Hybrid computational aeroacoustics applications approaches, in which the computational domain is split into an aerodynamic source domain and an acoustic propagation region, are commonly used for aeroacoustic engineering applications and have proven to be of acceptable efficiency and accuracy. The different coupling techniques tend to give erroneous results for a number of applications, which are mainly encountered in confined environments. Acoustic analogies are inaccurate if the acoustic variables are of the same order of magnitude as the flow variables, and an acoustic continuation of the source-domain simulation using the latter solution as acoustic boundary conditions is only possible if no vortical outflow is occurring. These inaccuracies can be avoided by using appropriate filtering techniques in which the source-domain solution is split into an acoustic and an aerodynamic fluctuating part. In this paper, such an aerodynamic/acoustic splitting technique is developed and validated for some simple test cases. The filtering method is valid for low-Mach-number applications, assuming that all compressibility effects are caused by the irrotational acoustic field and that the incompressible aerodynamic field is responsible for the vortical movement of the flowfield. Under these assumptions, it is shown that the aerodynamic and acoustic fields at every time step are obtained by solving a system of Poisson equations driven by the fluctuating expansion ratio and vorticity, obtained from the source-domain simulation. For hybrid computational aeroacoustics applications approaches, this filtering technique, generally applicable for both free-field and confined-flow applications, provides more accurate coupling information and improves the knowledge of aerodynamic-noise-generating mechanisms.
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