Investigation of bio-inspired passive flow control techniques for MAV application

Features like covert feathers and alula on birds’ wing aid them at high angles of attack flight making them more maneuverable. Rudimentary emulation of these features was attempted on low aspect ratio wings of different planforms to enhance their post-stall lift characteristics.  This simple biomimicry of covert feathers is referred to as self-adaptive flaps (SAF). Experiments were carried out in a low-speed wind tunnel at Re=10⁵ to ascertain the usefulness of these simple biomimicry over different wings for MAV application. Force measurements reveal that SAFs significantly improves post-stall lift characteristics of the wing when placed at an optimal chordwise location which varies with planform. PIV investigation carried out on the mid-span plane show that the SAF manipulates the separated shear layer from the leading edge (LE) in such a way that it prolongs its reattachment to the surface. Further, the strength/amount of vorticity shed from the trailing edge which inhibits the growth of the leading edge vortex is reduced. These changes result in enhanced lift and delayed stall. In a similar approach, the biomimicry of alula as well showed improvements for cases when it is placed in line with the LE of the wing. For cases where alula slightly protrudes out, lift is destroyed.