US20090155076A1

US20090155076A1 - Shrouded Dual-Swept Fan Impeller

Info

Publication number: US20090155076A1
Application number: US11/959,012
Authority: US
Inventors: Yousef Jarrah
Original assignee: Minebea Co Ltd
Current assignee: Minebea Co Ltd
Priority date: 2007-12-18
Filing date: 2007-12-18
Publication date: 2009-06-18

Abstract

A fan impeller includes rotating ring attached to the tip of dual-swept fan blades. Besides shrouding the impeller; the blades are dual-swept forward, and sweep increases in magnitude towards the tip. The shrouded dual-swept impeller resides inside classical fan housing. The integrated effects of shrouding the impeller, forward sweep into the direction of incoming flow, and forward sweep into the direction of rotation (circumferential forward sweep) render the fan quiet; the magnitude of noise reduction is between 7 and 12 dB.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to fans and in particular to impeller designs.
Axial fans comprise an impeller driven by a rotating force. Typically, the rotating force is a motor embedded in the hub of the impeller. Impeller designs abound with various design features to reduce noise and/or increase efficiency.
For example, one such design focuses on the shape of the blade. More specifically, the blade tip is swept to reduce noise. “Sweep” refers to the displacement of the centers of mass of successive airfoils of the blade. Many designs sweep only the tip forward (i.e., in the direction of incoming flow) to reduce noise by few (2 to 4) dB. A less tried approach is a circumferential sweep which claims to reduce noise by few dB. U.S. Pat. No. 5,064,345 teaches an example of a blade tip sweep design.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an impeller design that integrates three mechanisms into a single impeller design, namely a rotating tip shroud, forward blade sweep, and forward circumferential blade sweep. Also in accordance with the invention, the sweep is gradual as we move from the blade hub-section to the blade tip-section.
The term “shrouded” impeller is used to describe the rotating ring that covers or cloaks the fan blades. The term “dual-swept” is used because blades of the present invention are swept into two different directions: one along the axis of rotation, the other along the circumferential direction. The shrouded and dual-swept impeller can be housed inside a classical stationary housing.
The present invention integrates three elements to significantly reduce fan noise: (1) the use of a shroud; (2) the provision of forward axial sweep in the fan blades; and (3) the further provision of forward circumferential sweep in the fan blades.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows three views (top, perspective bottom, and profile) of a component of a fan in accordance with the present invention.

FIGS. 2A-2C illustrate axial details of a fan blade according to the present invention.

FIGS. 3A and 3B illustrate circumferential details of a fan blade according to the present invention.

FIG. 4 is a top view of the fan blades of an impeller according to the present invention.

FIG. 5 shows an illustrative embodiment of a fan according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a top view of the present invention as embodied in an axial fan impeller 100. FIG. 1 also shows a bottom perspective view of the fan impeller 100. The impeller 100 includes a hub 106 to which a set of blades 104 are attached. Each blade 104 is attached to the hub 106 at its blade root 104 a (or simply root) and terminates at its blade tip 104 b (or simply tip). A tip ring 102 (impeller shroud, or simply shroud) can be attached to tips 104 b of the blades 104.
The particular embodiment of the present invention provides for a space 106 a in the hub 106. The space 106 a can be used to contain a motor for driving the impeller. Referring to FIGS. 1 and 5, an illustrative example of a fan unit 500 embodied in accordance with the present invention is shown. The fan unit 500 comprises a motor 502 connected to the impeller 100. A cutaway view of hub 106 shows the motor 502 housed within hub. The motor 502 is encased in a suitable housing 522. The motor is shown mounted to a suitable base 524. Drive electronics for operating the motor 502 can be provided on the base 524, and connected with appropriate wiring.
In the particular embodiment shown, the motor 502 is a brushless DC (direct current) motor. The motor 502 includes stator windings 512 which can be affixed to the housing 522. The motor 502 further includes a permanent magnet rotor 514 comprising a shaft 516 and annular permanent magnet(s) 518. The rotor 514 is rotatably supported by shaft 516 on a portion of the housing 522 for rotation about the shaft.
Operation of the fan unit 500 results in an inflow of air toward the inlet face of the impeller 100 and a corresponding outflow of air (not illustrated) exiting the outlet face of the impeller. The direction of rotation is indicated in the figures. This direction of flow of air from the inlet face toward the outlet face is referred to as the downstream direction. The upstream direction is the opposite direction, namely the direction from the outlet face of the impeller 100 toward the inlet face of the impeller.
The fan unit 500 can be incorporated in a conventional stationary fan housing consisting of sidewalls 524′ (shown in phantom lines) mounted to the base 524. Common examples are PC fans comprising a housing within which is a fan unit.
FIGS. 2A-2C illustrate features of the present invention. The figures show a side view of a portion of the impeller 100 illustrated in FIG. 1. The hub 106 is shown with one fan blade 104. The axis of rotation 202 is shown for reference. Other points of reference include the direction of the incoming air during operation of the fan 500 as the impeller 100 is rotated in the direction shown about axis 202 by motor 502. The direction of the incoming airflow is referred to as the downstream direction, while the direction against the incoming airflow is referred to as the upstream direction.
FIG. 2B identifies representative airfoils 214 a-d of the blade 104. An airfoil is the shape of a wing or blade (of a propeller, rotor or turbine) as seen in cross-section. In practice, a blade is described in terms of its airfoils (also referred to as blade sections). Depending on the size of the blade and the desired resolution, a blade can be defined by a few as five airfoils to hundreds of airfoils. For the sake of clarity, the figures illustrate only four such airfoils including the airfoil at the blade tip 104 b. As is conventionally known, a center of mass is associated with each airfoil 214 a-d. In FIG. 2A, the centers of mass associated with the airfoils 214 a-d are shown projected onto an axial plane (explained below) and are represented as heavy dots 212.
As can be seen in FIGS. 2A-2C, a blade 104 in accordance with the present invention is characterized by a forward axial sweep, namely a sweep along the direction of the axis (axial direction) and in the upstream direction. Stated differently, the present invention teaches blades 104 having a sweep in the axial direction and heading into the incoming flow of air when the blades are rotated. The sweep is “axial” in the sense that the direction of the sweep is along the axis of rotation 202. The sweep is “forward” in the sense that the direction of the sweep is in the upstream direction. FIG. 2B identifies the leading edge (LE) and trailing edge (TE) of blade 104. Thus, a blade 104 of according to the present invention has an axial sweep toward the leading edge of the blade.
FIG. 2B further illustrates a blade dimension referred to as the blade section axial length (axial blade length) which measures the length of an airfoil in the axial direction. Two representative axial blade lengths B₁and B₂are shown in the figure. In accordance with the present invention, the blade section axial length increases with each successive airfoil 214 a-d progressing in the direction from the root 104 a toward the tip 104 b. Thus, the blade section axial length of airfoil 214 b is B₁, which is shorter than the blade section axial length B₂of airfoil 214 d at the blade tip 104 b. Forward axial sweep can be produced by increasing the blade section axial length gradually from the hub 106 to the tip 104 b and ending the trailing edges of all sections (airfoils) at the same axial location.
An “axial plane” can be defined by an axis (call it the Z-axis) parallel to the axis of rotation 202 serving as one axis of the plane and by an axis (call it the R-axis for the radial direction) that is perpendicular to the axis of rotation. Referring to FIG. 2C, the centers of mass 212 are shown projected onto the axial plane defined by the Z-axis and the R-axis. A forward axially swept blade 104 in accordance with the present invention can be defined by the locus of centers of mass 212 of the constituent airfoils 214 a-d projected on the axial plane. More specifically, for each airfoil 214 a-d of blade 104 along the R-axis and in the direction from the root 104 a toward the tip 104 b, the location of its center of mass 212 on the axial plane (Z-R plane) is forward (along the Z-axis) of the center of mass of the previous airfoil in the upstream direction.
Consider, for example, the innermost airfoil 214 a (blade section) illustrated in FIG. 2C. The distance on the axial plane of its associated center of mass 212 from the R-axis is d₁, in the upstream direction. Likewise, the center of mass 212 of the next airfoil 214 b has a distance d₂(d₂>d₁) from the R-axis. Thus on axial plane, the center of mass 212 of airfoil 214 b is axially forward (in the upstream direction) of the center of mass of the previous airfoil, namely airfoil 214 a. Likewise, the airfoil 214 c has a center of mass 212 having a distance d₃(d₃>d₂>d₁) which is forward of the center of masses of airfoils 214 a and 214 b in the upstream direction. Finally, the airfoil 214 d at the tip 104 b has its center of mass 212 at d₄(d₄>d₃>d₂>d₁) which is forward of the center of masses of airfoils 214 a-c in the upstream direction.
In the particular embodiment of the blade 104 shown in FIG. 2C, the locus of centers of mass 212 of airfoils 214 a-d defines a straight line, referred to herein as an “axial line” 216. It is noted that axial line 216 need not be straight and can be arcuate. An example of a line having an arcuate characteristic is shown in FIG. 3B, identified by the reference numeral 316. Thus, in accordance with the present invention, the locus of centers of mass 212 in the axial plane can define an arcuate axial line.
FIGS. 3A and 3B illustrate a further aspect of the present invention. These figures show a top view of the partial impeller 100 shown in FIGS. 2A-2C. An arrow indicates the direction of rotation of the impeller 100 in an operating fan (e.g., fan 500). In this case, the rotation is a counterclockwise rotation. Of course, it is understood that the blades can be designed for clockwise rotation. FIG. 3A shows the representative airfoils 214 a-d illustrated in FIG. 2B. Each airfoil 214 a-d is also shown with its corresponding center of mass 212 shown projected on the “radial plane” (explained below).
FIGS. 3A and 3B show that a blade 104 in accordance with the present invention is further characterized by having a forward circumferential sweep, in addition to the forward axial sweep described above. The sweep is “circumferential” in the sense that the sweep of the blade 104 is in the plane of rotation of the impeller 100 during operation. The sweep is “forward” in the sense that the sweep of the blade is in the direction of rotation of the impeller 100 during operation, which for the embodiment shown in the illustrations is a counterclockwise direction.
Referring to FIG. 3B, a “radial plane” can be defined by two axes that are both perpendicular to the Z-axis. One axis of the radial plane is a line tangent to the rotation of the impeller 100 (call it the θ-axis). The other axis of the radial plane is the R-axis described above and is perpendicular to both the θ-axis and the Z-axis.
FIG. 3A shows the centers of mass 212 projected onto the radial plane. As can be seen in FIG. 3B, a blade 104 according to the present invention is further defined by the locus of centers of mass 212 of the representative airfoils 214 a-d projected on the radial plane. More particularly, for each airfoil 214 a-d of blade 104 along the R-axis and in the direction from the root 104 a toward the tip 104 b, the location of its center of mass 212 in the radial plane (R-θ plane) is forward (along the θ-axis) of the center of mass of the previous airfoil in the direction of rotation of the impeller 100.
Consider for example, the locus of centers of mass 212 shown in FIG. 3B. The center of mass associated with airfoil 214 a has a measurement e₁on the radial plane that represents its distance from the R-axis along the θ-axis. Moving away from the root, the next airfoil 214 b has a center of mass that measures c₂(c₂>c₁) from the R-axis in the radial plane. As can be seen, the center of mass of airfoil 214 b is circumferentially forward (in the direction of rotation) of the center of mass of previous airfoil, namely airfoil 214 a. Likewise, the next airfoil 214 c has a center of mass that measures e₃(e₃>e₂>e₁) from the R-axis in the radial plane. The center of mass of airfoil 214 c is circumferentially forward of the centers of mass of previous airfoils, namely airfoils 214 a and 214 b. Finally, the airfoil 214 d has a center of mass that measures c₄(c₄>c₃>c₂>c₁) from the R-axis in the radial plane. The center of mass of airfoil 214 d is circumferentially forward of the centers of mass of previous airfoils, namely airfoils 214 a-c.
In the particular embodiment of the blade 104 shown in FIG. 3B, the locus of centers of mass 212 of airfoils 214 a-d defines an arcuate line, referred to herein as a “radial line” 316. It is noted that radial line 316 need not be arcuate and, in fact, can be substantially straight. An example of a straight line is shown in FIG. 2C discussed above. Thus, in accordance with the present invention, the locus of centers of mass 212 as projected on the radial plane can define a straight radial line or an arcuate radial line.
FIG. 4 shows a top view of the impeller 100 to illustrate a blade dimension referred to as the radial blade length. An outer circumference 402 of impeller 100 is delineated by the tips of blades 104. A radial measurement Rh represents the radius of the hub 106 from its center 202 to its outer wall 106 b (FIG. 1) where the blade roots attach. A radial measurement R_trepresents the radius of the impeller as measured from the center of the hub 106 to the blade tips. The radial length of the blade is (R_t-R_h).
Thus, an impeller in accordance with the present invention comprises blades 104 each characterized in having both a forward axial sweep and a forward circumferential sweep. Blades according to the present invention each is characterized by representative airfoils 214 a-d, each airfoil having an associated center of mass 212. For each successive airfoil 214 a-d of a blade along its length from the hub 106 toward the outer circumference 402, the airfoil's associated center of mass is axially forward and circumferentially forward of the center of mass associated with previous airfoils.
Referring back to FIG. 1, an impeller according to the present invention further includes the shroud 102. The shroud 102 in combination the blade forward-sweep and blade circumferential sweep (“dual swept”) into the direction of rotation results in significant noise reduction. Testing has shown that relative to conventional un-shrouded, un-swept fan blades the shrouded and dual-swept blades of the present invention reduce fan noise by 7 to 12 dB.
The embodiment shown in FIG. 3B shows that the forward circumferential sweep of the blade 104 becomes stronger as we move from the hub 106 to the tip 104 b. As can be seen in the figure, there is greater forward curvature in region B as compared to region A.

Claims

1. A fan comprising an impeller and a motor connected to the impeller to spin the impeller thereby creating an airflow, wherein the impeller comprises:

a hub;

a plurality of blades attached to and disposed about the hub; and

a tip ring attached to one or more tips of the plurality of blades,

wherein for each blade, respective centers of mass of successive blade sections from the hub toward the tip thereof are (1) located upstream of the airflow along an axial direction with respect to centers of mass of previous blade sections and (2) located forward in the direction of rotation of the impeller with respect to the centers of mass of the previous blade sections.

2. The fan of claim 1 wherein the blades are further characterized in having a forward axial sweep.

3. The fan of claim 1 wherein the blades are further characterized in having a forward circumferential sweep.

4. The fan of claim 1 wherein the blades are further characterized in having both a forward axial sweep and a forward circumferential sweep.

5. The fan of claim 4 wherein the forward axial sweep occurs along substantially the full length of each blade, where the forward circumferential sweep occurs along substantially the full length of each blade.

6. The fan of claim 1 wherein the distribution of the centers of mass of the blade sections define a straight line in a plane containing the axis of rotation of the impeller.

7. A method of operating a fan comprising:

providing a plurality of dual-swept fan blades disposed about a hub;

attaching a tip ring at tips of the dual-swept fan blades;

providing a motor having a rotor connected to the hub; and

providing a base to which the motor can be anchored,

wherein at least some of the dual-swept fan blade each is characterized in having a first sweep in an upstream direction along an axis of rotation,

wherein said at least some of the dual-swept fan blade each is further characterized in having a second sweep in a direction of rotation of the hub.

8. The method of claim 7 wherein the first sweep occurs along the length of the fan blade.

9. The method of claim 7 wherein the second sweep occurs along the length of the fan blade.

10. A fan comprising:

a hub; and

a plurality of fan blades attached to the hub at respective roots thereof, the fan blades creating an incoming flow of air when the fan blades are rotated,

each of the fan blades having a first sweep in the direction of rotation of the fan blades,

each of the fan blades further having a second sweep along an axis of rotation in a direction opposite the direction of the incoming flow of air.

11. The fan of claim 10 further comprising a tip ring disposed about an outer circumference circling the fan blades.

12. The fan of claim 10 wherein the locus of centers of mass of representative airfoils of each fan blade defines a first line projected onto a first plane and a second line projected onto a second plane, wherein the first line and the second line each is either a substantially straight line or an arcuate line.

13. The fan of claim 10 wherein the first sweep and the second sweep each occurs along the length of at least one of the fan blades.

14. The fan of claim 10 wherein for each of the fan blades, its axial blade length increases in the direction from the blade root to the blade tip.

15. A fan comprising:

a hub; and

a plurality of fan blades attached to and disposed about the hub,

for at least some of the fan blades, centers of mass of successive blade sections between the blade root and the blade tip thereof being displaced forward of the center of mass of a previous blade section in the upstream direction,

wherein the centers of mass are further displaced in the direction of rotation relative to the center of mass of a previous blade section.

16. The fan of claim 15 further comprising a tip ring disposed about an outer circumference circling the fan blades.

17. The fan of claim 15 wherein the center of mass of successive blade sections are displaced forward of the center of mass of a previous blade section in the upstream direction and along the length of said at least some of the fan blades.

18. The fan of claim 15 wherein the center of mass of the successive blade sections are displaced in the direction of rotation relative to the center of mass of a previous blade section and along the length of said at least some of the fan blades.

19. An impeller for a fan comprising:

a hub; and

a plurality of blades disposed about the hub,

wherein at least some of the blades each has a center of mass position that advances in the direction of rotation of the blades and in the upstream direction with successive airfoil sections between a root of said each blade to a tip of said each blade.

20. The impeller of claim 19 further comprising a tip ring disposed about an outer circumference of the impeller.

21. The impeller of claim 19 wherein the blades have a axial sweep in the upstream direction and a circumferential sweep in the direction of rotation of the blades.

22. The impeller of claim 19 wherein the center of mass position advances in the direction of rotation along either a substantially straight line or along an arcuate line as projected on a radial plane.

23. The impeller of claim 19 wherein the center of mass position advances in the upstream direction along either a substantially straight line or along an arcuate line as projected on an axial plane.