幂律型流体撞击射流破碎特性直接数值模拟

凝胶推进剂的双股射流撞击雾化广泛应用于液体火箭发动机的燃烧室中,其破碎特征及雾化效果直接影响燃烧效率。为探究雾化特性的发展规律,采用直接数值模拟DNS方法,对射流速度为100m/s的剪切稀化非牛顿液体正交撞击产生的雾化特征、液体表面积、表面波、涡特性以及非牛顿特性开展研究。结果表明,射流下形成的雾化流场迅速扩张形成液膜,液膜两侧边缘破碎成大量的液丝与液滴,核心部分产生撞击波后在气体力的作用下逐步发展为带有凸起和褶皱的不稳定表面波,其撞击波波长最大可达2.46倍射流直径。液体表面积不断增长,但无量纲表面积总体呈现先下降再上升的趋势。气体中的涡量分布则分为有序附着区和无序爆炸区两类,并且涡量主要集中分布于气相区域。此外,射流撞击时产生强剪切使该液体内部的粘性系数下降,最低仅为初始粘性系数的0.3倍。

Direct Numerical Simulation of Breakup Characteristics of Power Law Fluid Impingement Jet

Double jet impingement atomization of gel propellants is widely used in the combustion chamber of liquid rocket engines. The commonly used atomization method is impinging liquid jets. Its crushing characteristics and atomization effect directly affect the combustion efficiency. In order to explore the development law of atomization characteristics, direct numerical simulation is adopted in this paper to describe the atomization characteristics, liquid surface area, surface wave, vortex characteristics and non-Newtonian characteristics generated by orthogonal impact of shear dilute non-Newtonian liquid at the jet velocity of 100m/s. The results show that the atomized flow field formed at the jet velocity of 100m/s expands rapidly to form liquid sheet and the edge of liquid sheet on both sides breaks into a large number of ligaments and droplets. The maximum wavelength of the impact wave is 2.46D.The core of sheet produces impact waves, which gradually develop into unstable surface waves with bulges and folds under the action of gas force and the liquid surface area increased continuously, but the dimensionless surface area generally showed a tendency of first decreasing and then increasing. Vorticity distribution in gas is divided into two types: orderly attached region and disordered explosion region, and vorticity is mainly distributed in gas phase region. In addition, when the jet impinges, the strong shear will reduce the viscosity coefficient inside the liquid, which is only 0.3 times of the initial viscosity coefficient.