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dc.contributor.authorNewton, R
dc.contributor.authorChung, D
dc.contributor.authorHutchins, N
dc.identifier.citationNewton, R., Chung, D. & Hutchins, N. (2018). An experimental investigation into the breakdown of riblet drag reduction at post-optimal conditions. Proceedings of the 21st Australasian Fluid Mechanics Conference, AFMC 2018, Australasian Fluid Mechanics Society.
dc.description.abstractA long-standing question in riblet research is why drag reduction only occurs within a small, non-dimensionally scaled envelope, outside of which drag is significantly increased. For riblets with viscous-scaled spacings that are much larger than those required for drag reduction, one hypothesis is that the riblets exhibit k-type, ‘fully rough’ behaviour. However, this seems counter-intuitive since fully rough behaviour is typically associated with a dominance of pressure drag over viscous drag, and yet riblets can sustain no pressure drag. This study aims to investigate this issue by conducting single normal hot-wire traverses above a trapezoidal riblet surface, over a range of drag-increasing viscous-scaled riblet spacings. Novelty was added by also measuring within the riblet valleys, providing a unique look at the turbulent behaviour within them. Previously proposed mechanisms for the breakdown in drag reduction have included lodgement of turbulence within the riblet valleys, and the development of a Kelvin–Helmholtz instability, but neither mechanism appears active in our results. They instead show a reduction in turbulent energy as riblet spacing increases, despite a significant increase in drag, which does seem to be approaching a k-type roughness asymptote as hypothesised. This may be caused by the generation of time-invariant secondary flows above the riblet tips and corners of the riblet valleys, although this will require further investigation.
dc.publisherAustralasian Fluid Mechanics Society
dc.source21st Australasian Fluid Mechanics Conference
dc.titleAn experimental investigation into the breakdown of riblet drag reduction at post-optimal conditions
dc.typeConference Paper
melbourne.affiliation.departmentMechanical Engineering
melbourne.source.titleProceedings of the 21st Australasian Fluid Mechanics Conference, AFMC 2018
melbourne.openaccess.statusPublished version
melbourne.contributor.authorHutchins, Nicholas
melbourne.contributor.authorNewton, Ryan
melbourne.contributor.authorChung, Daniel
melbourne.event.locationAdelaide, Australia
melbourne.accessrightsAccess this item via the Open Access location

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