剪切稀化非牛顿射流撞击液膜破碎直接数值模拟

Direct numerical simulation of sheet breakup formed by two impinging jets with non-Newtonian shear thinning properties

液态射流撞击是液体火箭推进系统中广泛采用的一种燃料雾化方法,其破碎特征直接影响燃料最终的掺混及燃烧效率。采用直接数值模拟(DNS)工具,研究了低雷诺数(Rel=41)和中等韦伯数(Wel=163)条件下剪切稀化非牛顿射流撞击液膜破碎的问题,着重分析了对角液膜的三维结构、破碎特征和非牛顿特性等。研究结果表明:在所研究的射流参数下,该非牛顿撞击液膜破碎属于Open Rim类别,破碎过程具有三维特性并伴随液丝与边缘的融合、液丝向液滴的转变等时域流动特征。液体的总表面积随时间不断增长,但单位表面积随液膜破碎的发生而下降,液膜扩张半角随时间逐渐增加并趋于恒定值43°,而后部液膜的长度几乎不随时间发生变化。此外,撞击液膜表现出明显的剪切稀化特性,液体内部最低黏性系数仅为零剪切黏性系数的1/5。

Impinging liquid jets have been widely used in liquid rocket propulsion systems as a fuel atomization method. The breakup mechanism of impinging liquid jets directly affects the mixing and combustion efficiency of the fuel. In the present work, a Direct Numerical Simulation （DNS） tool is applied to study the sheet breakup formed by two impinging jets with non-Newtonian shear thinning properties under low Reynolds number （Rel = 41） and moderate Weber number (Wel = 163）, in-cluding in particular the three-dimensional structure, breakup mechanism, and non-Newtonian feature of the diagonal liquid sheet. The results indicate that the breakup regime of the impinging sheet under current conditions belongs to the Open Rim type. Collison of ligament with rim as well as transition from ligament to droplet can be observed during the sheet breakup. The total liquid surface area increases with time, whereas the specific surface area decreases with the occurrence of sheet breakup. The half-expansion angle of the liquid sheet increases with time and eventually tends to be a constant 43°, but the length of the back sheet shows no tendency of change with time. Additionally, a strong shear thinning feature can be found within the liquid sheet, with the lowest viscosity of the liquid sheet being only 1/5 of that at zero shear rate.