喷嘴距及混合室喉部长度对喷射器性能综合影响研究

The Comprehensive Influence of the Nozzle Distance and Throat Length of Mixing Chamber on the Performance of Ejector

在实际环境条件下,采用变几何喷射器是提高喷射器性能的重要途径。基于喷嘴距可调式的喷射器实验测试平台,采用实验和数值分析相结合的方法,研究不同无量纲混合室喉部长度下,无量纲喷嘴距对喷射器的性能及不可逆性影响。结果表明:在测试范围内,喷射器的临界喷射系数随着喷嘴距的增加先增加后减小,当达到最佳无量纲喷嘴距5.83时,临界喷射系数达到最大值0.45,合理的喷嘴距应避免激波链出现在混合室收缩段;喷射器的临界冷凝压力随喷嘴距的增加逐渐下降,当无量纲混合室喉部长度为4时,其临界冷凝压力下降7.36%,下降速度最慢,原因是较大的射流冲量提高了扩压室的压力恢复能力,使流体动能衰减速度有所减缓;当无量纲混合室喉部长度为4,无量纲喷嘴距为5.83时,热力学完善度达到最大值0.21;由喷嘴距引起的喷射器熵产主要来源于两股入口流在混合室收敛段的混合和第二冲击波向扩压室出口的移动,提高扩压室的压力恢复能力能有效避免熵产的急剧增加。研究结果对喷射器的结构及综合性能进行多目标优化,以减小喷射器不可逆性提供重要参考。

Under the actual environmental conditions,the use of variable geometry ejectors is an important way to improve the performance of ejectors.The effect of dimensionless nozzle distance on the performance and irreversibility of the ejector under different dimensionless throat lengths of the mixing chamber was studied by combining experimental and numerical analysis.The results show that in the test range,the critical entrainment ratio of the ejector first increases and then decreases with the increase of nozzle distance,and when the optimal dimensionless nozzle distance is 5.83,the critical entrainment ratio reaches a maximum value of 0.45.The critical condensation pressure of the ejector decreases gradually with the increase of nozzle distance.When the dimensionless throat length of the mixing chamber is 4,the critical condensation pressure decreases by 7.36%,and the decrease rate is the slowest.When the dimensionless throat length of the mixing chamber is 4 and the dimensionless nozzle distance is 5.83,the maximum thermodynamic perfection reaches 0.21.The entropy production of the ejector caused by the nozzle distance mainly comes from the mixing of the two inlet flows in the convergence section of the mixing chamber and the movement of the second shock wave towards the outlet of the diffuser chamber.Improving the pressure recovery ability of the diffuser can effectively avoid a sharp increase in entropy production.The results provide an important reference for the multi-objective optimization of the ejector structure and comprehensive performance to reduce the irreversibility of the ejector.