Leading-edge vortex evolution over an impulsively rotated wing

The flow over a rotating wing is 3D and unsteady in nature and is influenced by phenomena unique to the rotating frame. However, conventional PIV techniques are unable to comprehensively characterize these rotating frame physics. Hence, a novel methodology termed "Rotating Three-Dimensional Velocimetry" (R3DV) is developed to quantify the spatio-temporal evolution of the flow field in the rotating reference frame. The flow field in R3DV is imaged through a stationary plenoptic camera viewing a hub-mounted mirror that rotates with the wing. Experiments over an impulsively rotated flat plate showed a uniform shear layer separation along the span of the wing, that rolled up to form the leading-edge vortex (LEV). As the shear layer continuously feeds vorticity to the LEV, it strengthens in time. After the LEV saturates, the vortex separates from the shear layer and moves downstream. During the LEVs evolution, a region of secondary vorticity was observed due to the flow induced by the LEV. As time progressed, this region grew between the LEV and the shear layer, which led to the separation of the LEV. Following this, a continuous shedding of secondary LEVs was observed.