2nd Flow Control Conference
28 Jun - 1 Jul 2004 / Portland, Oregon

AIAA-2004-2319

Aerodynamic Performance of Biological Airfoils
Abel Vargas* and Rajat Mittal† The George Washington University, Washington, D.C., 20052 Experimental studies on static, non-flapping dragonfly wings have shown favorable aerodynamic performance at low Reynolds number (Re ≤ 10,000). High lift is hypothesized to arise from the dragonfly’s pleated wing structure. A numerical study of flow past a modeled dragonfly wing section as well as its comparison to a corresponding profiled airfoil and a flat plate were conducted at Re = 10,000. The main focus of the current investigation was to determine the primary flow features and mechanisms that are responsible for the enhanced performance of these biological wing sections at these relatively low Reynolds numbers. A time-accurate Cartesian grid based Navier-Stokes immersed boundary solver was utilized in the current study. The numerical results indicate that the pleated airfoil at a zero degree angle-of-attack generates the least drag despite its unconventional shape. Additionally, a higher transitory lift is produced by the pleated airfoil at a five degree angleof-attack when compared to the profiled airfoil.

Nomenclature c CD CDs CDp CL CLs CLp P Re τ t t* ui = = = = = = = = = = = = = = = = chord length drag coefficient shear drag coefficient pressure drag coefficient lift coefficient shear lift coefficient pressure lift coefficient Pressure Reynolds number thickness dimensionless time time xi component of velocity free stream velocity Cartesian coordinates angle of attack

U∞ xi α

I.

Introduction

A

number of insect species including locusts, dragonflies, and damselflies employ wings that are pleated along the chord. These ultra-light membranous insect wings support a variety of aerodynamic and inertial forces during