Effect of the wavy geometric disturbance on the flow over elliptic cylinders with different aspect ratios

Abstract

The present study investigates the effect of the wavy geometric disturbance as the flow control on the flow around elliptic cylinders with different aspect ratios at low Reynolds number of 100. The wide ranges of the wavelength (1.0≤λ/Lm,x≤8.0) and the aspect ratio of the ellipse (0.5≤AR≤1.0) are considered, where Lm,x is the streamwise mean body length. For AR=1.0 with the circular cross-section, the flow strongly depends on λ/Lm,x, resulting in the appearance of various flow structures. As AR decreases, the flow bifurcation occurs at the certain conditions of AR and λ/Lm,x. Therefore, the bifurcation map is presented in AR−λ/Lm,x plane, where flows are classified as three modes of the unsteady, steady and coexistence states. There are two effects of the waviness and the streamlined body on the flow bifurcation. At the large ARs in AR>0.6, the bifurcation early occurs from the long wavelengths, which is associated to two types of the streamwise vorticities. In AR≤0.6, the effect of the streamlined body on the flow overcomes the wavy geometric disturbance, resulting in undergoing the bifurcation, regardless of λ/Lm,x. Additionally, force coefficients and the Strouhal number are analyzed to understand the dependence of hydrodynamic performance and vortex shedding on AR and λ/Lm,x.