Numerical Analysis of Wind Turbine Airfoil Aerodynamic Performance with Leading Edge Bump

Abstract

Aerodynamic performance improvement of wind turbine blade is the key process to improve wind turbine performance in electricity generated and energy conversion in renewable energy sources concept. The flow behavior on wind turbine blades profile and the relevant phenomena like stall can be improved by some modifications. In the present paper, Humpback Whales flippers leading edge protuberances model as a novel passive stall control method was investigated on S809 as a thick airfoil. The airfoil was numerically analyzed by CFD method in Reynolds number of 10 6 and aerodynamic coefficients in static angle of attacks were validated with the experimental data reported by Somers in NREL. Therefore, computational results for modified airfoil with sinusoidal wavy leading edge were presented. The results revealed that, at low angles of attacks before the stall region, lift coefficient decreases slightly rather than baseline model. However, the modified airfoil has a smooth stall trend while baseline airfoil lift coefficient decreases sharply due to the separation which occurred on suction side. According to the flow physics over the airfoils, leading edge bumps act as vortex generator so vortices containing high level of momentum make the flow remain attached to the surface of the airfoil at high angle of attack and prevent it from having a deep stall.

Numerical study of Wavy Blade Section for Wind Turbines

“…Comparing the baseline S809 with WF geometry, it is seen that they agree very well up to approximately 9 degrees angle of attack where the WF starts to separate a few degrees earlier than the smooth blade thus having a lower C l,max , but what is more surprising is that the WF seems to stall more abruptly than the baseline blade. This is in contradiction to what is reported in most other studies [5], [6] and [9] and could be a result of the chosen baseline airfoil that itself has a smooth stall. It may be that in really deep stall the curves will cross so that the WF and WB geometries become better than the baseline airfoil, but this is not computed in this work and should be done with at least a DES model.…”

“…The S809 airfoil was chosen, since this was also used in one of the previous studies [9] and because this is an airfoil designed especially for wind turbines. Three geometries were modelled: 1) baseline S809 with a straight leading edge, 2) Wavy Front WF, where only the leading is modified to have a sinusoidal undulation and 3) Wavy Blade WB, where the sinusoidal undulation continues to the trailing edge.…”

“…However, in contrary with previous findings they report the beneficiary post stall aerodynamic properties to increase with increasing amplitudes and wavelengths. Asli et al [9] computed the S809 airfoil, the one also used on the NREL Phase VI rotor, using the k-ω DES turbulence model and applying an amplitude A/c=0.025 and wavelength λ/c=0.25 typical for a humpback whale. Again a smoother stall was observed compared to baseline geometry, but at the cost of an earlier stall and associated lower C l,max .…”

Flow separation control using a bio-inspired nose for NACA 4 and 6 series airfoils

“…However, shows a smooth stall trend at larger angles. The bumps acted as a vortex generator, which creates a high momentum vortex that prevents deep stall (Asli et al , 2015). As the airfoil thickness and flow Reynolds number increases, the effectiveness of wavy leading edge decreases (De Paula and Meneghini, 2016; De Paula et al , 2017).…”

Flow separation control of NACA-2412 airfoil with bio-inspired nose

“…For sinusoidal leading edge or L.E tubercles, at low angles of attacks before the stall region, lift coefficient decreases slightly than baseline model. And leading edge bumps act as vortex generator at high angle of attack and prevent it from having a deep stall (Asli et al, 2015).…”