Developing theory of probability density function for stochastic modeling of turbulent gas-particle flows

Turbulent gas-particle flows are studied by a kinetic description using a prob- ability density function （PDF）. Unlike other investigators deriving the particle Reynolds stress equations using the PDF equations, the particle PDF transport equations are di- rectly solved either using a finite-difference method for two-dimensional （2D） problems or using a Monte-Carlo （MC） method for three-dimensional （3D） problems. The proposed differential stress model together with the PDF （DSM-PDF） is used to simulate turbulent swirling gas-particle flows. The simulation results are compared with the experimental results and the second-order moment （SOM） two-phase modeling results. All of these simulation results are in agreement with the experimental results, implying that the PDF approach validates the SOM two-phase turbulence modeling. The PDF model with the SOM-MC method is used to simulate evaporating gas-droplet flows, and the simulation results are in good agreement with the experimental results.

Preferential concentration in supersonic gas-particle two-phase transverse jets

The supersonic gas-particle two-phase transverse jet is a typical flow process in many applications,such as solid rocket scramjet.This study carried out experimental tests as well as Large Eddy Simulation(LES)to investigate the evolution process of transverse gas-particle two-phase jets in supersonic crossflow,especially focusing on the phenomena called preferential concentration.The simulation is based on the Eulerian-Lagrangian method,which successfully reproduces the characteristic phenomena observed in experiments.The particle cloud forms three different characteristic distribution patterns:tooth-like waves near the jet port,quasi-ordered structures near counter-rotating vortex pairs(CVP),and filamentous clouds in the upper part.The turbulence and small unstable shock play a suppressing role in mixing small-diameter particles,which tend to aggregate in regions of high density and low vorticity.Furthermore,it is found that there exists a specific range of particle sizes,as particles'sizes approach this specific range,the influence of compressibility of the airflow on particle distribution becomes increasingly prominent.Overall,this study shed some light on the understanding of the complex and intricate nature of the supersonic gas-particle two-phase transverse jet.