The seminar is free to attend but registration is required – please email the organizers to receive an invitation.
Abstract
Experiments are presented to characterise low-drag turbulence events, or so-called intervals of hibernating turbulence, which lasts for a certain duration, in a turbulent boundary-layer flow in a wind tunnel at a friction Reynolds number of Reτ = 700. The spatiotemporal intermittencies are identified by applying conditional sampling techniques to simultaneously acquired wall-shear stress and pointwise streamwise velocity data. The instantaneous wall-shear stress is measured with either commercially available flush-mounted hot-film probes, or by our newly developed MEMS wall-shear stress sensor technology. It is shown that ensemble-averaged streamwise velocity during intervals of hibernating turbulence fall close to the so-called Maximum-Drag-Reduction (MDR) asymptote, an asymptotic upper limit to turbulent drag reduction that is more routinely found upon dissolution of polymer additive to wall-turbulent liquid flows. The turbulent boundary layer data presented is in excellent agreement with existing experimental and DNS data on hibernating turbulence in transitional channel flows.
Experiments are presented to characterise low-drag turbulence events, or so-called intervals of hibernating turbulence, which lasts for a certain duration, in a turbulent boundary-layer flow in a wind tunnel at a friction Reynolds number of Reτ = 700. The spatiotemporal intermittencies are identified by applying conditional sampling techniques to simultaneously acquired wall-shear stress and pointwise streamwise velocity data. The instantaneous wall-shear stress is measured with either commercially available flush-mounted hot-film probes, or by our newly developed MEMS wall-shear stress sensor technology. It is shown that ensemble-averaged streamwise velocity during intervals of hibernating turbulence fall close to the so-called Maximum-Drag-Reduction (MDR) asymptote, an asymptotic upper limit to turbulent drag reduction that is more routinely found upon dissolution of polymer additive to wall-turbulent liquid flows. The turbulent boundary layer data presented is in excellent agreement with existing experimental and DNS data on hibernating turbulence in transitional channel flows.
About the speaker
Dr. Whalley is a Senior Lecturer in Fluid Dynamics at Newcastle University. He is also a Chartered Engineer and a Chartered Scientist. He uses laser-based flow measurement techniques including laser Doppler velocimetry and particle image velocimetry to study fundamental and applied fluid dynamics. He has also an active interest in developing micro-sensing and micro-actuation systems to investigate and tame wall-turbulence. Dr. Whalley leads the EPSRC-funded EnAble project (EP/T020946/1 & EPT021144/1), which aims to develop, implement and exploit machine intelligence paradigms to enable new approaches to tame wall-turbulence. In addition, he leads an Air Force Research Laboratory (AFRL) grant (FA9550-17-1-0231), which investigates low-drag phenomena in wall-turbulent airflows. He is a work package leader for the NATO plasma flow control project AVT-254, and a technical team member for the NATO micro-technologies project AVT-344. Outside of wall-turbulence, Dr. Whalley has various interests in bio-related fluid flows. He currently leads a project investigating vitreous cutters for eye surgery and supports microfluidics research projects funded by i-Sense and NC3Rs, which investigate into rapidly detecting the MRSA resistant organism in nasal swabs from hospital patients and into developing micro-tissue based models of osteoarthritis using celling printing techniques, respectively.