Large eddy simulation of unsteady combustion

Abstract

The present study concerns the application of a large eddy simulation (LES) model, capable of dealing with chemical reactions described by multistep reaction mechanisms and thermal radiation. The LES model, based on prefiltering of the balance equations of mass, momentum, and energy, contains a variety of submodels for representing the residual stress tensor and flux vectors and the filtered reaction rates. Here, we have focused on the influence of modeling of the filtered reaction rates. Three different reaction rate formulations have been investigated, the eddy dissipation kinetic model, a model based on the presumed PDF approach, and finally a monotonically integrated LES model that does not explicitly take subgrid scale effects into account. The predictive capabilities of the LES model have been investigated by numerical simulations of the flow past a triangular-shaped flame holder in a rectilinear channel at various operating conditions parameterized by the equivalence ratio, inlet velocity, and temperature. In simulations of reacting flow situations, the fuel was propane and premixed conditions were enforced. Detailed experimental measurements of all operating conditions including temperature probability density functions are available. Comparison of simulated and measured quantities indicates that the LES model is capable of predicting the flow accurately under all three operating conditions and that the movement of the flame front can be captured. Moreover, a discussion describing the dissimilar modes of operation found in the test rig is presented.