A Alessio Fancello

Turbulent Combustion Modeling Using Flamelet-Generated Manifolds for Gas Turbine Applications in OpenFOAM

The continuous interest in reducing pollutions and developing both an efficient and clean combustion system require large attention in the design requirements, especially when related to industrial gas turbine application. Although in recent years the advancements in modelling have increased dramatically, combustion still needs a huge computational effort. The Flamelet-Generated Manifolds (FGM) method is considered a suitable solution with an accuracy that can be comparable with detailed chemistry simulations results. The full combustion system can be described by few controlling variables while the chemical details are stored in a database (manifold) as function of controlling variables. Transport equations are solved for the Navier-Stokes system and the controlling variables. The detailed chemistry code Chem1D is used to create the manifolds. Turbulence can be modeled using a PDF approach for the subgrid modeling of the chemistry terms. The OpenFOAM open source CFD package is used as CFD tool for the simulations. The aim of this work is to demonstrate the usage of FGM with OpenFOAM and figure out the status of the implementation. To achieve this goal, the work employs as test case a confined lean jet flame is used. For the case presented, an extensive experimental data set exist, including PIV and Raman data. Results are further compared with traditional methods, while FGM method might be easily extended to other scenarios.Copyright

Large Eddy simulations of a premixed jet combustor using flamelet-generated manifolds : effects of heat loss and subgrid-scale models

Large eddy simulations of a turbulent premixed jet flame in a confined chamber were conducted using the flamelet-generated manifold technique for chemistry tabulation. The configuration is characterized by an off-center nozzle having an inner diameter of 10 mm, supplying a lean methane-air mixture with an equivalence ratio of 0.71 and a mean velocity of 90 m/s, at 573 K and atmospheric pressure. Conductive heat loss is accounted for in the manifold via burner-stabilized flamelets and the subgrid-scale (SGS) turbulence-chemistry interaction is modeled via presumed probability density functions. Comparisons between numerical results and measured data show that a considerable improvement in the prediction of temperature is achieved when heat losses are included in the manifold, as compared to the adiabatic one. Additional improvement in the temperature predictions is obtained by incorporating radiative heat losses. Moreover, further enhancements in the LES predictions are achieved by employing SGS models based on transport equations, such as the SGS turbulence kinetic energy equation with dynamic coefficients. While the numerical results display good agreement up to a distance of 4 nozzle diameters downstream of the nozzle exit, the results become less satisfactory along the downstream, suggesting that further improvements in the modeling are required, among which a more accurate model for the SGS variance of progress variable can be relevant.

Large eddy simulation of a turbulent premixed jet flame using flamelet-generated manifolds

Large eddy simulations of a turbulent premixed jet flame in a confined chamber were conducted using the flamelet generated manifold technique. The scope of the present research is to investigate the effects of inflow boundary conditions in these simulations. To evaluate the effect of two kinds of inflow boundary conditions, the numerical solutions using those boundary conditions are compared with experimental results. Turbulent flow generated by the self-recycling boundary condition behaves in a more realistic way, while randomly distributed perturbation imposed on the inlet boundary immediately vanished due to the lack of the turbulence structure. Quantitative comparison between experimental and computational results was carried out and analized.

Towards numerical simulation of turbulent hydrogen combustion based on flamelet generated manifolds in OpenFOAM

This work proposes an application of the Flamelet-Generated Manifolds (FGM) technique in the OpenFOAM environment. FGM is a chemical reduced method for combustion modeling. This technique treats the combustion process as the solution of a small amount of controlling variables. Regarding laminar simulation, a progress variable and enthalpy evolution can describe satisfactorily the problem. From a turbulent point of view, FGM can be applied to LES and RANS simulations, where the subgrid chemical terms are described with a β - PDF approach. These approaches apply satisfactorily in relatively simple gases, nevertheless for hydrogen are not more valid, due to preferential diffusion effects and instability of the flame structure. The overall aim of this research is to find technical solution for hydrogen gas turbines design in the next generation of Integrated Gasification Combined Cycle (IGCC) plants.