气液比对气液同轴离心式喷嘴缩进室内流动过程的影响

Effects of Gas-Liquid Ratio on Internal Flow Dynamics of Gas-Liquid Swirl Coaxial Injector in Recess Chamber

关键词:  离心喷嘴  非定常流动  液膜  破碎  流场  压力振荡  自激振荡

Key words:  Centrifugal injector  Unsteady internal flow  Liquid sheet  Breakup  Fluid field  Pressure oscillation  Self-excited oscillation

摘要:

为了研究气液同轴离心式喷嘴缩进室内部非定常流动过程，采用Level Set和VOF（Volume of fluid）相耦合的方法，结合网格自适应技术对缩进长度为8mm的液体中心式气液同轴离心式喷嘴流动过程进行了数值仿真研究，计算得到了较为精细的液膜一次破碎过程、流场结构和压力振荡特性。结果表明：液膜的破碎模式受气液比的影响较大，随气液比的增加，液膜破碎模式由波动破碎逐步转变为湍流破碎。此外，清晰获得了自激振荡过程，分析了缩进室内部压力场及速度场分布特征。研究发现，随着气体压降增加，气体环缝出口会出现膨胀波和激波，形成一个“扇环形”的超声速流场区域；激波后气流分离，出现旋涡，形成局部高压区，旋涡中心随激波面周期性地上下移动，致使局部压力出现周期性振荡。

Abstract:

To study the unsteady internal flow dynamics of gas-liquid swirl coaxial injector in the recess chamber， the coupled Level Set and VOF（volume of fluid） method combined with adaptive mesh was used to research on the flow dynamics of liquid-centered gas-liquid swirl coaxial injector with the inner post recess length of 8 mm by numerical simulation. The detailed primary breakup processes of liquid sheet， fluid dynamics and the pressure oscillation characteristics were obtained by simulation. The results show that the breakup modes of liquid sheet are greatly affected by the gas-liquid ratio. With the increase of gas-liquid ratio， the breakup of liquid sheet transforms from the mode dominated by the surface wave to that dominated by turbulence. In addition， the self-pulsation process is clearly obtained， and the distributions of pressure and velocity field in recess chamber are analyzed. It is found that with the increase of gas pressure drop， both expansion wave and shock wave appear at the outlet of gas annulus， forming a ‘fan ring’ supersonic flow field region. After the shock wave， the airflow separates and vortices appear， forming a local high pressure region. The vortex center moves up and down periodically with the shock surface， the local pressure oscillates periodically.