Development of measurement in packed beds and analysis of turbulent characteristics in packed beds

对填料床内的湍流特性进行了实验研究和数值模拟。在实验中，填充床被简化为一组圆柱。进行了压力降和湍动能的测量，并进行了圆柱排列的流动显示。在数值模拟中，基于k-ε模型和k-l_m湍流模型，建立了描述填料床内湍流流动的数学模型。模拟在两种情况下进行。在情况1中，圆柱体交错排列以简化填充床。在情况2中，使用空隙率对圆柱体的布置进行建模。研究结果表明：1.压降随雷诺数的增大或含气率的减小而增大; 2.湍流动能在进入圆柱排列后迅速上升，然后在下游趋于恒定值。湍流动能随雷诺数的增加而增加。3.流动显示显示了圆柱引起的湍流的发展。4.在圆柱排列的模拟中，湍流动能的计算结果与实验结果具有相似的趋势; 5.当圆柱排列采用含气率模型时，湍流动能守恒方程中考虑了圆柱引起的湍流动能的产生。当采用k-l_m模型时，混合长度对计算结果的影响很大。当采用k-ε模型时，计算结果受进口条件的影响较大。因此，k-l_m模型中混合长度的确定和k-ε模型中入口条件的确定还有待于进一步的研究。

Turbulent characteristics in packed beds are investigated both experimentally and numerically. In the experiment, a packed bed is simplified as an arrangement of cylinders. Measurement of pressure drop and turbulent kinetic energy, and flow visualization in the arrangement of cylinders are conducted. In the numerical simulation, a mathematical model describing turbulent flows in packed beds is developed, based on k-ε model and k-l_m turbulence model. The simulation is conducted in two cases. In case1, the cylinders are staggeredly arranged to simplify packed beds. In case2, the arrangement of cylinders is modeled using void fraction. The results obtained in this study are summarized as follows.1.Pressure drop increases with increasing Reynolds number or decreasing void fraction.2.Turbulent kinetic energy rises rapidly after inflow to the arrangement of cylinders, and then approaches to a constant value in the downstream. Turbulent kinetic energy increases as Reynolds number increases.3.The flow visualization shows the development of turbulences caused by the cylinders. However, the turbulent eddy scale is limited by the gap between cylinders in the downstream.4.In the simulation when the cylinders are arranged, calculated results of the turbulent kinetic energy show the similar tendency with experimental ones.5.When the arrangement of cylinders is modeled by void fraction, the production of turbulent kinetic energy caused by the cylinders is considered in the conservation equation of turbulent kinetic energy. When k-l_m model is used, the calculated results are greatly affected by the mixing length. When k-ε model is used, on the other hand, the calculated results are greatly affected by the inlet condition. Therefore, the further research will be required for the determination of the mixing length in k-l_m model and the inlet condition in k-ε model.