Numerical analysis of aerodynamic sound radiated from rectangular cylinder

The flow around a rectangular cylinder involves various fluid-dynamic phenomena, such as separation, reattachment and vortex shedding. The fluid-dynamic characteristics of a cylinder change according to the side ratio D/H, where cylinder height is defined as H and depth as D, and Reynolds number Re=U∞H/ν, where U∞ is uniform flow velocity and ν is the kinetic viscosity coefficient. In the present study a three-dimensional turbulent flow calculation was carried out using large eddy simulation (LES) to solve the flow around rectangular cylinders with side ratios D/H of 0.6, 1.0, 2.0, 2.5 and 3.0, and quantitative predictions were made of the sound generated by dipoles involved in pressure fluctuations on the cylinder surface. The calculated results for flow characteristics and sound radiation were compared with the experimental results and showed good quantitative agreement. Then the variation in sound pressure level was studied as a function of side ratio and the relationship between the flow patterns and the sound radiation, indicating that the Strouhal number and the coherence length in the spanwise direction are very important parameters for predicting sound radiation. Notably, a drastic change in Strouhal number between D/H=2.5 and 3.0 causes discontinuous change in the sound radiation.