Turbulent combustion modeling using a flamelet generated manifold approach——a validation study in Open FOAM

An OpenFOAM based turbulence combustion solver with flamelet generated manifolds (FGMs) is presented in this paper. A series of flamelets, representative for turbulent flames, are calculated first by a one-dimensional (1D) detailed chemistry solver with the consideration of both transport and stretch/curvature contributions. The flame structure is then parameterized as a function of multiple reaction control variables. A manifold, which collects the 1D flame properties, is built from the 1D flame solutions. The control variables of the mixture fraction and the progress variable are solved from the corresponding transport equations. During the calculation, the scalar variables, e.g., temperature and species concentration, are retrieved from the manifolds by interpolation. A transport equation for NO is solved to improve its prediction accuracy. To verify the ability to deal with the enthalpy loss effect, the temperature retrieved directly from the manifolds is compared with the temperature solved from a transport equation of absolute enthalpy. The resulting FGM-computational fluid dynamics (CFD) coupled code has three significant features, i.e., accurate NO prediction, the ability to treat the heat loss effect and the adoption at the turbulence level, and high quality prediction within practical industrial configurations. The proposed method is validated against the Sandia flame D, and good agreement with the experimental data is obtained.

Large eddy simulation of spray combustion using flamelet generated manifolds combined with artificial neural networks

In the present work,artificial neural networks(ANN)technique combined with flamelet generated manifolds(FGM)is proposed to mitigate the memory issue of FGM models.A set of ANN models is firstly trained using a 68-species mass fractions in mixture fraction-progress variable space.The ANN prediction accuracy is examined in large eddy simulation(LES)and Reynolds averaged Navier-Stokes(RANS)simulations of spray combustion.It is shown that the present ANN models can properly replicate the FGM table for most of the species mass fractions.The network models with relative error less than 5%are considered in RANS and LES to simulate the Engine Combustion Network(ECN)Spray H flames.Validation of the method is firstly conducted in the framework of RANS.Both non-reacting and reacting cases show the present method predicts very well the trend of spray and combustion process under different ambient temperatures.The results show that FGM-ANN can replicate the ignition delay time(IDT)and lift-off length(LOL)precisely as the conventional FGM method,and the results agree very well with the experiments.With the help of ANN,it is possible to achieve high efficiency and accuracy,with a significantly reduced memory requirement of the FGM models.LES with FGM-ANN is then applied to explore the detailed spray combustion process.Chemical explosive mode analysis(CEMA)approach is used to identify the local combustion modes.It is found that before the spray flame is developed to the steady-state,the high CH_(2)O zone is always associated with ignition mode.However,high CH_(2)O zone together with high OH zone is dominated by the burned mode after the steady-state.The lift-off position is dominated mainly by the diffusion mode.

LES of the Sandia flame series D-F using the Eulerian stochastic field method coupled with tabulated chemistry

In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probability density function transport equation by ESF method that considers the interaction mechanism between flame and turbulence with high precision.At the same time,by making use of the advantage of the FGM model,this model is able to incorporate the detailed chemical reaction mechanism(GRI 3.0)with acceptable computational cost.The new model has been implemented in the open source CFD suite-Open FOAM.Validation of the model has been carried out by simulating the Sandia flame series(three turbulent piloted methane jet flames)issued by the National Laboratory of the United States.The accuracy and advancement of the ESF/FGM turbulent combustion model are verified by comparing the LES results of the new model with the rich experimental data as well as the RANS results.The results demonstrate that the model has a strong ability in capturing combustion phenomena such as extinction and re-ignition in turbulent flame,which is essential in the accurate prediction of the combustion process in real combustion devices,for example,aircraft engines.

Atmospheric Test and Numerical Models Assessment of Annular Combustor on ZK2000 Gas Turbine

ZK2000 is a newly developed 2 MW all radial gas turbine with an annular combustor. In this paper, the authors present the atmospheric test results of the combustor on test rig. Evaluation of several RANS turbulence models and reaction models were used in order to determine which model was the most appropriate combination for comparison with the test results. FGM with SST were selected because of the better agreement with test results in terms of combustor temperature rise, primary zone temperature, liner metal temperature, and NO_x emission predictions.