Homogenization Based LES for Turbulent Combustion

Abstract

In this work we propose a novel methodology for performing Large Eddy Simulations (LES) of premixed, non-premixed and partially premixed laminar and turbulent flames. The motivation behind this study is the need for more accurate and flexible LES computations of increasingly complex engineering applications, for which current LES models are limited. The main drawback of present LES methods for reactive flows is that most of the chemical activity, and thus also most of the exothermicity, occurs on the subgrid scales, and is hence subject to modeling using only information about the resolved scale flow. Reasonable results have been achieved in several studies with present LES models but improved accuracy, flexibility and reliability is needed. Here, we use a homogenization-based approach based on a multi-scale expansion technique to convert the reactive Navier-Stokes equations, with finite rate chemistry, into a cascade of equations for different scales. The equations of motion for the large-scale dependent variable dynamics are explicitly simulated, whereas the equations of motion for the small-scale dependent variable dynamics are simplified by reducing the spatial dimensions from three to one, thus permitting affordable simulations in a grid within the grid approach. Presently, the methodology is limited to low Ma number variable density flows, but can be extended to high Ma number reactive flows. This method has some similarities with the LES-LEM and the TLS models of Menon et al., but differs in some important aspects. The model developed is here applied to a bluff-body stabilized flame and comparisons with both experimental data and conventional flamelet and finite rate chemistry LES Track: SI DNS and LES of Reactive Flows. C. Fureby (B)Flow Turbulence Combust (2010) 84:459-480 models are made. The results show that the performance of this model is as good or better than any of the other models, and to a reasonable computational cost.

Modelling flame turbulence interaction in RANS simulation of premixed turbulent combustion

“…Further downstream at x/h = 5 and x/h = 7 the reaction rate prediction from the FTI (transport equation) model increases while the FTI (algebraic) model tends to predict a constant reaction rate as shown in figures 8c, 8d, 9d and 9e. An increase in the reaction rate in these regions is expected in the light of earlier results of Fureby [38] as regions of intense turbulence are bounded by the shear layer which widens as the distance from the step increases, thus leading to a much wider reaction zone. In order to quantify the difference between different models, percentage difference for the predicted peak reaction rate between the FTI (transport equation) and the other models is reported in table 3 for several locations downstream of the backward facing step.…”

“…Further details of the experiment and measuring techniques used can be found in [24,25]. This test case has been previously studied by Weller et al [37] (using flame wrinkling model) and Fureby [38] (using the newly proposed homogenisation based method) via Large Eddy Simulation (LES) and by Tangermann et al [39] (using a modified flame surface density model) via both Large Eddy Simulation (LES) and Reynolds Averaged Navier Stokes (RANS) approaches. This case represents a dump combustor configuration in gas turbine engines.…”

Implementation of Pod and DMD Methods in Apache Spark Framework for Simulation of Unsteady Turbulent Flow in the Model Combustor

“…Large-scale vortex structures are calculated by integrating the filtered Navier-Stokes equations [2,3]. To obtain the filtered equations the boxed filter is used.…”

“…This kind of flows occurs in various technical devices, including combustion chambers of aircraft engines and helicopters. The main feature of such flows is the formation of large-scale structures in the mixing layer behind a step, which is used as a flame stabilizer [1,2]. The extension of the mixing layer is determined by the dynamics of large vortices development, which are formed upstream and increase as the result of neighboring vortices merging and inclusions of viscous gases from the main flow (Fig.1).…”