Scott M. Martin

MODELING AN ENCLOSED, TURBULENT REACTING METHANE JET WITH THE PREMIXED CONDITIONAL MOMENT CLOSURE METHOD

Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided.The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled.The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors.Copyright

Large Eddy Simulation/Eulerian Probability Density Function Approach for Simulating Hydrogen-Enriched Gas Turbine Combustors

To describe partially-premixed combustion inside hydrogen-rich combustors, a novel quadrature-based probability density function (PDF) approach is studied here. The PDF approach is comprehensive in describing multiple combustion regimes, and multiple inlet streams. The methodology is implemented in the context of the large eddy simulation (LES) approach. The main bottleneck in utilizing the PDF approach is that the PDF transport equation, which needs to be evolved along with the LES equations, is high-dimensional and intractable using conventional discretization techniques. In order to ensure that the PDF approach is easily transferred to existing industrial flow solvers, a quadrature-based Eulerian method for solving the PDF transport equation is considered here. The corresponding Eulerian equations are implemented in the open source OpenFOAM code using an unstructured grid system. Simulations of an experimental high-pressure combustor demonstrate that the PDF approach significantly changes the reaction structure compared to laminar chemistry assumption.Copyright