三种湍流模型下搅拌釜内气含率特性的模拟

采用计算流体力学（CFD）方法，应用Euler-Euler双流体模型，桨叶采用多重参考系法（MFR），与考虑气泡聚并与破碎对气泡尺寸影响的群体平衡模型（PBM）相结合，比较了标准k-ε、Realizable k-ε和RNG k-ε3种湍流模型对双层涡轮搅拌釜内气-液两相液相流场、局部气含率及气泡尺寸分布的影响。结果表明：3种湍流模型预测的液相流场流型相似，总体气含率预测值相差不大，均与实验值吻合较好。对于局部气含率，标准k-ε和RNG k-ε模型在桨叶区的预测值偏大，在接近自由液面处三者预测值均偏低，Realizable k-ε模型预测结果与实验值符合最好；对于气泡尺寸，3种湍流模型预测结果均与实验值较吻合，在靠近自由液面处预测值均偏小，气泡尺寸分布与湍流长度分布相吻合。

Study of characteristics of gas holdup in stirred tank under three turbulence models

This paper investigated the simulation of liquid velocity, local gas holdup and bubble size in a stirred tank with dual turbine impellers using computational fluid dynamics(CFD). The results from three different turbulence models (Standard k-ε，RNG k-ε，Realizable k-ε) were compared. The Euler-Euler multiphase flow model and multiple frames of reference(MFR) method were used in the simulations. A population balance model(PBM) was implemented in order to account for the combined effect of bubble break-up and coalescence in the tank. The results showed that the flow patterns of liquid phase and the total gas holdups predicted by the three models had no significant difference, and the total gas holdups agreed well with the experimental data. The standard k-ε and RNG k-ε models over predicted the local gas holdup values at the impeller regions, and in the upper part of the vessel near the liquid-free surface where the local gas holdups predicted all were lower than the measurements. The realizable k-ε model gave the best result compared with the experimental data. The simulated results and experimental data agreed well at most of the points in the tank except for the part near the liquid-free face for the bubble sizes. The bubble size distribution was consistent with the turbulence length distribution.