基于欧拉多流体模型对喷嘴内流和射流破碎的研究

Numerical Study on the Nozzle Inner Flow and Jet Breakup Based on an Euler Multi-Fluid Model

在Open FOAM的框架下,采用多流体模型和大涡模拟方法研究不同背压对喷嘴内流和射流破碎的影响.利用已修正的空化模型考虑了空化现象,利用界面压缩法对两相界面进行捕捉,进而分析燃油的一次破碎过程.结果表明:降低背压有利于喷嘴内部空化的形成与发展,但会导致喷嘴喉部有效流通面积减小,流动阻力增加,质量流量降低.射流破碎中气/液相界面处气/液两相存在很大的速度差,导致产生很强的阻力,大大促进了一次破碎过程中主喷雾区和蘑菇头的破碎.背压越高,空气密度越大,则燃油受到的阻力越大,液柱破碎越剧烈且射流破碎角越大.因此,同时提高喷射压力和背压可以促进燃油与空气的混合,也可以有效抑制空化来避免空蚀现象以及流量系数降低,从而延长喷嘴的使用寿命.

Multi-fluid model and large eddy simulation(LES)method were used to study the effects of different back pressures on the nozzle inner flow and jet breakup in the framework of Open FOAM.The cavitation phenomenon was considered using the modified cavitation model.Meanwhile,the interface sharpening method was used to capture the two-phase interface and then to analyze the process of primary breakup.The results show that reducing the back pressure is beneficial to the formation and development of the internal cavitation of nozzle,but it will lead to the reduction of the effective flow area of the nozzle throat,the increase of flow resistance and the decrease of mass flow rate.There is a large speed difference resulting in a strong drag force at the gas-liquid interface in the jet breakup,which greatly promotes the breakup of the main spray and the mushroom head in primary breakup.With an increase of back pressure,the air density rises,leading to an increase of drag force,and then the liquid column breaks more dramatically and the jet breakup angle grows bigger.Therefore,in order to avoid erosion in the nozzle and reduce spray flow coefficient,the injection pressure and back pressure can be simultaneously increased,which can also promote the mixing of fuel and air and hence extend the life of nozzle.