The effect of Reynolds number on the elliptical cylinder wake

This work numerically investigates the effects of Reynolds number Re-D (= 100 - 150), cross-sectional aspect ratio AR = ( 0.25 -1.0), and attack angle alpha (= 0 degrees - 90 degrees) on the forces, Strouhal number, and wake of an elliptical cylinder, where Re-D is based on the freestream velocity and cylinder cross-section height normal to the freestream flow, AR is the ratio of the minor axis to the major axis of the elliptical cylinder, and alpha is the angle between the cylinder major axis and the incoming flow. At Re-D= 100, two distinct wake structures are identified, namely 'Steady wake' (pattern I) and 'Karman wake followed by a steady wake (pattern II) when AR and alpha are varied in the ranges specified. When Re-D is increased to 150, an additional wake pattern, 'Karman wake followed by secondary wake (pattern III) materializes. Pattern I is characterized by two steady bubbles forming behind the cylinder. Pattern II features Karman vortex street immediately behind the cylinder, with the vortex street transmuting to two steady shear layers downstream. Inflection angle alpha(i) = 32 degrees, 37.5 degrees and 45 degrees are identified for AR = 0.25, 0.5 and 0.75, respectively, where the wake asymmetry is the greatest. The alpha(i) effectively distinguishes the dependence on a and AR of force and vortex shedding frequency at either Re-D. In Pattern III, the Karman street forming behind the cylinder is modified to a secondary vortex street. At a given AR and alpha, Re-D = 150 renders higher fluctuating lift and Strouhal number than Re-D = 100.