基于不同亚格子尺度过滤模型下提升管内颗粒流动的数值模拟

Numerical Simulation of Flow Behavior of Particles Based on Two-Fluid Model with Different Filtered Drag Models in Riser

固相亚格子尺度过滤模型是在高精度的网格下,系统地过滤了基于结合颗粒动理学的双流体模型的模拟结果而得到的曳力和固相应力等本构关系的计算模型。今分别采用固相亚格子尺度过滤模型(Filtered Model I)、壁面修正固相亚格子尺度过滤模型(Filtered Model II)和改进的固相亚格子尺度过滤模型(Filtered Model III)模拟NETL/PSRI挑战问题中的提升管内的颗粒流动特性,得到了时均气体压力梯度和时均轴向颗粒速度等分布。亚格子尺度模型和均匀流动模型(Huilin-Gidaspow model)的研究结果相比,改进的固相亚格子尺度过滤模型(Filtered Model III)与实验值更接近,尤其是对于高颗粒浓度流动。壁面修正可以提高压力梯度,从时均轴向颗粒速度分布曲线,可以看出在提升管内颗粒流动结构呈现更为明显的环核流动结构;同时,研究了提升管内气体压缩性、壁面修正和计算网格对模拟结果的影响,分析表明气体的可压缩性对提升管内轴向气体压力梯度有影响,在模拟计算时考虑气体的压缩性,可以提高计算精度。

Three sets of filtered gas-particle two-fluid models were obtained by systematically filtering results generated through highly resolved simulations of a kinetic theory based two-fluid model（TFM）. Flow behaviors of particles in a three-dimensional riser in NETL/PSRI challenge problems of circulating fluidized beds（CFBs） were studied using filtered two-fluid model（Filtered Model I）, wall-correction model（Filtered Model II） and modified filtered model（Filtered Model III）. The distributions of time-averaged gas pressure gradient along height and time-averaged axial velocities of particles in the radical direction at different elevations were obtained and compared with experimental data. By comparison of simulation results obtained from the three filtered two-fluid model and the homogeneous drag model（Huilin-Gidaspow model）, we found that the Filtered Model III is better than others, in particular, for dense gas-solid flow. Wall correction of filtered TFM affects pressure gradient, and can clearly capture the core-annular structure for the flow behavior of particles in riser. In addition the effects of gas compressibility, wall corrections and grid resolution on predicted results were discussed. It was found that the gas compressibility had a quantitative effect on the simulation results. Such findings show that the consideration of gas compressibility can improve the simulation predictions.