Improvement of Airfoils Aerodynamic Efficiency by Thermal Camber Phenomenon at Low Reynolds Number

Small-scale drones have enough sensing and computing power to find use across a growing number of applications. However, flying in the low–Reynolds number regime remains challenging. High sensitivity to atmospheric turbulence compromises vehicle stability and control, and low aerodynamic efficiency limits flight duration. Conventional wing designs have thus far failed to address these two deficiencies simultaneously. Here, we draw inspiration from nature’s small flyers to design a wing with lift generation robust to gusts and freestream turbulence without sacrificing aerodynamic efficiency. This performance is achieved by forcing flow separation at the airfoil leading edge. Water and wind tunnel measurements are used to demonstrate the working principle and aerodynamic performance of the wing, showing a substantial reduction in the sensitivity of lift force production to freestream turbulence, as compared with the performance of an Eppler E423 low–Reynolds number wing. The minimum cruise power of a custom-built 104-gram fixed-wing drone equipped with the Separated Flow wing was measured in the wind tunnel indicating an upper limit for the flight time of 170 minutes, which is about four times higher than comparable existing fixed-wing drones. In addition, we present scaling guidelines and outline future design and manufacturing challenges.

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Numerical Investigation on Aerodynamic Performance of Bird’s Airfoils

Journal of Aerospace Technology and Management ◽

10.5028/jatm.v12.1182 ◽

2020 ◽

Author(s):

Ashraf Omar ◽

Rania Rahuma ◽

Abdulhaq Emhemmed

Keyword(s):

Reynolds Number ◽

Low Reynolds Number ◽

Angle Of Attack ◽

Aerodynamic Performance ◽

Airfoil Surface ◽

Aerodynamic Efficiency ◽

Gliding Flight ◽

Surface Permeability ◽

Low Reynolds ◽

Better Than

In this work, the aerodynamic performance of four types of bird’s airfoils (eagle, stork, hawk, and albatross) at low Reynolds number and a range of angles of attack during fixed (unflapping) gliding flight was numerically investigated utilizing open-source computational fluid dynamics (CFD) code Stanford University unstructured (SU2) and K-ω Shear Stress Transport (K-ω SST) turbulence model. The flow of the simulated cases was assumed to be incompressible, viscous, and steady. For verification and comparison, a low Reynolds number man-made Eppler 193’s airfoil was simulated. The results revealed that stork has the greatest aerodynamic efficiency followed by albatross and eagle. However, at zero angle of attack, the albatross aerodynamic efficiency exceeded all the other birds by a significant amount. In terms of aerodynamics efficiency, stork’s and albatross’s airfoils performed better than Eppler 193 at angles of attack less than 8°, while at a higher angle of attack all studied birds’ airfoils performed better than Eppler 193. The effect of surface permeability was also investigated for the eagle’s airfoil where the permeable surface occupied one-third of the total airfoil surface. Permeability increased the generated lift and the aerodynamic efficiency of the eagle’s airfoil for angles of attack less than 10°. The increase reached 58% for the lift at zero angle of attack. After the specified angle, the permeability had an adverse effect on the flow which may be due to the transition to turbulent ahead of the permeable section.

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Numerical investigation of Gurney flap influences on aerodynamic performance of a pitching airfoil in low Reynolds number flow

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410018808708 ◽

2018 ◽

Vol 233 (10) ◽

pp. 3819-3832

Author(s):

Alireza Naderi ◽

Alireza Beiki ◽

Bahram Tarvirdizadeh

Keyword(s):

Reynolds Number ◽

Low Reynolds Number ◽

Aerodynamic Performance ◽

Solid Boundary ◽

Aerodynamic Efficiency ◽

Drag Coefficients ◽

Gurney Flap ◽

Unified Algorithm ◽

Low Reynolds ◽

Lift And Drag

The main purpose of present work is to investigate the aerodynamic performance of a pitching NACA 0012 airfoil equipped with a Gurney flap in flow with low Reynolds number. The aerodynamic influences of flap location, mounting angle, and height are numerically studied. In this regard, a Lagrangian–Eulerian pressure-based numerical algorithm is developed on hybrid grids attached to a pitching solid boundary. A finite volume-based finite element method is used to discretize the governing equations. As reported in previously related studies, this unified algorithm could be used to solve the unsteady incompressible flow in domains with moving mesh and/or moving boundary with sufficient robustness and accuracy. The other advantage of this algorithm is that it does not need any type of dissipation term and/or damping function. Using this unified algorithm, the numerical experiments indicate that the Gurney flap increases the lift and drag coefficients and enhances the aerodynamic efficiency. The best aerodynamic performance is predicted for the case in which the flap is located at trailing edge with the mounting angle of 90°. The flap height is predicted to have different and most impacts on aerodynamic efficiency during upstroke and downstroke. The numerical results show that the airfoils equipped by flaps with height between 6% and 12% of the airfoil chord are the most aerodynamically efficient airfoils. Changing of lift and drag coefficients are due to increase of effective camber and thickness in all cases.

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