Wall pressure measurements and acoustics in turbulent pipe flow

Measurements of the turbulent boundary layer (TBL) wall pressure spectrum and acoustic field were conducted in the Boundary Layer Research Facility of the Applied Research Laboratory. This facility uses glycerine as the working fluid. Subminiature, piezoresistive pressure transducers were used for these measurements. The TBL wall pressure spectrum was obtained using a novel signal processing technique (transducer difference signals) that minimized both acoustic and vibration-induced noise while maintaining the integrity of the measured TBL wall pressure spectrum. A measurement involving the coherence function between these transducer difference signals validated the measured TBL wall pressure spectra and all assumptions used in the development of the measurement technique. The measured nondimensionalized spectra of the TBL fluctuating wall pressure are compared to those measured in previous investigations. These comparisons have substantiated a maximum, normalized transducer diameter for the complete resolution of the high-frequency spectral energy associated with the pressure fluctuations within the TBL. In this investigation, a transducer diameter of 2.1 viscous wall units is demonstrated. This is a factor of 9, smaller than ever before achieved. [Work supported by Applied Research Laboratory E/F Program under NAVSEA contract.]