Wavelet Analysis of Space-Varying Intermittent Wall Pressure Field of Transitional Boundary Layer

Measurements of the space-time fluctuating wall pressure field across the transition region of a flat plate zero pressure gradient boundary layer have been performed in an anechoic wind tunnel with a 64-element linear array of sub-miniature hearing-aid microphones (d⁺ = 15). Wavelet transforms are being used to quantify the structure and nonhomogeneous wavenumber-frequency spectral content of the field. The results illustrate that the fluctuations within the turbulent spots scale with those which exists in a fully developed turbulent boundary layer consistent with previous findings. The spectral contributions due to a second much larger length/time scale associated with the mean spacing between spots (e.g., turbulent spot wavepacket pulse trains) is under investigation. Based on an analysis of sinusoidal pulse train signals and consideration of the well established bursting frequency in turbulent boundary layers, it is conjectured here that the turbulent spot wavepacket pulse trains should produce a statistical distribution of energy about the mean fundamental pulse train frequency.