Experimental Observation On Dynamic Characteristic Of Liquid Nitrogen Cavitation In Venture Tube

Cavitation phenomenon is an important factor to influence the performance and life of the hydraulic mechanical. The venture tube is a key component in the rocket engine propelled by the liquid fuel, such as liquid hydrogen and liquid oxygen, while it also greatly suffers from the cavitating flow due to the larger density ratio of vapor to liquid and the working state at small sub-cooling. Furthermore, the cavitation for cryogenic fluids inevitably occurs accompanying with significant thermal effect, therefore, the numerical model applicable to normal fluids cavitation is no longer suitable for cryogenic fluids. In order to improve the modeling capacity for cryogenic fluid cavitating flow, the specialized researches are required.A visualization experiment equipment for the observation of cavitating flow of liquid nitrogen is designed, where, the venturi tube is made of transparent PMMA glass with temperature and pressure sensors flushed with the inner surface. The cryogenic self-sealing technology is figured out to connect the venturi tube and metal pipes at low temperature with a satisfactorily results. The experiment equipment is proved to be stable and reliable, the cavitation images are recorded with the high-speed camera, the temperature, pressure and flow rate data is also recorded synchronously by the data acquisition system.The experimental results show two typical cavity breakage patterns in the cavitation flow, namely the continuous mode and the intermittent mode. In the intermittent mode, the integral cavitation cloud periodically shed off from the wall. The fluctuation of pressure and flow rate under the effect of sonic speed is illuminated and the pressure data of cavitation zone is analyzed using FFT method. It is found that the shedding frequency, cavitation length and fluctuation amplitude increase with the increase of pressure ratio, while the Strouhal number changes very little, especially in the large pressure ratio range, The influence of the thermal effect helps reduce the intensity of cavitating flow of cryogenic fluids. The initial cavitation characteristics is analyzed and the critical cavitation pressure ratio is outlined. This work provides important guidance for the numerical model validation, and the future research direction is also pointed out.