Unsteady cavitation of liquid nitrogen flow in spray nozzles under fluctuating conditions

Liquid nitrogen spray cooling can achieve an excellent cooling performance in a cryogenic wind tunnel which can simulate supersonic flows with both high Reynolds number and Mach number for aerodynamic tests. However, the fluctuating flow of a liquid nitrogen supply system can lead to the fluctuation of the injection pressure which induces unsteady cavitation and makes it difficult to control the cooling and high-precision temperature in the cryogenic wind tunnel. To understand the characteristics of the unsteady cavitation in fluctuating flow, we developed the numerical models of liquid nitrogen cavitating flow through the spray nozzles. Sine functions are normally used to simulate the fluctuating inlet pressure, and the effects of the fluctuation amplitude and frequency on the cavitation processes are studied under different inlet temperatures. It is found that the cavitation changes periodically and is generally promoted by the pressure fluctuation. The increase of the frequency can slightly suppress the cavitation while the increase of the amplitude can promote the cavitation. The effects of amplitude and frequency are enhanced under a higher inlet temperature. These findings could benefit the design of cryogenic spray cooling systems in cryogenic wind tunnels.