Wall pressure fluctuations induced by transonic boundary layers on a launcher model

Wind tunnel tests on a scaled model of the VEGA aerospace launcher have been performed at transonic Mach numbers and for variable angle of incidence in order to characterize the statistics of the wall pressure fluctuations during different flight conditions. Pressure signals are measured simultaneously in several positions along the model and are analyzed both in the physical domain and in the Fourier space focalizing attention in the region where the payload would be located. The time domain analysis reveals that the propagation of pressure perturbations within the turbulent boundary layer is driven by two different mechanisms, one associated to hydrodynamic pseudo-sound effects and the other to pure acoustic effects. The statistical results are interpreted within the framework of literature spectral models and the physical mechanisms underlying the observed behaviours, in particular the effect of a shock wave moving downstream for increasing Mach numbers, are retrieved with the aid of Schlieren flow visualizations.