A numerical study on the acoustic radiation from a scarfed intake

A hybrid numerical procedure is developed to study the sound propagation and radiation from hard wall scarfed intakes. The three-dimensional linearized Euler equations are solved by a computational aeroacoustics (CAA) approach in the near field with the assumed sound source in the duct intake in front of the fan. The near field solution is then extended to the far field with a penetrable Ffowcs Williams-Hawkings (FW-H) time domain integration method. In the CAA procedure, the high-order dispersion-relation-preserving scheme is applied for spatial discretization whereas the 2N storage low-dissipation and low-dispersion Runge-Kutta scheme is employed for time integration. Much attention has been paid to grid generation and far field boundary conditions. The main advantage of the hybrid procedure is that the effects due to complex intake geometries can be accounted for while the far field directivities can be obtained very efficiently. The hybrid procedure is firstly validated by a zero thickness circular duct intake with uniform mean flow. Then a family of scarfed intakes with different scarf angles are numerically studied. The numerical results show that the noise reduction increases increase with the scarf angle. For a moderate scarfed inlet (-15°), roughly 4dB peak noise reduction can be achieved.