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25 April 2024 |
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Article overview
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Convection Velocity in Turbulent Boundary Layers under Adverse Pressure Gradient | | Artur Dróżdż
; Paweł Niegodajew
; Mathias Romańczyk
; Witold Elsner
; | | Date: |
22 Nov 2022 | | Abstract: | The convection velocity ($U_C$) of turbulent structures has been studied in
adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) for a wide
range of Reynolds numbers $Re_ au = 1400 - 4000$. The study is based on
estimation of the convection velocity using decomposed streamwise skewness
factor introduced in (Drozdz A., Elsner W., Int. J. of Heat and Fluid Flow. 63
(2017) 67-74) and verified by means of two-point correlation method. It was
shown that in the overlapping region of APG flows, the convection velocity
profiles (when scaled in viscous units) reassemble the universal logarithmic
law characteristic for the ZPG flows up to Clauser-Rota pressure gradient
parameter $eta lesssim 19$ for the considered range of Reynolds number, what
means that in the inner region of TBL the friction velocity in APG is not
proportional to $U$ (as in ZPG) but to $U_C$ instead. The physical mechanism
that explains the impact of increased convection velocity on the mean flow is
proposed. The difference between $U_C$ and $U$ increases as a function of APG,
which causes the stronger sweeping that enhances momentum transfer to the wall
and compensates the weaker mean shear profile that is created by lower
vorticity near the wall. This effect is a result of an enhancement of amplitude
modulation of the small scales by large scale motion. The process becomes more
pronounced as eddy density grows, so with increasing Re. The proposed model
addresses a number of literature observations found in adverse pressure
gradient flows which have been so far left without a well-founded explanation. | | Source: | arXiv, 2211.12152 | | Services: | Forum | Review | PDF | Favorites | |
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