APS -70th Annual Meeting of the APS Division of Fluid Dynamics- Event - Drag control of wall-bounded turbulent flows.

摘要

Using direct numerical simulations of turbulent channel flow, we present a new method for skin friction reduction, enabling large-scale flow forcing without requiring instantaneous flow information. We show that the lack of drag reduction at high Re (Re$_{mathrm{au }}$egin{figure}[htbp]centerline{includegraphics[width=0.25in,height=0.20in]{300720171.eps}}label{fig1}end{figure}$=quad 550)$ recently reported by Canton extit{et al. }[J. Canton extit{et al.}, PRF (2016)] is remedied by a proper choice of the large-scale control flow, i.e. via near-wall spanwise opposed wall-jet forcing (SOWF), each wall-jet covering multiple streaks. The control method is characterized by three parameters, namely, the wall-jet amplitude A$^{mathrm{+}}$, the spanwise wall-jet spacing $Lambda^{mathrm{+}}$, and the wall-jet height y$^{mathrm{+}}_{mathrm{c}}$ ($+$ indicates viscous scaling). We show as an example that with a choice of A$^{mathrm{+}}approx $.015, $Lambda ^{mathrm{+}}approx $1200 and y$^{mathrm{+}}_{mathrm{c}} quad =$30 (these three parameters values were found to produce maximum drag reduction for Re$_{mathrm{au hinspace }}=$ 180), the flow control definitely suppresses the wall shear stress at a series of Reynolds numbers, namely, 19{%}, 14{%}, and 12{%} drag reductions at Re$_{mathrm{au }}=$ 180, 395, and 550, respectively. Vortex structures ($lambda_{mathrm{2}})$ and flow statistics (Reynolds shear stress, rms of vorticities, kinetic energy budget, etc.) are further examined to explain the mechanism of drag reduction and increase.