Large Eddy Simulations (LES) is increasingly becoming a feasible tool for industrial design purposes on account of ongoing advancements in computational power. It is a promising arena in the field of computational fluid dynamics where more details of flow-turbulence are explicitly captured and lesser are modeled as compared to the traditional Reynolds-average (RANS) approaches. For the gas turbine combustors particularly, it is a promising tool for better predictions of reactants mixing and hence the combustion, flame shape and temperature profiles. Also, as inherent unsteady nature of the flow is captured, it can predict combustion dynamics due to heat-release (and hence pressure) fluctuations. The main factor for performing a successful and reliable LES is to find an appropriate filter size for different regions of the CFD domain. This filter size is typically same as the CFD mesh size and turbulent scales larger than this are explicitly solved in LES. In industrial gas turbine combustors, due to complex geometry and numerous small cooling flow passages, unnecessary mesh refinement may make the mesh size prohibitive for a time-marching LES simulation. Hence, judicious selection of important flow features and geometry is important. Still not much experience is available on the quantification of LES meshing requirements for practical gas turbine combustors. In this study, two different LES meshing approaches, namely one based on Taylor length scales and other based on theoretical turbulence energy spectrum are compared for various medium scale gas turbine combustors. While the former approach requires a prior RANS simulation and provides a spatial distribution of the grid size, the latter just requires mean flow properties and global length scale at various inlets but produces only a global mesh value. It is found for all combustor designs under study that the two approaches agree well with each other for predicting mesh size requirements for LES where 85–90% of turbulent length scales are captured. This helps towards standardizing LES meshing procedure in industrial scenarios and helps a user to choose meshing option based on the level of details needed and time-resource constraints.

This content is only available via PDF.
You do not currently have access to this content.