直接模拟蒙特卡罗方法在CFD冲蚀预测中的应用

Application of Direct Simulation Monte Carlo method in CFD-based erosion prediction

为研究气固两相流中固体颗粒间碰撞对冲蚀的影响,提出一种利用直接模拟蒙特卡罗(Direct Simulation Monte Carlo,DSMC)方法和计算流体力学(CFD)计算颗粒间碰撞的冲蚀预测方法。使用Eulerian-Lagrangian方法,将气相作为连续相,通过Navier-Stokes方程求解,颗粒平移运动由离散相模型(DPM)求解。颗粒平移运动由Eulerian-Lagrangian框架下的DPM求解,计算颗粒间碰撞运动时采用DSMC方法以少量采样颗粒代替真实颗粒,碰撞的发生条件通过修正的Nanbu方法判定。分析气固两相流中颗粒间碰撞对弯管冲蚀速率和颗粒分布的影响,结果表明:使用DSMC方法计算颗粒间碰撞,Oka模型的平均百分误差从39.2%降低至27.4%;计算颗粒间碰撞时弯管内拱侧的无颗粒区变小,最大冲蚀位置沿外拱轴线后移5°,同时V形冲蚀痕迹的两翼向外侧扩大。使用DSMC方法计算颗粒间碰撞可以明显降低模型误差,考虑颗粒间碰撞的Oka模型与实验结果偏差最小,是冲蚀预测的最佳模型。

In order to study the influence of collision between solid particles in gas-solid two-phase flow on erosion, an erosion prediction method based on the Direct Simulation Monte Carlo(DSMC) method for calculation of particle collision and computational fluid dynamics was proposed. Herein, the Eulerian-Lagrangian method was adopted, the gas was taken as the continuous phase, the Navier-Stokes equations were solved, and the particle translation motion was solved by the Discrete Phase Model(DPM). For calculation of particle collision motion, the DSMC method was used to replace the real particles with a small number of sampled particles, and the collision conditions were judged by the corrected Nanbu method. Additionally, the effect of particle collision on elbow erosion rate and particle distribution in gas-solid two-phase flow was studied. The results show that the model error can be significantly reduced by calculating the particle collision with DSMC method, and the average percentage error of Oka model is reduced from 39.2% to 27.4%. For calculation of particle collision, the non-particle area on the inner arch side of the elbow becomes smaller, and the maximum erosion position moves backward 5° along the outer arch axis. Meanwhile, the flanks of the "V-shaped" erosion trace expand outward. Calculating the particle collision with DSMC method could significantly reduce the model error, and due to the small deviation from the experimental results, the Oka model considering particle collision is the best model for erosion prediction.