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

Agrawal, R, Ng, HCH ORCID: 0000-0003-4926-7622, Dennis, DJC ORCID: 0000-0003-0214-7885 and Poole, RJ 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. ISSN 0142-727X, 1879-2278

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Abstract

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 Re<inf>τ</inf>(=u<inf>τ</inf>h/ν)≈43 in our channel flow facility, where u<inf>τ</inf>, 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 Re<inf>τ</inf> ≈ 48. After this Reynolds number, these two higher order moments start to decrease gradually with increasing Reynolds number and after Re<inf>τ</inf>≈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 Re<inf>τ</inf> between 46.8 and 53.9. Two-point spatial correlations reveal that on average these large structures are angled at approximately 17^o for Re<inf>τ</inf>=46.8 and roughly between 32^o and 37^o for 48.7 < Re<inf>τ</inf> < 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:	01 Mar 2026 09:23
DOI:	10.1016/j.ijheatfluidflow.2019.108525
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3074344
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