Subgrid Scale Combustion Modeling Based on Stochastic Model Parameterization

ABSTRACT: The technical objective of this program is to develop a fast running, subgrid scale turbulence-chemistry interaction model for large-eddy simulation (LES) of aircraft combustors and augmentors that can accurately capture critical phenomena such as extinction and re-ignition effects. To accurately capture these phenomena, this model is based upon a parameterization of the linear-eddy model (LEM). The LEM is a comprehensive mixing model that separately treats molecular diffusion, small scale turbulent stirring and finite-rate kinetics. Because the model resolves the microscale flame structure, extinction and re-ignition may be accurately captured. Under this program, statistics from this mixing model will be parameterized to form a computationally inexpensive run time model. This parameterization will be accomplished through a unique application of the LEM to a flow configuration designed to capture mean or resolved scale strain effects on the subgrid statistics. Consequently, this novel modeling approach may be used to predict turbulent extinction limits by directly accounting for both small and large scale turbulent strain effects. Parameterized statistics generated from this formulation are then stored using artificial neural networks (ANNs). The resulting computational model is a fast running subroutine to provide closure for the LES filtered transport equations that is portable to any CFD flow solver. The model subroutines, or user defined functions, for this formulation may be generated using a software tool kit developed in this program given user specified conditions. These user defined functions may be easily implemented within any CFD flow solver for LES applications. The software tool kit will also be able to generate RANS flow solver user defined functions with only minor changes to the input parameters. Combustion models generated by the tool kit will be applicable to a wide range of military and commercial combustion applications. These applications include gas turbines, power generation systems, furnaces, incinerators, internal combustion engines, etc. BENEFIT: At the conclusion of this program, CRAFT Tech will have completed the development of an advanced turbulent combustion subgrid model for LES of reacting flows. This effort involves the development of a generalized software tool kit for the generation of user defined functions (UDFs) for specified combustion problems. These UDFs may be easily implemented within any CFD flow solver for LES applications. The software tool kit will also be able to generate RANS flow solver UDFs with only minor changes in the input parameters. Combustion models generated by the tool kit will be applicable to a wide range of military and commercial combustion applications. These applications include gas turbines, power generation systems, furnaces, incinerators, internal combustion engines, etc. The commercial opportunities for this software tool kit are enormous. CRAFT Tech will market this tool kit for license to commercial customers as well as to other CFD flow solver development companies. Since the UDFs generated by the tool kit will be flow solver independent and completely portable, customers of other CFD flow solver development companies may use the tool kit for their applications. With this goal in mind, the software tool kit was developed to produce UDFs that are compatible with popular commercial flow solvers that are used for a broad range of applications. This fact greatly expands the commercial opportunities of the software tool kit.