Gas-solid Flow And Reaction Simulation Based On A Finite Volume Fictitious Domain Method

Numerical simulation methods are widely used for the research of gas-solid flow and combustion.Currently,the interaction models between different phases are not accurate enough when it comes to dense phase and inhomogeneous flows.Direct numerical simulation methods,which do not need models to describe interactions,can be used to obtain results and data for model modifications,thus is an important research topic for multiphase flow and reaction study.In this paper,a finite volume fictitious domain method which can be used for analyzing gas solid flow and combustion is developed.The analyses for multi-particle flow and combustion processes are conducted on particles' scale,which can shed light on the development of multiphase reaction models.This paper first establishes a finite volume fictitious domain method for gas-solid flow.According to the momentum equations for particles and the fluid,an accurate source term is derived to add the rigid body constraint onto the area covered by the particles.A pressure gradient term in the source term will make the pressure equation singular,increasing instabilities for the calculation process.This problem is solved by dividing the source term into one particle part and one fluid part.The equations are then solved by applying different source terms in momentum and pressure equations.For the cells covered by the particle boundaries,the equations are modified by the solid volume fraction on that cell.This action lowers the result fluctuation and improves the calculation efficiency.The comparison of simulation and experimental results show that the calculation method can produce accurate resultsfor particle diameter /mesh size>16.The method also shows high accuracy for different particle-fluid density ratios and different inlet Re numbers.This paper also builts a finite volume fictious domain method for gas-solid combustion calculation.The method mentioned above is modified to solve compressible Navier-Stokes equations.The fictitious source term for enery equation is derived according to the temperature distribution inside particles.The surface reaction heat is first added to the particle,then transferred to the fluid by thermal convection and heat conduction.This process improves the numerical stability of the method.For the species equation,the method of calculating species source terms with reaction rates is raised.The calculation results agree well with the experimental data,which proves the applicability and accuracy of the method for solving gas-solid combustion problems.The simulation of large numbers of particles moving and buring processes are conducted and the combustion properties for multiparticulate flow is analyzed.In order to modify the drag model and the combustion rate model for multiphase flow and reaction,numerical simulations for multi-particulate flow and combustion with different Renolds numbers and particle volume fractions are conducted,and the flow and combustion behaviors are studied with the calculation results.The particle non-uniform distribution along the flow direction is observed to play an important role on the particle drag force and combustion rate.According to this,the drag model and combustion model are modified with this flow direction non-uniform coefficient,and the parameters in these models are connected with inlet flow velocities and particle concentrations.In addition,the drag force during combustion process is studied.There is a positive correlation between the drag for during a single particle combustion and the particle reaction rate.The research result makes contribution to the development of accurate phase interaction models in multiphase flows.