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The investigated case is the o w past a generic side mirror mounted on a at plate at the Reynolds number of ReD = 5:2 10 5 based on the mirror diameter. The o w eld over the mirror is identied as sub-critical which makes LES an attractive candidate to the DES model used by some of the previous researchers. The present paper is a rst attempt to investigate the o w and acoustics of a generic side mirror at the Reynolds number of ReD = 5:2 10 5 by comparing DES and LES results using identical grid, second order schemes and the incompressible assumption. Two dieren t cases are investigated for this purpose. The rst case uses the hybrid DES-modelling technique combined with a "Trip-Less" approach proposed by Shur et al. and the second case is a partially resolved LES-simulation using the dynamic Smagorinsky model. The sound radiation for the present simulations is predicted from the Ffowkes-Williams and Hawkings analogy where the wall pressure uctuations and the pressure temporal derivative are the two source terms treated. The result shows good agreement for both cases in wall source levels even with the rather coarse mesh used in the mirror wake. The trends are however in slightly better agreement for the LES case than the DES case compared to the corresponding measured levels. The radiated sound for the DES case agrees signican tly better with the measured results compared to the LES results. The overprediction in radiated sound observed in the LES case is argued to primarily be caused by unresolved uctuations included in the surface integration. The DES model on the other hand is far more dissipative and reduces pollution of numerical noise in the signals. For an automotive application the wall pressure level results is by far the most important due to the interest in the driver and passengers subjective experience. Thus, the conclusion is that the LES approach is a better candidate compared to DES even though the mesh resolution over the plate by no means fullls the traditional restrictions in LES.

The Sub-Critical Flow Past a Generic Side Mirror and its Impact on Sound Generation and Propagation