Separation of convective and acoustic pressure fluctuations on the front side window of DrivAer model based on pellicular mode decomposition

Abstract

When a car is driven at high speed, the total pressure fluctuations on the side window include convective pressure fluctuation and acoustic pressure fluctuation, which have different generation mechanisms, transmission characteristics and efficiency. In order to understand the aerodynamic noise transmission mechanisms through the side window and calculate the aerodynamic noise accurately inside the car, it is necessary to separate these two kinds of pressure fluctuations. Based on the existing full-size DrivAer model, the pellicular mode decomposition theory proposed in recent years was investigated. With this approach, the two pressure fluctuations from a compressible CFD calculation acting on the side window were separated successfully. Through comparison with the pressure data obtained with the improved wavenumber decomposition approach, the reliability and accuracy of the pellicular mode decomposition approach for solving the acoustic pressure fluctuation was validated. Moreover, in comparison with wavenumber decomposition, the pellicular mode decomposition can be applied easily to any surface with arbitrary shape, even the surface curved in 3D. Further advantage of this approach is the ability to reconstruct the pressure field of convective and acoustic components individually at any frequency, which can help to understand the characteristics of these two pressure components. Disadvantage is however the handling of a large number of numerically computed pellicular modes, which is limited in principle by the implementation of finite element method. As a consequence, a reliable convective pressure fluctuation is difficult to be acquired directly with this approach.