Radial propagation of turbulence in pulsatile pipe flow.

Abstract

Turbulence generated near the wall of a pipe propagates both in the radial and the axial directions. Compared to the axial propagation, knowledge of radial propagation is very limited. This investigation is intended to clarify the radial propagation of wall turbulence in pulsatile turbulent pipe flows. It becomes evident that the turbulence is mainly generated around y+ = 20 and propagates toward the wall as well as the pipe center, where y+ = yu^-*, ta/v, y the distance from the wall, u^-*, ta the time-averaged friction velocity, and ν the kinematic viscosity. The propagation time near the generation region scales well with inner variables, u^-*, ta and ν, whereas in the central part of the pipe it scales with u^-*, ta and the pipe radius R. Empirical expressions for the propagation time are derived, and models for Reynolds shear stress and eddy viscosity are proposed.