Suggestions for Improving Wind Turbines Blade Characteristics

2012

Int. J. Energy Res.

SUMMARY The designers of horizontal axis wind turbines and tidal current turbines are increasingly focusing their attention on the design of blade sections appropriate for specific applications. In modern large wind turbines, the blade tip is designed using a thin airfoil for high lift : drag ratio, and the root region is designed using a thick version of the same airfoil for structural support. A high lift to drag ratio is a generally accepted requirement; however, although a reduction in the drag coefficient directly contributes to a higher aerodynamic efficiency, an increase in the lift coefficient does not have a significant contribution to the torque, as it is only a small component of lift that increases the tangential force while the larger component increases the thrust, necessitating an optimization. An airfoil with a curvature close to the leading edge that contributes more to the rotation will be a good choice; however, it is still a challenge to design such an airfoil. The design of special purpose airfoils started with LS and SERI airfoils, which are followed by many series of airfoils, including the new CAS airfoils. After nearly two decades of extensive research, a number of airfoils are available; however, majority of them are thick airfoils as the strength is still a major concern. Many of these still show deterioration in performance with leading edge contamination. Similarly, a change in the freestream turbulence level affects the performance of the blade. A number of active and passive flow control devices have been proposed and tested to improve the performance of blades/turbines. The structural requirements for tidal current turbines tend to lead to thicker sections, particularly near the root, which will cause a higher drag coefficient. A bigger challenge in the design of blades for these turbines is to avoid cavitation (which also leads to thicker sections) and still obtain an acceptably high lift coefficient. Another challenge for the designers is to design blades that give consistent output at varying flow conditions with a simple control system. The performance of a rotating blade may be significantly different from a non‐rotating blade, which requires that the design process should continue till the blade is tested under different operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.

Section: Introductionmentioning

confidence: 99%

Blade sections for wind turbine and tidal current turbine applications-current status and future challenges

2012

Int. J. Energy Res.

“…For example, the stall angle reported in one of the databases is 10.5 o for Re = 100,000 [8], while some researchers have reported stalling at about 15 o for this Re. The shape of the profile indicates that it is a good compromise between the NACA airfoils and the highly cambered very low Re airfoils [2].…”

Section: Introductionmentioning

confidence: 98%

“…The commonly used NACA airfoils are not appropriate for wind turbines that need to operate in regions of low wind. The NACA airfoils are suitable for applications where the Reynolds numbers (Re) are high and the angles of attack are relatively small [1,2]. Attempts are being made to develop good airfoil geometries that are appropriate at low Re for energy extraction from the wind at low wind speeds.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Experimental and Numerical Studies on a Low Reynolds Number Airfoil for Wind Turbine Blades

Narayan

Zullah

et al. 2011

JFST

Testing of a low Reynolds number airfoil designed for low speed horizontal axis wind turbine (HAWT) blades was performed to study its aerodynamic characteristics. Experiments were conducted at Reynolds numbers (Re) of 38,000 to 200,000 at angles of attack from-2 o to 20 o. The airfoil geometry was chosen after testing a number of profiles with XFOIL software. The pressure distribution, lift and drag coefficients and the flow characteristics were also studied with ANSYS-CFX software. The freestream turbulence level was increased from 1% to 5% and 10% which shifted the transition point on the upper surface upstream, resulting in increased skin friction drag for lower angles of attack due to a larger turbulent boundary layer region. The slope of the lift curve did not change much at higher turbulence levels; however, for higher angles of attack, the separation from the upper surface was delayed resulting in an increase in lift and a reduction in drag. The lift to drag ratio increased by 8% to 15% as a result of increasing the turbulence level in the angles of attack-range of interest.

“…4 NACA airfoils are suitable mainly for high Reynolds numbers and relatively small angles of attack (a). 5 Wind turbine airfoils need to perform well over a wide range of angles of attack. This means that the L/D ratio should not drop abruptly as a changes.…”

Section: Introductionmentioning

confidence: 99%

Low Reynolds number airfoil optimization for wind turbine applications using genetic algorithm

Ram

Lal

Journal of Renewable and Sustainable Energy

2013

Optimization of a low Reynolds number airfoil for use in small wind turbines is carried out using a Genetic Algorithm (GA) optimization technique. With the aim of creating a roughness insensitive airfoil for the tip region of turbine blades, a multi-objective genetic algorithm code is developed. A review of existing parameterization and optimization methods is presented along with the strategies applied to optimize the airfoil in this study. A composite Bezier curve is used to parameterize the airfoil. The resulting airfoil, the USPT2 has a maximum thickness of 10% and shows insensitivity to roughness at the optimized angles and at other angles of attack as well. The characteristics of USPT2 are studies by comparing it against the popular SG6043 airfoil. While a slight loss in lift is noticed for both airfoils, the drag increments due to early transition are noticeable as well. The airfoil is also studied using computational fluid dynamics (CFD) and wind tunnel experiments during free and forced transition. The USPT2 airfoil will be useful in small wind turbines for locations where blade soiling is likely or where other flow phenomena may cause early transition of the boundary layer.