Prediction of Aeroacoustical Interior Noise of a Car, Part-1 Prediction of Pressure Fluctuations on External Surfaces of a Car

A wall-resolving Large Eddy Simulation (LES) has been performed by using up to 40 billion grids with a minimum grid resolution of 0.1 mm for predicting the exterior hydrodynamic pressure fluctuations in the turbulent boundary layers of a test car with simplified geometry. At several sampling points on the car surface, which included a point on the side window, the door panel, and the front fender panel, the computed hydrodynamic pressure fluctuations were compared with those measured by microphones installed on the surface of the car in a wind tunnel, and effects of the grid resolution on the accuracy of the predicted frequency spectra were discussed. The power spectra of the pressure fluctuations computed with 5 billion grid LES agreed reasonably well with those measured in the wind tunnel up to around 2 kHz although they had some discrepancy with the measured ones in the low and middle frequencies. The Dynamic Smagorinsky Model (DSM) was adopted for the subgrid-scale turbulence model of LES while the resulting spatially-filtered Navier-Stokes equations of the incompressible fluid flow were solved by a Finite Element Method. In the second paper of this series of studies, the hydrodynamic pressure fluctuations computed on the car surfaces will be used as the unsteady loading for computing the panel vibration of the test car by using Finite Element Method, and finally the interior acoustical fields will be predicted by solving the Helmholtz equation for sound propagation. The contribution from the external acoustical field to the interior noise, which was not simulated by the present incompressible LES-based approach, was estimated based on the acoustic analogy, and was confirmed to be negligibly small compared with those from the hydrodynamic loading in the present case.