FAN BLADE TIPS
Fans having blade tips with downwardly extending airfoil surfaces are disclosed herein. In one embodiment, for example, a high volume low speed ceiling fan includes a plurality of blades, each having an anhedral or downward sloping tip portion. The blade tips can also include an aft swept portion that extends between the main airfoil portion of the fan blade and the anhedral tip portion.
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The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/416,680, filed Nov. 23, 2010, and entitled “FAN BLADE TIPS,” which is incorporated herein by reference in its entirety.
TECHNICAL FIELDThe following disclosure relates generally to fan blades and, more particularly, to high efficiency fan blade tips.
BACKGROUNDMulti-blade, high velocity low speed (HVLS) cooling fans are often used in warehouses, loading docks, and other large structures to provide a comfortable work environment and/or to maintain suitable temperatures for product storage. Such fans are typically hung from the ceiling, and can include a plurality of blades extending outwardly from a central, motor-driven hub.
Conventional ceiling fan blades are generally flat and have constant cross-sections from root to tip. Others can include upwardly-angled airfoil extensions on the tips, or flat plates that simply cap off the tips as taught in, for example, U.S. patent application Ser. No. 12/038,873, and U.S. Pat. Nos. 7,252,478, 7,284,960 and 7,654,798 (each of these patents and applications is incorporated herein by reference). While these tip devices may improve the aerodynamic characteristics of conventional fan blades, further reductions in aerodynamic drag, power consumption, and acoustic signature would be beneficial.
The present disclosure describes various embodiments of fan blade tips for use with various types of cooling fans. In one embodiment, a ceiling fan configured in accordance with the present disclosure can include a plurality of blades having tips with an anhedral portion. More specifically, the blade tips can include a winglet or similar airfoil surface that slopes downwardly and away from the main airfoil portion of the fan blade. In another embodiment, the blade tips can include an aft swept portion that lies in the same plane as the main airfoil portion, and an anhedral portion that extends downwardly from the aft swept portion. The anhedral portion can also be swept aft and can include a tapered profile. As discussed in greater detail below, providing fan blades with downwardly sloping (i.e., anhedral) winglets or tip portions with or without an aft swept horizontal portion can reduce air dynamic drag on the fan blades during operation, thereby improving efficiency, reducing power requirements, and reducing the acoustic signature of the fan.
Certain details are set forth in the following description and in
Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular embodiments of the disclosure. Accordingly, other embodiments can have other details, dimensions, angles and features without departing from the spirit or scope of the present invention. In addition, those of ordinary skill in the art will appreciate that further embodiments of the invention can be practiced without several of the details described below.
In the Figures, identical reference numbers identify identical, or at least generally similar, elements. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refers to the Figure in which that element is first introduced. For example, element 110 is first introduced and discussed with reference to
In the illustrated embodiment, each of the fan blades 110 includes a main airfoil 120 having an inboard end portion 116 fixedly attached to the central hub 112, and an outboard end portion 118 fixedly attached to a blade tip 122. In one aspect of this embodiment, the blade tip 122 includes an aft swept portion 124 and a downwardly sloping “anhedral” portion 126. Without wishing to be bound by theory, the blade tips 122 are believed to produce tip vortices with improved drag characteristics as the fan blades 110 rotate through the air in the direction of arrow R. As is known, wingtip or blade tip vortices are spirals of circulating air which are shed from the tips as the blades deflect the air downwardly in the direction of arrow D. As the vortex curls over the tip of a conventional fan blade, it reduces lift near the tip of the fan blade and creates turbulent air through which the trailing blade must move. Each of these factors increases the drag and reduces the efficiency of the fan. It is believed that by providing the anhedral portion 126 at a downward slope, the vortex is shed from the tip 122 at a vertical location that is below the waterline of the main airfoil 120. This tends to direct the vortex downward and away from the trailing blade. It is also believed that by angling the swept portion 124 aft, the vortex curls over the blade tip 122 aft of the trailing edge of the main airfoil 120, thereby reducing the turbulent airflow striking the upper surface of the main airfoil 120. It is further believed that tapering the profile of the anhedral portion 126 can reduce turbulence generated by the blade tip 122. All of the foregoing factors contribute to a cooling fan blade that generates less aerodynamic drag, thereby improving efficiency and reducing power requirements for a given output, as well as reducing the acoustic signature of the fan.
As shown in
The present disclosure is not limited to the particular embodiment of fan blade tip described above with reference to
Although the blade tips 222 and 322 described above with reference to
The various embodiments of fan blades and blade tips described above can be manufactured using any number of different materials and methods known in the art. For example, all or a portion of the fan blades can be formed from plastic, such as injection molded plastic, composites, metal, and/or other suitable materials. Moreover, in some embodiments the main airfoil (e.g., the main airfoil 120, 320, or 420) and the blade tip (e.g., the blade tip 122, 322, or 422) can be integrally formed as single unit. In another embodiment, the blade tip can be manufactured as a separate unit that is retrofit to existing fan blades to increase efficiency and enhance performance.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the various embodiments of the invention. Further, while various advantages associated with certain embodiments of the invention have been described above in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited, except as by the appended claims.
Claims
1. A ceiling fan comprising:
- a central hub configured to be suspended from a ceiling of a building; and
- a plurality of blades extending outwardly from the central hub, wherein each blade includes: a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and a tip portion attached toward the outboard end portion of the main airfoil and extending downwardly relative to the main airfoil portion.
2. The ceiling fan of claim 1 wherein the plurality of blades define a fan outer diameter of from about 6 feet to about 24 feet.
3. The ceiling fan of claim 1 wherein the main airfoils extend horizontally outward from the hub.
4. The ceiling fan of claim 1 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, and wherein the tip portion extends downwardly relative to the aft swept portion.
5. The ceiling fan of claim 1 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, wherein the main airfoil and the aft swept portion of each blade lie in a horizontal plane, and wherein the tip portion extends downwardly relative to the aft swept portion.
6. A fan comprising:
- a motor driven central hub; and
- a plurality of blades extending outwardly from the central hub fan, wherein the plurality of blades are configured to move air in a direction D when rotating in a direction R during normal operation, wherein each blade includes: a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and a tip having: an aft swept portion; and an anhedral portion, wherein the aft swept portion has an inboard chord attached to the outboard end portion of the main airfoil and an outboard chord attached to anhedral portion, and wherein the anhedral portion extends away from the main airfoil in direction D.
7. The fan of claim 6 wherein the inboard end portion and the outboard end portion of the main airfoil lie in a common plane, and wherein the anhedral portion is positioned at an angle relative to the plane.
8. The fan of claim 6 wherein the main airfoil and the aft swept portion lie in a common plane, and wherein the anhedral portion is positioned at an angle relative to the plane.
9. The fan of claim 6 wherein the aft swept portion extends away from the main airfoil opposite to the direction R.
10. The fan of claim 6 wherein the anhedral portion extends away from the aft swept portion opposite to the direction R.
11. The fan of claim 6 wherein the main airfoil and the aft swept portion lie in a common plane, wherein the anhedral portion is positioned at an angle relative to the plane, wherein the aft swept portion extends away from the main airfoil opposite to the direction R, and wherein the anhedral portion extends away from the aft swept portion opposite to the direction R.
12. The ceiling fan of claim 6 wherein the main airfoil and the aft swept portion have complimentary airfoil cross sections and lie in a common horizontal plane, and wherein the anhedral portion has a first chord thickness where it attaches to the aft swept portion and a second chord thickness a distal tip, and wherein the first chord thickness is greater than the second chord thickness.
13. The ceiling fan of claim 6 wherein the main airfoil has a rectangular planform and the aft swept portion and the anhedral portion taper outwardly.
14. The ceiling fan of claim 6 wherein the anhedral has a curved leading edge and a curved trailing edge.
15. The ceiling fan of claim 6 wherein the anhedral portion has a curved leading edge that forms a convex parabolic curve and a curved trailing edge that forms a concave parabolic curve.
16. A fan comprising:
- a central hub;
- means for rotating the central hub;
- means for coupling the means for rotating to a ceiling or other elevated structure in a building; and
- a plurality of blades extending outwardly from the central hub, wherein each blade includes: a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and a tip portion attached toward the outboard end portion of the main airfoil and extending downwardly relative to the main airfoil portion.
17. The fan of claim 16 wherein the plurality of blades define a fan outer diameter of from about 6 feet to about 24 feet.
18. The fan of claim 18 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, and wherein the tip portion extends downwardly relative to the aft swept portion.
19. The fan of claim 18 wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, wherein the main airfoil and the aft swept portion of each blade lie in a horizontal plane, and wherein the tip portion extends downwardly relative to the aft swept portion.
Type: Application
Filed: Nov 22, 2011
Publication Date: May 24, 2012
Applicant: 4Front Engineered Solutions, Inc. (Carollton, TX)
Inventors: Richard K. Hoofard (Dallas, TX), L. B. Whitley (Arlington, TX)
Application Number: 13/302,507
International Classification: F01D 5/14 (20060101);