On the development and early observations from a towing tank-based transverse wing-gust encounter test rig

Small unmanned aerial vehicles and biological fliers can experience wind gusts of similar magnitude to the flight speed, which is detrimental to flight stability. For one encounter type, the low Reynolds number transverse gust, little is known about the fundamental fluid mechanics due in part to the difficulties in replicating the scenario experimentally or computationally. The aim of this work is thus to present the development and characterisation of an apparatus capable of generating and measuring the transient response of large amplitude transverse wing-gust encounters. The system is designed to produce a sharp-edged gust profile for direct comparison with the linear Kussner model. Particle image velocimetry (PIV) measurements show that the system successfully generated a steady top-hat shaped gust. A technique using inertial sensors has been used to minimise the effects of model vibration in measuring the unsteady forces. A wing-gust interaction with cross flow velocity equal to the flight speed is also presented. For this interaction, a strong leading edge vortex forms and vorticity of opposite sense is shed at the trailing edge. The trailing edge vorticity remains relatively planar, which is similar to the planar wake assumption of the Kussner model. Large deformation of the gust shear layers is visible upon wing entry, which is a deviation from the 'rigid' shear layers assumed by linear theory. Despite differences in flow topology between theory and experiment, the lift force coefficients match surprisingly well during entry into the gust, but deviate upon exit. [GRAPHICS] .