CFD Modeling And Experimental Study Of Cavitation In Cryogenic Liquids

This paper conducts CFD numerical simulation and preliminary experimental study on cavitation in cryogenic liquids. This specific issue is important in improving the stable operation of the propulsion system in liquid-fuel rocket. It also represents a broader class of problems where the fluid is operating close to its critical temperature and thermal effects of cavitation are pronounced. Characteristics of cryogenic cavitation, comparing with that of water, are changes in temperature, more porous cavity, mushy interface and decreased intensity of cavitation under similar conditions.The present paper investigates the status quo in research of thermal effects in cavitation of cryogenic fluids, which are primarily based on CFD simulation of water cavitation. Then the model on which the essay focuses is presented in detail It combines "full cavitation model" with energy equation to account for the mass and energy exchange between liquid and vapor. Turbulence model based on RANS equations are also resolved. Using the experiments of NASA as a model problem, numerical simulation is conducted on cryogenic cavitation in two-dimensional hydrofoil, axisymmetrical ogive and venturi. Careful considerations in gird structure, near-wall treatment and model parameter selection are first included in the simulation. Then experimental data of NASA and computational profile of pioneering researchers are then compared with our simulation results, which is solved in Fluent 6.3 under different working conditions, to validate the correctness of this model. The mechanism of cryogenic cavitation and its sensitivity to cavitation number are further analyzed.In considering the fact that the assumption in full cavitation model, which set the bubble radius to be constant, is unjustifiable for dynamic cavitation, the second important part of this paper is focusing on the development of a so-called dynamic cavitation model. It is obtained by combing Rayleigh-Plesset bubble dynamic equation with homogenous nucleation theory. The deduction process considers the radius of single bubble to be a function of local pressure based on the assumption of quasi-steady thermodynamic equilibrium during the cavitating process. When the empirical parameters are set to be Ce=0.018,Cc=0.01, dynamic cavitation model is validated by simulating quasi-steady cavitation in hydrofoil and ogive from NASA with consideration of the phase-change thermal effects. The computational results accord well with the experimental data reported by NASA as well as the numerical calculations with previously discussed full cavitation model.Experimental study on visualization of cryogenic cavitation is also conducted in this paper. The finished part of this work is schematic system design and instrument selection, including temperature sensors, pressure sensors, mass flow meter and high speed camera. By now, the rudiment of the experimental system is set up.