Conditionally averaged flow topology about a critical point pair in the skin friction field of pipe flows using direct numerical simulations

Abstract

It has recently been shown that critical points in the skin friction field of wall turbulence exist and negative streamwise skin friction events occur. Further analysis of the critical points at the wall using direct numerical simulation data of turbulent pipe flow is presented here. After identifying and characterizing features of the "no-slip" critical points in a turbulent pipe flow, conditional averages of the flow are presented to reveal the magnitude and extent of the fluctuations in the flow around these extreme events. It is found that the velocity and skin friction fields near critical points resemble the three-dimensional U separation proposed by Perry and Chong [J. Fluid Mech. 173..