Numerical investigation into energy extraction of flapping airfoil with Gurney flaps
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- A new type of Gurney flap is proposed.
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- Application of Gurney flaps on a flapping airfoil for energy extraction is studied numerically.
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- The effects of various motion parameters and Gurney flap heights are investigated.
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- The mechanisms of energy extraction enhancement are analyzed.
Abstract
A new type of Gurney flap is applied for energy extraction enhancement of a flapping airfoil. Two-dimensional Navier-Stokes simulations at Re = 104 are conducted to study the effect of Gurney flaps with various heights. The investigations are undertaken over a wide range of kinematic parameters (reduced frequency k, pitching amplitude θ0). Numerical results show that the application of a Gurney flap notably increases the maximum output power and efficiency compared with a clean NACA0012 airfoil. By affecting the flow structure and the pressure distribution around the trailing edge of the airfoil, the Gurney flap is beneficial to the lift force generation, thus leading to a higher power coefficient. The maximum power coefficient increases with Gurney flap height hg at first between hg = 0c–0.3c (c is the airfoil chord length), while a further increase in hg provides no further energy extraction enhancement. Besides, the increasing hg results in stronger trailing edge vortices and higher drag force.
Keywords
- Flapping airfoil;
- Energy extraction;
- Gurney flap
Automatic modelling of airfoil data points
Abstract
This paper presents a computer-based technique to construct B-spline parametric models from a large set of airfoil data points, with a reduced number of parameters involved in the geometric representation of the airfoil profile. The proposed method uses different techniques related with the B-spline properties adapted to the geometry of an airfoil (a thin section with great changes of curvature) and produces a B-spline curve that is close to the data points maintaining a maximum tolerance distance. This curve can be used for calculations and is expected to provide a good framework for aerodynamic or hydrodynamic optimization, based on its reduced number of geometric parameters and on its calculation time, when compared with other methodologies. The method stresses the fitting of the airfoil's leading edge, which has a significant impact on the properties of the airfoil. B-spline curves and surfaces are used in this method because they are widely used in CAD-CAM software products and can be easily exported to other programs.
Keywords
- Airfoils;
- B-splines;
- Parametric design;
- Least squared fitting
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