr'$ (low buoyancy), dispersion is driven by inertial forces in the wake and the amount of a pollutant in the wake is independent of $Fr'$. For moderate $Fr'$, a wall plume develops up the back of the step, directly feeding the pollutant into the shear layer, but without altering the shape of the wake. This wall plume reduces the amount of pollutant trapped behind the step. We developed an analytic model to describe the quantity of pollutant trapped behind the step. The model predicts the transition from buoyancy being negligible to being the dominant transport mechanism within the wake. We have hypothesised and observed some evidence of a third regime at low $Fr'$, when the buoyancy is sufficient to distort the macrostructure of the shear layer and wake.https://www.cambridge.org/core/product/identifier/S2633425923000144/type/journal_articleBuoyancyPollutionWakesWall plumesConvection |
| spellingShingle | Samuel Charlwood Daria Frank Megan Davies Wykes The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step Flow Buoyancy Pollution Wakes Wall plumes Convection |
| title | The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step |
| title_full | The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step |
| title_fullStr | The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step |
| title_full_unstemmed | The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step |
| title_short | The influence of buoyancy upon pollution trapping and dispersal in the wake of a backward-facing step |
| title_sort | influence of buoyancy upon pollution trapping and dispersal in the wake of a backward facing step |
| topic | Buoyancy Pollution Wakes Wall plumes Convection |
| url | https://www.cambridge.org/core/product/identifier/S2633425923000144/type/journal_article |
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