Wall-Pressure Fluctuations Inside Attached Cavitation

This study experimentally investigates the statistics of wall-pressure fluctuations and their source inside attached cavitation under different cavity regimes. Experiments were conducted in the divergent section of a convergent-divergent channel at a constant Reynolds number of Re = 7.8 × 105 based on throat height, and different cavitation numbers σ = 1.18, 0.92, 0.82 and 0.78. Four high-frequency unsteady pressure transducers were flushed-mounted in the divergent section downstream the throat where cavitation develops to sample the unsteady pressure signals induced by cavity behaviors. Flow visualization and wall-pressure measurement in high frequency on the order of MHz were employed using a synchronizing sampling technique. Results are presented for sheet/cloud cavitating flows. Specifically, sheet cavitation with both inception shear layer and fully cavitated shear layer and cloud cavitation under re-entrant jet dominated shedding and shock wave dominated shedding are studied. Compared with re-entrant jet, the interactions between shock wave and cavity could induce pressure peaks with high magnitude within cavity, which will collapse the local vapor along its propagating path and reduce local void fraction. Furthermore, statistics analysis shows that within the cavity, wall-pressure fluctuations increase with the distance to cavity leading edge increase in the first half of cavity length, and the moments of the probability density distribution skewness and kurtosis factor decrease, indicating the asymmetry and intermittency of wall-pressure fluctuation signals decrease. In shock wave dominated cavity shedding condition, the skewness and kurtosis factor increase. These results can provide data to improve the accuracy of turbulence modeling in numerical simulation of turbulent cavitating flow.