无人机机翼减阻技术研究

American Institute of Aeronautics and Astronautics

1

Drag Reduction of Light UA V Wing with Deflectable Surface

in Low Reynolds Number Flows

Masoud Darbandi * and Ali Nazari †

Sharif University of Technology, Tehran, P.O. Box 11365-8639, Iran Gerry E. Schneider ‡

University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada

The most effective approach to drag reduction is to concentrate on the components that make up the largest percentage of the overall drag. Small improvements on large quantities can become in fact remarkable aerodynamic improvements. Our experience shows that the use of light material in constructing human-powered airplanes and unmanned-air-vehicles UAVs has a few side effects on the aerodynamic characteristics of their wings. One important side effect is the unwanted deflection on wing shell. It is because of high flexibility and low solidity of the light material, which covers the wing skeleton. The created curvature has direct impact on the separation phenomenon occurred over the wing in low Reynolds number flows. In this work, we numerically simulate the flow over a UAV wing with and without considering the generated deflection on its shell. It is shown that the curvature on the wing surface between two supporting airfoil frames causes total drag coefficient reduction. Indeed, this drag reduction is automatically achieved without benefiting from additional drag-reduction devices and/or drag-reduction considerations. The current investigation has been conducted on a UAV wing with fxmp-160 airfoil section. This airfoil normally provides high lift coefficient in low Reynolds flows because of having suitable camber. The drag of a wing with this airfoil section can be reduced by the proper usage of low weight material as its wing shell providing that the wing shell deflects between its supporting frames during stretching the shell in manufacturing stage.

Nomenclature

α = angles of attack C d =

total drag coefficient

C dp =

profile drag C ds =

skin friction drag C l = two-dimensional lift coefficient

C L

three-dimensional lift coefficient L/D =

lift-drag ratio Re = Reynolds number

I. Introduction

RAG reduction is one of the major objectives to the air vehicle designers and manufacturers 1. The study of air

vehicles at their cruise shows that there are two main sources of drag force including lift-induced and skin-friction drags. It is reported that these two sources of drag are approximately one-third and one-half of the total drag, respectively, in civil transport aircraft. Reneaux 2 emphasizes that hybrid laminar flow technology and innovates wing tip devices offer the greatest potential for drag reduction. With respect to lift-induced drag, the classical way to reduce drag has been to increase the wing aspect ratio, which is automatically provided in UAV wings. However, for the wings with low aspect-ratio, it is suggested to use various winglet devices such as wing tip sails, wing grid, *

Associate Professor, Department of Aerospace Engineering. †

Graduate Student, Department of Aerospace Engineering. ‡

Professor and Chair, Department of Mechanical Engineering, AIAA Fellow.

D

3rd AIAA Flow Control Conference

5-8 June 2006, San Francisco, California

AIAA 2006-3680