GB2348671A

GB2348671A - Ramjet-driven axial flow fan

Info

Publication number: GB2348671A
Application number: GB9908092A
Authority: GB
Inventors: Frank Iles
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-04-10
Filing date: 1999-04-10
Publication date: 2000-10-11
Anticipated expiration: 2019-04-10
Also published as: GB9908092D0; GB2348671B

Abstract

An axial flow fan assembly comprises a fan matrix including radially-disposed blades terminating outwardly in a cylindrical wall and rotatably mounted in a support structure, two or more ramjets being mounted on the external surface of the wall and oriented to cause the thrust in use to rotate the fan matrix within the supporting structure. Preferably, the ramjets exhaust impinges on an annular series of vanes to increase the thrust and deflect the exhaust gases away from the air intakes of the ramjets.

Description

AXIAL FLOW FAN This invention relates to axial flow fans and in particular provides such a fan having improved efficiency.

The use of axial flow fans is known for both movable and stationary applications. Examples of movable applications include aircraft such as helicopters and hovercraft and examples of stationary applications include power generation plant and wind tunnels. Fans for both applications, however, rely on airflow created by rotation of the fan to perform a specified function.

The efficiency of an axial flow fan depends primarily on its effective surface area, that is, the area swept by the fan blades on rotation thereof and available for unimpeded flow of the resulting airstream. Since conventional axial flow fans are powered by motors which drive the axial shaft of the fan, a certain proportion of the swept area is occupied by the motor or other mechanical device such as a gearbox or other transmission means, which restricts a portion of the airstream and reduces the efficiency of the fan. It follows that, for a given required airflow, either the fan must be larger than would otherwise be necessary or the fan must be driven faster.

Prior proposals have been made for driving fans by mounting ramjets on the outer extremities of the blades thereof. However, such proposals have required the fan to be mounted in a tubular structure with a secondary fan at one end to draw combustion air therethrough.

It is an object of the present invention to provide an axial flow fan which avoids the disadvantages of prior proposals.

According to the invention, an axial flow fan comprises a fan matrix including radially-disposed blades terminating outwardly in a cylindrical wall and rotatably mounted in a support structure, two or more ramjets being mounted on the external surface of the wall and oriented to cause the thrust to rotate the fan matrix within the supporting structure.

The ramjets are disposed equi-angularly around the periphery of the fan matrix in such a way that the fan is balanced. For example, if two ramjets are utilised they are disposed diammetrically of the matrix and if four are utilised they are disposed at 90 increments around the periphery of the matrix.

The supporting structure in which the matrix is rotatably mounted preferably comprises a central housing enclosing a hub bearing for the fan matrix.

Radial struts may extend from the central housing above and/or below the fan blades and ramjets to an external annular cylinder so that the fan matrix, together with the ramjets, is rotatable within the cylinder.

Preferably, an annular series of angled vanes, of the type used as stationary vanes in a turbine, is disposed within and attached to the cylinder, slightly below the ramjets, and the ramjets are angled about a lateral axis so that the exhaust impinges upon the vanes, thereby enhancing the forward thrust exerted by the ramjets. It is also preferred that the ramjets are mounted within housings which define at one end an intake for combustion air and at the other end an exhaust duct. The mouth of the air intake is preferably shaped and angled for optimum efficiency in collection of air, particularly in view of the fact that the flow of air through the fan will be substantially at a right angle to the plane of rotation of the fan and therefore to the direction of motion of the ramjets.

The fan blades may be of the variable pitch type and for this purpose may be pivotally mounted about longitudinal (that is, radial with respect to the fan matrix) support members extending between the central housing and cylindrical wall. Means for adjusting the pitch may be incorporated in the central housing and operated remotely via connection means located in a radial strut of the supporting structure. Similarly, fuel for the ramjets may be supplied from an external source via ducting in a radial strut to the central housing and thence via ducting in one or more of the fan blades to the ramjets, suitable seals being provided at junctions between moving and stationary parts.

Auxiliary starting means are provided for initially causing the fan matrix to rotate at a sufficiently high speed for the ramjets to begin operating. Thereafter, the rotation is self-sustaining provided that fuel is continually supplied. The shape of the ramjets'air intakes may be such as to increase the velocity of air into the combustion chamber, thereby reducing the minimum rotational speed of the matrix required for starting of the ramjets. For starting purposes, the fan blades are preferably feathered to minimise their drag.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 is a plan view of a fan according to the invention, Figure 2 is a cross section along the line A-A of Figure 1, Figure 3 is a cross section along the line B-B of Figure 1: Figure 4 is a plan view of the supporting structure of the fan of Figure 1 ; Figure 5 is a cross section along the line C-C of Figure 4; and Figure 6 is a plan view of the fan matrix and ramjet housings of the fan of Figure 1.

Referring firstly to Figure 1, an axial-flow fan is shown generally at 10 and consists of a fan matrix including fan blades 11 the outer edges of which abut the inside wall of an annular cylindrical ring 12 (see also Figures 2 and 6). The fan blades 11 are of the variable pitch type and are pivotable about shafts 13 which extend between a central hub 14 and the ring 12.

Ramjets 15 (Figures 2 and 3) are mounted in housings 16 attached to the outside wall of the cylindrical ring 12; the housings define air intake scoops at their front ends 17, considered in relation to the direction of rotation of the fan, and exhaust ducts at their rear ends 18. The ramjets and housings are mounted at an angle so that their thrust is directed to have a rearward and a downward component, as illustrated in Figure 3.

The hub 14 of the fan matrix is rotatably carried by a shaft 19 journalled in bearings 20 located in a streamlined axial housing 21 from which extend radial upper 22 and lower 23 struts to an outer annular cylindrical wall 24. Fixed to the inside of the wall 24 are angled vanes 25 (see in particular Figures 4 and 5). The vanes are so arranged that the thrust from the ramjets impinges upon them.

One of the struts 22 carries a fuel line 26 which communicates via a seal 27 in the housing 21 with a passageway 28 formed in the hub 14 and radial lines 29 formed through the fan blades with the ramjets. The fuel, once fed to the hub, is urged to the ramjets by centrifugal force, once the fan matrix is revolving. A variable pitch control shaft 30 is carried within one of the struts 23 and controls a variable pitch mechanism 31. A starter motor 32 is contained within the housing 20. In use, the fan blades are feathered and the starter motor is caused to initiate rotation of the fan matrix.

When the matrix has attained a suitable peripheral speed, that is, when incoming air is compressed in the combustion chambers by the ram effect to a sufficient extent, the fuel is admitted to the combustion chambers and combustion takes place. The peripheral speed then increases further, the starter motor is disengaged and stopped, and the fan operation is self-sustaining. The fan blades may then be adjusted to the required pitch to create the necessary air flow.

Fans according to the invention may be incorporated into hovercraft, vertical and short take-off and landing aircraft, either in an air-foil section thereof such as a wing or into a fuselage.

Claims

CLAIMS I. An axial flow fan, said fan comprising : a fan matrix, said fan matrix comprising a plurality of radiaily disposed blade means, each of said blade means being connected at its root to a hub means, and at its tip to the inner surface of an annular wall means. At least two raz-jet means, said ram-jet means being mounted on the external surface of said annular wall means, and being equi-angu ! arly disposed around its periphery. An annular supporting structure means within which said fan matrix and ram-jet means assembly is rotatably mounted, said supporting structure means further comprising a plurality of stationary vane means, said vane means being so disposed as to present a surface to the efflux of each said ram-jet means.

Amendments to the claims have been filed as follows 1. An axial flow fan assembly comprising a fan matrix including radially-disposed blades terminating outwardly in a cylindrical wall and rotatably mounted in a support structure, two or more ramjets being mounted on the external surface of the wall and oriented to cause the thrust in use to rotate the fan matrix within the supporting structure.
2. A fan assembly according to claim 1, in which the supporting structure comprises a central housing enclosing a hub bearing for the fan matrix, radial struts extending from the central housing above and/or below the fan blades and ramjets to an external annular cylinder so that the fan matrix, together with the ramjets, is rotatable within the cylinder.
3. A fan assembly according to claim 1 or claim 2, in which an annular series of angled vanes is disposed below the ramjets, the ramjets being angled about a lateral axis so that the exhaust impinges upon the vanes.
4. A fan assembly according to any preceding claim, in which the ramjets are mounted within housings which define at one end an intake for combustion air and at the other end an exhaust duct.
5. A fan assembly according to any preceding claim, in which the fan blades have variable pitch
6. An aircraft including a fan assembly according to any of claims 1 to 5.
7. An aircraft according to claim 6, in which the aircraft is a vertical or short take-off and landing aircraft.
8. A fan assembly substantially as herein described with reference to and as illustrated in the accompanying drawings.