Unsteady cavitation characteristics of liquid nitrogen flows through venturi tube

The dynamic cavitation characteristics of liquid nitrogen flow through a transparent venturi tube are experimentally investigated in a variable pressure ratio tunnel. The common results are presented at different pressure ratio, including the temporal and spatial changes of the temperature and pressure as well as the flow rate, together with the visual observation of the cavitation unsteady behaviors using the high-speed camera. The analyses on the measured dynamic pressure data and images reveal that the shedding frequency and length of cavity linearly increases, while the pressure amplitude exponentially increases, as the pressure ratio increases. Specially, a shock wave induced condensation front is observed propagating upstream within the attached cavity when the pressure ratio approximately exceeds 2.23. The wave generates from the collapse of the cavitation cloud and is considered to be the predominate mechanism of the cavitation shedding. A one dimensional theoretical equation in consideration of thermal effect is developed to estimate the speed of condensation front. And, the Strouhal number based on the condensation wave speed is found to be close to 0.5 for both water and liquid nitrogen cavitation, which can be utilized to estimate shedding frequencies for both cryogenic and room-temperature fluids. The initial cavitation development and characteristics are also investigated. The data from the present study can be used as a bench mark for CFD code validations.