A numerical method for calculating three-dimensional (3D) fan tonal noise due to rotor-stator interaction has been developed at CIAM. The method is based on direct numerical solution of linearized 3D Euler equations in the frequency domain (so-called harmonic balance technique proposed by Hall et. al. [1]) using the numerical methods of computational aeroacoustics (CAA). The method is based on the assumption that the flowfield parameters can be split into two parts: the steady mean flowfield and unsteady disturbances. Note that the disturbances are assumed to be periodical in time at each point of the computational domain, so the solution can be expanded at each point in Fourier series with respect to time. Hence, a steady-state problem for a set of Fourier coefficients, which satisfy the linearized Euler equations with a source term in the right-hand side is solved. The mean flowfield is calculated using the Reynolds averaged Navier-Stokes (RANS) equations with a turbulence model and a "mixing plane" interface. To obtain the steady-state solution of the linearized Euler equations, the dual time stepping technique is used. The method allows one to calculate potential, wake, and vortex interactions.
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