Experimental investigation of the global cavitation dynamic behavior in a venturi tube with special emphasis on the cavity length variation

Experiments were conducted to investigate the global cavitation behavior in a venturi tube. Images of various cavitation stages were captured and analyzed to study the development characteristics of the cavity length and the factors influencing the cavity growth. The results show that once cavitation occurs, the flow rate remains almost constant regardless of the outlet pressures variations, and the pressure ratio and cavitation number are linearly related. Cavitation occurs each time regardless of the inlet or outlet pressure at the same critical pressure ratio of 0.89, which corresponds to a critical cavitation number of 0.99. The cavity length is only the function of the pressure ratio or the cavitation number independent of the inlet pressures. The development tendency of the cavitation structure and the cavity length can be divided into two sections by a transition pressure ratio of 0.47 (corresponding to a transition cavitation number of 0.51). When the pressure ratio is greater than the transition value, the upper and lower parts of the cavity cloud do not touch each other yet and the cavity length increases relatively slowly as the pressure ratio decreases. Below the transition value, the upper and the lower parts of the cavity cloud meet along the centerline and the cavitation becomes more sensitive to the decreasing outlet pressure resulting in the cavity length increasing faster. However, the cavity lengths in the both parts are linearly related to the pressure ratios or cavitation numbers.