Large Eddy Simulation of self excited azimuthal modes in annular combustors
01 Jan 2009-Vol. 32, Iss: 2, pp 2909-2916
TL;DR: In this article, a massively parallel Large Eddy Simulation (LES) of a full helicopter combustion chamber is presented, in which a self-excited azimuthal mode develops naturally.
Abstract: While most academic set ups used to study combustion instabilities are limited to single burners and are submitted mainly to longitudinal acoustic modes, real gas turbines exhibit mostly azimuthal modes due to the annular shape of their chambers. This study presents a massively parallel Large Eddy Simulation (LES) of a full helicopter combustion chamber in which a self-excited azimuthal mode develops naturally. The whole chamber is computed from the diffuser outlet to the high pressure stator nozzle. LES captures this self-excited instability and results (unsteady pressure RMS and phase fields) show that it is characterized by two superimposed rotating modes with different amplitudes. These turning modes modulate the flow rate through the 15 burners and the flames oscillate back and forth in front of each burner, leading to local heat release fluctuations. LES demonstrates that the first effect of the turning modes is to induce longitudinal pulsations of the flow rates through individual burners. The transfer functions of all burners are the same and no mechanism of flame interactions between burners within the chamber is identified.
Citations
More filters
01 Jan 2017
TL;DR: In this paper, the authors present recent progress in the field of thermoacoustic combustion instabilities in propulsion engines such as rockets or gas turbines, and show that LES is not sufficient and that theory, even in these complex systems, plays a major role to understand both experimental and LES results and to identify mitigation techniques.
Abstract: This paper presents recent progress in the field of thermoacoustic combustion instabilities in propulsion engines such as rockets or gas turbines. Combustion instabilities have been studied for more than a century in simple laminar configurations as well as in laboratory-scale turbulent flames. These instabilities are also encountered in real engines but new mechanisms appear in these systems because of obvious differences with academic burners: larger Reynolds numbers, higher pressures and power densities, multiple inlet systems, complex fuels. Other differences are more subtle: real engines often feature specific unstable modes such as azimuthal instabilities in gas turbines or transverse modes in rocket chambers. Hydrodynamic instability modes can also differ as well as the combustion regimes, which can require very different simulation models. The integration of chambers in real engines implies that compressor and turbine impedances control instabilities directly so that the determination of the impedances of turbomachinery elements becomes a key issue. Gathering experimental data on combustion instabilities is difficult in real engines and Large Eddy Simulation (LES) has become a major tool in this field. Recent examples, however, show that LES is not sufficient and that theory, even in these complex systems, plays a major role to understand both experimental and LES results and to identify mitigation techniques.
445 citations
TL;DR: In this article, two types of LES in complex geometry combustors and of specific interest for aeronautical gas turbine burners are reviewed: (1) laboratory-scale combustors, without compressor or turbine, in which advanced measurements are possible and (2) combustion chambers of existing engines operated in realistic operating conditions.
396 citations
Cites background from "Large Eddy Simulation of self excit..."
...captured with a single sector hypothesis: for example to simulate flame propagation from a burner to the next after ignition of a flame kernel [307], neighboring flames that interact with each other or the existence of an azimuthal thermo-acoustic instabilities [356]....
[...]
TL;DR: In this paper, the authors present a review of transverse acoustic wave motions in air-breathing systems and discuss issues associated with simulating or scaling instabilities, either in subscale experimental geometries or by attempting to understand instability physics using identical axial oscillations of the same frequency as the transverse mode of interest.
257 citations
TL;DR: Large-eddy simulation (LES) was originally proposed for simulating atmospheric flows in the 1960s and has become one of the most promising and successful methodology for simulation of turbulent flows with the improvement of computing power as mentioned in this paper.
252 citations
TL;DR: In this article, the interaction of a helical mode with acoustic oscillations is studied experimentally in a turbulent swirl-stabilized premixed flame, and the authors show that the heat release rate perturbation associated with the nonlinear interaction of the helical model and the acoustic oscillation produces a "yin and yang" -type pattern rotating with the interaction frequency in the direction of the mean swirl.
197 citations
References
More filters
TL;DR: In this article, a boundary condition formulation for the Navier-Stokes equations is proposed, which is compatible with non-disjoint algorithms applicable to direct simulations of turbulent flows.
3,214 citations
Book•
01 Jan 2001
2,834 citations
"Large Eddy Simulation of self excit..." refers background in this paper
...Recent studies using LES have shown the potential of this approach for reacting flows (see reviews in [3] or [11])....
[...]
...A compressible LES solver has the capacity to predict instabilities in a reacting flow configuration [3, 10]....
[...]
TL;DR: In this article, a subgrid scale model for large eddy simulations of turbulent premixed combustion is developed and validated, based on the concept of artificially thickened flames, keeping constant the laminar flame speed sl 0.
Abstract: A subgrid scale model for large eddy simulations of turbulent premixed combustion is developed and validated. The approach is based on the concept of artificially thickened flames, keeping constant the laminar flame speed sl0. This thickening is simply achieved by decreasing the pre-exponential factor of the chemical Arrhenius law whereas the molecular diffusion is enhanced. When the flame is thickened, the combustion–turbulence interaction is affected and must be modeled. This point is investigated here using direct numerical simulations of flame–vortex interactions and an efficiency function E is introduced to incorporate thickening effects in the subgrid scale model. The input parameters in E are related to the subgrid scale turbulence (velocity and length scales). An efficient approach, based on similarity assumptions, is developed to extract these quantities from the resolved velocity field. A specific operator is developed to exclude the dilatational part of the velocity field from the estimation of...
956 citations
TL;DR: In this article, the authors highlight the fundamental differences between Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for non-premixed and premixed turbulent combustion, identify some of the open questions and modeling issues for LES, and provide future perspectives.
Abstract: Large-eddy simulation (LES) of turbulent combustion is a relatively new research field. Much research has been carried out over the past years, but to realize the full predictive potential of combustion LES, many fundamental questions still have to be addressed, and common practices of LES of nonreacting flows revisited. The focus of the present review is to highlight the fundamental differences between Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for nonpremixed and premixed turbulent combustion, to identify some of the open questions and modeling issues for LES, and to provide future perspectives.
922 citations
01 Jan 2006
TL;DR: In this paper, the authors compile these results into a series of chapters that address the various facets of the combustion instabilities in low-emission gas turbines and provide a valuable resource to help turbine users and manufacturers.
Abstract: Higher operating efficiencies, fewer pollutant emissions, and low capital investment have made gas turbines a dominant technology for a new power generating capacity in the US and worldwide. This book offers gas turbine users and manufacturers a valuable resource to help them sort through issues associated with combustion instabilities. In the last ten years, substantial efforts have been made in the industrial, governmental, and academic communities to understand the unique issues associated with combustion instabilities in low-emission gas turbines. The objective of this book is to compile these results into a series of chapters that address the various facets of the problem. The Case Studies section speaks to specific manufacturer and user experiences with combustion instabilities in the development stage and in fielded turbine engines. The book then goes on to examine The Fundamental Mechanisms, The Combustor Modeling, and Control Approaches.
902 citations
"Large Eddy Simulation of self excit..." refers background in this paper
...Both cases are observed in gas turbines [4]....
[...]