孔流型液体分布器二级槽内的流场分析

CFD Simulation of Fluid Flow in Secondary Trough of Bottom-hole-type Liquid Distributor

为了研究底孔型液体分布器二级槽中的流动特性和考察挡板与液位两种因素对性能的影响,采用数值模拟方法,通过SST湍流模型和VOF多相流模型获得槽内的气液两相流场,分析了不同液位下挡板对底孔流量均匀性的影响。结果表明:低液位时槽底附近有明显的横向流动,挡板可以抑制这种横向流并将入口射流带进的湍流扰动移向液面。高液位时槽底横向流不明显,但射流点附近液面以下有大尺度涡流,挡板顶部绕流使相应区域产生速度波动并沿高度方向衰减。液位无论高低,设置挡板都使槽底横向流被阻滞,挡板对不同位置孔附近流场的改变方式不同,射流落点位置和板后回流涡形态的改变造成流经孔口上方介质中进入孔内的比例和孔内流速的改变,共同影响孔内流量的变化。挡板使底孔流量均匀性有所下降,主要原因是射流点下游底孔附近射流和涡流的不良分布,而较高的液位由于增加了对射流、横向流和挡板扰流的惯性和黏性阻滞,可以改善底孔流量均匀性。

In order to study the characteristics of fluid flow in the secondary trough of bottom-hole-type liquid distributor and to investigate the influence of liquid level and baffle on the trough performance,a numerical approach is adopted and turbulent SST model and multiphase VOF model are employed to obtain the air-liquid flow field inside the trough.The influence of baffle on the mass flow uniformity under different liquid levels is analyzed.The result shows that there exists lateral flow near the bottom if liquid level is lower,which could be restrained by the baffle,moreover,the turbulence brought in by the jet from the inlet can be transferred to the surface by the baffles.If liquid level is higher,the lateral flow near the bottom is unobvious but large-scale swirl motion is produced near the surface under the jet inlet.Also,the disturbance of baffles created velocity fluctuations nearby which deteriorates on the vertical direction.No matter higher or lower the liquid level is,the lateral flow near bottom can be restrained by the baffles.Baffles exert different influence upon different holes,the variation of location of jet impingements and recirculation behind baffles lead to a difference in the fraction of fluid flow into the holes and velocity magnitude in the holes,which have a combined effect on the mass flow rate through holes.Baffles lead to a decreased uniformity of mass flow through holes which is due to the badly distributed jet flow and vortexes above the bottom.In higher level cases the mass flow uniformity is consistently improved which could be explained by the fact that jet flow,lateral flow and baffle disturbance can be restrained by the higher inertial and viscous effect.