Numerical Simulation of Flow Characteristics in Fuel Nozzles Under Cavitation and Flash-Boiling Conditions

Abstract

Cavitation plays a crucial role in various fuel systems and sprays applications. Due to the limitation in measuring the cavitation flow in fuel nozzles experimentally, numerical simulations can be used as an alternative in exploring the underlying physics. Most of the previous simulations of cavitation flow in nozzles were carried out under isothermal conditions, which becomes invalid when the thermal effect is strong. To consider the thermal effect on the flow characteristics in fuel nozzles, a modified cavitation model is adopted in this study to simulate the fuel flow in a plain orifice nozzle under cavitation and flash-boiling conditions. The thermal effect is considered by modifying the source/sink terms representing condensation/evaporation based on energy balance. The comparison with experimental data shows that the traditional cavitation model overpredicts the vapor generation, while the modified cavitation model can predict better the relationship of the flow coefficient and the fuel temperature, including the cavitation at the throat and the flash boiling at the outlet. The effects of key parameters are also analyzed. The results show that with increasing the inlet fuel temperature, the cavitation at the throat and the flash boiling at the outlet occur gradually and then mix at high-temperature conditions. With the decrease in the ambient pressure, the flow in the nozzle gradually transits from single-phase flow to cavitation flow and then to flash-boiling flow. Increasing the injection pressure can inhibit the generation and the growth of superheated vapor near the nozzle outlet.