Experimental research on the mixture properties inside cloud cavitation region

Cavitating flows are unique phenomena in the research field of hydrodynamics. Within the cavitation region, vapor and water are mixed in a complex state. Special experimental techniques are required to obtain the mixture properties. Both non-intrusive and intrusive techniques for cavitating mixture measurement are reviewed, including ionizing radiation, endoscopy, electrical impedance probes and optical fiber probes. In comparison with the experimentally demanding non-intrusive methods, intrusive probe techniques provide simple and stable single-point measurements for the void fraction, bubble velocity and bubble size. Recent applications of phase-resolved probe techniques are then introduced. The electrical impedance probe and optical fiber probe were used in the mixture property measurements in wedge-plate and hydrofoil cavitation, respectively. The time-averaged void fraction and statistical distribution of the bubble size were obtained. The results indicate that the void fraction within cloud cavitation is closely related to the cavitation number, and the characteristics of the bubble size distribution are quite similar between the two kinds of cloud-cavitating flows (wedge-plate and hydrofoil cavitation).