A COMPARISON OF MODELS FOR THE WAVENUMBER–FREQUENCY SPECTRUM OF TURBULENT BOUNDARY LAYER PRESSURES

Aircraft cabin noise due to the fuselage boundary layer is determined by, among other factors, the wavenumber–frequency spectrum of the fluctuating boundary layer pressures, a quantity for which a number of models have been proposed. In this work predictions for the sound radiated by a boundary layer driven plate are investigated, with a view to determining which model is most appropriate to the cabin noise problem. It is found that, for the structural and boundary layer parameters typical of transport aircraft, the contributions of resonant, acoustically inefficient plate modes dominate the radiated power. When these modes are strongly driven by the boundary layer, their excitation levels are determined by the “convective peak” of the wavenumber–frequency spectrum (where most of the fluctuation energy lies), and the radiated sound is found to be sensitive to details of the shape and location of the peak, giving differing results for models normally thought to agree at this point. Otherwise, it is the sub-convective region of the wavenumber–frequency spectrum that is important, and differences between models here lead to corresponding discrepancies in radiated sound predictions. Since the first case is generally more problematic, one can conclude that a suitable model must above all describe the convective peak accurately; however, the extent to which existing alternatives do so remains unclear.