The structure of turbulence in pulsatile pipe flow accompanied by relaminarization.

Abstract

Hot wire measurements of three fluctuating velocity components u', v', and w' have been carried out in a pulsatile pipe flow accompanied by relaminarization. Conditional sampling was made in addition to the evaluation of turbulence intensities and Reynolds shear stresses. The onset of relaminarization and the following retransition to turbulent flow were judged from these experimental results. Turbulent motions were classified into four distinct categories. The contributions of sweep and outward interaction to the Reynolds shear stress and the turbulence energy are dominant in the earliest stage of the accelerating period where the ordered motions called bursting gradually cease due to a combined effect of viscosity and acceleration. Meanwhile, the ejection and the wallward interaction play an important role when the production of turbulence occurs again in the last stage of the accelerating period. After the turbulence generated near the wall reaches the pipe center, the ordered motions become the same as those in steady pipe flow.