21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-2.4.2

ACCURACY OF UNSTEADY TRANSONIC FLOW COMPUTATIONS

Gronland T. -A., Eliasson P., Nordstrom J.
The Aeronautical Research Institute, Sweden

Keywords: accuracy, unsteady, transonic flow computations

In this work we will discuss the accuracy one can obtain in predictions of unsteady transonic flows by a modern CFD method, in this case a time accurate Reynolds-averaged Navier-Stokes solver. The test case used in this study is an 18% thick biconvex, two-dimensional airfoil. Experiments have revealed that this geometry shows a strong oscillatory flow in a certain Mach number regime, often referred to as buffet. Sensitivity to numerical and physical modeling is assessed through repeated computations with various spatial and temporal discretization, numerical schemes and different types of turbulence models. The correlation between the airfoil in a free flight-and in a wind-tunnel environment is also investigated. It is shown that modem CFD methods can indeed predict the complex buffet phenomena with reasonable accuracy. This work highlights some of the most critical aspects of physical and numerical modeling of buffet. It is also shown that lift and drag on the airfoil differs considerably between the free flight-and wind tunnel environments.

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