基于音速喷嘴固体内部温度分布的“热效应”分析
Analysis of Thermal Effects on Body Temperature Distribution of Sonic Nozzles

由于音速喷嘴自身特殊的结构, 气体在喷嘴中膨胀降温, 低温气体与喷嘴固体内部结构的传热过程一方面会使喷嘴固体内部结构产生热膨胀现象, 另一方面会使热边界层发生变化, 称之为音速喷嘴“热效应”．作为“热效应”的基本特性, 音速喷嘴固体内部温度分布特性值得深入研究．首先结合音速喷嘴固体内部瞬态温度分布测量传感器及克里金空间插值算法, 获得了瞬态温度分布云图．实验结果表明, 喷嘴固体内部温度轴向分布呈现两端高中间低特点, 实验最大温降达14.2 ℃．接着分析了“热效应”对流量计量的影响．一方面, 从有限元分析角度研究了喷嘴固体内部结构约束膨胀对流动特性的影响, 对于喉径为2.15 mm的喷嘴, 将喷嘴固体内部结构约束膨胀简化为自由膨胀修正流出系数会引起较大误差．另一方面, 根据热边界层理论修正式计算发现, 当温降为10 ℃、喉部雷诺数为1.0×103时, 由热边界层变化引起的流出系数误差达到0.408% ．
For the special structure of the sonic nozzle，the gas expands and its temperature drops greatly when flowing through the sonic nozzle. The heat transfer between the nozzle body and the fluid produces a series of complex effects on nozzle body and thermal boundary layer called “thermal effects”. As the essential characteristics of thermal effects，temperature distribution of the nozzle body was investigated further. Firstly，based on the temperature distribution sensors and Kriging’s interpolation method，the transient isothermal maps of nozzle body were obtained. It is found that the minimum temperature point appears in the middle of the nozzle and the temperature drop could be up to 14.2 ℃. Then，thermal effects on mass flow-rate of sonic nozzle were discussed from two aspects. The first one is constrained thermal expansion. Based on the FEA method，for the 2.15 mm nozzle，it is found that the constrained thermal deformation could not be simplified as free expansion to correct the discharge coefficient. The second one is thermal boundary layer. According to boundary layer theory，for typical body temperature drop of 10 ℃，the discharge coefficient at Re＝1.0×103 will increase to 0.408% which cannot be ignored