Unsteady Rans Simulation of an Enclosed, Turbulent Reacting Methane Jet with the Premixed CMC Method

Abstract

The premixed conditional moment closure (CMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed CMC method is extended to Unsteady RANS. The new model is validated with the PIV and Raman turbulent, enclosed reacting methane jet data from DLR [2]. The experimental data has a rectangular test section at atmospheric pressure and 573 K 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 equivalence ratio along with their rms values are provided. The CMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. The unsteady RANS version of the open source CFD code OpenFOAM is used with the PISO algorithm solved with the finite volume method. Velocity, temperature and major species are compared to the experimental data. Once validated, this tool will be useful for designing lean premixed combustors for gas turbines. The results match the experimental data better than the steady RANS of [1] and are able to pick up the unsteadiness of the flame.