Prediction and analysis of vehicle interior noise according to incompressible and compressible external surface pressure fluctuations due to external flow

The vehicle interior noise caused by high-speed external flow is one of critical issues for product developers in a design state. However, the pressure fluctuation in external flow is transferred though the vibration of vehicle structure to the interior pressure fluctuation, and the external pressure fluctuations consist of incompressible and compressible waves. The former is associated with the turbulence fluctuation and the latter is related to the acoustic waves. Although the magnitudes of the compressible components were generally lower than those of the compressible ones, its contribution to the interior noise level cannot be neglected because the transmission paths of incompressible and compressible pressure waves through the wind shield and window glass of the vehicle are quite different from each other. Therefore, it is essential to assess the relative contributions of the compressible and incompressible pressure fluctuation components of external flow to the interior noise of high-speed vehicle in a design stage. In this paper, the vehicle interior noise caused by exterior flow field is predicted and analyzed using the high-accurate large eddy simulation techniques and the wavenumber-frequency analysis. First, Large Eddy Simulation (LES) techniques were employed to accurately predict the external flow field including the acoustic field around a vehicle running at a speed of 110 km/h. Second, surface pressure fluctuations on the vehicle front wind shield and side windows were decomposed into incompressible and compressible ones using the wavenumber-frequency analysis. Lastly, the interior sound pressure levels are predicted by solving the one-way fluid-structure-fluid interaction with input of each incompressible and compressible pressure fluctuations. The results showed that the contribution of compressible component to interior noise level is crucial in the high frequency range.