Investigation on the Effect of Surface Impedance for Reducing Aerodynamic Sound from Circular Cylinder

This paper describes a mathematical formulation and numerical implementation on the effect of surface impedance for reducing aerodynamic sound radiated from a circular cylinder. Firstly, mathematical derivation of the ideal surface impedance that eliminates the pressure fluctuation on the body surface, utilizing the Green's function, is discussed. Secondly, a numerical simulation is explained with using the Large Eddy Simulation (LES) techniques at Reynolds number 3000, with boundary conditions of, (i) rigid, (ii) finite uniform impedance, and (iii) our new approach of optimized surface impedance, inducing flow by a Helmholtz resonator. In the simulation only larger impedance than the ideal one is applied to the surface due to computational instability which restrains the lower limit of impedance. The effect of optimized surface impedance is verified by the simulation via the fact that the amplitude of the surface pressure fluctuation decreases remarkably.