空化热力学效应对相间质量传输过程的影响

Thermodynamics Effect on the Mass Transport Process in Cavitation

为了分析空化热力学效应对相间质量传输过程的影响,应用二次开发技术在商业软件中引入修正的Merkle空化模型及液氮物性参数随流场温度的变化,并在能量方程的源项中考虑了空化的影响,对绕对称回转体液氮空化流动进行了计算.通过将计算结果与实验数据进行对比,对计算方法进行了验证.基于数值计算结果分析了空化热力学效应对质量传输过程的影响.相间质量传输过程包括蒸发和凝结过程.在蒸发过程中,低温流体空化的发展不仅与当地空化数σ有关,且依赖于流场的密度比R(T).随温度升高,液体/蒸汽的密度比梯度(dR/dT)增加,导致蒸发量减小;随温度升高,饱和蒸汽压变化梯度升高,导致蒸发量减小.凝结过程中,随温度升高,(1-φl)值减小,凝结量减小;随温度升高,max(0,Cp+σ)值增大,凝结量增加.

In order to analyze the influence of thermal effect on the mass transport process in cavitation,the modified Merkle cavitation model and the material properties of the liquid nitrogen at different temperatures are introduced into a software solver via a UDF（user defined function） with the consideration of cavitation influence on source term in energy equation.Computations are then conducted on an axisymmetric ogive in nitrogen under various cavitation conditions.The results are compared with the experimental data to verify the numerical method.Based on the numerical results,the influence of the thermal effect on the mass transport process could be analyzed as follows.The mass transport process includes the processes of evaporation and condensation.In the evaporation process,the cavitation characteristics is not only related to the local cavitation number σ,but also dependent on the liquid-vapour density ratio R（T）.With temperature increasing,the gradient of liquid/vapor density ratio dR/dT increases,which would tend to decrease the strength of the evaporation rate;on the other hand,with temperature increasing,the gradient of vapor pressure becomes larger,which would suppress the evaporation rate.In the condensation process,with temperature increasing,（1-φl） becomes smaller,that leads to the decrease of condensation rate;while,the increase of max（0,Cp＋σ） leads to the strength increase of the condensation rate.