Buffet Characterization and Control for Turbulent Wings
J. Dandois, P. Molton, A. Lepage, A. Geeraert, V. Brunet, J.-B. Dor, E. Coustols (Onera)
The objective of this paper is to present an overview of the work performed at Onera over the last decade on the characterization and control of the buffet phenomenon. This aerodynamic instability induces strong wall pressure fluctuations and as such limits aircraft envelope, consequently it is interesting to understand the origin of this instability and to try to delay its onset, in order to improve aircraft performance, but also to provide more flexibility during the design phase. First, results from wind tunnel tests on 2D airfoils are presented to explain the 2D buffet phenomenon and since it is used as validation test case for numerical simulations. Then, results from several wind tunnel tests on a 3D configuration are presented. The 3D buffet phenomenon is characterized using steady and unsteady wall pressure measurements and LDV. Then, several types of flow control have been investigated, either passive (mechanical vortex generators) or active (fluidic VGs, fluidic trailing-edge device (TED)). It is shown than mechanical and fluidic VGs are able to delay buffet onset in the angle-of-attack domain by suppressing the separation downstream of the shock. The effect of the fluidic TED is different, the separation is not suppressed but the rear wing loading is increased and consequently the buffet onset is not delayed in the angle-of-attack domain, but only in the lift domain. Closed-loop control of the fluidic VGs is also investigated, to adapt the mass flow rate to the aerodynamic conditions.