Fethi Bouras^ e-mail: f.bouras@holmail.fr Azeddine Soudani Mohamed Si-Ameur Universify of iHL-Bafna, 05000 Batna, Aigeria Numerical Study of the Turhulent Flow Inside an ORACLES Configuration This numerical investigation deals with the validation of the experimental results in the inert cases of Nguyen et ai, obtained in the framework of the European Union-funded research program MOLECULES (Modelling of Low Emissions Combustors Using Large Eddy Simulations). This study is based on the benchmark of testing one rig for accurate comparisons with large eddy simulations configuration (ORACLES), aimed at helping the design of reliable lean premixed prevaporized) combustion chambers and supplied with two identical flows of air channels. Therefore, this study is based on the 3D numerical simulation using large eddy simulation-wall adapting local eddy viscosity (LES-WALE) model that aims to determine the longitudinal velocity, the longitudinal velocity fluctua- tion and the length of recirculation zone for the three cases of flow in different inlet Reyn- olds (Re = 25,000, 50,000, 75,000). Calculations are carried out by the FLUENT CFD. Tiie results obtained are compared with experimental measurements of Nguyen et al. The LES WALE eddy viscosity computation presents a good agreement with the experimental data where we could observe the asymmetrical flow and also detect the recirculation zones and the differences between the cases of the flow. [DOI: 10.1115/1.4006455] Keywords: turbulence, large eddy simuiation, WALE eddy viscosity, ORACLES configu- ration, CFD 1 Introduction Very common observations teaeh us that the majority of the flows met in praetiee do not represent the laminar ideal properties. In 1980, R. Legendre observed the distinction between various regimes of flows and stated that it is wrong to say that turbulence is not a property of the fluid; instead it is a eharacteristie of the flow. Simulating turbulent flows in realistic conditions is a formi- dable computational task. Many approaches have been proposed to understand and model the turbulent flow. They are summarized in the recent reviews [1,2]. Among these techniques, we can men- tion the Reynolds averaged Navier-Stokes (RANS), the direct nu- merical simulation (DNS) and the large eddy simulation (LES) which are very rapidly growing tools, mainly because of the pro- gress of turbulent flow modeling, numerics, and computer scienee. These techniques also provide the numerical solutions of the coupled, nonlinear set of (spatially) three-dimensional Navier- Stokes equations describing time evolution of the flow over a mesh of nodes and volumes or elements covering the flow domain. In 2000, Besson et al. were testing a facility named one rig for accurate comparisons with large eddy simulations (ORACLES) which has been designed and developed in the framework of a Eu- ropean research program large-eddy simulations for lean pre- mixed prevaporised combustion, where a zone of combustion of the type LPP [3], supplied with two flows of channel constituted of a premixture of air and commercial propane, with the primary and specific long-term objective of progressively building up an experimental database adapted and useful for testing the modeling of LPP flows configurations by a LES based approach [3,4]. Moreover, Reynolds averaged Navier-Stokes based simulations can also be tested. In particular, it allows a first characterization of the unsteady structure of the inert and reactive flows that are 'Corresponding author. Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received October 27, 2010; final manu- script received March U, 2012; accepted manuscript posted March 29, 2012; pub- lished online June 28, 2012. Assoc. Editor; Arif Masud. developed in the combustion chamber to emphasize the following: an asymmetrical flow without combustion, a symmetrical flow with combustion and the presence of a strong component of the velocity fluctuations in certain configurations with combustion [3,5]. Following, Nguyen et al. have pursued this objective in the framework of the European program modeling Of low emission combustors using large eddy simulations (MOLECULES) aimed at promoting the extensive use of LES to model low emissions combustors. The motivations of this benchmark are for testing the main properties of the veloeity field for different cases of flows (inert/ reactive). The investigation is based on the inlet Reynolds to determine each case. However, the reactive flow is character- ized by the equivalence ratio in order to determine the characteris- tics of the lean extinction according to the different parameters in ORACLES configuration [4,5]. In addition, Nguyen et al. meas- urements confirmed the asymmetrical and symmetrical flow in inert and reactive case and maitily the important amplitudes of ve- locity fluctuation in the inert case [3,4]. Kurenkov and Oberlack were focusing on numerical modeling of the turbulent premixed combustion using the level set approach for Reynolds averaged models in ORACLE configuration. They based their simulation on 2D and all results were computed for half of the chamber and then mirrored with respect to the symmetry plan. However, this did not allow visualizing asymmetrical flow and the difference between the two zones of recirculation [6]. In addition Reynolds Averaged Models is only applicable enough far from the wall and is based on unicity of the scale [7,8]. This prevents modeling other scales which causes impaets on the results [9,10]. Domingo et al. was interesting in the DNS of a premixed turbulent V flame in the first part of his work but he did not succeed in finding a fully appropriate velocity in the Flame/wall interaction. In the seeond part, he gave LES for validating the case of higher Reynolds num- ber of flows in ORACLE configuration. For LES numerical treat- ment, this is preferred for solving the scale equations for the variance itself [11]. Duwig and Fureby were interested in LES based on the flamelet models of unsteady lean stratified premixed combustion in ORACLE geometries in different cases of the grid. The subgrid viscosity is modeled by a one-equation eddy viscosity Journal of Applied Mechanics Copyright © 2012 by ASME SEPTEMBER 2012, Vol.79 / 051014-1