Effect of axis ratio on unsteady wake of surface mounted elliptic cylinder immersed in shear flow

Abstract

Three-dimensional flow past surface mounted elliptic cylinder has been investigated numerically using OpenFOAM. Axis ratio (AR) of the elliptic cylinder is varied from 0.5 to 2. Effects of shear intensity (K) of the nonuniform incoming flow and Reynolds number (Re) varying from 150 to 250 on wake dynamics have been examined using Hilbert Huang transformation and Recurrence analysis. Qualitative and quantitative analyses of wake unsteadiness are illustrated using Hilbert spectra and degree of stationarity. Various recurrence quantification estimates have been reported to reveal insight about unsteady wake transition with the change in Re, AR and K. Four types of distinguishable wake flows, viz., steady, periodic, quasi-periodic and chaotic have been characterized with the help of vorticity contours, frequency spectra and bifurcation diagram. In aperiodic flow, wake oscillation contains multiple laminar states or slow changing states which has been disclosed using laminarity and trapping time. Nonstationarity and synchronous wake behavior along the height of the cylinder have been examined using cross-recurrence analysis and quantified in terms of recurrence rate, determinism and average diagonal length. In addition, the effect of change in K for each value of Re and AR has been studied on the mean drag coefficient of the cylinder.