Helmholtz Resonance of Pinhole-Mounted Sensors for Wall Pressure Fluctuations Measurements

The effect of turbulent boundary layer flows on the Helmholtz resonance of pinhole-mounted sensors for the measurement of wall pressure fluctuations is investigated. With different pinhole sizes and volumes behind the pinholes, different resonance amplitudes and frequencies are produced. The test flows cover a large range of Reynolds numbers, 2100 < Re θ < 14500, and include favorable and adverse pressure gradients. The results show that the resonance amplitude and frequency depend on the flow conditions. With the modification of the damping factor and the resonance frequency of the pinhole-mounted sensors determined with acoustic excitation, the flow-induced resonance can be corrected for the measured wall pressure spectra. Based on the present test results and a database from the literature, it is assumed that the first Rossiter mode is excited when its frequency coincides with the Helmholtz resonance frequency.