The flow characteristics of the plume ejected from a micro-jet engine’s rectangular exhaust nozzle have been studied by conducting experimental and numerical analyses. The radiated infrared signature of a plume ejected from a rectangular exhaust nozzle with a large aspect ratio in a jet propulsion engine is known to be significantly lower than that of a plume ejected from a circular exhaust nozzle. The velocity and temperature distributions, which are the flow characteristics of the jet, were measured to investigate this phenomenon. For this purpose, we installed a circular nozzle and a rectangular exhaust nozzle with an aspect ratio of five to a micro-jet engine. The results showed that the plume spreads wider as it moves away from the nozzle exit and that the velocity rapidly decreases in the case of the rectangular nozzle, contrary to the case of the circular nozzle. Similar tendencies were observed for the temperature distribution and magnitude of the ejected plume. Thus, we concluded that the flow distribution caused by the nozzle shape induces a greater drop in the radiated infrared signature of the plume ejected from the rectangular nozzle than the circular nozzle. Flow analysis was conducted to evaluate the flow in and outside the exhaust nozzle; results similar to those of the experiment were obtained. These results show that the ejecting jet has a greater mixing effect on the air outside when using the rectangular nozzle than the circular nozzle.

通过实验和数值分析，研究了从微型喷气发动机矩形排气喷嘴喷出的羽流的流动特性。众所周知，从喷气推进发动机中具有大长宽比的矩形排气喷嘴喷出的羽流的辐射红外特征明显低于从圆形排气喷嘴喷出的羽流的辐射红外特征。测量了速度和温度分布（射流的流动特性）来研究这种现象。为此，我们为微型喷气发动机安装了圆形喷嘴和长径比为5的矩形排气喷嘴。结果表明，与圆形喷嘴的情况相反，在矩形喷嘴的情况下，羽流随着远离喷嘴出口而散布得更宽，并且速度迅速减小。喷射羽流的温度分布和强度也观察到类似的趋势。因此，我们得出的结论是，与圆形喷嘴相比，由喷嘴形状引起的流量分布导致从矩形喷嘴喷出的羽流的辐射红外特征有更大的下降。进行流动分析以评估排气喷嘴内外的流动；得到了与实验相似的结果。这些结果表明，使用矩形喷嘴时，喷射射流对外部空气的混合效果比使用圆形喷嘴时更大。