壁面边界对撞击合成动量角的影响研究

为了研究动量比对针栓式喷注器撞击雾化合成动量角的影响规律,基于三相的与水平集耦合流体容积法(CLSVOF)对贴壁液膜/自由液膜撞击的合成动量角进行了数值模拟,并与自由液膜/自由液膜撞击的合成动量角进行了对比,结合试验结果及理论预估结果详细考察了有无壁面条件下合成动量角与动量比的关系,深入分析了造成两者之间差异的根源,揭示了壁面边界对合成动量角产生影响的作用机制。结果表明:CLSVOF方法计算的合成动量角与试验结果一致,最大相对误差约为10%,大多数工况点的相对误差小于5%;有壁面边界的贴壁液膜/自由液膜撞击合成动量角显著大于无壁面边界的自由液膜/自由液膜撞击的;仅一路流体贴壁的撞击合成动量角与常用的入口动量比理论预测值最大相差20°以上,而两路均无贴壁或者均贴壁的撞击合成动量角与理论预测值吻合很好。这一显著差异的根源在于两者撞击形成的高压区分布显著不同。壁面的存在使得撞击点附近形成的高压区对两路流体作用不对称,有壁面边界时壁面承受高压迫使其对贴壁流体有强的作用力,导致垂直于壁面方向动量不守恒,根据入口动量比预测的理论不再适用。

Effects of Wall Boundary on Resultant Momentum Angle of Impinging Jets

In order to study the effects of momentum ratio on the resultant momentum angle of impinging jets of the pintle injector, the resultant momentum angle of the impingement between an adherent liquid sheet and a free liquid sheet was simulated based on three phases CLSVOF (Coupled Level Set and Volume of Fluid) method, and compared with that of a free liquid sheet/ another free liquid sheet. The relationship between the resultant momentum angle and the momentum ratio was investigated in detail by combining the experimental results and the theoretical results in the presence or absence of wall. The causes of the differences between the two were analyzed in depth, and the mechanism of the effects of wall boundary on the resultant momentum angle was revealed. The results show that the resultant momentum angle calculated by the CLSVOF method is consistent with the experimental ones. The maximum relative error between them is about 10%, and the relative errors at most operating conditions are less than 5%. The resultant momentum angle of the impingement between the adherent liquid sheet and the free liquid sheet with wall boundary is remarkably larger than that of the free liquid sheet/ free liquid sheet with no wall boundary. The maximum error between the resultant momentum angle with only one-path adherent liquid and the common theoretical value predicted by using inlet momentum ratio is up to 20°.The resultant momentum angle that both or neither of two path fluids is adherent is in good agreement with the theoretical predictions. The cause of the marked difference is the significantly different distribution of the high pressure zones formed by the impact of the two. The existence of the wall makes the high pressure zone near the impact point act asymmetrically on the two fluids. When there is a wall boundary, the wall is subjected to high pressure, which forces also wall to exert a strong force on the adherent fluid because of action and reaction. As a result, the interaction between wall and fluid leads to non-conservation of momentum in the direction perpendicular to the wall. The prediction theory of inlet momentum ratio is no longer applicable.