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利用暂冲式环形射流诱导非定常激波聚焦实验装置,在环形喷口宽度为9.4mm,喷口前后压比分别为6.1和17.9的条件下进行了环形射流聚心碰撞诱导非定常激波聚焦的实验研究,并以数值计算为补充,对流场的演化过程进行了详细的分析。结果表明,环形射流启动时形成的前导激波聚心碰撞是产生非定常激波的主要原因。在环形喷口宽度d=9.4mm,压比π=6.1的条件下,激波聚焦的峰值压力可达2.16MPa,为凹面腔内部初始压力的21.8倍。激波在凹面腔内聚焦后形成回传激波,凹面腔底部的气流经入射激波与回传激波两次压缩后,压力大大提升,向环形喷口回流,使下一循环中环形射流的欠膨胀度降低,前导激波强度也相应减弱,随之产生的非定常激波和激波聚焦强度也有所降低。此外,一个循环中输入凹面腔的能量由环形喷口宽度所决定,因此,当喷口前后压比大于临界压比1.89时,保持喷口宽度不变而仅改变喷口前后压比,所产生的非定常激波和激波聚焦强度基本不变。
Using the tentative annular jet-induced unsteady shock focusing experimental apparatus, the experiment of inducing the unsteady shock focusing by annular jet centripetal collisions was carried out under the condition that the annular orifice width is 9.4mm and the pressure ratio before and after the orifice is respectively 6.1 and 17.9 Studied and calculated by numerical calculation, the evolution of the flow field was analyzed in detail. The results show that the leading shock wave formed at the start of toroidal jet is the main cause of unsteady shock wave. Under the circumstance that the annular orifice width d = 9.4mm and the pressure ratio π = 6.1, the peak pressure of shock focusing can reach 2.16MPa, which is 21.8 times of the initial pressure in the concave cavity. After the shock wave is focused in the concave cavity, a return shock wave is formed. After the gas flow at the bottom of the concave cavity is compressed twice by the incident shock wave and the return shock wave, the pressure is greatly increased and flows back to the annular orifice so that the annular jet in the next cycle Under-dilatancy decreases and the leading shockwave intensity also decreases correspondingly. As a result, unsteady shockwaves and shockwave intensities also decrease. In addition, the energy input into the concave cavity in one cycle is determined by the width of the annular nozzle. Therefore, when the pressure ratio before and after the nozzle is greater than the critical pressure ratio of 1.89, the nozzle width is kept unchanged and the pressure ratio before and after the nozzle is changed. Wave and shock focus intensity is basically unchanged.