This paper deals with the numerical prediction of the aeroacoustic behavior of orifices under grazing flow conditions. A hybrid computational aeroacoustics approach is adopted where the steady, incompressible, mean flow over the orifice is obtained from a RANS simulation. In a next step, the mean flow variables are used to solve the linearized Navier-Stokes equations (LNSE), using a Runge-Kutta Discontinuous Galerkin (RKDG) method. In this way, the linear interaction mechanisms between the aerodynamic and acoustic fluctuations are studied which enables an aeroacoustic characterization of the orifice. A methodology is presented involving a virtual impedance tube and two computations for each geometrical configuration: one with the presence of a mean flow and one for a quiescent medium. This allows to isolate the contribution of the mean flow to the orifice impedance. The method is verified against theoretical models and experimental data from literature, and is used to study the influence of orifice geometry variations, such as the orifice length, the plate thickness and the edge rounding, on the mean flow contribution to the impedance.
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