The Characteristics of Sub-Convective Wall Pressure Fluctuations in a Turbulent Boundary Layer

The characteristics of sub-convective pressure fluctuations under a 2D homogeneous turbulent boundary layer has been a topic of debate due to limited data availability. Experimental measurements suffer from spatial aliasing and poor signal-to-noise ratios which make it difficult to quantify these pressure fluctuations. This experimental study explores a measurement technique with large sensors and a large array. The sensors are developed in-house with a large surface area and comprise of a volumetric acoustic cavity with one end housing a microphone and the other with small pores which communicate the pressure fluctuations in the flow. A wall pressure spectrum prediction model for a group of sensors is presented by convolving existing wall pressure models and the spatial sensitivity function of the sensor defined by its pore distribution. The design proposed by the modeling procedure was manufactured and tested in a fully developed boundary flow of a wind tunnel revealing sub-convective pressure fluctuations 45 dB below the convective ridge. Comparisons between the measured data and existing models reveal a need to modify or develop a new wall pressure spectrum model with better sub-convective pressure predictions.