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.
Modeling of Turbulence Modification Using Two-Time-Scale Dissipation Models and Accounting for the Particle Wake Effect
The presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot totally reflect the effect of particles. In this paper, a two-time-scale dissipation model of turbulence modification, including a two-time-scale dissipation model for the two-phase velocity correlation and a two-time-scale dissipation model for the dissipation rate of gas turbulent kinetic energy, is proposed and used to simulate swirling gas-particle flows with a swirl number of 0.47. Besides, a gas turbulence augmentation model accounting for the finite-size particle wake effect in the gas Reynolds stress equation is proposed. The proposed turbulence modification models are used to simulate two-phase pipe flows. It can predict not only the turbulence reduction by small particles but also the turbulence enhancement by large particles.Copyright © 2003 by ASME
Increasing heat and/or mass transfer rates in impinging jets
First part of a survey drawing together findings of authors’ research over a period of two decades on enhancing performance of impinging jets. The limiting factor is stagnant near-wall layer across which the transfer takes place by conduction. Results of research aimed at removing this limitation have been partly published but mostly in literature inaccessible to international readers. Flow visualizations played an important role in identifying the problem areas, leading to a number of novel implementation concepts to be described in the second part.