Research Initiative for Numerical and Experimental Studies on High-Speed Stall of Civil Aircraft

The aerodynamics of transport aircraft at the borders of the flight envelope is characterized by complex interactions and nonlinear, unsteady flow phenomena. The underlying physical mechanisms are not fully understood, and a prediction of aerodynamic properties, transient loads, and aeroelastic behavior is a major challenge that requires the use of sophisticated numerical models and dedicated experiments. A new research initiative investigates the three-dimensional buffet mechanisms at high-speed stall, the interaction of the wing wake with the empennage, and the influence of ultra-high-bypass-ratio-type engines on these phenomena. It comprises unsteady pressure-sensitive paint surface pressure and time-resolved particle image velocimetry flowfield measurements carried out in the cryogenic European Transonic Windtunnel. The experiments are conducted at different Mach numbers and cover a broad Reynolds number regime up to 25x106 using the generic Airbus XRF1 configuration as a reference. This paper explains the rationale of the research initiative, introduces the planned test entries and test conditions, and presents selected results of the first measurement campaign and associated numerical analyses by means of the computational fluid dynamics code TAU, including usage of locally scale resolving simulations. An analysis of numerical and experimental results is presented for a high incidence transonic condition that serves to discuss the topology of wing root flow separation, the evolution of the associated wake, and its interaction with the empennage.