Direct Numerical Simulation Of The Tombustion In Supersonic Tuibulent Flow

As the evolution of the human civilization, the scope of human activy becomes more and more broad. The development of the new generation of long-distance civile aerocraft depends on the design of the supersonic combustor with higher combustion efficiency and cleaner exust gas. Since the fast development of the computer, computational simulation turns into a significant instrument for science study, which has the advantages of higher efficency and lower cost. And it is possible to compute supersonic turbulent flow using direct numerical simuatlion (DNS) method, as the fast development of the parallel computer. Using DNS method, tiny flame scales and small vortex structures in supersonic turbulence combution can be captured, which is very helpful to understand the complex phenomena therein, and to improve the models for mixing and combustion using in the Reynald average simulationg (RANS) or large eddy simulation (LES) method. In the present paper, a supersonic turbulence jet flame was studied using DNS method.Firstly, compouled three dimensional characteristic boundary conditons were improved by the author, and the characteristic system of conservation system of compressible reactive flow was derived. Using the boundary conditions and the characteristic updated together with the detailed computation of the thermal properties and the transport properties, a bandwidth-optimized WENO scheme and eighth-oder center difference schem, a methodology for computation of supersonic turbulent combustion with high precision was developed. Based on the methodology, a codepacage which has higher efficnecy for paralle computation was developed.Secondly, using the codepacage developed by the author, one dimensional premixed flame, one dimensional shock tube problem, two dimensional supersociwind tunnel flow with forth-face step, the coupling action between a stational shock and a vortex, a spherical shock and a turbulent jet flow were computed. By compare the resolutions with the convergency resolution, the classic resolution or the experimental data, the abillity of the present codepackage to capture the flame scales, the shock wave and the turbulent sacals was confirmed.Using the codepackage developed by the author, a supersonic jet flame with a Mach number of1.2and a Reynald number of22,000was computed. The number of the total grids is about0.972billion. The computation was performed on2000 processors, and about500million cpu-hours were costed totally. In present paper, the characteriscs of the flow field and the flame structure, the mechanism of the flame stabilization, the vortex structure, the structure of shock wave and detonation, the interaction between the movement of the vortex and the reaction are studied.Three characteristic elements of the supersonic flame are discovered:the quasi laminar flame base, a violent mixing region with higher heat release rate and lower temprature, far flame field with lower reaction rate. Due to the compressibility, the half width of the jet flame developes more slowly than that in the subsonic jet flow, and the stream velocity becomes selfsimilar later.With the accumulation of HO2upstream of OH and the higher Da as the characteristic phenomena, auto-ignition is the main stabilization mechanism for the flame base, which firstly occurs in lean fuel mixture of higher temperature and lower dissipation rate. The lifted height of the jet flame can be controled through controling the temperature and the velocity of the co-flow and the inflow boundary conditions. Through analizing the flame index, it is found that the auto-ignition of the flame base belongs to non-premixed combustion. The non-premixed combustion occurs in the stoichiometric mixture in most of the flame region. The other non-premixed combustion region occurs in the vicinity of the sonic surface. The premixed flame region lies between the two non-premixed flame regions. In the violent mixing reigon, both the premixed and non-premixed combustion are vigorous, and about35%of the total heat release rate comes from the premixed combustion. In the far field, the outer non-premixed combustion is more significant, and provides about80%of the total heat release rate.In the present study, it is confirmed that the vortex structure is mainly three dimensional streamwise in near flield of the supersonic jet. Once the turbulence is developed, the radial and the circumferential vortexs become abundance, too. It is helpful to add a proper inspiring or design a proper figure of the nozzle for increasing the mixing rate of the ractants. The configurations of the normal flame and the detonation are also presented in the paper. The compressive region occurs downstream the detonation while it occurs upstream the normal flame. Due to the influence of the turbulent and the detonation, the configuration of the shockwave becomes very shirring, or even broken. As a result, shocklets and supersonic "islands" occur. Since turbulent mixing is inactive in supersonic flow, the appearance of the shocklets and supersonic "islands" boosts the mixing of the reactants. The interactions of the vortex movement and the combustion are also studied in the paper. In the low speed region of the supersonic jet flame (ξ=0.0983and ξ=0.2), both the higher compressive and expansive power rate correspond to the higher heat release rate. Most of the heat release comes from the samples with a compressive (or expansive) power rate of1Jmm-3s-1. The expansion of the vortex due to the heat release is the main phenomena in the low speed mixture. In the high speed region of the supersonic jet flame (ξ=0.8andξ=0.9), the higher compressive power rate corresponds to the higher heat release rate, while the higher expansive power rate can not influence the heat release distinctly. Most of the heat release comes from the samples with a compressive (or expansive) power rate of10Jmm-3s-1. The increase of the reaction rate caused by the higher compressive power rate is the main phenomena in the high speed mixture.Base on the work in the paper, a database with about15T bytes of data was built. The study of the physical phenomena in supersonic turbulent combustion and the improvement of the models related can be boosted by the database.