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978-3-8439-0740-8, Reihe Ingenieurwissenschaften
Computational Aeroacoustics with a High Order Discontinuous Galerkin Scheme
135 Seiten, Dissertation Universität Stuttgart (2012), Hardcover, A5
The high order discontinuous Galerkin solver NoisSol for the linearized acoustic equations and its application to airfoil noise simulation are presented. Aiming at the fast simulation of the noise generation and propagation in domains with complex geometries, the discretization based on unstructured grids is seen as the favorable strategy. Further important requirements for an aeroacoustic solver are low dissipation and dispersion errors to enable the propagation of waves over a long distance to the far field. Discontinuous Galerkin schemes outrange finite volume schemes in these properties and are consequently the optimum choice for computational aeroacoustics (CAA) on unstructured grids. They furthermore convince with their low demands in grid quality.
For the simulation of aeroacoustics in flows with a low Mach number, the separation of flow and acoustic simulation is favorable, since both have to deal with different space and energy scales. For the acoustic calculation linearized equations can be used. They have transient source terms, which describe the excitation of the sound by flow phenomena. These sources as well as the linearization state of the equations depend on the local flow state. The linearization is done around the time averaged (’mean’) flow field.
A hybrid grid coupling has been developed and implemented with the DLR code PIANO to combine the advantages of the presented DG solver with the advantages of a finite difference (FD) solver in the obstacle free far field, which include a straightforward mesh generation for rectangular or cuboidal domains and a low memory demand. This work is based on ideas of T. Schwartzkopff and J. Utzmann and transfers them to the field of hybrid aeroacoustics. Furthermore, it has focused on industrial applications. Hence the number of schemes, codes and equations involved has been kept very low and the initialization process has been automated as far as possible.
A slat noise propagation simulation has been chosen to show the capabilities of the new framework. It deals with a NASA 30P30N three part airfoil with extended high lift devices in a low Mach flow. The acoustic simulations with NoisSol and with the coupled framework have shown a very good agreement, both in the pressure field as well as in the frequency spectrum. For the pure DG calculation the spectrum has also been compared to previous CAA results, which are based on the same source data. The spectra show a very good agreement.