Influence of reaction mechanisms, grid spacing, and inflow conditions on the numerical simulation of lifted supersonic flames

Abstract

SUMMARYThe simulation of supersonic combustion requires finite-rate chemistry because chemical and fluid mechanical time scales may be of the same order of magnitude. The size of the chosen reaction mechanism (number of species and reactions involved) has a strong influence on the computational time and thus should be chosen carefully. This paper investigates several hydrogen/air reaction mechanisms frequently used in supersonic combustion. It is shown that at low flight Mach numbers of a supersonic combustion ramjet (scramjet), some kinetic schemes can cause highly erroneous results. Moreover, extremely fine computational grids are required in the lift-off region of supersonic flames to obtain grid-independent solutions. The fully turbulent Mach 2 combustion experiment of Cheng et al. (Comb. Flame 1994; 99: 157-173) is chosen to investigate the influences of different reaction mechanisms, grid spacing, and inflow conditions (contaminations caused by precombustion). A detailed analysis of the experiment will be given and errors of previous simulations are identified. Thus, the paper provides important information for an accurate simulation of the Cheng et al. experiment. The importance of this experiment results from the fact that it is the only supersonic combustion test case where temperature and species fluctuations have been measured simultaneously. Such data are needed for the validation of probability density function methods.

Simulation of a supersonic hydrogen–air autoignition-stabilized flame using reduced chemistry

“…This error is recurrent in all recent simulations of this flame [20][21][22][23][24][25], and may be lessened by a more realistic boundary condition including, for instance, a realistic burner geometry. Besides these inaccuracies, this flame simulation captures the correct physics, and is a good reference for studying the impact of the chemistry model, which is the objective of the present work.…”

“…To handle shocks in the supersonic jet the strategy proposed in [18] was followed: the sub-grid scale turbulent viscosity µ t is modeled through a standard Smagorinsky model, a centered numerical scheme is chosen and a hyperviscosity like in [19] is used for capturing shocks. A subgrid scale diffusivity is introduced for chemical species via a turbulent Schmidt number equal to 0.6 (molecular diffusivity is different for each species, and specified by the A number of groups have simulated the main characteristics of the supersonic flame using Eulerian and Lagrangian Monte Carlo Probability Density Function (PDF), or flamelet models [20][21][22][23][24][25], in a Reynolds Averaged Navier-Stokes (RANS) context. The boundary conditions have proven to be one of the most sensitive elements in simulating this flame.…”

Numerical Simulation of Hydrogen Air Supersonic Coaxial Jet

“…The computed peak of water mass fraction is higher compared to experimental data because of fast chemistry assumption. Computed water mass fractions with different chemical schemes presented in the literature [21] almost coincide with each other indicating the marginal effect of detailed chemical kinetics for this experimental condition. Present computations also demonstrate that standard two equation class turbulence model with single step kinetics based turbulence chemistry interaction can describe H 2 -air reaction adequately in high speed flows.…”

“…Though this flowfield does not possess the complexities arising from the geometry of a scramjet combustor, nevertheless, it does possess the fundamental physical interaction of a turbulent flow mixing and burning within a chemically reacting environment. Calculations with different chemical schemes for this experimental condition presented in the literature [21] did not make remarkable improvement in the mean temperature in the flow field. Also, most of the studies carried out in the literature did not take into account the fluctuating species flow field caused by turbulence in the combustion process.…”

“…In most of the studies, although turbulence closure is employed, turbulence-chemistry interaction was not modelled. Gerlinger et al [21] compared different chemical schemes to assess their predictive capabilities for high speed reacting flows.…”