低温风洞大空间液氮喷雾冷却数值模拟分析

Numerical simulation of liquid nitrogen spray cooling in cryogenic wind tunnel

液氮喷雾冷却技术是实现低温风洞的降温及提高风洞试验雷诺数的最佳途径,为了深入研究液氮喷雾在风洞内的降温特性,应用CFD软件对低温风洞中液氮喷射制冷段部分的流动换热进行了数值模拟,分析了不同流场速度对于下游温度场的影响。建立了三维流体动力学模型,考虑顺流与垂直喷射两种喷嘴布置结构,考虑了液滴的蒸发、碰撞与破碎,在不同气流速度和温度下,获得了下游雾场分布特性。数值结果显示:来流速度的增加会加速液氮蒸发,从而降低下游的平均温度,但来流速度的增加会减小下游雾场的覆盖区域,导致计算区域温度不均匀;垂直喷射增加了来流与液氮颗粒之间的相对速度,降温效果优于顺流喷射。

Spray cooling with liquid nitrogen is a best way to obtain requisite temperature in cryogenic wind tunnel and gain large Reynolds number.In order to better understand the cooling characteristics,the nitrogen injection part of cryogenic wind tunnel is simulated through CFD software.The influence of flow velocitiy on the downstream temperature field is analyzed.The comparisons between parallel spray and vertical spray are presented.Under different fluid velocities and temperatures,downstream temperature field is obtained from the three-dimensional fluid dynamics model in which the droplet evaporation,droplet break up and droplet collision are taken into account.The results show that high velocity of the gas flow can accelerate the droplet evaporation,and then decrease downstream temperature.But the cross-sectional distribution of the temperature becomes less uniform.In vertical spray scheme,the droplet evaporation as well as the cooling of the stream are much better than that in the parallel spray scheme due to the higher relative velocity between the LN2 droplets and continuous phase.