Flow Field and Deformation Measurements of a Membrane Wing for Unsteady Inflow Conditions

Unmanned and micro aerial vehicles operate in a highly unsteady flight environment. The application of morphing wing technologies for these aircraft offer the possibility to improve flight characteristics. The investigated concept consists of port and starboard adjustable wings, which are covered by an elasto-flexible membrane. For wind tunnel investigations at low Reynolds numbers the aspect ratio and the sweep of the wings can be changed. Especially interesting for the present study is the deformable wing surface, which can adapt to changing aerodynamic loads. The membrane wing is investigated under the impact of an one-minus-cosine gust profile, which is provided by a gust generator mounted in front of the wind tunnel model. During the wind tunnel tests, the freestream velocity, the angle of attack, the wing position and the gust length are varied. The deformation of the membrane is measured by a high-speed digital image correlation system. The flow field above and behind the wing is examined by a high-speed particle image velocimetry system on slices perpendicular and parallel to the inflow. The impact of the investigated gust, which refers to a severe unsteady inflow condition, increases the camber of the airfoil and leads to greater areas of a separated flow.