WO2002059484A1

WO2002059484A1 - Fan blade with accelerated twist angle

Info

Publication number: WO2002059484A1
Application number: PCT/NL2002/000061
Authority: WO
Inventors: Hendrik Fedde Van Der Spek
Original assignee: Ventilatoren Sirocco Howden B.V.
Priority date: 2001-01-25
Filing date: 2002-01-25
Publication date: 2002-08-01
Also published as: ITMI20010131A1; ITMI20010131A0

Abstract

The invention relates to fan blade having a substantially aerofoil shaped profile, comprising a first blade zone having a first continuous differentiated geometric angle of attack over the length of the first zone and a second blade zone, having a second continuous differentiated geometric angle of attack over the length of the second zone, which second blade is located near the tip of the fan blade, whereby the derivative of the differentiated geometric angle of attack of the first and second zone comprises a discontinuity at the transition of the first and the second zone.

Description

FAN BLADE WITH ACCELERATED TWIST ANGLE

The invention relates to axial fans for industrial applications, in particular to a fan blade having a substantially aerofoil shaped profile, comprising a first blade zone having a first continuous differentiated geometric angle of attack over the length of the first zone and a second blade zone, having a second continuous differentiated geometric angle of attack over the length of the second zone, which second blade is located near the tip of the fan blade. Axial fans are for example used to provide large quantities of air for cooling. Such axial fans are suspended above the ground and could have a diameter of up to 12 metres .

As the axial fan is suspended above the ground, the air will be sucked radially into the fan. This means that the air flow is not fully perpendicular to the fan blades. Also wind causes variations in the air flow direction relative to the fan blade .

This variation in air flow direction relative to the fan blades causes a non optimal functioning of the fan. It is known to use twisted fan blades to optimize the aerodynamic angle of attack of the fan blade. However, due to wind and to other particular conditions that can create turbulence at the outboard edge of the blade, twisting of the fan blade does not provide an optimal solution for the outboard edge zone of a fan blade. These conditions could cause such an air flow direction relative to the tip of the fan blade, that stall can occur in the outboard edge zone resulting in lower performance, lower efficiency of the fan blade and causing extra noise.

It is an object of the invention to provide a fan blade, which at least partially eliminates the above mentioned disadvantages .

This object is reached by a fan blade according to the invention, which is characterized in that the derivative of the differentiated geometric angle of attack of the first and second zone comprises a discontinuity at the transition of the first and the second zone.

By providing the second blade zone with a differentiated geometric angle of attack different from the differentiated geometric angle of attack of the first zone, this second blade zone will not come into a stall situation that easily. The influence of the wind or other factors causing turbulence at the blade tip will not have such a large effect on the stall. This will provide for a better performance, better efficiency and lower noise, as the stall moment is delayed. In a preferred embodiment of the fan blade according to the invention, the length of the first blade zone is larger than the length of the second blade zone.

According to another embodiment of the fan blade of the invention, the second blade zone has over its length a constant geometric angle of attack. This provides for a fan blade, which can be more easily manufactured.

According to again another embodiment of the fan blade according to the invention, the second blade zone has over the length of the zone a variable geometric angle of attack.

This variation could be up to 10^° per metre, preferably about 3° per metre. In another preferred embodiment of the fan blade according to the invention the second blade zone has a length up to 30%, preferably up to 15% of the length of the fan blade . Just this small part of the fan blade has to be altered in order to provide a better efficiency relative to conventional fan blades .

The difference between the geometric angle of attack of the outboard end of the first zone and of the outboard end of the second zone is between 4 ° and 12 ' , preferably about 6^° .

In a last preferred embodiment of the invention a plate is substantially perpendicular arranged to the length of the fan blade between the first blade zone and the second blade zone. First of all this plate directs the air in the transition from the first zone to the second zone, such that no, or at least less turbulence of the air occurs. Secondly, this plate provides an advantage when manufacturing such a fan blade. A fan blade could be manufactured for the first zone, the plate could be connected to the tip of this fan blade and subsequently a second fan blade part could be connected to the plate as second zone. The angle relative to the first zone and the second zone could be easily set.

These and other advantages of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows in perspective view an axial fan for an industrial application with fan blades according to the invention.

Figures 2A and 2B show a first embodiment of a fan blade according to the invention.

Figures 3A and 3B show a second embodiment of a fan blade according to the invention. Figure 1 shows an axial fan 1, which is suspended above the ground by a frame 2. The axial fan 1 comprises a hub 3 to which the fan blades 4 are connected. A bell 5 is arranged around the fan blades in order to direct the air L. The bell 5 is composed out of segments 6.

Figure 2A shows a side view of a fan blade 4 according to the invention.

Figure 2B shows a perspective view of the fan blade of figure 2A. The fan blade 4 has a first blade zone 6 and a second blade zone 1 , which are separated by guide plate 8. The first blade zone 6 has a geometric angle of attack 9 and the second blade zone 7 has a geometric angle of attack 10. Both geometric angles of attack are referenced from the plane of rotation 16. The difference between the first geometric angle of attack 9 and the second geometric angle of attack 10 is the angle . In this case the second geometric angle of attack 10 is smaller than the first angle of attack 9. The plate 8 provides a guide for the air flowing along the first and second zone 6, 7. If no plate 8 is used, the disruption between the first zone 6 and the second zone 7 will cause turbulence of the air, which affects the efficiency, the performance and the noise of the fan blade .

Figures 3A and 3B show a second embodiment of a fan blade 11 according to the invention. The fan blade 11 comprises a first blade zone 12 and a second blade zone 13. The first blade zone is in this embodiment straight while the second blade zone 13 is twisted. The first blade zone 12 has an constant angle of attack 14. The second blade zone 13 has an angle of attack, which varies from the constant angle of attack 14 to a smaller angle of attack that is represented by the angle of attack 15. The difference between the constant angle of attack 14 of the first blade zone 12 and the angle of attack 15 at the outboard end of the second blade zone 13 is the angle α.

Claims

1. Fan blade having a substantially aerofoil shaped profile, comprising a first blade zone having a first continuous differentiated geometric angle of attack over the length of the first zone and a second blade zone, having a second continuous differentiated geometric angle of attack over the length of the second zone, which second blade is located near the tip of the fan blade, characterized in that the derivative of the differentiated geometric angle of attack of the first and second zone comprises a discontinuity at the transition of the first and the second zone .

2. Fan blade according to claim 1, wherein the length of the first blade zone is larger than the length of the second blade zone.

3. Fan blade according to claim 1 or 2, wherein the second blade zone has over its length a constant geometric angle of attack.

4. Fan blade according to claim 1 or 2, wherein the second blade zone has over the length of the zone a variable geometric angle of attack.

5. Fan blade according to claim 4, wherein the variation is up to 10° per meter, preferably up to 3° per meter.

6. Fan blade according to any of the preceding claims, wherein the second blade zone has a length up to 30%, preferably up to 15% of the total length of the fan blade.

7. Fan blade according to any of the preceding claims, wherein the difference between the geometric angle of attack at the end of the first zone and the geometric angle of attack at the end of the second zone is between 4° and 12°, preferably about 6°.

8. Fan blade according to any of the preceding claims, wherein a plate is substantially perpendicular connected to the length of fan blade between the first blade zone and the second blade zone .