二维湍流气固两相射流的数值模拟

NUMERICAL ANALYSIS OF TWO-PHASE TURBULENT JETS LADEN WITH PARTICLES

本文采用两相湍流的K—ε模型和颗粒湍流扩散的Peskin公式,对含有相同尺寸的球状颗粒的圆截面湍流射流进行了数值分析。计算采用对抛物型方程的推进求解技巧。研究了两种不同的阻力系数公式对两相湍射流的影响。一个阻力系数公式是由谢定国和周红宇最近推导出来的,它反映了颗粒体积率对阻力的影响。另一阻力系数公式是Clift等人根据单颗粒球的标准实验阻力曲线推导出来的。计算结果和实验进行了比较。 结果表明,谢一周阻力系数公式的引入改进了小颗粒的两相湍射流的预测;但是,对于大颗料,由于颗粒雷诺数超出了谢一周公式的有效范围,不太理想。结果还表明,反映颗粒体积率等影响的阻力系数公式的引入和使用是改善两相湍射流流动特性的预测的有效途径之一。

A turbulent round jet laden with spherical particles of uniform size is numerically investigated with the K-ε model of two-phase turbulence and Peskin formulae on the particle turbulent diffusion. A marching technique along the axial direction, which is popular for the solution of parabolic equations, is adopted in the computational scheme. The main emphasis of the present study is on the effects of different drag laws on results of the numerical analysis. A drag coefficient formulae recently developed by Xie Dingguo & Zhou Hongyu, which reflects the effect of particle concentration on the drag force, and the drag coefficient derived by Clift et al. from the standard experimental drag curve of the single sphere are both utilized in the calulation. The results including distributions of mean velocity and volue fractions of two phases are presented for these two drag laws respectively. The comparison with relevent experimental data shows that Xie-Zhou's drag coefficient improves predictions in the case of small particles, meanwhile it does not help in the case of large particles, where the particle Reynolds number is far beyond the validity range of this drag coefficient. The present study indicates introduction and utilization of new drag coefficients, which are able to represent the particle concentration effect, provide an efficient means to improve the numerical prediction of turbulent jets laden with particles and, probably, other two-phase flows.