障碍物强化爆震起爆和传播的数值模拟与验证

Numerical Simulation of and Experimental Study on Effect of Ring Obstacles on Detonation Initiation and Propagation

采用非稳态二维轴对称数值模拟的方法研究了圆环形障碍物对爆震起爆和传播的影响,并通过实验进行了验证。研究表明:爆震形成之前,激波的反射与聚交能够产生高温高压点,并大大提高该区域的反应速率,促成局部能量的快速释放,产生局部爆炸;火焰传播速度与相对于障碍物的位置有关,具有极高的脉动特性;DDT(deflagration to detonation transition)过程中迅速增压是在火焰传播到一定区域后开始,在该区域形成向2个方向传播的压缩波,向未燃区传播的压缩波不断加强形成爆震,向已燃区传播的压缩波称为回传爆震,不断衰减;障碍物导致爆震管中压力温度分布极不均匀,与没有障碍物的爆震管完全不同。

Purpose. Shortening the distance and time of DDT （Deflagration to Detonation Transition） stage is crucial in the development of PDE （Pulse Detonation Engine）. Shchelkin spiral has attracted much interest as an obstacle that disturbs free flow of combustible liquid/gaseous fuel mixture and consequently shortens the distance and time of DDT stage. But the 3D geometry of Shchelkin spiral makes numerical simulation very difficult. We use ring obstacles so that numerical simulation and experimental study can go hand in hand. In numerical simulation, unsteady 2D axisymmetric N-S （Navier-Stokes） equations and finite rate model for chemical reaction are used. Near the thrust wall, high pressure and high tempera ignition zone initiates the detonation of mixture. Experiments are performed on the platform of a 60 I.D. （inside diameter） detonation tube. The simulations show that： （1） before detonation, reflection focusing of shockwave produce local high temperature and high pressure zones in which chemical react become very fast and energy is released immediately; such zones can cause local constant vol ture mm and ions ume explosion; （2） ring obstacles inside detonation tube can shorten time and distance of detonation initiation as compared with those in smooth detonation tube; when spacing interval of ring obstacles is increased from 40 mm to 60 mm, initiation time and distance become longer. Both simulations and experiments show that： （1） sudden increase of pressure during DDT process will not occur until flame has spread to a certain region upstream of the position where detonation wave forms; meanwhile two compression waves, which propagate in opposite directions, come into being, one is strengthened by combustion and detonates rapidly, but the other is weakened as a result of fuel lack; （2） retonation wave forms before detonation wave, and can combust the unburned mixture behind obstacles in deflagration zone.