Measurements of the fluctuating wall pressure field across the transition region of a flat plate zero pressure gradient boundary layer have been performed with a 64-element linear array of sub-miniature hearing-aid microphones. The measurements provide a unique description of the formation, convection, and growth of turbulent spots in the transition zone and insight into a potential source of low-wavenumber energy. A model for the nonhomogeneous wavenumber-frequency spectrum has been formulated based on the observed spatio-temporal properties of the field. Measured array-averaged wavenumber-frequency spectral levels for the transitional boundary layer collapse with fully turbulent spectra in the vicinity of the convective ridge when scaled by intermittency, similar to previous findings for single point spectra. The transition zone convective ridge is broader, however, consistent with the notion of rapidly evolving (versus equilibrium) structures. Insight into the low-wavenumber portions of the spectra requires an improved array phase calibration. Wavelet based transform methods are being pursued to understand the evolution of spectral components during spot formation and to resolve the space-varying wavenumber content of the field.

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