Aerodynamic characteristics of a square cylinder in streamwise sinusoidal flows

Abstract

The aerodynamic characteristics of a square cylinder in streamwise sinusoidal flows with non-zero mean velocity are investigated numerically by large eddy simulation. The ratio of the inflow frequency fu to the natural Karman vortex shedding frequency fvs varies from 0.125 to 8. The inflow fluctuating intensity varies from 5% to 20%. The aerodynamic forces, pressures, time-averaged flow structures, and flow dynamics are investigated. The results show that the effects of sinusoidal inflow are limited for cases with lower fu within (0.125fvs, fvs) and become pronounced when inflow frequencies are within (fvs, 8fvs). As the inflow frequency increases from fvs to 4 fvs, the recirculation regions on the lateral surface keep shrinking toward the leading edge, resulting in the reattachment of the shear layer on the side surface. The strength of Karman vortex shedding is weakened due to the less intensified shear layer interactions in the wake region, and the Karman vortex shedding intensity attains a minimum in the separated–reattaching flow fields. The variation of flow structures results in a deformation of the surface pressure distribution, with lager negative pressures on the lateral surfaces and a recovery of the negative pressures on the leeward wall. The mean drag and root mean square (r.m.s.) lift forces decrease during this process. As the inflow frequency further increases from 4 fvs to 8 fvs, the shear layers tend to vent again. The Karman vortex shedding intensity, mean drag force, and r.m.s. lift force increase reversely, maintaining a lower level than those in smooth flow. In addition, the r.m.s. drag force is found to be dominated by the inflow-induced pressure gradient in the flow field. The increase in inflow fluctuating intensities magnifies the effects of sinusoidal flows.