GB2077855A - Reversible Pitch Bladed Rotor - Google Patents

Abstract

An axial flow fan has means, such as hydraulic actuator 14, for pivoting the fan blades 4 during fan operation from one setting giving airflow in one direction to a second setting giving air flow in the reverse direction. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Axial Flow Fluid Machines especially Fans The present invention relates to axial flow fluid machines, especially axial fans, and is particularly concerned with the provision of reverse fluid flows in a fluid flow system.

Axial flow fans find extensive application in ventilation systems, such as for example in mines, and in these systems the axial fan directs ventilating air through ducting to selected discharge locations. In some ventilating systems, particularly in mines, it is a requirement that a reverse air flow can be created in the ducting, such as for example when an outbreak of fire occurs, and it is frequently an additional requirement that the change in air flow direction is achieved promptly. One known arrangement for creating this charge involved the use of diverter flaps in the ducting but this had the disadvantage of being cumbersome (and costly), since the ducting can be of substantial cross-section.An alternative arrangement, involves reverse rotation of the fan but some disadvantages of this arrangement are the delay in effecting reverse fan operation, of obtaining adequate reverse flow and additional costly equipment will be necessary. It is an object of the present invention to obviate or mitigate these disadvantages.

According to the present invention a fluid flow machine for use in a fluid ducting system comprises a rotor adapted for connection to a drive, an annular series of axial vanes pivotally mounted on the rotor, and means for pivoting the vanes whereby the vanes can be moved during rotation of the rotor from a first setting creating a fluid flow in one direction to a second setting creating a fluid flow in a reverse direction.

Thus at the first vane setting the vanes can have a positive blade pitch angle or blade root setting (as hereinafter defined) for normal fluid flow, a 600 blade root setting would be suitable, while at the second vane setting a negative blade pitch angle would be present for reverse flow.

Preferably for the second setting, a blade root setting of up to 400 is employed and preferably not greater than --200 a preferred value being approximately --100. It may be desired however to pivot the vanes through a much greater angle e.g. up to 1 600 blade root setting for the second vane setting position.

Pivoting of the vanes can be achieved by means of a suitable lever mechanism-a preferred mechanism utilises a fluid piston cylinder and crank system.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig. 1 shows a schematic side view of a ventilating ducting including an axial flow fan; Fig. 2 shows a sectional side view of the fan of Fig. 1 to a larger scale; Fig. 3 shows a plan view of the fan blading for various blade settings; Fig. 4 shows a blade set for normal air flow; Fig. 5 shows the blade pivoted to a second .position for reverse air flow.

Fig. 6 shows the blade pivoted to yet a further position for reverse air flow.

Referring to-the drawings, a ventilating system, for example for a mine, includes a ducting 1 housing an axial fan 2 which is driven by a motor (not shown) located in central housing 3. The fan 2 has an annular series of axial blades or vanes 4 mounted on rotor 5, and the discharge from vanes 4 is guided by stationary guide vanes 6 serving to support housing 3. 7 is the front hub, the vanes 4 are pivotally mounted in bearings 9 (see Fig. 2) and have lower cranks 10 carrying thrust blocks 11 located between annular cheek plates 12 of regulating disc 13. The disc 13 is secured to the cylinder of a hydraulic piston/cylinder actuator 14 controlled by sleeve valve 1 4A, positioned in hub 7. Operation of the actuator 14 causes axial movement of disc 13 and hence pivoting of vanes 4.

Fig. 4 shows a vanes 4 set for normal air flow in direction of arrow A: as can be seen the vane has a positive pitch angle (a 600 setting angle being shown). The blade root setting angle (or blade pitch angle) a is the angle subtended between the lines AB and AC in Fig. 3, wherein AC is a line parallel to the root chord line D-D and passing through blade pivoted axis, and AB is the line projection of AC on the plane containing blade pivotal axis and normal to the axis of rotation of the rotor.

To reverse air flow in arrow direction B, the vanes 4 are rotated negatively in direction RN to the setting shown in Fig. 5: the negative root setting can be up to 400 but a value in range -100 to --200 may be preferred. At the 100 setting a reverse flow of approximately 65% forward can be achieved for the same rotor speed.

Reverse flow can also be achieved by positive vane rotation in direction RP to a blade root setting of approximately 1600 as shown in Fig. 6.

This will give equal flow rate in reverse as that of a 550 set blade (with a pressure value reduced to 80%). However performance at some angle ranges in the increased positive blade settings up to 1 600 can be unstable and/or unsatisfactory.

The arrangement also enable variation in the blade setting for normal flow discharge (arrow A), and the catering for a negative setting of -100 (or even --200) does not require considerable additional displacement capability of the actuating mechanism so that a reverse flow characteristic can be included without great additional expense.

It is an advantageous feature of the arrangement that pivoting of the blades 4 can be effected during rotation of the rotor 5, and consequently change to the reverse flow mode can be achieved very promptly.

Modifications are of course possible. For example, it will be appreciated that the actuating mechanism could be of some other form than the piston-and-crank system described. It will be understood that for different blade forms (particularly twist), the preferred blade angle settings could be different from those detailed above.

Claims (9)

Claims

1. A fluid flow machine for use in a fluid ducting system comprising a rotor adapted for connection to a drive, an annular series of axial vanes pivotally mounted on the rotor, and means for pivoting the vanes whereby the vanes can be moved during rotation of the rotor from a first setting creating a fluid flow in one direction to a second setting creating a fluid flow in a reverse direction.

2. A machine as claimed in claim 1, wherein at the second setting the axial blades are set at a negative blade pitch angle up to 400.

3. A machine as claimed in claim 2, wherein the negative angle is not greater than 200.

4. A machine as claimed in claim 3, wherein the negative angle is approximately 100.

5. A machine as claimed in claim 1 , wherein the blades are pivoted positively to a blade pitch angle of up to 1 600 for said second setting.

6. A machine as claimed in any one of the preceding claims, wherein a lever mechanism is provided for pivoting of the blades between said settings.

7. A machine as claimed in claim 6, wherein the lever mechanism is actuated by a fluid operable piston/cylinder device.

8. A machine as claimed in claim 7, wherein the axial vanes have crank form root elements carried by an axially-movable annular member mechanically coupled to the piston/cylinder device.

9. A machine as claimed in claim 8, wherein the piston/cylinder device is co-axial with the rotor.

1 0. A fluid flow machine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.