Study On The Transonic Expansion And Supercooling Condensation Of Cryogenic Nitrogen

In cryogenic wind tunnels,liquid nitrogen spray is often used to reduce the airflow temperature,so as to increase the test Reynolds number and reduce the operating power of the wind tunnel.However,when pure cryogenic nitrogen flows through the airfoil surface,condensation is very likely to occur due to expansion and cooling.However,gas expansion and supercooling condensation in transonic process is a very complex phase transformation process,and its nucleation is a heat and mass transfer process on the nanometer scale,which leads to the inapplicability of the macro continuum on the micro scale.Therefore,the study of cryogenic nitrogen microscale nucleation mechanism and supercooling condensation characteristics under transonic expansion is beneficial to realize effective operation of full-size Reynolds number simulation in cryogenic wind tunnel,and is of great value to meet the needs of domestic aerodynamic tests of new aircraft.In this paper,a visual experimental device for spontaneous condensation two-phase flow of transonic Laval nozzle was developed,and experimental research on supercooling condensation characteristics of cryogenic nitrogen transonic expansion under different inlet conditions and different profiles was carried out by using the Laval nozzle designed with equal expansion rate.Pressure measurement at Wilson point and droplet parameter measurement were respectively carried out.The pressure jump caused by condensation effect and corresponding positions in the nozzle were captured successfully,as well as the droplet size and number density distribution formed by spontaneous condensation of nitrogen.Based on the experimental data of cryogenic nitrogen transonic expansion and supercooling condensation,the non-isothermal modified nucleation model proposed by Kantrowitz and Gyarmathy droplet growth model were used to conduct numerical verification of key parameters in various experimental conditions,and to analyze the flow law and droplet size and distribution.It is found that the numerical results of this model are consistent with the static pressure distribution and liquid phase parameters under different conditions,but there are differences in the prediction of the initial location of condensation,droplet size and number density distribution.By introducing different nucleation rate correction factors for calculation and comparing the experimental data,it is found that the nucleation rate correction factor f is 0.4 can predict Wilson point more accurately.The Young(β = 2,ε = 9)droplet growth model was used to further verify the droplet size and density distribution.It was found that the prediction of liquid phase parameters can be greatly improved by introducing the droplet growth coefficient K =12.On this basis,the influence of nozzle inlet superheat,nozzle inlet pressure and different nozzle expansion rate on the flow of supercooling condensation is analyzed.It is found that the change of any parameter will lead to the change of the initial position of condensation and the amount of liquid.Based on the established flow mathematical model,the transonic expansion flow process of low-temperature nitrogen flowing through the NACA 0012-64 airfoil was numerically studied,and the interaction between the boundary layer on the airfoil surface,aerodynamic shock wave and supercooling condensation was paid attention to.The results show that: For a given test Reynolds number,a finite reduction of operating pressure and temperature within a reasonable range will not produce condensation effect on aerodynamic tests.Reasonable use of the total temperature and pressure of the gas for the test,lower working pressure will provide less liquid nitrogen injection and lower fan drive power.Under the same inlet pressure,the experimental Reynolds number can be greatly increased by making full use of the gas supercooling area and appropriately decreasing the inlet temperature.