Effect of shape of frontbody and afterbody on flow past a stationary cylinder at Re = 100

Abstract

We numerically study the effect of the shape of frontbody and afterbody on the flow past a cylinder at a Reynolds number of 100. Two-dimensional simulations have been carried out using an in-house sharp-interface immersed boundary method-based flow solver. The cylinder cross section is considered as a semi ellipse on both windward and leeward sides. The semi-minor axis on the windward side (frontbody parameter, LF) and the leeward side (afterbody parameter, LA) varies from 0 to 0.5 to render cylinders of different cross sections. The effect of LF and LA is quantified on the following variables: drag coefficient, lift coefficient, the Strouhal number, vortex formation length, vortex fluctuation energy, the flow separation point, and cylinder bluffness. While the drag linearly decreases with both LF and LA, the gradient with respect to LF is nearly twice larger than LA. The computed vortex formation length scales directly with drag in the LF- LA plane, while the vortex fluctuation energy scales inversely. The lift and the Strouhal number vary non-monotonically in the LF- LA plane, explained in terms of vortex formation length and the flow separation point, respectively. We briefly quantify wake signatures in the LF- LA plane. The downstream vortex paths are traced, and in general, two vortex shedding patterns, 2 S and C(2 S), are correlated with values of LF and LA. A dynamic mode decomposition analysis of the flow modes helps to explain the computed fluid-flow characteristics.