偏心撞击对撞击式喷嘴雾化特性的影响

为研究偏心撞击对撞击式喷嘴雾化特性的影响,建立了求解自燃推进剂冷态射流撞击雾化过程的数值模拟方案,计算了不同偏心度条件下的射流撞击雾化过程。采用树形自适应加密算法直接求解不可压Navier-Stokes方程组,由分段线性的流体体积(VOF)方法对流体界面进行捕捉。结果表明偏心撞击会导致雾场发生偏转,当无量纲偏心度E为1/8时,雾场偏转角度约为9.2°,应控制加工偏差小于该值。随着偏心度的增大,液膜的偏转角度增大,理论推导得到的液膜偏转角度要小于数值计算得到的液膜偏转角度。正心撞击时燃料与氧化剂流强峰值接近,雾场的流强分布呈单峰分布。当发生偏心撞击时,由于燃料与氧化剂部分射流未参与撞击导致流强峰值出现交错,雾场的流强分布呈双峰分布,混合比的空间分布发生较大改变。正心撞击时撞击点下游液滴的速度分布近似呈轴对称分布,而偏心撞击之后的速度分布则呈中心对称分布。偏心撞击导致的射流动量损失使得雾化性能变差,当无量纲偏心度E为1/8时,一甲基肼(MMH)的Sauter平均直径增大约4.8%,四氧化二氮(NTO)的Sauter平均直径增大约5.8%。 

Effects of misaligned impingement on atomization characteristics of impinging jet injector

In order to investigate the effects of misaligned impingement on the atomization characteristics of impinging jet injector, a numerical scheme to simulate cold atomization process of hypergolic propellants was established. Also atomization process with different misaligned degrees was simulated. Incompressible Navier-Stokes equations were directly solved by employing tree-based adaptive refinement algorithm. Interfaces of different fluids were captured by piecewise linear volume-of-fluid (VOF) method. The results revealed that atomization field was deflected due to misaligned impingement. When the dimensionless misaligned degree E was 1/8, the deflection angle of the atomization filed was about 9.2°, so the machining deviation should be controlled below this value. The deflected angle increased with the misaligned degree. The angle obtained by theoretical analysis was smaller than that of numerical simulation. When aligned impingement occurred, mass flow rate flux peaks of fuel and oxide were close in space and unimodal distribution of the total mass flow rate flux appeared. When misaligned impingement occurred, for the reason that partial momentums of fuel and oxide jet didn’t participate in impingement, mass flow rate flux distribution of fuel and oxide interlaced and bimodal distribution of the total mass flow rate flux appeared. Mixture ratio distribution in space changed a lot. Droplet velocity distribution of aligned impingement downstream the impingement point was approximately axial symmetric while that of misaligned impingement was approximately central symmetric. Jet momentum loss caused by misaligned impingement led to poorer atomization performance. When dimensionless misaligned degree E was 1/8, Sauter mean diameter of monomethylhydrazine(MMH) increased about 4.8% and that of nitrogen tetroxide(NTO) increased about 5.8%.