基于正交法和Kriging模型的液体火箭发动机液膜冷却优化

通过FLUENT对火箭发动机推力室中跨临界甲烷液膜冷却稳态流场进行数值传热计算。根据正交法设计试验,得到不同膜孔孔径、轴向夹角、径向夹角和孔型四个影响因素共同作用下的冷却效果,选出最优的膜孔几何参数组合.在采用最优膜孔几何参数组合的条件下,基于最优拉丁超立方抽样建立Kriging模型,利用遗传算法得到多目标条件下最优的跨临界液膜质量流量、冷却环带的分配比和位置。结果表明,正交法和Kriging模型可以解决液体火箭发动机液膜冷却优化高设计成本和数值噪声问题。正交试验设计考虑的因素中,影响冷却效率和不均匀度的最大的因素依次为孔型、孔径、径向夹角和轴向夹角。最优的几何参数组合为孔径0.003mm,轴向夹角45°,径向夹角15°,孔型为扩散型。建立的Kriging模型能准确反映液膜质量流量、液膜分配比和冷却环带位置与目标函数的关系。最终得到的优化方案平均冷却效率提高4.9%,不均匀度减少0.025,比冲损失增加0.37%,总目标函数提高184%。优化后涡对的不对称性使得冷却剂展向分布更加均匀,同时反向涡对衰减更快,增强了液膜的附壁性,从而提高冷却效果。

Optimization for liquid film cooling based on orthogonal methodology and Kriging model in liquid rocket engine

Transcritical methane film cooling steady flow field was calculated by numerical transfer study in the rocket engine chamber by FLUENT. Through the orthogonal methodology, cooling performance under the combined action of different diameters, axial angle, radial angle and shape of hole was simulated to choose the optimal geometric parameters. Based on the optimal geometric parameters, the optimal latin hypercube design was adopted to get sample points that can be used to establish Kriging model. Then the optimal transcritical liquid film mass flow, the partition ratio and location of cooling ring under multi-objective conditions can be calculated through genetic algorithm. The results showed that orthogonal methodology and Kriging model could resolve problems of high design cost and numerical noise in liquid rocket engine design. In the considered geometrical factors above, the significance order from big to small effects on cooling efficiency and non-uniformity degree was: shape, diameter, radial angle, axial angle; the optimal geometric parameter combination was 0.003mm diameter, 45° axial angle, 15° radial angle, and diffused shape. The Kriging model established precisely reflected the relation between objective function and the liquid film mass flow, partition ratio and location of cooling ring. The average cooling efficiency and specific impulse loss increased by 4.9% and 0.37%, respectively, and non-uniformity degree was reduced by 0.025, while the total objective function was increased by 184%. After the optimization, asymmetry of vortex pair made coolant spanwise well-distributed, while reversed vortex pair attenuated faster, and the property of liquid film attaching to the wall increased, thus improving the cooling efficiency.