Drag reduction effect by streamwise traveling wave-like wall-surface heating/cooling in a turbulent channel flow

Abstract

We conduct a direct numerical simulation of a turbulent channel flow controlled using the buoyancy force induced by streamwise traveling wave-like wall-surface heating/cooling under a constant pressure gradient condition. According to a parametric study of wavelength, phasespeed, and Richardson number, the maximum drag reduction rate attained is about 10% in the case where the wavelength, phasespeed, and Richardson number are λ_x⁺ ≈ 1130, c⁺ = 90, and Ri = 1000, respectively (the superscript + represents wall units). The drag reduction rate at a high Reynolds number of Re_τ = 360 is smaller than that at a low Reynolds number of Re_τ = 180, resulting in the drag increase effect in all cases at a high Reynolds number. In the maximum drag reduction case, we observe a region where quasi-streamwise vortices (QSVs) are significantly suppressed and a region where they remain nearly unchanged. In addition, the temperature distribution with relatively high regularity, which is inclined in the direction opposite to the streamwise traveling wave, is formed only near the wall. This distribution was observed by Mamori and Fukagata (2014), who investigated the drag reduction effect by a wave-like wall-normal body force in a turbulent channel flow. On the other hand, in the drag increase case, the temperature distribution with high irregularity extends far from the wall, which means that the body force with three–dimensionality is imposed in the entire region of the channel. As a result, the QSVs are significantly enhanced in the entire region of the channel, leading to a significant drag increase effect.