Experimental Study of the Wake of a Truncated Wall-Mounted Circular Cylinder at High Reynolds Numbers

Abstract

The paper presents the Particle Image Velocimetry (PIV) analysis of the wake of the wall mountedtruncated cylinder with an Aspect Ratio (AR) of 4 at a range of high Reynolds numbers from 6.4*10 4 to 2.41*10 5 . The velocity distributions are measured using a two-dimensional three-components PIV(2D-3C PIV) system in two horizontal sections. In order to choose a proper measurement window,preliminary smoke tests are conducted. The snapshots of the velocity field are subjected to the ProperOrthogonal Decomposition (POD) analysis in order to understand the structure of the unsteady flow.The influence of the Reynolds number on the POD modes and the distribution of the fluctuation energyamong the velocity components are studied.Additionally, a so-called amplitude analysis for each of the first three strongest modes is conductedin order to give a physical interpretation to each of them. The mode structures have been found toremain similar in the mention Re range, so the complete description of the POD results is given forRe = 1.28*10 5 . The most modes are connected to symmetric (about x-axis) fluctuations of the wakein transversal, vertical or longitudinal directions. At the top of the cylinder the wandering and thechange of the tip vortices’ (TV) intensity also contribute to the fluctuation energy. In the consideredmeasurement windows the modes which could be associated with the von Karman vortex sheddinghave not been identified.

Keywords: truncated cylinderunsteady flowparticle image velocimetryproper orthogonal decomposition