1 NUMERICAL PREDICTION OF TRANSONIC BUFFETING BY MEANS OF STANDARD AND TIME-DEPENDENT TURBULENT MODELS E. Orlik Laboratoire PRISME, Université d'Orléans, 8, rue Léonard de Vinci, 45071 Orléans cedex 2, France N. Mazellier Laboratoire PRISME, Université d'Orléans, 8, rue Léonard de Vinci, 45071 Orléans cedex 2, France A. Kourta Laboratoire PRISME, Université d'Orléans, 8, rue Léonard de Vinci, 45071 Orléans cedex 2, France ABSTRACT We present the preliminary results from a numerical investigation of transonic buffeting on an OAT15A airfoil using the two-equation transport models k-ω SST and k-ε with low-Re corrections by means of damping functions. The influence of the turbulence model, the transition and 3D configurations onto the physics of the buffeting are presented. Even though shock-induced oscillations are observed, some discrepancies with experimental results are found. A refined model of turbulent viscosity, based on a semi-deterministic approach, is proposed and is currently implemented in the computational software and used in order to improve the buffeting prediction. INTRODUCTION Airfoil submitted to an external fluctuating force undergoes buffeting. In the case of a transonic airfoil, buffeting results from the shock/boundary-layer interaction inducing self-sustained oscillations which strongly alter the airfoil performances (Lee 1990). The complex physics underlying the transonic buffeting currently suffers of an accurate prediction in order to either prevent its occurrence or to minimize its influence. Garnier and Deck (2010) investigated the buffeting process by means of Large Eddy Simulations (LES) coupled with Reynolds-Averaged Numerical Simulation (RANS). The spectral content was well reproduced in comparison with the experimental results reported by Jacquin et al. (2005). Nevertheless, the statistics of the static pressure differed significantly from the experiments, partly because the convergence of the computation is not ensured accounting for the time and resource consuming feature of LES. The slow dynamics featuring the transonic buffeting process allows for the use of low-consuming numerical approaches such as the Unsteady Reynolds-Averaged Simulation (URANS). However, the prediction of the buffeting phenomenon is extremely sensitive to the closure turbulent model, as shown by Thiery and Coustol (2006) who pointed out that the two- equation transport model k-ω SST performed the best. Nevertheless, the authors reported some discrepancies between their results and an experimental database (Jacquin et al. 2005), especially regarding the dynamics. In order to overcome this drawback, we propose to couple the standard turbulence models with a refined eddy turbulent viscosity model, first introduced by Kourta (1999) and afterwards validated by Kourta et al. (2005) for the buffeting prediction. The paper is organized as follows. The computation conditions and numerical influence are first briefly described. Then, the preliminary results from URANS computations obtained with standard turbulence models are discussed. Also the influence of the transition and 3D configurations on the buffeting are reported. Finally, the time- dependent Reynolds-stress model is presented and preliminary results in steady regime are shown and discussed. COMPUTATIONAL CONDITIONS In this study, we simulate the flow over an OAT15A airfoil with a chord of 0.23m allowing for the comparison with the experiments reported by Jacquin et al. (2005). This airfoil is a supercritical airfoil with a thickness to chord ratio of 12.3% and a thick trailing edge of 0.5% of the chord length. Computations have been done at angle of attack (AoA) 3.5°, 4° and 4.5°.