Turbomachinery Aeroacoustic Calculations using Nonlinear Methods

Sammanfattning: Noise regulations for aircraft that fly over populated areas are becoming continuously stricter. This in combination with increasing computational capabilities has boosted interest in aeroacoustic computations in the aerospace industry. New numerical methods that are able to predict noise will play a major role in future aircraft and engine designs, and validation and possibly improvements of these new methods are needed for results with satisfying accuracy. This thesis shows how nonlinear blade row interaction computations that focus on aeroacoustics can be made in an accurate and efficient way. It is shown how the computations of a succession of blade rows with non-matching blade count can be made more efficient by utilizing the chorochronic periodicity. The tonal acoustic response from a stator vane with rotor wake impingement is calculated with the chorochronic method and compared to a linear method, and the results are in good agreement. The harmonic balance technique was also tested for tone noise predictions and shows a good potential to be a more efficient tool than using standard time stepping for obtaining periodic solutions. The Newton-GMRES method is shown to be a suitable algorithm for obtaining convergence and for better performance of the harmonic balance computations. Broadband noise predictions from rotor wake impingement on stators are calculated with a hybrid RANS/LES method and chorochronic buffer zones. The noise is evaluated with a FWH surface integral method.