             !  "  # ISABE-2007-1188 TOWARDS LES OF MIXING PROCESSES INSIDE A RESEARCH RAMJET COMBUSTOR Sebastien REICHSTADT * , Nicolas BERTIER * , Arnaud RISTORI * , Pascal BRUEL  * Office National d’Etudes et de Recherches Aérospatiales (ONERA) 29, Avenue de la Division Leclerc F-92322 Châtillon Cedex, France  Centre National de la Recherche Scientifique (CNRS) Université de Pau et des Pays de l’Adour Laboratoire de Mathématiques Appliquées Avenue de l’Université BP 1155 64013 Pau Cedex, France Abstract In 1995, ONERA initiated a research program on ramjet developments with the support of the French “Délégation Générale de l’Armement” (DGA/SPNuM, Ministry of Defense). The targeted final objective of this program was to improve the ramjet combustion chamber design by using both experiments and validated CFD codes. Among the various mechanisms that are controlling the development of the combustion processes inside the combustor, the mixing is certainly one of the most crucial as far as stability or efficiency are concerned. Thus, the present study, carried out in the framework of the aforementioned research program, is mainly devoted to the analysis of the fuel-to-air mixing properties in the combustion chamber of a generic research ramjet combustor. Accordingly, the first objective of this work was to characterize, in absence of combustion, the turbulent flow velocity and scalar fields associated to the mixing between the fuel and air. Thus, particle image velocimetry (PIV) and gas sampling analysis are the two techniques that were used to serve that purpose. A second objective of this study was to assess the ability of numerical computations, based either on Reynolds-Average Navier- Stokes (RANS) or Large-Eddy Simulations (LES) approaches, to predict accurately the properties of the velocity and the fuel concentration fields. Introduction ONERA has been involved in the field of ramjet propulsion since its creation in 1946. For the last twenty years, work conducted in close cooperation with industrial partners has greatly developed its know-how of this propulsion system. Numerous projects have been conducted up to flight tests such as ASMP (Air To Ground Medium Range Missile) operational since 1986 in the French Air Force. Until recently, the methodology used to develop ramjet engines and to study combustor performances was mainly based on an experimental approach consisting of conducting combustion tests in connected pipe mode under conditions representative of the real flight situations. In addition to these combustion tests, a method based on cold flow simulations and simplified models of flows and combustion was carried out to predict the overall combustor