EP1669610A1

EP1669610A1 - Axial fan

Info

Publication number: EP1669610A1
Application number: EP04106529A
Authority: EP
Inventors: Tolga Dogan
Original assignee: Faz Elektrik Motor Makina Sanayi ve Ticaret AS
Current assignee: Faz Elektrik Motor Makina Sanayi ve Ticaret AS
Priority date: 2004-12-13
Filing date: 2004-12-13
Publication date: 2006-06-14

Abstract

The present invention relates to a multiple sweep axial fan for producing axial gas flow in the direction of center of rotation. The term multiple sweep indicates a number of different sections along the leading edge and trailing edge of blades of the fan. The fan can be designed as a back skewed or front skewed low noise fan. Each blade of the fan has starting at its first end secured on the hub, a first section in which the leading edge of the blade is defined by a concave arc and at least one other section along which the leading edge is defined by a convex arc between the first section and the second end of said blade.

Description

Technical Field of Invention

The present invention relates to a multiple sweep fan for producing gas flow in the direction of center of rotation. The term multiple sweep indicates a number of different sections along the leading edge and optionally the trailing edge of blades of the fan.
The fan is particularly designed as a back skewed or front skewed low noise axial fan.

Background of the Invention

Conventional fans in the technical field have a number of blades secured at a hub which is generally driven by a rotating shaft. In addition, an outer ring surrounding the blades is secured to the outer ends of the blades to provide enhanced mechanical support, stability and for a number of other reasons. While some of the fans have flat surfaces with negligible thicknesses, many have airfoil sections having variable chord length and angle of attack along the radii. More recently, leading edges and tailing edges of the blades are not made straight but they are given curved geometries for practical reasons, such as reducing noise level or enhancing the fan performance. Though straight edged blades were used to be fairly good for ventilation purposes, they imposed the disadvantage of high noise levels during operation as their blades cut the air along their whole longitudinal portion at once. Significant noise produced by these fans led the designers to develop alternate fans that operate rather quietly in order to enhance comfort, especially in the automotive and HVAC technology. Obviously, changes made to reduce noise were accompanied by disadvantages, mainly in the performance of the fans.

Objectives of the Invention

An object of the present invention is to provide a backward or forward skewed low noise fan having enhanced flow rates.
Another object of the present invention is to provide and axial fan having reduced operational costs.
Yet another object of the present invention is to provide a fan which would require less motor power for outputting the same amount of physical flow and thereby to reduce the size, weight and cost of the electric motor used in especially in an HVAC system.
It is therefore a principal aspect of this invention to provide a fan suitable for both moderate noise operation and efficiency compared to fans of similar size and function in the prior art.

Summary

The present invention accomplishes above mentioned objects and provides a low noise axial fan having improved performance properties through use of novel design multiple sweep blades in the fans.
Each blade of a fan proposed by the present invention is divided into multiple sections along its leading and optionally trailing edges. The leading edge on the first section which is closest to the hub of a blade is defined by a concave arc while the leading edges on the second and the subsequent sections are defined by convex arcs. Though not essential, the trailing edge on the first section of a blade is defined by a concave arc while the trailing edges on the other sections are defined by convex arcs. The radius and the center of these arcs determine the performance parameters of multiple sweep fans.
Apparently, the center of the arc which forms the leading edge of the blade stands in the upstream locations for the first section which is closest to the hub, whereas the center of the arc which forms the leading edge of the blade stands in the downstream locations for the second and each subsequent sections, if there is any.
The leading edge of a blade resembles the leading edge of an eagle wing in the attack position. Upper projection of an eagle wing shows a concave arc on the proximity of the eagle's body and a sharp convex arc between the second end of the concave arc and the wing tip.

Brief Description of Figures

Further characteristics and advantages of the present invention will better emerge from the detailed description which follows, made with reference to the accompanying drawings which represent a preferred but non-limiting triple sectioned embodiment of the present invention in which;

Fig. 1 shows an upper view of a hub and a blade on a quadratic plane with the angular locations of the centers of arcs at each of the three sweep sections is marked.
Fig. 2 is an upper view of an hub and a blade showing the sweep sections s1, s2, s3 on the leading edge of the blade.
Fig. 3-a is an upper plane view of the preferred embodiment of an axial fan proposed by the present invention.
Fig. 3-b shows the side plane view of the fan shown in Fig. 3-a.
Fig. 4 shows a 3-D illustration of a blade according to the present invention.
Fig. 5-a is a 2-D upper plane view of a blade showing the inner radius (Ri) defined by the hub and the outer radius (Ra) defined by the outer stiffening ring.
Fig. 5-b shows the front projectional view of the blade shown in Fig. 5-a with the illustration of change in the angle of a line drawn between the innermost and outermost points on the trailing edge of a blade.
Fig. 5-c shows the side projectional view of the blade shown in Fig. 5-a with the illustration of change in the angle of a line drawn between the innermost and outermost points on the leading edge of a blade.
Fig. 6-a shows an upper view of a hub and a blade with a number of circular markings (1-2-3-4-5) in the transversal direction of the blades.
Fig. 6-b illustrates the angle of attack and chord length of a blade at each station defined by circular markings of Fig. 6-a.
Fig. 7 is a 3-D illustration of an hub, a blade attached to the hub and the stations on the blade.

Detailed Description of the Invention

Referring now back to the drawings, the axial flow fan (10) according to the present invention comprises a set of blades (11) placed at symmetric angular locations around a central hub (20). The blades (11) are conventionally secured at their root end (21) to the hub which is generally driven by a rotating shaft or which comprises a motor located within a part of said hub (20). The leading edge of a blade is neither defined by a straight line nor by one or more circular arcs of the same type as typically encountered in classical back or forward skewed fans. Instead, the leading edge of a blade is typically divided in a number of sections (s1, s2, s3....S_n).
The preferred embodiment shown in the figures have triple sweep (n=3) blades, i.e. the leading edge of each blade on the fans is divided into three sweep sections (s1, s2, s3). The first section s1 is defined in the form of a concave arc whereas the second the third sweep sections (s2, s3) are defined in the form of convex arcs. The outer ends (22) of the blades (11) in the preferred embodiment are secured in a conventional manner by means of an outer stiffening ring (26).
The blades (11) according to the present invention have varying pitch with respect to the rotation plane of the fan (10). While the preferred embodiment of the present invention has a constant variation pitch, the pitch of a blade may decrease in constant or variable ratios from the hub (20) to the outer ring (26) as a function of the radius. Similarly, the chord length (t) of a blade changes as a function of the radial distance from the hub. The outer ends (22) of the blades (11) are secured to a ring (13) continuously along their full transversal dimension.
The leading edge of a blade according to the present invention forms a concave arc on its first sweep section starting immediately around the perimeter of the hub and extending in the radial direction. The center of this concave arc defining the first weep sections s1 is marked as C1 located at a point of (R1, ⊝1) in the angular coordinates as shown in Fig. 1. The leading edge forms a convex arc on the second sweep section which starts immediately at the end of the first sweep section s1 and extends in the radial direction. The center of this convex arc of the second sweep section is marked as C2 which is defined at a point of (R2, 02) as shown in Fig. 1. The example shown in the figures have a third sweep section which having a center marked as (R3, 03) in the same figure 1 and ending at the outer stiffening ring (26). It is an essential part of the present invention that center point of an arc forming the leading edge of at least one section is located in the lower part of the quadratic plane while center point of another arc forming the leading edge of at least one other section is located in the upper part of the quadratic plane when the center of the transversal dimension at the root of a blade is located on the x-axis.
The blades (11) have maximum pitch (β) at their root ends at which they are fixed to the hub (20). Apart from that, the leading edges of the blades increasingly protrude towards front at the inner parts whereas the trailing edges of the blades protrude towards rear as shown in Fig 3-b. The distance k1 on the front of the fan and the distance (k-k1-k2) on the rear of the fan denote the maximum protrusion amounts marked in the vicinity of the hub respectively on the leading edges and on the trailing edges. Angular deflections shown in Fig 5-b and 5-c help to understand the slight protrusions which become more apparent towards the inner parts of the fan.
The projection k1 of Fig. 3-b will be apparent upon examination of α₁ and α₂ of Fig. 5-c and 5-b respectively. These angular deflections are found to accord the eagle wing like shape of the blades on the x-y plane and correspond to a higher elevation in the inner parts of a wing. It is also found that these help to maintain a uniform flow in the downstream area, which is of utmost importance in HVAC systems. The leading edges of the blades, when looked at the side view Fig. 3-b of the fan (10), do not form a flat plane and protrude (k1) towards the upstream area more in the central regions so as to form an elliptic spheroid on their front. Likewise, the trailing edges also protrude (k-k1-k2) towards the downstream area.
Fig. 6-a shows five equally spaced stations between Da and Di to illustrate the variation in the chord length and twist angle (attack angle) of a blade. Fig. 6-b. shows that the twist angle (β) with respect to the plane of rotation decreases along the radial direction. Those skilled in the art can easily appreciate that the chord length (t) and twist angle (β) are very important two parameters determining the performance characteristics of an axial fan. Since the principle underlying the present invention relates to performance enhancement through use of different sections defined by the circular characteristics of the leading edges and optionally the trailing edges of blades of a fan, no more explanation with regard to the transversal dimension or the twist angle will be given here.
The projection of leading edge of a blade on a two dimensional plane according to the present invention was calculated by a combined exponential and logarithmic function in the following form ; $F (y) = A + B \frac{1}{x^{3}} + C \frac{1}{x} + D x^{7} + E Ln (x) {r i < x < r a}$
In which F(y) is the function which defines the leading edge of a blade, x is the coordinate in the horizontal plane, r_i is the radius of the hub, r_a is radius of the stiffening ring (26) and A, B, C, D, E are constant coefficients.
The hub (20), blades (11) and ring (26) according to the present invention are preferably made out of a single, integral unit molded from a plastic material.

Claims

An axial flow (10) fan for producing gas flow along the axis of rotation of the fan comprising a number of blades (11) and a hub (20) to which the blades (11) are secured characterized in that each blade has, starting at its first end secured on the hub (20), a first section (s₁) in which the leading edge (12) of the blade (11) is defined by a concave arc and at least one other section (s₂,... s_n) along which the leading edge (12) is defined by a convex arc between the first section and the second end of the blade.
An axial flow fan according to Claim 1 wherein the second ends of the blades are secured to a stiffening ring (26).
An axial flow fan according to Claim 1 wherein the fan (10) has three sections (s₁, s₂, s₃) in which the center (C1) of the arc which forms the leading edge of the first section (s₁) is located in the upstream part whereas the centers (C2, C3) of the arcs which form the leading edge of the second and third sections (s₂, s₃) are located in the downstream part.
An axial flow fan according to Claim 1 wherein the leading edges (12) of the blades (11), when looked at the side view of the fan (10), do not form a flat plane and protrude (k1) towards the upstream area more in the central regions so as to form a semi-elliptic spheroid up their front.
An axial flow fan according to Claim 1 wherein the trailing edge of a blade (11) have at least one section which is defined by an arc whose center is located in the upstream part and at least one other section which is defined by an arc whose center is located in the downstream part.