Research On Dilute Gas-solid Two-phase Cross Jets With Low/Moderate Reynolds Number Based On Lattice Boltzmann Method

Researching gas-solid two-phase cross jets provides technical support to both industrial production and environmental protection in certain degrees.However,most of numerical studies on gas phase of gas-solid two-phase cross jets were implemented by macro-scale approaches including Reynolds Averaged Navier-Stokes method,large eddy simulation,direct numerical simulation.Carrying out simulation of both flow and heat transfer phenomena in gas phase with meso-scale approaches,including lattice Boltzmann method,is beneficial for enhancing understanding of mechanisms in cross jets.Lattice Boltzmann method has advantages in simulating complex flows for their clear physical background,easy for parallel computing and coding,and flexible for dealing with boundary conditions.By utilizing coupled model of lattice Boltzmann equation method and discrete element method,this dissertation investigates characteristics of flow field in gas phase,dispersion and collision of particles and so on,and mechanisms of interaction between gas and solid phases in gas-solid two-phase cross jets.Firstly,a lattice Boltzmann equation-discrete element method(LBE-DEM)coupled simulation method under the Eulerian-Lagrangian framework is established,and it is applied to simulate a two-dimensional gas-solid two-phase cross jets.The gas phase is simulated by the lattice-Boltzmann method via the TD2G9 model,which is a double distribution function model;the solid phase is traced by the Lagrangian method and the inter-particle collision is calculated by the DEM method.The inlet velocities of both horizontal and vertical jets are the same,and particles with of different Stokes number are simulated under the same mass loading.Characteristics of vortex structure,particle distribution,and the reverse-flow/ rebounding rate in cross jets are studied.Based on established LBE-DEM coupled model,heat transfer process between phases is taken into account,investigations of gas-particle two-way coupling heat transfer and its effect on heat transfer characteristics are implemented.The Reynolds number is 1000,inlet temperatures of jets are different,and particle Stokes numbers are 10,25,and 50 under the same number flow rate of particles.The gas phase temperature field and particle distribution as well as the inter-phase heat transfer characteristics are studied and analyzed.Furthermore,coherent characteristics of flow field of transverse jet in cross flow with various inlet velocities are studied.TD2G9 model is used to simulate the coherent vortex motions and interactions and the heat transfer characteristics of jets in cross flow(JICF)via TD2G9 model.After validation,the characteristics of cross flow under different Reynolds numbers are illustrated,including the mean profiles,the Reynolds stress tensor,the vortex and temperature fields,the temperature gradients near the walls,and the coherent correlation of vortex motions.Finally,TD2G9 model is utilized to simulate transverse jet in cross flow(TJi CF)under various velocity ratios to investigate the interaction between the transverse jet and the main flow.Seven cases with various flow ratios(Jr = 0.3,0.6,0.9,1.2,1.5,1.8,2.0)are simulated.The influences of flow ratio(Jr)of the transverse jet to the main flow on vortex streets and temperature fields are studied.The characteristics of fluid vortex,mean axial velocity,mean temperature,fluctuating velocity,etc.,are studied in details to show the effects of Jr.