Numerical Optimization and Wind-Tunnel Testing of Low Reynolds-Number Airfoils
Th. Lutz, W. Würz and S. Wagner
Proceedings Conference on: Fixed, Flapping and Rotary Wing Vehicles At Very Low Reynolds Numbers, University of Notre Dame, Indiana, USA, June 5 - 7, 2000
A numerical optimization tool has been applied to the design of low Reynolds number airfoils (200,000 < Re < 400,000). The aerodynamic model is based on the Eppler code with major extensions. A new, robust model for the calculation of short transitional separation bubbles was implemented, along with an e^n transition criterion and Drela's turbulent boundary-layer procedure with a modified shape-factor relation. The method was coupled with a commercial hybrid optimizer and applied to perform unconstrained high degree of freedom optimizations with objective to minimize the drag for a specified lift range. One resulting airfoil was tested in the Model Wind-Tunnel (MWT) of the institute and compared to the classical RG-15 airfoil. In order to allow a realistic recalculation of experiments conducted in the MWT the limiting n-factor was evaluated for this facility. A special airfoil featuring an extensive instability zone was designed for this purpose. The investigation was supplemented by detailed measurements of the turbulence level. To get more insight in design guidelines for very low Reynolds number airfoils the influence of variations of the leading-edge geometry on the aerodynamic characteristics was studied experimentally at Re = 50,000.
In: Progress in Astronautics and Aeronautics, Vol.195, Fixed, Flapping,..., ISBN 1-56347-517-0, 2001