Efficient Evaluation of Flow Induced Sound Sources at Low Frequency by Fast Multipole BEM
Proceedings of the ICA congress
Recently, application fields of the BEM have been expanding using the fast multipole BEM (FMBEM), which is an efficient BEM solver with the application of the fast multipole method to the BEM. However, when applying the BEM to flow induced noise analyses based on Lighthill's analogy, since the number of sound sources is enormous, the processing time for sound source evaluation increases. This markedly impairs the overall computational efficiency. To solve this problem, we have been studying a
... thod to apply the FMBEM for sound source evaluation. Specifically, the hierarchical cell structure for grouping the boundary elements was expanded to a structure including the sound sources which are widely distributed outside the boundary, and the expanded representation of the contribution from the sound sources was introduced. However, since we used the high-frequency FMBEM which is based on Rokhlin's diagonal form, it was unstable at low frequencies. In this paper, we propose a stable sound source evaluation method at low frequencies using the low-frequency FMBEM which is based on the original multipole expansions. We also show its effect on the computational load through a numerical example: a flow induced noise analysis around a side view mirror where the number of elements and sources are roughly six thousand and three million, respectively.