Turbulent Structure of a Concentric Annular Flow

Abstract

Turbulent flow in the annular gap between two concentric tubes of 38 and 95 mm diameter at Reynolds number of 79’000 is experimentally investigated. Measurements are conducted using planar particle image velocimetry (PIV) with spatial resolution of 23 $\upmu$m/pix and interrogation windows of 0.74 $\times$ 0.74 mm$^{2}$. The experiments are aimed at scrutinizing the location of the extremums of the asymmetric profiles of velocity and turbulent statistics along with the relevant turbulent structures. The location of maximum average streamwise velocity $<$ $U$ $>_\mathrm{max}$ and zero Reynolds shear stress $<$ $uv$ $>$ are observed to be apart. Local minimum of $<$ $u^{2}$ $>$ and $<$ $v^{2}$ $>$ is also observed to coincide with $<$ $uv$ $>\, = 0$ and different from $<$ $U$ $>_\mathrm{max}$. The experiments also demonstrate that the ejection events originating from the inner and outer walls play a dominant role in transport of turbulence toward the midsection of the annulus.