Stationary and Moving Surface Ffowcs Williams and Hawkings Computations of an Isolated Radial Impeller

D1 - Computational Aeroacoustics

Numerical methods based on Lighthill's acoustic analogy can help to predict the noise emission of technical products such as radial fan impellers. The surface integral method of Ffowcs Williams and Hawkings (FW-H) uses the flow field data from a transient fluid computation as input. Pressure, velocity, and density distributions on an enclosed surface around the solid body represent all acoustic sources inside it. From this surface, the acoustic signals can be computed at observer points with distance-independent precision.
This work introduces two different FW-H formulations based on the flow field computed with a compressible unsteady Reynolds averaged Navier Stokes (URANS) simulation. Both FW-H formulations employ advanced time algorithms and comply with Farassat's Formulation 1, i.e. time differentiation is performed after surface integration.
The first algorithm bases on a stationary surface formulation. It uses the pressure, velocity, and density distributions on a stationary surface around the rotating solid body as input data. Advanced time interpolation and differentiation are optimized with respect to memory usage.
The second FW-H algorithm employs a moving surface formulation with input data from a co-rotating wrapping surface of constant shape on the solid body. The correctness of the code is proven with an analytical test case for different time and grid resolutions. Its technical application is demonstrated with an isolated radial fan impeller, with maximum blade tip velocities of Mach 0.12.