The field of the disclosure relates generally to centrifugal fans and, more specifically, to centrifugal fan impellers with variable shape fan blades for use in air moving applications.
Centrifugal fans generally use one or a combination of three basic fan blade designs: radial, forward curved, and backward curved. Generally, radial bladed fans may have fewer fan blades than forward curved and backward curved designs. In at least some radial bladed fans, the blades extend straight from the axis of rotation of the wheel hub. Typically, radial bladed fans are less efficient than forward curved and backward curved designs. At least some forward curved fans include a large number of fan blades with the blades generally having a short chord length. Forward curved blade designs have fan blades that generally curve in the direction of the wheel hub's rotation. Some forward curved fans are more efficient than radial bladed fans, but less efficient than backward curved fans. Generally, backward curved fans are more efficient than forward curved fans and radial bladed fans. Backward curved fans have fan blades that curve against the direction of the wheel hub's rotation. The blades of a backward curved fan may be flat, slightly curved, or airfoil shaped.
In general, the three basic fan blade designs result in fans with specific performance curves. Typically, a fan's performance curve is determined by the shape of the blades and cannot be altered after the fan is fabricated. As a result, the stable and unstable operating range of the fan is generally fixed. With at least some centrifugal fans, as the flow rate of air through the fan is reduced and the pressure increases, the fan blades may begin to experience stall conditions, i.e., the airflow separates form the surface of the airfoil and changes the pressure distribution to a less favorable condition. A fan with an adjustable blade design may facilitate enlarging the operating range and improving the performance curve of the fan by providing a means for the blade to change to a more favorable geometry for the specified operating point or application and reducing the tendency to stall.
In one aspect, a flexible fan blade for use in a centrifugal fan impeller having at least one of a rear plate and a front plate with an air inlet is provided. The flexible fan blade comprises a fixed central portion fixedly coupled to at least one of the front plate and the rear plate of the centrifugal fan impeller. The flexible fan blade also includes a trailing edge extending from the fixed central portion and being moveable between a first position and a second position. The trailing edge is fabricated from a compliant material. Furthermore, the trailing edge is flexible in relation to the fixed central portion between a first position and a second position. The flexible fan blade also includes a leading edge extending from the fixed central portion in opposed relation to the trailing edge.
In another aspect, a flexible fan blade for use in a centrifugal fan impeller having at least one of a rear plate and a front plate with an air inlet is provided. The flexible fan blade comprises a leading edge portion fixedly coupled to at least of one the front plate and the rear plate of the centrifugal fan impeller. In addition, the leading edge portion comprises a leading edge and a trailing edge. Furthermore, the flexible fan blade includes a flap hingedly coupled to the leading edge portion. The flap is rotatable in relation to the leading edge portion between a first position and a second position.
In another aspect, a centrifugal fan impeller is provided. The impeller includes a rear plate including a center axis. In addition, the impeller includes a plurality of flexible fans blades. Each of the flexible fan blades include a fixed portion fixedly coupled to the rear plate of the impeller. Furthermore, each of the flexible fan blades includes a moveable portion extending from the fixed portion, where the moveable portion is moveable between a first position and a second position.
In another aspect, a flexible fan blade for use in a centrifugal fan impeller having at least one of a rear plate and a front plate with an air inlet. The flexible fan blade includes a leading edge fixedly coupled to at least of one the front plate and the rear plate of the centrifugal fan impeller. The flexible blade also includes a trailing edge fixedly coupled to at least of one the front plate and the rear plate of the centrifugal fan impeller. In addition, the flexible fan blade includes a flexible portion extending between the leading edge and the trailing edge and being moveable between a first position and a second position. The flexible portion being fabricated from a compliant material. The flexible portion also being flexible in relation to the leading edge and the trailing edge between the first position and the second position.
In another aspect, a method of assembling a centrifugal fan impeller is provided. The method includes providing at least one of a rear plate and a front plate. In addition, the method includes providing a plurality of flexible fan blades. Each of the flexible fan blades includes a fixed central portion. In addition, the flexible fan blades include a trailing edge extending from the fixed central portion with the trailing edge being fabricated from a compliant material. The trailing edge is also flexible in relation to the fixed central portion between a first position and a second position. The fan blades also include a leading edge extending from the fixed central portion in opposed relation to the trailing edge. The method also includes coupling the plurality of flexible fan blades to at least one of the rear plate and the front plate.
Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. Any feature of any drawing may be referenced and/or claimed in combination with any feature of any other drawing.
The present disclosure provides a centrifugal fan impeller with a variable shape fan blade that is configured to dynamically change its shape in response to aerodynamic and centrifugal forces in a manner that improves the overall performance of the centrifugal fan. The dynamic changing in shape of the variable shape fan blade directly affects the aerodynamic coefficients used in the aerodynamic lift and aerodynamic drag equations of an airfoil. Specifically, the centrifugal fan impeller includes a unique fan blade that transforms shape during the fan's use to facilitate improving efficiency, expanding the fan's performance curve, reducing noise, reducing blade stall, and maintaining a uniform volume air flow at different fan speeds. The exemplary variable shape fan blade is self-cleaning and facilitates improving dynamic balancing of the fan. Dynamic balancing of the blades is facilitated by the flexing of blades moving towards a natural forced state which can improve overall balance to the airflow and the inertial balance of the centrifugal fan impeller.
In the exemplary embodiment, blade 30 has an upper surface 32 and a lower surface 34. Both upper surface 32 and lower surface 34 extend from leading edge 36 to trailing edge 38. As illustrated in
Blade 30 includes a fixed portion or mounting location 50, which is generally positioned near the central area of blade 30. Alternatively, mounting location 50 may be positioned in any location along blade 30 that permits blade 30 to operate as described herein. In the exemplary embodiment, mounting location 50 is configured to fixedly attach to rear plate 12 and/or front plate 14 using any suitable fastening means that permits blade 30 to operate as described herein. In one suitable embodiment, blade 30 may attached to rear plate 12 and/or front plate 14 via features formed in rear plate 12 and/or front plate 14 such as an opening, e.g., a groove or a slot, configured to restrict an amount of movement of blade 30 between rear plate 12 and front plate 14 while permitting blade 30 to operate as described herein.
In the exemplary embodiment, blade 30 includes a flexible portion 52 and a flexible portion 54, which are movable relative to fixed mounting location 50. Flexible portion 52 forms at least part of leading edge 36 and flexible portion 54 forms at least part of trailing edge 38. Flexible portions 52 and 54 are fabricated from a compliant material as described above and may also incorporate counterweights or stiffening elements 56 and 58, e.g., fibers, filaments, metals, and the like.
In the exemplary embodiment, when fan impeller 10 is in operation, air enters through central air inlet 16 and is deflected radially outward from central axis 18 of fan impeller 10 towards blades 30. Blades 30 are configured to pull the air from the area of central air inlet 16. The air passes through channels between blades 30 and is forced outwards due to the centrifugal force generated by rotating blades 30. In addition, in some known fans, the volume of airflow forced outwards changes with respect to the speed of the fan's rotation. If the speed of the air passing over the blades drops too low then the lift is lost and the blade stalls. In the exemplary embodiment, blade 30 is configured to vary its shape to facilitate increasing efficiency and reducing the blade's 30 tendency to stall.
Further, first position 100 increases the aerodynamic drag 44 associated with blade 30. The term “aerodynamic drag,” as used herein, refers to the component of aerodynamic force parallel to the direction of motion of airflow 42 over blade 30. Increasing aerodynamic drag 44 requires more torque to rotate fan impeller 10 resulting in a greater disparity of the torque requirement at low rotation speed as compared to reduced aerodynamic drag. The greater torque requirement disparity facilitates increasing the control of fan impeller 10 at low rotation speed. An increase in the torque necessary to operate fan impeller 10 at low rotation speed enables a motor controller (not shown) of a motor (not shown) of fan impeller 10 to execute more control over the motor torque at the low rotation speed. The ability to depart from the standard force relations to modifiable force relations on blade 30 facilitates increasing the ability to control the airflow 42 more precisely.
In the exemplary embodiment, as fan impeller 10 is operated, centrifugal forces and air pressure forces generated by the rotation of fan impeller 10 causes flexible portions 52 and 54 of blade 30 to move outward from the axis of rotation of fan impeller 10. As blade 30 changes shape, the moment of inertia of fan impeller 10 also changes. The changes in the blade's 30 shape facilitates dynamically balancing an inertial balance of fan impeller 10, which can help reduce vibration of fan impeller 10.
In the exemplary embodiment, flexible portions 52 and 54 generally move about the mounting location 50 of blade 30. Blade 30 continues to change its shape until fan impeller 10 has reached a maximum operating speed, at which point blade 30 has reached a second position 150 indicated by the dashed lines of
In the exemplary embodiment, the speed and amount that flexible portions 52 and 54 move is controlled by stiffening elements 56 and 58, and/or, with reference to
Blade 130 includes a flexible portion 53, which is movable relative to mounting locations 51a and 51b between a first position 105 indicated by the solid lines of
In the exemplary embodiment, blade 60 has an upper surface 62 and a lower surface 64. Both upper surface 62 and lower surface 64 extend from leading edge 66 to trailing edge 68. As illustrated in
In the exemplary embodiment, blade 60 includes a flap 70 and a leading edge portion or fixed airfoil 61. Fixed airfoil 61 includes leading edge 66 and trailing edge 68. Flap 70 extends from trailing edge 68 and includes approximately 5% to 50% of the chord length C of blade 60. Alternatively, flap 70 may have a length that is 5% to 50% of the overall length of blade 60, where blade 60 is not an airfoil shape. Flap 70 includes flap trailing edge 71 and is movable relative to fixed airfoil 61 of blade 60. Flap 70 is suitably hinged to fixed airfoil 61, such as by a mechanical hinge 72 or other suitable hinge configuration to permit hinged movement of flap 70 between a first position 110 and a second position 160 while maintaining connection of flap 70 with fixed airfoil 61. Alternatively, flap 70 may be attached by a living hinge (or a plurality of living hinges) in which a continuous piece of material formed integrally with flap 70 and fixed airfoil 61 defines the hinge. In other embodiments, flap 70 may be attached to fixed airfoil 61 by any means that permits flap 70 to operate as described herein.
Flap 70 is biased toward first position 110. In the exemplary embodiment, a torsional spring 74 is coupled between fixed airfoil 61 and flap 70 to bias flap 70 to first position 110 about hinge 72. Optionally, flap 70 may have a counterweight 76 coupled to a portion of flap 70 to facilitate biasing flap 70 toward first position 110, the position of counterweight 76 being adjustable to change an amount of bias applied to flap 70. Alternatively, flap 70 may be biased toward first position 110 using any suitable bias component that permits flap 70 to operate described herein.
A first position 110 of blade 60 is indicated by the solid lines of
In operation, centrifugal forces generated by the rotation of fan impeller 10 causes flap 70 to rotate about hinge 72 toward second position 160. Alternatively, flap 70 may be actively controlled, e.g., flap 70 may be rotated by an electric motor or other active control mechanism. In the exemplary embodiment, flap 70 rotates about hinge 72 until fan impeller 10 has reached a maximum operating speed, at which point flap 70 has reached second position 160 indicated by the dashed lines of
An exemplary method of assembly fan impeller of
The apparatus and methods described herein provide a centrifugal fan impeller with variable shape fan blades that are configured to change shape to facilitate increasing the efficiency of a centrifugal fan. Moreover, the benefits derived from the unique fan blades include expanding the fan's performance curve, reducing noise, reducing blade stall, and maintaining a uniform volume of air flow at different fan speeds. In addition, the exemplary variable shape fan blade of the impeller is self-cleaning and facilitates improving dynamic balancing of the fan. The exemplary embodiments described herein provide apparatus and methods particularly well-suited for residential HVAC systems.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
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