Influence of diffuser angle on cavitation evolution laws and regime transitions in a slit Venturi

This study experimentally investigates cavitation regime transitions and unsteady dynamics in a slit Venturi with a throat height of 1 mm under strong geometric confinement. Synchronized high-speed visualization and pressure measurements are conducted for two diffuser angles, β1=14° and β2=8°. The results show that diffuser angle strongly affects cavitation morphology and regime transition under the present confined-flow conditions. For β1, the flow evolves successively through supercavity, supercavitation, cloud cavitation, and shear-layer-like cavitation as the pressure recovery coefficient κ increases, whereas for β2, it develops through supercavitation, cloud cavitation, and sheet cavitation. A stable transparent supercavity and a highly irregular shear-cavitation regime are observed only in the β1 slit Venturi, while the β2 configuration favors denser cavitating structures and wall attachment. Near the transition from supercavity to supercavitation, a low-frequency unsteady mode is identified, characterized by upstream propagation of the vapor–liquid interface. Quantitative analysis further shows that the normalized average cavitation length increases as κ decreases within the present measured range and reaches values much larger than those reported in larger-scale Venturi flows. Under 1 mm confinement, the β2 configuration maintains a nearly constant Strouhal number of 0.04–0.06, whereas in the β1 cloud-cavitation regime, the shedding frequency can reach approximately 550 Hz under certain conditions and decreases rapidly with decreasing κ. These results indicate pronounced confinement and geometry effects on cavitation evolution, scaling behavior, and unsteady characteristics in slit Venturi flows within the tested operating range.