基于能量最小多尺度曳力模型的搅拌槽内气液两相流计算液体力学模拟及实验研究

Experimental study and CFD simulation of gas-liquid flow in a stirred tank using the EMMS drag model

采用双电导探针和欧拉-欧拉双流体模型对涡轮桨搅拌槽内局部气液分散特性分别进行了实验和三维计算流体力学(CFD)数值模拟研究。重点研究了转速对搅拌槽上下循环区局部气含率分布、全槽液相流场和湍动动能的影响。实验表明,转速对上循环区气含率分布的影响大于下循环区,且上循环区气含率随转速的增大而增大。CFD模拟比较了TOMIYAMA曳力模型和基于能量最小多尺度理论(EMMS)的DBS-Local曳力模型对局部气含率的预测结果。结果显示DBS-Local曳力模型能够较好地预测出不同搅拌转速下搅拌槽循环区气含率径向分布;TOMIYAMA曳力模型只能定量预测出低搅拌转速下(140r/min,280r/min)循环区的气含率分布,高转速下(420r/min,560r/min)该曳力模型不能模拟出下循环区壁面附近的气体,且低估了上循环区气含率。

The characteristics of local gas-liquid dispersion characteristics in a stirred tank of Rushton impellers were studied by experiments and CFD simulation.The local gas holdup distribution was measured by using a double conductance probe.The gas-liquid flow was modeled by an Eulerian-Eulerian two-fluid model along with the k-?turbulence mixture model.Effects of rotational speed on the local gas holdup distribution in the upper and lower circulation zone were studied.The experiments showed that the effect of rotational speed on gas holdup distribution in the upper circulation zone was larger than that in the lower circulation zone,and the gas holdup increased with increasing rotational speed.The prediction of the TOMIYAMA drag model and the DBS-Local drag model based on the EMMS theory was compared.The results showed that the DBS-Local drag model could reasonably predict the local gas holdup distribution under different rotational speeds.The TOMIYAMA drag model can only reasonably predict the local gas holdup distribution under lower rotational speeds(N=140r/min,280r/min).It cannot predict the gas bubbles near the tank wall of the lower circulation region,and underestimated the gas holdup in the upper recirculation region at higher rotational speeds(420r/min,560r/min).