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爆轰波与激波对撞的实验研究

An experimental study on head-on collision of detonation with shock

  • 摘要: 对乙炔氧气混合气体中爆轰波与激波的正面对撞现象的实验研究是以高速摄影获取两波对撞的x-t纹影图,以烟迹板记录对撞中的爆轰胞格图案,并基于激波理论和经典CJ爆轰理论求解了两波对撞的稳态解并探寻其规律. 研究发现透射波系包括一道激波和爆轰波,以及紧随爆轰波后的稀疏波区,这一结果对应于一维理论分析中的CJ解. 透射波系基本不受初始压强影响;初始温度也只成比例地改变流场整体速度,温度越高,速度越快;对波系起实质影响作用的是入射激波强度,激波越强,则整个透射流场呈现偏向激波的趋势;理论分析还指出,稀疏波区的出现不可避免,当激波强度趋于声波稀疏波区趋于消失,激波越强则疏波区趋于扩大. 两波对撞存在一个有限的转变阶段,透射爆轰首先减缓,接着迅速迸发为过驱爆轰,然后再逐渐平衡为CJ爆轰. 对于强不稳定的燃气,对撞后爆轰波在空间上的发展极不均衡,一些区域发生火焰面与诱导激波的严重脱离,随后的火焰面失稳发展为诱导激波区内的爆轰波,实验观察到了这种爆轰在烟迹板上留下的极为精细的迹线.

     

    Abstract: An experimental study on head-on collision of adetonation wave with shock wave in a straight tube was carried out. Highspeed streak schlieren photography was used to illustrate the interactingflow field, and smoke foils were adopted to record the detonation cellularstructure around collision. Based on the theories of shock wave andclassical CJ detonation, the theoectical analyses were also performed toacquire its steady solution and the essential characteristics. Theexperimental showed that the steady wave system after collision consists ofa shock wave and a detonation wave followed by a rarefaction wave fan, whichis consistent with the CJ solution of 1-D theoretical analysis. The initialwave pressure has no effect on the wave system and the initial temperatureremarkably affects the wave and flow velocities. Meanwhile, the strength ofthe incident shock wave has the most important influence on the transmittedflow system, that is, strong shock induces the whole flow field towards theshock direction. Rarefaction is inevitable in the system unless the incidentshock tends to Mach one, and stronger shock usually results in more expandedrarefaction zone. Experimental study also revealed that the detonation waveexperiences a transit process after collision, where it first slows down andthen bursts into an overdrived detonation which then undergoes a subsequentequilibrium process towards CJ state. This transit process usually developsunsteadily in the highly irregular mixture. Seroius decoupling of shock andflame may occur in some region, and the decoupled flame could rapidlydevelop new cellular detonation even before it overtakes the decoupledprecursor shock. Very fine cellular traces printed by this kind ofdetonation were observed in our smoke foil results.

     

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