S弯收扩喷管过膨胀状态下流动分离特性研究

Flow separation characteristics of S-shaped convergent- divergent nozzle under overexpanded condition

关键词:  S弯收扩喷管  过膨胀状态  流动分离  落压比  推力矢量角

Key words:  S-shaped convergent-divergent nozzle  Overexpanded condition  Flow separation  Nozzle pressure ratio  Thrust vector angle

摘要:

为了研究S弯收扩喷管过膨胀状态下的流动分离特性，数值模拟了不同落压比（NPR）下S弯收扩喷管内的流动特征。结果表明：在落压比为2.0时，喷管内发生非对称分离，出现非对称的双“λ”激波结构，喷流整体向上偏转，上侧出现限制性流动分离RSS，下侧出现自由性流动分离FSS，并产生三维分离涡，喷流出现明显的三维效应。随着落压比从高度过膨胀状态下开始增加，喷管下侧保持FSS不变，喷管上侧RSS逐渐向后移动，直至与外界大气相连，转变为FSS，之后随着落压比增加，上下侧分离结构逐渐对称。推力矢量角随着落压比的增加先增加，后在极小的落压比变化范围内快速降低，直至变为0°，之后保持0°不变。

Abstract:

In order to investigate the flow separation characteristics of S-shaped convergent-divergent nozzle under overexpanded condition， the flow characteristics in S-shaped convergent-divergent nozzle were numerically simulated under different nozzle pressure ratios （NPR）. The results show that at a nozzle pressure ratio of 2.0， asymmetric separation occurs in the nozzle， and an asymmetric double “λ” shock wave structure appears. The jet is deflected upward， with restricted shock separation（RSS） on the upper side and free shock separation（FSS） on the lower side. The three-dimensional separation vortices are generated， and the jet appears to have a significant three-dimensional effect. As the NPR increases from the highly overexpanded condition， the lower side of the nozzle maintains the FSS， and the RSS on the upper side of the nozzle gradually moves backward until it is connected to the outside atmosphere and transforms into FSS. Then as the NPR increases， the upper and lower side separation structure gradually becomes symmetrical. The thrust vector angle increases with the nozzle pressure ratio and then decreases rapidly to 0° in a very small variation range of nozzle pressure ratio， and then remains constant at 0°.