超声速气流中液滴破碎的大涡模拟

Large Eddy Simulation of Droplet Breakup in Supersonic Flow

关键词:  CLSVOF  超声速流动  液滴破碎  数值模拟

Key words:  CLSVOF  Supersonic flow  Droplet breakup  Numerical simulation

摘要:

为了研究超声速气流中的液滴破碎过程，采用基于CLSVOF界面追踪方法的大涡模拟方法。该方法中用可压流和不可压流求解器分别计算超声速气流流场和液体流场，并且在分别计算气相或液相时，另一相作为该相计算时的边界条件参与计算，从而实现可压流求解器和不可压求解的融合。通过去散度化液体速度外推解决界面处大液气密度比所带来的动量误差大的问题。利用该方法对来流Ma=1.358的超声速气流中的水滴破碎进行了数值模拟。模拟结果展示了超声速气流中液滴破碎的几何结构变化细节和基本破碎形态，且与实验吻合较好。数值模拟结果揭示了Rayleigh-Taylor不稳定和气动剪切力对液滴破碎的作用过程。破碎过程中，液滴在垂直来流方向上的最大无量纲宽度([Dmax/D0])约为4.5，无量纲破碎时间([tbU∞/D0])约为29.85。

Abstract:

Droplet breakup in a supersonic flow is predicted by large eddy simulation with CLSVOF applied to capture the interface. The supersonic gas flow field and liquid flow field are simulated by compressible and incompressible solvers respectively. And when calculating gas phase or liquid phase，the other one is used to specify the boundary condition. Thereby the compressible and incompressible solvers are coupled. The momentum error induced by high liquid-gas density ratio is reduced by liquid velocity extrapolation approach with a divergence free step. This method is applied to simulate the breakup of a water droplet in a supersonic air flow of Ma=1.358 in details. The results from simulation reveal the deformation and breakup of droplet in supersonic flow. The predicted droplet breakup in simulation matches well with the experimental results. Through the numerical simulation the action of Rayleigh-Taylor instability and aerodynamic force is revealed. The maximum dimensionless width in the direction across the flow ([Dmax/D0]) is about 4.5，and the dimensionless breakup time ([tbU∞/D0]) is about 29.85.