Turbulent structures and dynamic mechanisms in transonic airfoil buffet and in the interaction between airfoil wake and tailplane

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Close to the boundaries of the flight envelope, the transonic flow around modern transport aircraft is characterized by a complex coupling of unsteady aerodynamic phenomena at the wing and horizontal tailplane. On the suction side of transonic airfoils, local supersonic regions are terminated by a shock wave whose strength increases with angle of attack and Mach number, and can cause massive flow separation on the airfoil. The interaction between the shock and the boundary layer can incite periodic self-sustained shock oscillations (buffet), which can induce potentially detrimental structural oscillations (buffeting), thus limiting the life span and the usable flight envelope. In addition, these unsteady buffet-induced effects on the airfoil are also imprinted on the flow around the tailplane via the wake of the airfoil. This leads to complex flow configurations that have not yet been investigated and understood in detail. Therefore, the understanding and predictability of buffet mechanisms is necessary to safely expand the boundaries of the flight envelope. The prerequisite for this is a fundamental understanding of the interplay and potential superposition of different buffet mechanisms in 2D and 3D. The basis of these investigations is the initially decoupled consideration of the structurally stiff and vibration-affected cases, taking into account a stepwise transition from 2D, via 2.5D to 3D swept-wing geometries. The overall goal of TP6 is therefore the fundamental identification of the relationships between structural vibrations, sweep effects and the mechanisms of transonic buffet as well as their effects on the horizontal tailplane aerodynamics. To achieve this, high-resolution experimental data will be generated and assessed in synergy with the numerical data generated within the Research Unit. Detailed fundamental experiments are carried out on a swept tandem wing at a Reynolds number accessible to high-fidelity numerical methods. The synergetic evaluation with the measurement data acquired in the European Transonic Windtunnel (ETW) closes the gap to flight-realistic Reynolds numbers. Thus, flow physics and the influence of Reynolds number and airfoil sweep can be investigated, also supporting the further development of numerical methods. The implementation of synchronized DIC (Digital Image Correlation) and focusing-schlieren measurements allows the simultaneous acquisition of the coupled aerodynamic and structural dynamic phenomena. Stereo-Dual-Particle Image Velocimetry measurements provide access to velocity-field and acceleration information. Combined with advanced post-processing methods for the analysis of coherent turbulent structures (Proper Orthogonal Decomposition; Dynamic Mode Decomposition) and spectral analyses, this unique data set will allow insights that will significantly advance the understanding of transonic airfoil buffet and its influence on the tailplane aerodynamics at the boundary of the flight envelope.