An experimental and computational investigation of slender wings undergoing wing rock.

摘要

The problem of self-induced roll oscillations of slender delta wings has been studied in order to identify physical mechanisms responsible for the limit cycle oscillations. The investigation is a combination of both experimental and computational methodologies. The experimental and computational investigations focussed on the wing rock characteristics of a slender flat plate delta wing with 80{dollar}spcirc{dollar} leading edge sweep.; Two unique experimental apparatus have been developed for the investigation. A free to roll system was developed using an air bearing spindle which allows the isolation of applied torques due to the flowfield. An unsteady pressure acquisition system was also developed in order to measure the unsteady surface pressure distributions acting on the wing during wing rock time histories. The system consists of a motion control system which accurately matches the time dependent boundary conditions of wing rock, and is synchronized with a pressure acquisition system.; The computational model is a discrete vortex potential flow method. The time dependent positions and strengths of the leading edge vortices are solved by coupling the flowfield equations to the rigid body equation of motion in roll for the wing. The computational model has captured all of the qualitative characteristics of the wing motion and flowfield behavior observed in experiment with the exception of the secondary vortices which are not modelled.; Based on the results of the experimental and computational investigations a theory has been developed for the cause of wing rock of slender wings. The theory is broad enough to account for variations in sweep angle and angle of attack. Wing rock is initiated by some initial perturbation or wing imperfection. The motion builds in time due to an instability caused by a time lag in the position of the vortices normal to the wing surface. A steady state is reached when damping contributions from the top and bottom surfaces are in equilibrium with the instability. Damping is provided by conventional roll damping on the bottom surface of the wing, and by the unsteady behavior of vortex strength on the top surface.