Investigating channel flow using wall shear stress signals at transitional Reynolds numbers

Agrawal, Rishav, Ng, Henry C-H ORCID: 0000-0003-4926-7622, Dennis, David JC ORCID: 0000-0003-0214-7885 and Poole, Robert J ORCID: 0000-0001-6686-4301
(2020) Investigating channel flow using wall shear stress signals at transitional Reynolds numbers. INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, 82. p. 108525.

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Time-resolved wall shear stress measurements are conducted to investigate channel flow at transitional Reynolds numbers. Constant temperature anemometry (CTA) is employed to measure the instantaneous wall shear stress using glue-on hot films as the sensing probes. Pressure-drop measurements are conducted to calibrate the mean hot-film voltage signals and to ensure that the pressure drop is measured in the so-called “fully-developed” region of the channel, a study of effect of entrance length on the pressure-drop measurements is carried out. Time history and higher order statistics of wall shear stress fluctuations reveal that the flow remains laminar until Reτ(=uτh/ν)≈43 in our channel flow facility, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. Third and fourth order moments of wall shear stress jump at the onset of transition and increase significantly until they reach maxima at about Reτ ≈ 48. After this Reynolds number, these two higher order moments start to decrease gradually with increasing Reynolds number and after Reτ≈73−79, any significant dependence of these two moments on Reynolds number disappears. Multiple hot-film measurements, which are located at different spatial locations, are conducted to characterize the large-scale turbulent structures. It is observed that there are structures, at least 7h wide, for Reτ between 46.8 and 53.9. Two-point spatial correlations reveal that on average these large structures are angled at approximately 17o for Reτ=46.8 and roughly between 32o and 37o for 48.7 < Reτ < 53.9 relative to the streamwise direction.

Item Type: Article
Uncontrolled Keywords: Transition to turbulence, Hot-film anemometry
Depositing User: Symplectic Admin
Date Deposited: 10 Feb 2020 09:40
Last Modified: 19 Jan 2023 00:03
DOI: 10.1016/j.ijheatfluidflow.2019.108525
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