Modeling of Installation Effects on the Noise from Subsonic Axial Fans

Analytical modeling of the tonal noise radiated by a subsonic axial-flow fan placed in an air-cooling system is considered, instead of the more classical formulation neglecting installation effects. Two mechanisms are addressed separately, namely the noise associated with a stationary distorted inflow, and the potential-interaction noise due to downstream structural elements. For the first mechanism the distortion is determined from CFD computations and used as input data for the analytical calculation of the blade-loading harmonics. The tip-gap flow of the fan is investigated as the origin of a specific distortion. For the second mechanism, the distortion field is also modeled analytically. In both cases the radiation is considered in free field because the model is dedicated to unducted fans. The brake cooling fan of an aircraft landing gear is chosen as test case for the sake of illustration.