The comprehension of the flow over a vehicle has become a topic of high concern for the transport industry. The pressure fluctuations beneath a turbulent boundary layer (TBL) are a source of excitation for the structure which radiates into vehicle and impairs the comfort of the passengers. The main vortices present in a turbulent boundary layer are hairpins structures which group into hairpin packets which seem to be playing a major role in TBL noise generation mechanisms. Their presence is demonstrated through instantaneous and statistical analyses of the velocity field extracted from the computation of a Mach 0.5 TBL on a flat plate performed using Large Eddy Simulation (LES) method. Therefore, a stochastic wall pressure model based on hairpin vortices is introduced to study the effect of streamwise pressure gradients on the wall-pressure wavenumber spectrum. The angle of individual hairpins as well as the mean velocity profile are implemented into the hairpin model as both these parameters are affected by pressure gradients. The model reveals that the angle of a single eddy influences the pressure field and spectrum in such way that the lower angle provides the higher levels. However, when implementing a superposition of several hairpins throughout the entire boundary layer thickness, high angle hairpins provide higher levels, meaning that adverse-pressure-gradient boundary layers provide the highest levels. This outcome is supported by results from LES computations of turbulent boundary layers subjected to both adverse and favorable pressure gradients.
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