Simulations of Particle-Wall-Turbulence Interactions, Particle Motion and Erosion in With a Commercial CFD Code

Abstract

Calculation of a representative particle impacting velocity is an important component in calculating solid particle erosion inside a pipe geometry. Experiences in calculating erosion for solid-gas systems indicate that gases normally do not affect particle motion near a solid wall. However, solid particles that are entrained in a liquid system tend to undergo a considerable momentum exchange before impacting the solid wall. Currently, most commercial CFD codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near wall region. This wall-function velocity field near the wall can affect the small particle motion in the near wall region. Furthermore, the CFD codes assume particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near wall velocity profile is implemented. In addition, effects of particle size are investigated in the near wall region of a turbulent flow in a 90 degree sharp bend. A CFD code is modified to account for particle size effects in the near wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid non-physical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25 μm) due to turbulent velocity fluctuations. For large particles (256 μm), however, non-physical impacts were not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications and the results are compared with experimental data. It is shown that the near wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling.