Large Eddy Simulations

Large Eddy Simulations (LES) is considered as one of the more promising numerical approaches for the analysis of turbulent combustion, balancing computational complexity and predictive accuracy. While DNS resolves all the turbulent scales, it is computationally expensive and impractical for high Reynolds number large scale applications. RANS, on the other hand, models the influence of turbulence on the mean flow and hence can not capture the unsteady flow. In LES, rather than averaging the effect of turbulence, the equations are filtered, enabling the larger scales of turbulence to be explicitly resolved and computed (as with DNS), while the smallest ones are modeled (as with RANS modeling). This enables capturing the unsteadiness in the flow and results in better predictions as compared to RANS technique, because the effect of turbulence is represented more accurately due to the explicit computation of the large eddies. Modeling the sub-grid scale effects on the other hand ensures that the approach is computationally manageable.

An integral component of LES is the turbulent combustion sub-grid model, which is necessary to incorporate the effect of turbulence-chemistry interactions at the under-resolved scales on the reaction rate. The reaction mechanism incorporated is also important, particularly when studying unconventional combustion (e.g. oxy-fuel combustion conditions). Our study involves developing high fidelity LES solvers in OpenFOAM, focusing on the implementation of turbulent combustion models (such as the thickened flame model) and chemistry integration approaches (eg flamelet generated manifolds). These will be used to study the dynamic response of lean premixed flames in step and swirl systems, while also focusing on instability mitigation approaches.