An Investigation Of Wing Morphing Phenomena In The Educational Wind Tunnel

Wing morphing is an important technique currently under investigation to reduce drag as well as noise associated with the design of aircraft. The general term “morphing” includes use of a variety of control mechanisms to reduce drag by altering the air flow around the surface of an aerodynamic shape. This would in general include the direct alteration of the shape of an aerodynamic surface, as well as the use of localized jets or other surface structures to likewise dynamically influence the flow. Bird flight, is one example of morphing which occurs in nature, and the highly flexible adaptive control exhibited by birds in flight is really quite remarkable. It would be desirable to mimic such behavior in order to improve practical aerodynamic performance. Of primary engineering interest is the control of so-called boundary layer separation, which is characterized by streamlines breaking away from the aerodynamic surface, ultimately leading to the onset of “stall” or loss of lift in the case of a wing surface, as well as severe increase in drag. Such phenomena can be studied both qualitatively and quantitatively using a wind tunnel or water tunnel test facility. Wind and water tunnel testing has long been an important component common to many introductory fluid mechanics and aerodynamics courses, but usually involves steady-state measurements of lift, drag, pitching moment, and pressure distribution on small-scale models. With morphing, there is an added “dynamic” dimension to the flow structure, which is characteristic of unsteady aerodynamics. This involves time dependent boundary layer separation and vortex shedding phenomena. A long-range goal would be to actively control this unsteady boundary layer separation to reduce the overall drag force, but not at the expense of too much complexity or the need for significant expenditure of energy. Understanding these physical characteristics is very important to future aerodynamic design, for the purpose of maximizing fuel economy. This area also represents an important topic associated with the teaching of basic principles of modern aerodynamic design as applied to existing aircraft control structures, such as flaps or elevator control surfaces. The work presented here is the outgrowth of a one semester senior undergraduate mechanical engineering student honors research project, which makes use of our Aerolab educational wind tunnel test facility. The focus of this paper is to demonstrate basic characteristics of one type of wing morphing on a dynamic wing model, inexpensively fabricated using a rapid prototyping facility. Flow visualization of vortex shedding phenomena is illustrated for the dynamic wing morphing design. The pivoted wing structure test model is driven in periodic rotational motion by a mechanism designed by the associated honors student. This mechanical setup is used in conjunction with a recently developed special-purpose aerodynamic smoke rake system, and a relatively inexpensive low-power laser-based lighting system, for visualization of the associated air flow and vortex shedding phenomena.