Effect of sensor size on the wall pressure coherence measurement beneath turbulent boundary layers

Kurzfassung

The wall pressure fluctuations beneath turbulent boundary layer flows can be measured by flush- and pinhole-mounted sensors. The pinhole-mounted sensors have a small sensing area that can resolve the high-frequency pressure fluctuations induced by the small-scale structures of turbulence. However, the resonance of the pinhole structure and the difficulty of mounting are the disadvantages for practical use. In contrast, the flush- mounted sensors are mostly more accessible for practical application and do not face the resonance problem. The cost is the high-frequency attenuation for the one-point spectra measurement caused by the signal averaging over the 'large' sensor surface. This effect has been reported by several studies, which showed that the attenuation increases with decreasing flow velocity and adverse pressure gradients. Besides the one-point spectra, the wall pressure coherence is an important feature that can significantly affect the noise generation. To the best of the author’s knowledge, the sensor-size effect on the wall pressure coherence has not been systematically reported. In this work, the coherence was measured by pinhole and flush-mounted sensors on a flat plate with and without pressure gradients. The sensor-size effect is presented using different pairs of sensors with equal sensor distances in the spanwise direction.