Please use this identifier to cite or link to this item: https://doi.org/10.1007/s10494-020-00112-6
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dc.titleGeometric Effects of Shallow Dimples in Turbulent Channel Flows at Reτ ≈ 180: A Vorticity Transport Perspective
dc.contributor.authorNG JEE HANN
dc.contributor.authorRAJEEV KUMAR JAIMAN
dc.contributor.authorLIM TEE TAI
dc.contributor.authorTay Chien Ming,Jonathan
dc.contributor.authorKHOO BOO CHEONG
dc.date.accessioned2020-12-02T03:02:39Z
dc.date.available2020-12-02T03:02:39Z
dc.date.issued2020-06-01
dc.identifier.citationNG JEE HANN, RAJEEV KUMAR JAIMAN, LIM TEE TAI, Tay Chien Ming,Jonathan, KHOO BOO CHEONG (2020-06-01). Geometric Effects of Shallow Dimples in Turbulent Channel Flows at Reτ ≈ 180: A Vorticity Transport Perspective. Flow, Turbulence and Combustion 105 (1) : 83-122. ScholarBank@NUS Repository. https://doi.org/10.1007/s10494-020-00112-6
dc.identifier.issn1386-6184
dc.identifier.issn1573-1987
dc.identifier.urihttps://scholarbank.nus.edu.sg/handle/10635/184410
dc.description.abstractShallow dimples have shown a great potential to reduce turbulent drag in several experiments. However, the mechanism underlying their effects on turbulence dynamics remains a subject of deliberation. In this numerical study, a vorticity transport perspective is adopted to elucidate the geometric effects of shallow dimples on the turbulence dynamics in a fully-developed turbulent channel flow. The geometric modifications considered in the present direct numerical simulation at a bulk Reynolds number of 2800 include changing the planform design and modulating the streamwise wall slope. The planform design had a significant impact on the mean flow topology and the drag property. Out of the five planform designs, diamond (shape) dimples produced the highest amount of total drag reduction of ≈7%, whereas symmetric circular dimples caused the greatest increase in total drag by ≈6%. Results revealed that geometric modifications of shallow dimples mainly affect the vorticity redistribution process that predominates in the inner region of a turbulent boundary layer, and in turn the generation of Reynolds stress. The drag property of a dimpled surface was found to scale with the velocity–vorticity correlation term representing the physical process of vorticity stretching and reorientation. The occurrence of flow separation near the leading edge of the dimple altered the vorticity dispersion process in the outer region, thereby modifying the generation of Reynolds stress in the bulk flow. On the other hand, the vortex dispersion process in the inner layer can be altered by modulating the streamwise wall slope. Accordingly, the vorticity redistribution process was modified but the near-wall generation of Reynolds stress was unaffected. Thus, only the form drag varied with the streamwise wall slope, while the viscous drag remained largely the same.
dc.language.isoen
dc.publisherSpringer
dc.subjectShallow dimples
dc.subjectVorticity transport
dc.subjectTurbulent drag reduction
dc.subjectDirect numerical simulation
dc.typeArticle
dc.contributor.departmentDEPT OF MECHANICAL ENGINEERING
dc.description.doi10.1007/s10494-020-00112-6
dc.description.sourcetitleFlow, Turbulence and Combustion
dc.description.volume105
dc.description.issue1
dc.description.page83-122
dc.published.statePublished
dc.grant.idMOE2015-T2-1-128
dc.grant.fundingagencySingapore Ministry of Education
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