Optimization of the dynamic of a rigid airfoil mounted of elastic supports

Jean-Christophe Veilleux

Master degree student
jean-christophe.veilleux.1@ulaval.ca

A rigid symmetrical wing which is elastically supported both in heave (translation) and in pitch (rotation) may develop self-induced oscillations when sustained in a freestream flow. This flutter phenomenon is mainly associated to the dynamic stall of the airfoil combined with the aerodynamic and structural coupling between both degrees of freedom. When self-induced oscillations are observed, the energy required to sustain the wing's motion is provided from the flow itself, thus transforming the oscillating wing apparatus in a form of energy extraction device.  

Numerical simulations and wind tunnel experiments showed that the self-induced oscillations of the wing can reach relatively high amplitudes of motion. Some recent numerical simulations also proved that the amount of energy transferred from the flow to the airfoil can be positively influenced (increased) by adjusting judiciously the multiple free parameters of the apparatus. This strongly suggests that optimizing the amount of energy extracted by the oscillating wing could transform this relatively simple apparatus in a new form of attractive hydrokinetic turbine that could be used for producing hydroelectricity. 

The optimization of extracted energy through the oscillating wing is achieved using OpenFOAM, a free finite-volume open source code for computational fluid dynamics (CFD). In order to achieve reliable computations of the wing's motion and the extracted energy from the flow, the interaction between the wing and the flow must be taken into account. This interaction between the fluid and the structure, most commonly referred to as fluid structure interaction (FSI), is bidirectional; the fluid flow influences the wing's motion and the wing influences the fluid flow. Although the complexity of the computations is increased by this fluid structure interaction, the numerical results  show a fairly good agreement with the results obtained through the wind tunnel experiment. This provides enough confidence that the numerical methods used are trustworthy and can therefore be used to conduct a parametric study of the passive oscillating airfoil as an energy harvesting device. 

oscillating airfoil as an energy harvesting device.

This parametric study should provide a better understanding of the mechanism through which the wing undergoes self-induced limit cycle oscillations and, more interestingly, provide an insight about the control one may have over the wing's motion in order to maximize the amount of energy extracted from the flow.