Contribution of large-scale motions to the Reynolds shear stress in turbulent pipe flows

Abstract

Direct numerical simulation data for turbulent pipe flows with Re-tau = 544, 934, and 3008 were used to investigate the contribution of large-scale motions (LSMs) to the Reynolds shear stress. The relationship between viscous force (d(2)U(+)/dy(+2),VF) and turbulent inertia (d(-u'v')(+)/dy(+),TI) results in a transition from the inner length scale to the intermediate length scale in the meso-layer. The acceleration force of the LSMs is balanced by the deceleration force of the small-scale motions (SSMs), which makes the zero TI at the wall -normal location of the maximum Reynolds shear stress (y(m)(+)). As the Reynolds number increases, the enhanced acceleration force of the LSMs expands the nearly zero TI region. The constant stress layer is formed in the neighborhood of the zero TI, having the relatively strong VF. For sufficiently high Reynolds number flows, the log law is established beyond the meso-layer due to the fact that VF loses its leading order. The role of the LSMs in the wall -scaling behavior of y(m)(+) is examined. (C) 2017 Elsevier Inc. All rights reserved.