Prediction of Hydrodynamic Noise Scattered by the Non-Compact Circular Cylinder

A numerical investigation is carried out to predict the noise radiated from high Reynolds number incompressible flow over the circular cylinder. The study focuses on the scattering effect of cylinder surface to the propagation of noise at different frequencies. A boundary integral equation which extends the acoustic analogy to predict the hydrodynamic noise scattered by the non-compact surface is employed. Methods of unsteady flow simulation and noise prediction are validated by the experimental data and analytical result, respectively. Computational results of the noise at different frequencies show that the diffraction of cylinder surface to low-frequency noise is equivalent to a compact dipole source, but the scattering effect to the high-frequency noise gives a trefoil-like pattern which is much different from the directivity pattern of both quadrupole and dipole sources. Moreover, the advantage of the method is to avoid the time-consuming volume integral, which has to be implemented by using theory of vortex sound and method of the tailored Green’s function.