Three-Dimensional Numerical Simulation Of Cavitating Flows In Thermosensitive Fluids

In recent years, the demands for the liquid rocket thrust vehicle has increased to meet the activities of manned spaceflight and deep-space exploration. The cryogenics fluids are used as rocket propellant, at low inlet pressure and high pump rotational speeds, cavitation is prone to appear in the inducer section. Cavitation induces strong mechanical vibration and can severely impact the reliability and performance of the liquid rocket engine. In general, liquid hydrogen and liquid oxygen used in rocket propulsion are very thermosensitive and consequently the cavitating flows become more complex due to the thermal effects. Therefore, it is very important to devolep a robust computational strategy to address the rich physical characteristic involved in the thermodynamic effects on cavitation. In present study, steady cavitating flows and unsteady cavitating flows in thermosensitive fluids are investigated by combining numerical method and experimental data. The main research contents are as follows:Based on the theory of homogeneous equilibrium flow model, the basic mathematical models and numerial methods for cavitating flows in thermosensitive fluids are established. Temperature dependent physical properties of liquid nitrogen, liquid hydrogen and fluoroketone are implanted to the CFX solver code through the secondary development of CFX software, and the thermodynamic effects in the cavitation are taken into account as a source term based on the latent heat in the energy equation. The cavitation model and turbulence model are solved in conjunction with the mass, momentum conservation and engery equation.Based on the characteristic of steady cavtating flows in thermosensitive fluids, we evaluate the application of modified empirical constants and thermodynamic cavitation model, a numerical approach are modeled for steady cavitating flows in thermosensitive fluids. The pressure distribution and temperature drop are different due to difference of the mass transfer mechanism of the three cavitation models, Zwart and Merkle cavitation model predict better results than Kunz cavitation model, but the numerical results still show some difference from the experimental data. Based on the heat diffusion equation and energy balance energy equation, the extended Zwart cavitation model predicted more accurately for the cavitating flows in thermosensitive fluids.Based on the numerical method of steady cavitating flows, numerical simulation of cavitating flows are conducted over three dimensional hydrofoil and ogive in liquid hydrogen and liquid nitrogen respectively, the pressure, temperature, liquid volume fraction, vapor volume fraction, mass transfer rate and typical thermal parameters are obtained. Furthermore, the efffets of physical properties on the cavitating flows characteristic are analyzed. The obtained results provide an insight into the thermodynamic effect on the cavitating flows.Based on the characteristic of cavitating turbulent flow, a three-dimensional numerical simulation method of unsteady cavitating flows is established by conducting the sensitivity of control parameter in the Partially-averaged Navier-Stokes(PANS) turbulence model. The numerical resolution can be performed from Reynolds-averaged Navier-Stokes(RANS) to direct numerical simulation(DNS) by varying the filter parameter. Therefore, it can improve the prediction of turbulence viscosity and smallscale vortices. Compared with the experimental data, more complicated cavitating flow and cavity shedding can be captured well with smaller fiter parameter in PANS model.Based on the numerical method of unsteady cavitating flows, numerical simulation of unsteady cavitating flows in fluoroketone, liquid hydrogen and liquid nitrogen are conducted over three-dimensional NACA0015 hydrofoil, vortex structure, vorticity, velocity vector, hydrodynamic and temperature gradient in the cavitating flows field are analyzed. The obtained results provide an insight into the evolution mechanism of unsteady cavitating flows in thermosensitive fluids.