Dense Gas-Solid Multiphase Flows-A Direct Numerical Simulation Approach

Dense gas-solid multiphase flows were studied. The time history of the instantaneous turbulent velocity vector field was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudo-spectral method. The effect of particles on the flow was included in the analysis via a feedback force that acted on the computational grid points. In addition, the effects of particle-particle collisions on the dispersed and carrier phase turbulence fluctuations are accounted for in the analysis. A series of numerical experiments for different particle relaxation times and particle mass loadings were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration profiles were studied.It was shown that: • For the size ranges considered, the addition of particles attenuates the intensity of fluid turbulence fluctuations and as particle mass loading increases, the level of attenuation increases. •Inter-particle collisions increase the particle deposition velocity as mass loading increases, while two way coupling decreases it. In the physical case (four way coupling), the particle deposition velocity increases comparing with the one way coupling case.•Four-way coupling decreases the particle normal fluctuating velocity, far from the wall region and increases it in the wall region compared with the one-way coupling case. The two-way coupling effects decrease the particle normal fluctuating velocity, while inter-particle collisions enhance it.

کلیدواژه ها:

DNS ، Particle-particle collisions ، Particle deposition velocity ، Four-way coupling