A Unified Manifold-Based Approach to Modeling Turbulent Combustion

Princeton University, Princeton NJ

Investigators

Abstract

One of the major impediments to the development of new high-efficiency low-emissions combustion systems is the lack of reliable, affordable, predictive computational models for describing turbulent combustion. The primary challenge in developing such models is describing the relationship between combustion processes and turbulence. While a broad range of models have been developed for describing the effects of turbulence on combustion processes, no general models exist for describing the effects of combustion processes on turbulence. Current turbulence models implicitly assume that combustion heat release has no effect on turbulence, a fact contrary to observation. This project will develop a new modeling approach capable of capturing the two-way coupling between combustion processes and turbulence. In the new approach, information about the combustion processes is directly embedded into the turbulence model. The new model will be evaluated against a set of computational databases and experimental databases of laboratory-scale turbulent combustion. With the two-way coupling between combustion processes and turbulence fully captured, the new modeling approach will enable truly predictive simulations of turbulent combustion, facilitating the development of new clean combustion systems. The software implementation of the new modeling approach will also be made publicly available for use by other researchers and in industry. Despite the known influences of combustion heat release on turbulence, notably the phenomenon of counter-gradient-transport, turbulence models in reacting flows are usually adapted from the non-reacting flow community, implicitly assuming no effect of combustion heat release on turbulence. This project will develop a fundamentally new approach for Large Eddy Simulation (LES) of turbulent combustion that accounts for fully coupled interactions between turbulence and combustion. The approach relies on the conditional filtering of not only the thermochemical scalar equations but also the momentum equation with respect to one or more flame structure variables. With this approach, the modeling of turbulence is divorced from the flame dynamics, which are embedded into the conditional filtering, and simplifies closure modeling. After deriving the conditionally filtered governing equations and analyzing their budgets using data from Direct Numerical Simulation (DNS), closure models will be developed using a combination of physics-based approaches and data-based approaches. Ultimately, the unified manifold-based approach will be implemented into a computational tool, benchmarked against current modeling approaches, and validated against experimental measurements of turbulent premixed and stratified flames. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.