WAVE-NUMBER SPECTRA OF HIGH MAGNITUDE WALL-PRESSURE EVENTS IN A NUMERICALLY SIMULATED TURBULENT BOUNDARY-LAYER

A method for conditionally sampling the spatial field of the wall pres sure beneath a turbulent boundary layer in order to search for high ma gnitude events and calculate the corresponding wavenumber spectrum is presented. The high magnitude events are found using a simple peak det ection algorithm at a fixed instant in time and the wavenumber spectra are calculated using discrete Fourier transforms. The frequency of oc currence Soi high magnitude positive events is found to be approximate ly the same as for high magnitude negative events. The contribution of the high magnitude events to the rms wall pressure for various trigge r levels is calculated and compared with results from similar experime ntal studies performed in the time domain. The high magnitude events a re shown to occur infrequently and to contribute significantly to the rms wall pressure. Wavenumber spectra from the high magnitude positive and negative events are calculated and compared with the unconditiona lly sampled spectra. The high magnitude events contain energy focused around a particular streamwise wavenumber and have high broadband spec tral levels.