Patent Application
20210285329
The present specification relates generally to an airfoil, and more particularly to an airfoil that leads to improved power production at lower wind speeds.
The following includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art nor material to the presently described or claimed inventions, nor that any publication or document that is specifically or implicitly referenced is prior art.
The use of wind turbines for power generation has increased rapidly along with the demand for clean, sustainable energy sources. In addition to other constraints, a key element of turbine design is the blade design. More particularly, the airfoil (cross-sectional shape) of the blade represents a determining factor in the blade's operating capabilities and efficiency.
Accordingly, much work has been conducted on airfoils to address operating parameters for wind turbines. The majority of current airfoils in use result in blades and turbines that require a certain level of input wind speed in order to operate efficiently for power conversion by the turbine. Thus, such turbines are limited in location and operating conditions by this requirement.
Therefore, it would be desirable to have an airfoil which results in a blade and turbine which is capable of operating at a desirable efficiency at a lower input wind speed.
Additionally, given the prevalence of existing blades using existing airfoils, it would also be desirable to provide a method of modifying an existing airfoil into a new shape which provides the capabilities discussed above.
Accordingly, there remains a need for improvements in the art.
In accordance with an aspect of the invention, there is provided generally to an airfoil, and more particularly to an airfoil modified with a droop that leads to improved power production at lower wind speeds.
According to an embodiment of the invention, there is provided a modified airfoil, comprising: an original airfoil having an original leading edge profile with an original leading edge terminating at an x,y co-ordinate of 0,0 and a trailing edge terminating at an x,y co-ordinate of 1,0; and a shape modification element attached to the original airfoil such that a new leading edge of a new leading edge profile formed by the shape modification element terminates at a negative x co-ordinate relative to the original leading edge, wherein the new leading edge profile has a new leading edge profile shape with a NACA mean chord line between 0.3 and 0.7, a thickness between 12% and 17% of the chord line, with a maximum thickness located between 10% and 40% of the chord line, starting from the new leading edge of the new leading edge profile; and a leading edge radius between 1% and 6% of the chord line.
According to a further embodiment of the invention, there is provided a method for modifying an airfoil, comprising: defining the airfoil with a airfoil shape such that an original leading edge of an original leading edge profile is positioned at an 0,0 x,y co-ordinate and an original trailing edge is positioned at an 1,0 x,y co-ordinate; and modifying the original leading edge profile such that a new leading edge of a new leading edge profile is positioned at a negative x co-ordinate relative to the original leading edge, wherein the new leading edge profile has a new leading edge profile shape with a NACA mean chord line between 0.3 and 0.7, a thickness between 12% and 17% of the chord line, with a maximum thickness located between 10% and 40% of the chord line, starting from the new leading edge of the new leading edge profile; and a leading edge radius between 1% and 6% of the chord line.
For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. The features of the invention which are believed to be novel are particularly pointed out and distinctly claimed in the concluding portion of the specification. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings and detailed description.
Other aspects and features according to the present application will become apparent to those ordinarily skilled in the art upon review of the following description of embodiments of the invention in conjunction with the accompanying figures.
Reference will now be made to the accompanying drawings which show, by way of example only, embodiments of the invention, and how they may be carried into effect, and in which:
Like reference numerals indicated like or corresponding elements in the drawings.
The present invention relates to an airfoil and, in particular, a modified airfoil incorporating a droop to improve performance at lower wind speed.
A reference airfoil profile geometry is shown in
Considering the airfoil as used in a blade, an original blade is designed to operate at a specific tip speed ratio. If the blade is to be modified, the profile needs to be able to develop an increase in Lift to Drag ratio across the entire blade platform from root to tip. Through modification of the profile (airfoil), a new hybrid profile may be developed as a blend between two non-related profiles to improve performance.
According to an embodiment of the present invention, this hybrid profile may be created from an existing designed airfoil profiles (i.e. NACA profiles or the like) for a new leading edge redesign. The redesign may be developed over a grid platform to constrain the geometry of the original airfoil. The original profile is laid out on a grid with the chord line connecting the leading edge and the trailing running on top of one of the horizontal grid lines, similarly to as shown in
The new leading edge profile is then located forward of the 0,0 coordinate such that the new leading edge is at a negative x-location in relation to the original leading edge location i.e. a droop. The leading edge may further be located, in some designs, at a negative y-location (i.e. below the x plane) as well. The new leading edge profile may also be rotated about this new location at a − or + angle to allow the new profile to blend into the upper surface of the original profile surfaces. Lastly, the new leading edge profile may be scaled compared to the normalized original profile so there can be a ratio developed between the original to new leading edge profile, for example, the ratio may be 0.8:1.0 or 80% of the original profile chord length (treated as 100%).
The scaling ratio required is related to the thickness of the original profile as well as the change in thickness from the root to the tip of the blade. Therefore in order to match to the upper surface contour of the original profile, the new leading edge profile results in a chord length that may range from 50% of the original profile chord length to as much as 250% of the original chord length.
When the process is completed, the new leading edge profile shape should have a NACA Mean chord line between 0.3 to 0.7. The new leading edge profile shape should also have a thickness of 12% to 17% of the new leading edge profile chord line (10% to 48% for larger rotors). The new leading edge profile shape should have a maximum thickness that is located between 10% and 40% of the chord line as located from the leading edge of the new leading edge profile. The new leading edge profile shape should have a leading edge radius between 1% to 6% of the new leading edge profile normalized chord line.
Creation of the new airfoil profile may be performed by the addition of a shape modification element to an existing blade (the original airfoil) to create the new profile shape with the new leading edge. The shape modification element may be permanently secured to the blade or may be detachable to permit for repair and replacement if needed, without requiring replacement of the entire blade. Accordingly, the shape modification element may be made of the same material as the existing blade, or a different material, depending on the materials used and the effect on performance parameters.
Alternatively, the new airfoil profile may be applied to a completely new blade built to the new profile specification. In this case, the new airfoil profile may still be based on a modification of an existing (original) airfoil profile, but rather than modifying an existing blade, a new blade is built to the new airfoil profile according to known methods for the manufacture of blades.
When modifying an existing airfoil, the existing symmetry or asymmetry, as well as the degree (positive or negative) and nature (reflexed or non-reflexed) of the camber, may be preserved, although the absolute values may change. In particular, the camber line is generally expected to move forward from the original, which may break symmetry, and the location of the maximum camber is expected to change with the modification to the new leading edge.
Accordingly, when creating a new blade, the airfoil may be symmetric or asymmetric, as desired, based on other operating parameters and requirements. Similarly, the airfoil may be designed with either a positive or negative camber, considering the expected operating parameters and requirements. Finally, the camber may be reflexed or non-reflexed, again following the operating parameters and requirements.
Modifications and supporting experimental data for the existing airfoils are shown in
Airfoil coefficients were modelled using one or both of XFOIL and CFD (computation fluid dynamics) software. Performance of the airfoil was then modelled using a BEM (Blade Element Momentum) model. As shown, the resulting calculated performance of the modified airfoil produces improved results for lift coefficient (Cl), drag coefficient (Cd) and lift/drag coefficient (Cl/Cd) at higher angles of attack (Alpha or AOA). Such results are further found to be generally consistent across all modified airfoils of a given class.
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As described above, the airfoil was tested for use with turbines, particularly wind turbines. However, it may be expected that the airfoil may be used for other blade and rotor applications, with or without improved performance parameters. Such applications may include, but are not limited to, propellers, helicopter rotors, and drone rotors.
It should also be noted that the steps described in the method of use can be carried out in many different orders according to user preference. The use of “step of” should not be interpreted as “step for”, in the claims herein and is not intended to invoke the provisions of 35 U.S.C. § 112(f). It should also be noted that, under appropriate circumstances, considering such issues as design preference, user preferences, marketing preferences, cost, structural requirements, available materials, technological advances, etc., other methods are taught herein.
The embodiments of the invention described herein are exemplary and numerous modifications, variations and rearrangements can be readily envisioned to achieve substantially equivalent results, all of which are intended to be embraced within the spirit and scope of the invention. Further, the purpose of the foregoing abstract is to enable the U.S. Patent and Trademark Office and the public generally, and especially the scientist, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application.
The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Certain adaptations and modifications of the invention will be obvious to those skilled in the art. Therefore, the presently discussed embodiments are considered to be illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
