低温流体闪蒸喷雾研究

Investigation of Cryogenic Flashing Sprays

为了研究低温流体闪蒸喷雾特性,建立了低温流体闪蒸计算模型,并通过试验进行了验证。在欧拉-拉格朗日框架下采用CFD-DPM方法模拟了闪蒸过程的气-液两相流场。研究表明,在闪蒸喷雾形态和温度分布特性方面,数值模拟与试验结果吻合。低温流体喷入低压环境后,在喷嘴出口附近便发生剧烈的闪蒸现象,呈现出巨大的喷雾角,并且喷雾温度急剧下降至环境压力对应的饱和温度;在喷嘴出口附近区域(x/d~40),过热闪蒸占据绝对主导地位,其蒸发速率高出其他换热2个数量级,随着喷雾液滴运动至流场下游,对流换热与热传导逐渐占据主导地位。闪蒸带来的强烈换热导致喷嘴附近可能会发生复杂的气-液-固相变,将会对发动机高空可靠点火带来风险。

In order to understand the characteristics of the cryogenic flashing sprays,a numerical model of flashing sprays was developed and validated with experiments.By employing the flashing model,a gas-liquid two phase flow was numerical investigated with CFD-DPM method in the Euler-Lagrange framework.The simulation results show fairly good agreement with experiments,both for the flashing spray morphology and temperature distribution.Once the cryogenic fluids were injected into low-pressure environment,a flash atomization and vaporization happened near the injector outlet with huge spray angles,and the sprays temperature dropped drastically to the saturation temperature corresponding to the ambient pressure.In the near-injector region(x/d~40),the flashing evaporation dominates the spray vaporization with the evaporation mass flow rate of about 2 orders of magnitude higher than that by the other heat transfers,whereas downstream the injector,the external heat transfer(i.e.heat convection and conduction)does.The violent heat transfer by flashing phenomena may result in complex phase transitions near the injector orifice,which will bring potential risks to the reliable high-altitude ignition of thrusters.