Simulation of the effects of body shape on lock-in characteristics in pulsating flow by the discrete vortex method

Abstract

The viscous flow around rectangles defined by afterbody length, L, and cross-stream dimension, D, is investigated through a hybrid discrete vortex method. The side ratio, LD, varies over the range 0.4 ⩽ LD ⩽ 2.5. In the case of the square cylinder, LD = 1.0, results are presented for the variation of drag coefficient and Strouhal number with Reynolds number, Re ⩽ 1000. A good agreement with experiment is shown although for Re ⩾ 500 the calculated Strouhal number is found to be higher than experimental values. At a fixed Reynolds number, Re = 200, the variation of drag coefficient with side ratio shows Cd increasing with decreasing LD. Experimental work at higher Re predicts a drag maximum at LD ≌0.62 but such a maximum has not been determined in this study. Pulsating flows are reported for LD values of 0.62, 1.0, 2.0 and the ‘lock-in’ characteristics are shown to be highly dependent on the side ratio. In particular, with LD = 2.0, a strong regime of symmetric vortex shedding is found when the forcing frequency is more than double the natural shedding frequency value.