Computation of noise due to the flow over a half cylinder in ground effect

Abstract

The objective of the study is to predict the acoustic radiation from a flow over a half circular cylinder near a plane. The approach uses a two step process. Time dependent flow over the half circular cylinder 1.583 diameters above a plane at a Reynolds number of 500,000 is computed using a Reynolds Averaged Navier Stokes (RANS) solver. Time dependent acoustic sources are calculated from the RANS results. Computational predictions of the Strouhal number associated with the time histories of the lift and drag variations and the time averaged pressure distributions are compared to experimental results. The RANS results are coupled with Lighthill's Acoustic Analogy (LAA) to solve for the acoustic pressures. The time dependence of the pressure signals is tonal so the wave equation is transformed into a Helmholtz equation in the complex plane by Fourier transformation. The Helmholtz equation is solved using the finite analytic method, which is akin to finite differencing, with a radiation boundary condition applied in the far field. The linear system resulting from the finite analytic discretization is complex and non-positive definite due to the radiation boundary conditions. The linear system is solved using a Bi-Conjugate Gradient Stabilized (BiCG-STAB) method. The resulting acoustic predictions are compared with similar results for a half circular cylinder in an unbounded flow.