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978-3-8439-1907-4, Reihe Luftfahrt
Entwicklung einer Berechnungsmethode zur Vorhersage der Schallausbreitung im Nahfeld eines umströmten Kraftfahrzeugs
237 Seiten, Dissertation Universität Stuttgart (2014), Softcover, A5
This work deals with the numerical calculation of aeroacoustic excitations to estimate the interior noise level of a passenger car. Based on transient Detached Eddy Simulations with the commercial CFD code StarCCM+ direct and hybrid Computational AeroAcoustic methods are investigated and validated in the acoustic near and far field of adequate experiments. Synthesized pressure loadings (like Corcos or a diffuse sound field) on a finite element side window model of a Mercedes-Benz S-class pronounce the importance of the acoustic excitation in regard to structural vibrations.
As a first step the acoustics is investigated and validated in the far field of a rod-airfoil configuration to avoid masking effects of the weak acoustic content within the turbulent flow field. Besides of the direct CAA approach with the compressible Navier-Stokes solution two hybrid CAA methods based on the Lighthill and Möhring analogy are used in the commercial acoustic solver Actran.
The overall process from the excitation to the cabin noise is validated on a modified SAE body with an interior cavity and clamped side window. Due to wavenumber decompositions the acoustic near field can be analysed and the low acoustic content can be evaluated within the strong hydrodynamic pressure fluctuations of the compressible flow field. Numerical artefacts in the direct CAA approach can be observed. Additionally in the hybrid approaches beamforming results of digital microphone arrays confirm these artefacts and visualize further issues. Both the Lighthill and Möhring analogy provide no acoustic pressure in the source region and show a strong mesh dependency due to the separately used acoustic model.
To solve these challenges a new hybrid method based on the APE-2 equations is integrated into the commercial flow solver StarCCM+. This scalar wave equation derived from the APE-2 equation set solves the acoustic pressure field based on incompressible source terms. The approach combines the availability of both excitation fields separately, hydrodynamics and acoustics, in one software environment at the same time. The computed excitations are validated on the side window as well as the interior noise level with a combined FE/SEA structural model.
Finally the developed hybrid method is applied to a real passenger car of a Mercedes-Benz S-class.