Experimental and Computational Analysis of Bio-Inspired Winglets for Micro Air Vehicles

Abstract

Micro Air Vehicles (MAVs) are increasingly being used for civil and military surveillance. As the surveillance requirements are increasing, improving the range of MAVs becomes imperative. The performance of MAVs can be improved if the induced drag due to wingtip vortices can be reduced. In the present study, we try to decrease the induced drag caused by the wingtip vortices, which makes up a major part of the total drag, by introducing a winglet. A unique yet simple design, which has not yet been studied thoroughly, is explored. Inspiration is taken from the feather structures of birds to design the proposed winglet. The performance of a fixed-wing MAV at a free stream velocity (U∞) of 20 m/s is studied. Multiple winglet configurations are used to compare the results with the baseline wing. An incompressible, steady three-dimensional simulation is carried out using the k-ω SST turbulence model. The experimental studies carried out for the baseline wing matched well with those obtained from CFD. Since the numerical model is valid, only computational study is done for the modified wing. The stall angle of the baseline wing is around 26°. Numerical results show that when the proposed winglet is used, the stall angle for the wing is increased to around 32°. The use of the winglet did not produce a considerable advantage at the lower Angle of Attack (AOA), but at higher AOA, the lift coefficient (CL) was considerably higher. The overall drag coefficient (CD) was higher at lower AOA when the winglet is used. But at AOAs greater than 5°, the CD reduced. Other effects of the winglet are addressed in terms of improvement in Lift-to-Drag ratio (L/D) and reduction in vorticity. The effect of the location and number of the feathers was studied to come up with an optimum winglet configuration. The experiments were carried for the wing with optimum winglet configuration and the results agreed fairly with the numerical results.