Studies of the Wall Shear Stress in a Turbulent Pulsating Pipe Flow

摘要

Measurements are presented of the time variation of the wall shear stress caused by the imposition of a sinusoidal oscillation on a turbulent pipe flow. The amplitude of the oscillation is small enough that a linear response is obtained and the dimensionless frequency, omega +, is large compared to that studied by most previous investigators. The most striking feature of the results is a relaxation effect, similar to what has been observed for flow over a wavy surface, whereby the phase angle characterizing the temporal variation of the wall shear stress undergoes a sharp change over a rather narrow range of omega +. At omega + larger than the median frequency of the turbulence there appears to be an interaction between the imposed flow oscillation and the turbulence fluctuations in the viscous sublayer, which is not described by present theories of turbulence.