A Wave Propagation Solver for Computational Aero-Acoustics

E Solberg, Master thesis, University of Gothenburg, supervisor R Sandboge, examiner S Larsson, February 2012.

Simulation software is increasingly replacing traditional physical testing in the process of product development, as it can in many cases reduce development times and costs. In a variety of applications, the reduction of noise is an important aspect of the product design and using methods from the field of computational aero-acoustics (CAA), the generation and propagation of sound in air may be simulated.

In this project, a FEM-based solver for the three-dimensional Helmholtz equation, modeling the propagation of sound waves, has been developed and tested. The implementation includes Galerkin/least-squares stabilization. Both interior and exterior problems are handled; the latter by a coupled finite-infinite element method. Further, using a hybrid CAA methodology the solver may be coupled to a CFD solver, to simulate the sound arising from transient fluid flows.

The solver has been tested, and observed to perform well, on a set of interior and exterior problems. Results are presented for three cases of increasing complexity: first an interior, homogeneous problem with a known analytical solution, second an exterior problem with point sources and third an exterior problem with acoustic sources from a CFD computation, i.e. a full hybrid CAA simulation. In the two latter cases, the frequencies at which standing waves appear in a pipe and a deep cavity, respectively, are compared to theoretically computed values, and are seen to be well captured by the simulations. Moreover, the results of the full CAA simulation are compared to experimental data, to which they show good resemblance.

The mathematical model, numerical methods and implementation are presented in the report along with numerical results.


Photo credits: Nic McPhee