In this paper a flapping and flexible airfoil is investigated at low Reynolds number flow conditions with the aid of a coupling simulation environment. A laminar separation bubble occurs on the upper side of the airfoil, which moves during a flapping period along the airfoil. Therefore, laminar-turbulent transition prediction has to be taken into account as part of the fluid solver. A coupled steady state analysis is used to calculate the jig-shape of the airfoil to create a flexible model for wind tunnel test campaigns. Flapping flight simulations for a specific testcase are compared with experimental data, which are conducted with the aid of stereoscopic PIV measurements. The comparison of experimental and numerical data has shown a good agreement. However, discrepancy has found in the rate of transition location change and the trailing edge deformation. Further, parameter studies are systematically made, with the goal to improve the propulsive efficiency. A better flapping flight efficiency could be found, when the plunging amplitude is increased, but only to a certain value, when no leading edge separation occurs. More flexible airfoils reduce the propulsive efficiency. However, with the aid of a temporal adaptive stiffness of the airfoil (more stiff during downstroke, more flexible during the upstroke), an improvement of the efficiency could be noticed. Here, it is found that the upper bound of temporal adaptive stiffness mainly influences the highest thrust peak during the downstroke, whereas the lower bound is responsible for the highest drag peak during the upstroke. Future work lies on the development on a flapping flight motion of a flexible airfoil with an adaptive controlled camber to take advantage of the results found in this paper. Such adaptive structure can be realized through macro fiber composite actuators, which show a light weight in conjunction with a reasonable change in the camber of the airfoil (Bilgen et al., 2007). Moreover, it remains to investigate the influence of the angle of attack amplitude. That this parameter has an effect on the propulsive efficiency could be shown in Windte and Radespiel (2008) and is therefore a further parameter to increase the efficiency of the flapping system.
Fluid-structure analysis of a flexible flapping airfoil at low Reynolds number flow
Fluid-Struktur-Analyse eines flexiblen Schlagflügels bei niedrigen Reynolds-Zahlen
Journal of Fluids and Structures ; 28 ; 72-88
2012
17 Seiten, 19 Bilder, 4 Tabellen, 37 Quellen
Aufsatz (Zeitschrift)
Englisch
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