Yincheng Guo

CFD simulation of hydrodynamics in the entrance region of a downer

Abstract A gas turbulence–solid turbulence model ( k – e – Θ – k p ) was used to simulate the hydrodynamics in the entrance region of a downer. This model incorporates a k – e turbulence model for gas phase, a k p turbulence model and a kinetic theory description of solid stresses characterized by granular temperature ( Θ ) for solid phase. The predicted profiles of local solids fraction and particle velocity have good agreement with the experimental data in a wide range of solids fraction. The solid pressure has a large gradient in the inlet region, which becomes a main driving force for the particles to move from the center to the wall. The sensitivity analysis shows that the inlet granular temperature has a large influence on the predicted results. Over the whole flow field, a clear relationship between the diffusion coefficient of particles and the local solids fraction is found, that is, a smaller solids fraction corresponds to a larger diffusion coefficient.

A multi-fluid model for simulating turbulent gas–particle flow and pulverized coal combustion

Based on the pure two-fluid model for turbulent reacting gas–particle flows with combusting pulverized coal particles, a new comprehensive model for pulverized coal combustion was developed by incorporating a modified k–ϵ–kp model, a general model of pulverized coal devolatilization and a general model of char combustion. Both gas-phase and particle-phase conservation equations are described using Eulerian coordinates, and these equations are discretized and integrated in the computational cell. As the first stage of numerical modeling of pulverized coal combustion in the cyclone furnace, three-dimensional simulation of turbulent gas combustion and gas–particle flows has been made. The predicted results show that there is a near wall recirculating zone at the bottom of the cyclone furnace, and the recirculating zone enhances ignition and flame stabilization. The predicted tangential velocity distribution of both the gas phase and the particle phase similar to those of the Rankine vortex.

A pure Eulerian model for simulating dilute spray combustion

A pure Eulerian model is developed to simulate steady-state dilute spray combustion. This model is based on a fundamental description of various interacting processes which occur during spray combustion including gas-phase and spray droplet-phase turbulent flow, gas-phase turbulent combustion, radiation heat transfer and spray droplet evaporation. Both gas-phase and spray droplet-phase conservation equations are described using Eulerian coordinates. A comprehensive mathematical model is used to simulate isothermal flow, combusting flow and kerosene spray combusting flow in an axisymmetric sudden-expansion combustor. Validity of the model and the simulation scheme are established from the good agreement of the prediction with experimental data in gas-phase isothermal flow and propane combusting flow. Simulation of kerosene spray combustion shows that small droplets evaporate rapidly and do not enter the recirculation zone. For larger droplets, the length of recirculation zone is almost the same as that of the gas-phase. Simulated velocity, temperature and oxygen concentration for kerosene combustion also agrees well with experimental results.

Mechanisms for Particle Clustering in Upward Gas-Solid Flows

Two-dimensional unsteady cocurrent upward gas-solid flows in the vertical channel are simulated and the mechanisms of particles accumulation are analyzed according to the simulation results. The gaseous turbulent flow is simulated using the large eddy simulation (LES) method and the solid phase is treated using the Lagrangian approach, and the motion of the gas and particles are coupled. The formation of clusters and the accumulation of particles near the wall in dense gas-solid flows are demonstrated even if the particle-particle collisions were ignored. It is found that a cluster grows up by capturing the particles in the dilute phase due to its lower vertical velocity. By this way the small size clusters can evolve to large-scale clusters. Due to the interaction of gas and particles, the large-scale vortices appear in the channel and the boundary layer separates from the wall, which results in very high particle concentration in the near wall region and a very large-scale cluster formed near the separation point.

Simulations of Binary Droplets Collisions with SPH

The smoothed particle hydrodynamics (SPH) method for two‐phase fluid flows with large density ratio and viscosity ratio is applied to the simulations of the head‐on collision dynamics of binary equal‐sized droplets. Assistant with information obtained from experiments reported by literature, this method can successfully simulate the different outcomes of bounce and coalescence.