Computational aeroacoustics of the flow over a half cylinder

Abstract

Time dependent, incompressible flow over a half cylinder at a nominal Reynolds number of half a million was computed by a Reynolds Averaged Navier Stokes (RANS) solver. Computational predictions of the Strouhal number and the time averaged pressure distributions are compared to the experimental results. The RANS results were coupled with Lighthill's Acoustic Analogy (LAA) to compute time dependent sources and subsequently to solve for the acoustic pressures. Due to the tonal characteristic of the signal, the wave equation was transformed into the Helmholtz equation in the complex plane by applying a Fourier transform. The Helmholtz equation was solved using the finite analytic method, akin to finite differencing, with a radiation boundary condition at the far field. The linear system resulting from the finite analytic discretization is complex and nonpositive definite due to the radiation boundary conditions. The system was solved by a Bi-Conjugate Gradient Stabilized method. The acoustic code was validated for the case of a monopole at the origin. The final coupled results for the case of the half cylinder show the dipole nature of the radiated sound pressure. These results are compared to the classic point dipole prediction. (Author)