FLOW VISUALIZATION OF INTERACTIONS BETWEEN PARTICLE WAKES AND JET VORTICES
The interactions between vortices of a round free shear jet and particle’s wakes are visualized by means of smoke-gas flow visualization technology. Particles in different diameters are fixed at different positions along the jet axial central line. The typical flow structural compositions of the gas jet at the different flow developing stages are presented. Particle wakes occur obviously for the larger particle when the particle Reynolds number is larger than 100, and they change the overall flow structural pattern. More ejections in the vortex rings are accused in the radial direction at the initial flow status. The large-scale structures are broken up because of the presence of the wakes behind large particles. The local turbulence anisotropy is then attenuated in the downstream. Small particles without wakes do not change the flow structure pattern. The results are valuable to develop accurate turbulence modulation models including wake effects.
Numerical Simulation of Gas Turbulence Enhancement by Particle-Wake Effect
A new turbulence enhancement model was incorporated into the second-order moment two-phase turbulence model and was used to simulate gas-particle flows in swirling chambers and channels with different wall roughness. The results show that compared with the turbulence modification model not accounting for the wake effect, this model, together with the conventional particle source term, gives simulation results in better agreement with the experimental data.
Visualization of fan-spreading in two-phase jet flows
ConclusionsFlow visualizations obtained in a two-phase jet flow with 80 μm particles at a mass loading of 5% revealed the following.1.Particles exited the jet tube in straight trajectories with “fan-spreading” angles of up to ±30°. The velocities of those particles having large angles were considerably lower (40% or more) than the mean particle velocity of the bulk flow.2.Reducing the mean particle velocity at the exit from 25 m/s to 7 m/s reduced the “fan-spreading” effect with a maximum angle of around 10°.