Numerical Methods For Complex Combustion Flowfields

With the development of the air-breathing hypersonic vehicle, supersonic combustion ramjet (Scramjet in short) has received more and more attention. In the combustor of scramjet, there are complex phenomena, such as shock, combustion, vortex, turbulence, and the interactions between them. If liquid fuels, such as kerosene, the flowfields of combustor will also contain complex droplet acts, such as droplet evaporation, droplet oscillation and distortion, droplet breakup, droplet collision and coalescence. As one of the key methods, numerical methods for simulating complex combustion flowfields are very important. In this dissert, involving many subjects, such as Computational Fluid Dynamics, combustion science, heat transfer theory, multiphase flow, an efficient parallel method based on unstructured/hybrid meshes for simulating combustion problems at all speeds was developed, and used to analyze the complex phenomenon in the combustor of scramjet, which is helpful for the advanced aircraft propulsion design.A rapid means of predicting the propulsion system is needed for the concept stage and preliminary stage of the scramjet design, so a quasi-one-dimensional analysis model was developed. The equations, experimental models, numerical methods were discussed in detail. Numerical result was compared with Billig's experiment, which shows the reliability of this analysis model. Using this model, the effects of the expansion angle and the fuel-injector location on the performance of typical supersonic combustor have been studied.Numerical methods for combustion flowlfields of gas fuel were investigated. Based on the multi-component Navier-Stokes equations, an efficient parallel method on the unstructured/hybrid meshes was developed, using higher-order upwind schemes, turbulence models and finite rate chemical reaction model. The equations are solved using the cell-centered finite volume method. Four schemes including AUFS, Van Leer, AUSM+ and HLLC/E can be used for the inviscid flux vector calculation. S-A one-equation turbulence model, k-εCMOTT and k-ωSST two-equation turbulence model are implemented to evaluate the turbulent viscosity. Taking the case of symmetry boundary, the differences between two methods of the boundary were discussed. An order analysis was conducted to search for the convergence characteristics of Euler equations with Weiss-Smith preconditioner in low speed flow. Then several preconditioned upwind schemes were introduced. Many benchmark cases were simulated to validate the capabilities of this numerical method for the invisid, laminar, turbulence, chemical reacting flow, all speeds flow. The results indicate that the numerical method has good resolution and reliability.Numerical methods for combustion of liquid fuels were developed with Eulerian-Lagrangian method. A stochastic particle method was used to calculate the liquid sprays with turbulence effects. Many spray models were implemented to control the behavior of the spray droplets, including evaporation, droplet oscillation and distortion, droplet breakup, and droplet collision and coalescence, the interaction between the ambient fluid and the spray. The performance of individual spray submodels has been validated by comparing the numerical results of some benchmark cases to theory and experimental results from the literature. The performance of the complete numerical method has been explored by investigating the flowfield of a kerosene scramjet model with cavity and pilot hydrogen.