The numerical calculation of fricative sounds with a FEM code in realistic 3D geometries requires a very fine spatial discretization in order to capture all relevant turbulent scales, which leads to heavy parallel computations. For low speed flows, like in the present case, conservative compressible flow formulations might fail, for which the more affordable incompressible approach is often used. However, most available formulations in Computational Aeroacoustics based on incompressible flow either require modeling acoustic source terms or are not valid at the near field, where flow perturbations are still non-negligible. Therefore, new developments in both incompressible and compressible formulations and the corresponding results will be presented.