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Turbulent combustion

Large Eddy Simulation (LES) techniques have revolutionized the field of turbulent flows and more recently of turbulent combustion. Many codes are able to perform LES in simplified geometries but very few can simulate flows within complex geometries. AVBP is one such tool. It has been jointly developed by CERFACS and IFP to perform Large Eddy Simulation (LES) of reacting flows, in gas turbines, piston engines or industrial furnaces... This compressible LES solver on unstructured and hybrid grids is employed in multiple configurations for industrial gas turbines (Alstom, Siemens, Turbomeca), aero gas turbines (SNECMA, Turbomeca), rocket engines (SNECMA DMF Vernon), laboratory burners used to study unsteady combustion (Cambridge, École Centrale Paris, Coria Rouen, DLR, Karlsruhe University, Munich University).

In European projects, AVBP has been used in multiple programmes dedicated to reacting flows:

It has aslo been identified for National Research Programmes (ANR) in France or in the United States (U.S. Department of Energy) for research in massively parallel applications:

Figure 1: Example of LES in a full annular industrial gas turbine: viualisation of the temperature field inside the combustor
(paper submitted to the 32nd International Symposium on Combustion).

Unsteady combustion and combustion instabilities are a key issue in the development of gas turbines (see for example http://ceigt.ist.rwth-aachen.de/eumigt/ for examples of practical challenges in turbines developments). LES is one of the most promising method to study these mechanisms. AVBP incorporates multiple features which make it a unique tool to study unsteady combustion, combustion instabilities for gaseous and two-phase flows within the context of Gas Turbines and Automotive Engines or Rocket Propulsion:

• High-order spatial schemes ([Colin and Rugdyard, 2000], [Moureau et al., 2005]).

• Hybrid meshes ([Schönfeld and Rugdyard, 1999]).

• Multiple classical and new turbulence models for the turbulent stresses ([Ducros et al., 1997], [Ducros et al., 1998], [Nicoud et al., 1998]).

• Specific LES models to describe the interaction between turbulence and combustion. These models are based on Direct Numerical Simulation (DNS) results obtained over the last ten years in Toulouse, Paris (École Centrale) and Stanford CTR (Center for Turbulence Research) as well as CORIA (Rouen) and IFP (Institut Français du Pétrole). The Thickened Flame model was developed by CERFACS and École Centrale Paris for perfectly premixed flames and then extended to all flame regimes in a series of studies: [Colin et al., 2000], [Angelberger et al., 2000], [Selle et al., 2004], [Roux et al., 2005].

• Boundary conditions are also a unique feature of AVBP. Developed on the basis of the NSCBC method ([Poinsot and Lele, 1992], [Nicoud, 1999], [Moureau et al., 2005]), they have been extended to handle flow and acoustics inside a combustion chamber. A full discussion of these conditions may be found in two books: Poinsot and Veynante, "Theoretical and Numerical Combustion" 2005 (Second Edition), edited by R.T. Edwards (http://www.rtedwards.com/) and in "Artificial Boundary Conditions with Applications to Computational Fluid Dynamics Problems" 2001 edited by Novasciences.

• The baseline version of AVBP is limited to gaseous fuels but a two-phase flow extensions based on Eulerian-Eulerian and Eulerian-Lagrangian formulations are being implemented in collaboration with Institut de Mécanique des Fluides de Toulouse (www.imft.fr). Developments dealing with real gas application are also being addressed to further widden the range of applicability of the code (Rocket Propulsions).

• Finally, the Arbitrary Lagrangian Eulerian (ALE) mesh management approach allows the solver to be applied for piston engine simulations.

Figure 2: Example of LES obtained with AVBP for an aero gas turbine ([Boudier et al., 2007]), a car engine, a rocket propulsor
(Lacaze et al., paper submitted to the 32nd Comb. Symp., 2008), a laboratory experiment on two-phase flows ([Boileau et al., 2008]), a helicopter engine, a ramjet combustor ([Roux et al., 2008]) and a rocket propulsor
(Lacaze et al., paper submitted to the 32nd Comb. Symp., 2008).

AVBP has been validated on multiple cases both for reacting and non reacting flows. Specific LES sets of QPF (Quality Program Forms) are available upon request at CERFACS: these test cases allow verification of the code versions for test cases which are correct samples for LES applications: wave propagation, transmission of waves through boundaries, vortex convection, homogeneous isotropic turbulence, one-dimensional premixed flames, etc. These QPFs are stored on the web and can be consulted by outside users (ask poinsot@cerfacs.fr).

More details on the code itself can be found in the AVBP home page. The Gallery of images displays examples of snapshots of computations performed with AVBP while animations can be seen in the Gallery of movies.