Controlling the break-up distance of aircraft trailing vortices

The results of an experimental investigation into aircraft vortex wakes are presented. The main aims of this research were to gain insight into the development and eventual destruction of the vortex wake, and to identify a mechanism for controlling the break-up distance of these trailing vortices. Two different types of model were used to generate the counter-rotating vortex pairs, that characterise the rolled-up vortex wake of an aircraft. Visualisation experiments were conducted in water at a Reynolds number based on chord of Rec = 5,000, and quantitative experiments were conducted in a wind tunnel at a chord Reynolds number of Rec = 195,000. The far wake of the models was studied so that the breakdown process could be identified and quantified. The data from vortex wakes of different strengths and separation distances was correlated. Then a variety of control mechanisms were used to excite an instability in the wake, and the perturbed vortex wake was measured. The breakdown distance of the vortex wake was shown to be affected by perturbations made at the generating model. The effects of the perturbations were highly dependent on the perturbation wavelength. Perturbations at wavelengths close to the natural instability wavelength were found to accelerate the destruction of the vortex wake, whereas those at wavelengths away from the natural wavelength were shown to delay its break-up. A control mechanism was identified that was effective at accelerating the breakup of the vortex wake. This mechanism had no lift or drag penalty, on the contrary, it was shown to create a small increase in the lift on the wing. No oscillating forces due to the periodic nature of the excitation mechanism were found on the wing.Open Acces