Computational Fluid Dynamics and Computational Aeroacoustics: What Are Their Differences

This paper highlights the differences between Computational Fluid Dynamics (CFD) and Computational Aeroacoustics (CAA). The two major differences are in the design of the computational algorithm and the distinct differences between boundary conditions for fluid problem used in CFD and fluid and wave boundary conditions used in CAA problems. In regard to computational algorithm, CFD methods are primarily designed to compute fluid flows. Many CFD time marching algorithms are based on truncated Taylor serous. Whereas CAA methods are designed to compute fluid flows and the waves supported by the flow. The Dispersion-Relation-Preservation (DRP) scheme which is a CAA method uses Fourier-Laplace transforms to form its finite differences in space and time. Boundary conditions are specific to each problem. Here three selected problems are considered to show the richness of CAA boundary conditions. First problem involves outgoing waves. Radiation boundary conditions are required to avoid waves reflecting back into the computational domain and cause numerical pollution of the solution. Second problem has incoming and outgoing waves at the domain boundary. Boundary conditions that generate the incoming wave and absorbs all outgoing waves are necessary. Third problem involves an incoming mean flow, incoming waves and a spectrum of outgoing waves at the computational boundary. For this type of problems, boundary conditions imposed at the inflow boundary are required to generate the mean flow, the incoming wave and at the same time be capable of absorbing all outgoing waves.