Sub-particle Scale Direct Numerical Simulations Of Multiphase Combustion

Gas-solid reacting flows are significant in many industrial systems. With compu-tational fluid dynamics, these flows and reactions can be predicted. The interaction ofparticle cluster flows, heat transfer and reactions is a state-of-art topic in multiphase reac-tion flow studies. In this thesis, direct numerical simulations(DNS) methods are studied,target to the so-called sub-particle scale, and this is different from most researches in thisarea, which adopted point source models to describe particles. The DNS method pro-posed in this thesis is of significance in obtaining the insights of complicated interactionsbetween phases, as well as gaining the detailed law of multiphase combustion.AsDNSrequiresahighresolutionflowsolver, amovingmeshbased, high-orderandstablediscontinuousspacemethodisdevelopedinthisthesis. Basedonthecuttingedgeinthe field, the flux reconstruction method, an arbitrary Lagrangian-Eulerian(ALE) methodfor high-order moving mesh simulations is proposed here. The geometric conservationlaw(GCL)problemforhigh-ordermethodisstudiedinthisthesis, andawidelyapplicableGCLsourcetermmethodisdevelopedtoensureGCLforanyhigh-ordermethod. Thefluxreconstruction method is extended to combustion simulating in this work by studying thespecies equation solving method. A series of validation test cases, including comparisonswith combustion experiments, verify the method proposed.To simulate a large scale many-particle flow and combustion problem, the currentwork proposed a new finite element based fictitious domain method to discretize low-Mach number reacting flow control equations. By introducing fictitious domain energysourceterms,speciessourcetermsandchemicalreactionsourceterms,thecurrentmethodis capable to simulate multiphase combustion phenomenon in a sub-particle scale. In thesame time, the particle description method is improved in this work to strengthen both theaccuracy and stability. Validated with the high-order moving mesh solver, the fictitiousdomain flow solver is proved to be correct, and by the comparison work with carboncombustion experiment, the fictitious domain reacting solver is also verified.Mediumandlargescaleparticulateflowsandcombustionprocessesdirectnumericalsimulations of-D or-D are carried out. With several different condition, the flowpatternsandparticlesdistributionpatternsarestudied. Thedragforcesandcarbonburningrates are also recorded and analysed in the current work. Based on the DNS data, a non- uniform drag force model proposed previously is checked and improved here. Similarnon-uniform model is firstly proposed in this thesis for carbon burning rate from-Dcombustion simulations, and it is checked in the-D simulation.