Author(s): Munz Claus-Dieter, Kempf Daniel, Beck Andrea, Kuhn Thomas
Beside engine and tires the sound generated by fluid flow around a car may be an important acoustic noise source. One of the key objectives in aeroacoustic optimization is the prevention of tonal noise, which is perceived as most annoying by the observer. Strong tonal noise may occur due to the interaction of acoustic waves with the fluid flow and resulting feedback. Situations considered in this paper is the side-view mirror problem, but also flow and acoustics over slots and cavities. \n\nWe show high fidelity large-scale simulations based on the compressible Navier Stokes equations resolving acoustic sources and acoustic propagation within the fluid flow. \nDue to the large range of spatial, temporal and energetic scales occurring in the acoustic field as well as in the transitional and turbulent flow, this direct approach demands high numerical accuracy, while maintaining a certain robustness required for large eddy\nsimulations (LES). We employ a high order discontinuous Galerkin spectral element method, which exhibits arbitrary high order accuracy as well as excellent scaling for massively parallel simulations. Cell-local polynomial cut-off filters are employed to avoid aliasing. Due to the fact that the problem is quite sensitive with respect to the fluid flow and the frequency may switch by small fluctuations a non-intrusive method for quantifying uncertainties is combined with the deterministic simulations. \n\nAs applications we discuss the simulations of a side mirror exhibiting tonal noise generation. The computational flow field is shown to agree remarkably well with the corresponding experimental one. Discrete peaks are obtained in the computational acoustic spectrum, originating at the trailing edge of the mirror downstream of laminar separation. Based on a perturbation analysis, the tonal noise is deduced to be caused by an acoustic feedback loop. \nNumerical results are also shown for cavity problems with different uncertain parameters.
Name: Prof Claus-Dieter Munz