Flow field characteristics of underwater supersonic over⁃expanded gas jet
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摘要:
为研究水下超声速过膨胀燃气射流的流场特性,在压力水筒中开展了大扩张比锥形喷管的固体火箭发动机水下点火实验,并基于雷诺时均Navier⁃Stokes(RANS)方法和流体体积(VOF)模型进行数值求解,分析了过膨胀燃气射流与水介质的相互作用过程。研究表明:超声速过膨胀燃气建立射流通道后,射流核心区长度随喷管落压比的减少而减少;射流核心区剧烈振荡,表现为高频的膨胀和收缩,振荡频率随喷管落压比的减小而增加,范围为100~200 Hz;射流边界不断振荡,并伴随波系结构变化,当过膨胀程度较大时,激波进入喷管使其发生流动分离现象,流动分离点周期性往复移动;分离区内压力脉动没有显著的特征频率,主要集中在100~600 Hz的宽频带,锥形喷管水下流动分离的简易判据为喷管出口压力不低于环境背压的0.44倍。
Abstract:To investigate the flow field characteristics of underwater supersonic over⁃expanded gas jet,ignition experiment of solid rocket motors using conical nozzles with a large expansion ratio was conducted in the pressure tank.Combined with numerically simulated results obtained by Reynolds⁃averaged Navier⁃Stokes (RANS) and volume of fluid (VOF) model,the interactions between over⁃expanded gas jet and water were analyzed.The results showed that,the over⁃expanded gas jet formed a jet channel in the near depression area of the nozzle,and the length of the core area of the jet decreased with the decrease of drop pressure ratio.Dramatic periodic oscillation changes occurred in the core area of the jet,which was specifically manifested as the high⁃frequency expansion and contraction process.The oscillation frequency increased with the decrease of drop pressure ratio,within a range of 100-200 Hz.The boundary of the jet may constantly oscillate,accompanied by the synchronous change of the shock wave structure.When the degree of overexpansion was larger,the shock wave entered the nozzle to cause the flow separation phenomenon,and the flow separation point moved periodically and reciprocally.The pressure pulsation in the separation area presented the characteristic of high oscillation,but it had no significant characteristic frequency,which was mainly concentrated in the broadband of 100-600 Hz.The simple criterion for underwater flow separation of conical nozzle is that the pressure at the nozzle exit is not less than 0.44 times of the back pressure.
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Key words:
- underwater gas jet /
- over⁃expanded /
- supersonic /
- momentum jet /
- flow field characteristics
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表 1 水下超声速过膨胀燃气射流参数
Table 1. Parameters of underwater supersonic over⁃expanded gas jet
测点 1 10 0.2 50 0.40 2 30 0.4 25 0.20 3 50 0.6 17 0.14 -
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