旋流器内部流场的数值模拟方法研究

旋流器以其操作简单,运行成本低,物理尺寸小等优点广泛应用于化工分离行业。其内部流场情况对其分离精度及分离效率起着关键作用,准确模拟该流场具有重要意义。流场变量梯度高、旋流特征强,尤其中心空气柱的存在增加了其数值模拟的不确定性。借助CFD(Computational Fluid Dynamics)软件,对75 mm经典旋流器系统地进行了气-液两相流非稳态数值模拟,研究了湍流模型,压力-速度耦合方式以及离散格式对旋流器内部流场计算结果的影响,并将其空气柱直径、切向速度以及轴向速度进行对比。结果表明:RSM(Reynolds Stress Model)湍流模型可以较为准确地预测旋流器流场,仅在空气柱附近区域预测的速度值偏低。RNG k-ε(RNG k-epsilon)、Realizable k-ε(Realizable k-epsilon)以及Standard k-ε(Standard k-epsilon)湍流模型预测的该流场与实际流场存在较大差异。其中,RNG k-ε模型误差较Realizable k-ε以及Standard k-ε模型稍低;QUICK与Second Order Upwind离散格式在预测旋流器内部流场时差别不大。Third-order MUSCL,Power Law以及First Order Upwind离散格式没有求解出流场中完整的空气柱;SIMPLE,PISO及Coupled三种压力-速度耦合方式对计算结果的影响不大,相比较而言SIMPLE算法为较适合计算旋流器流场的压力-速度耦合方式。Coupled较其他2种算法在溢流管段预测的空气柱直径偏大,速度偏小,部分锥段空气柱直径偏小,速度偏大。

Numerical simulation on internal fluid field in cyclone

Because of its simple operation,low operation cost and small physical size,cyclone is widely used in chemical separation industry.The internal flow field plays a key role in its separation accuracy and efficiency.It is important to simulate the flow field accurately.The internal flow field of cyclone has a high gradient and strong swirl characteristics,especially the presence of central air core,which increases the uncertainty of its numerical simulation.Using the CFD software,a gas fluid unsteady numerical simulation was carried out systematically for a 75 mm classic cyclone.The effect of different turbulence models,pressure velocity coupling methods and discrete schemes on the calculation results of flow field were studied.Also,the diameter of the air core,tangential and axial velocity were compared to find more suitable numerical solution methods for calculating the flow fields of cyclone.The results show that RSM can accurately predict the flow field of cyclone,except the velocity near the air core which is lower than the experimental data.The flow fields predicted by RNG kepsilon,Realizable kepsilon and Standard kepsilon turbulence models are quite different from the actual flow field.And the error of RNG k epsilon model is slightly lower than that of Realizable kepsilon and Standard kepsilon turbulence models.There is little difference between QUICK and Second Order Upwind discrete schemes in predicting the internal flow field of cyclone.The Third order MUSCL,Power Law,and First Order Upwind discrete formats could not obtain the complete air core in the flow field.The pressure velocity coupling methods,including PISO,Coupled and SIMPLE algorithm have little effect on the calculation results.The SIMPLE algorithm is more suitable to predict the flow field of cyclone.Compared with PISO,SIMPLE algorithm,the diameter of air core predicted by the Coupled algorithm is larger and velocity is smaller in the overflow section.In the partial cone,the diameter of air core is smaller,but velocity is higher.