GB2186639A

GB2186639A - Improvements in or relating to bladed structures for fluid flow propulsion engines

Info

Publication number: GB2186639A
Application number: GB08604113A
Authority: GB
Inventors: Martin John Dobson
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1986-02-19
Filing date: 1986-02-19
Publication date: 1987-08-19
Also published as: GB2186639B; GB8604113D0

Abstract

In order to facilitate assembly and disassembly of blades from a disc without having to remove more than two members, the blades (18, Fig. 2) are made without platforms, the platforms 26 are separately formed and have tined roots 28a, 28b and 28c. The disc (20) has peripheral grooves 36 into which the tines 28a,28b and 28c can be inserted radially inwardly of the disc. The platforms 26 when their tines contact the bottoms of the peripheral grooves 36, are moved forwardly into dovetail grooves 32, for radial retention. A platform is located between each adjacent pair of blades which are located in dovetail grooves 22. Any known axial location means may be utilised. <IMAGE>

Description

SPECIFICATION Improvements in or relating to bladed structures for fluid flow propulsion engines This invention relates to bladed rotors for use in e.g. ducted fan gas turbine engine.

A bladed rotor is a disc which has a peripheral array of aerofoil blades thereon. In operation the disc rotates in a duct and the blades displace ambient air axially of the disc and through the duct to provide a propulsive force.

It is common practice to form a part of the inner wall of the duct with platforms which extend from blade to blade in a direction peripherally of the disc, in radially spaced relationship therewith. In one example, a platform is formed on each blade and when the blades are fitted to the disc, the platforms abut each other to complete the wall portion.

In another example and as is shown in the drawings of British patent specification 1093,568, the platforms are separate members. Each member is fitted radially inwardly through a widened slot in the periphery of the disc and moved round to its place, followed by the fitting of a blade in an adjacent groove.

A drawback of the arrangement is that, if a blade or platform member fails, all of the blades and platforms between the failed member and the slot have to be removed, before the failed member can be removed.

The invention seeks to provide an improved bladed rrotor for a fluid flow propulsion engine.

According to the present invention a bladed rotor for a fluid flow propulsion engine comprises a disc supporting a peripherally arranged row of equi-angularly spaced blades, a re-entrant groove through the rim of the disc between each adjacent pair of blades for the receipt and retention of respective platforms, furthe grooving peripherally of the disc and platforms having tined roots which are complementary in profile with the re-entrant grooves and which can be inserted in the peripheral grooving in a direction radially inwardly of the disc and then in a direction longitudinally of the re-entrant grooves so as to locate therein.

Preferably the peripheral grooving comprises at least two annular grooves.

Preferably further grooves which have blade retention features therein are provided through the rim of the disc and the blades have root forms which are complementary thereto and fit therein.

The further grooves through the rim of the disc may comprise re-entrant grooves of dovetail form.

Alternatively, the further grooves through the rim of the disc may comprise vee grooves which have serrations in their flanks.

The platforms are preferably manufactured from a thermosetting plastic.

The preferred thermo setting plastic is polyetheretherketone.

The invention will now be described, by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a fluid flow propulsion engine.

Figure 2 is a view on line 2-2 of Fig. 1.

Figure 3 is an enlarged, pictorial part view of Fig. 2.

Referring to Fig. 1. A ducted fan gas turbine engine 10 comprises a well known arrangement of a core gas generator 12 which takes in a fluid, which in the present case is ambient air, mixes the air with fuel, burns the mixture and expands the resulting gases through a turbine structure (not shown) and finally, through a propulsion nozzle 14.

The turbine structure (not shown) also drives a ducted fan 16 which includes a stage of fan blades 18, in known manner.

Referring now to Fig. 2. The fan blades 18 consist of aerofoil portions 18a and root portions 18b. In the present example, the root portions 1 8b have a dovetail shape. The blades 18 are equi-angularly spaced around the periphery of a disc 20 which has grooves 22 in its periphery which are complementary in form to the roots 18b of the blades 18. On assembly, the blade roots 1 8b are slid into the grooves 22 and during operation, are retained against being thrown out under centrifugal force by the abutting shoulders of the complementary dovetails. No means are shown by which the blades are retained in the axial sense, but any means already known to those skilled in the art, may be utilised for such a purpose.

The blades 18 of the present example, consist simply of the aerofoil portions 1 8a extending into root portions 18b. The blades have no lateral protuberances in the form of platforms by which to provide an inner wall of the duct 24, through which air is pumped during operation. The platforms 26 are separate members, each of which has its own root 28, which terminates in a dovetail form 30. Complementary dovetail grooves 32 are formed through the rim of the disc 20, alternately with respect to the blade grooves 22 and the platforms 26 are retained therein in the same manner as are the blades 18 in their respective grooves 22.

The edges of the platforms 26 engage the flanks of adjacent blades 18 and are so formed as to provide a close fit therewith for the full length of the relevant blade chordal length.

Referring now to Fig. 3. The roots 28 of the platforms 26 are tined i.e. they are divided by slots 34 which in the present example provides three tines 28a, 28b, and 28c on each root 28 respectively. The disc 20 has a pair of annular grooves 36 formed in its rim, which are so proportioned as to enable re ceipt therein of two of the tines, say 28b and 28c. The tines 28b and 28c can be inserted radially inwardly of the disc so as to enable engagement of the undersides of the dovetail portions 30 of the roots with the floors of respective grooves 32. The platforms 26 are then moved longitudinally of the grooves 32, until the dovetail portions of all three tines 28a, 28b and 28c on each platform 26 is nested within the dovetail portions of the respective grooves 32.

The first main advantage which accrues from the invention, is the simplicity of assembly and disassembly of blades 18 and platforms 26 to the disc 20, in that the blades 18 can simply be slid longitudinally into their respective grooves 22 and the platform need only radial insertion between adjacent blades 18, followed by a short movement longitudinally of their respective grooves 32. If a single blade needs to be removed, only the two immediaytely adjacent platforms 26 need be removed before hand. Any single platform 26 may of course be removed by itself.

A further main advantage is that as the blades need not (with certain limitations described later in this specification) be manufactured with their own platforms, their manufacturing process is much simplified. The invention thus has particular efficacy when used in conjunction with hollow blades which are constructed from thin sheets of metal which embrace a cellular core. Generally, such blades have little or no camber and this greatly reduced the necessity for including any significant curvature on the associated platform edges which curvature if present would, where the platforms are made from rigid material, make difficult the longitudinal movement of the platform into its final position.

Where blades are made by forging or casting, it would be a relatively simple task to form a chordal rib on the concave side of any camber and a bridge on the convex side much as is disclosed in the prior art specification 1093,568. This would avoid any necessity for curved platform edges. If however, a plastic material which has some degree of flexibility were used to form the platform 26, then blade camber would not be such a problem.

One suitable material is known as polyetheretherketone. The main body of the platform 26 could be manufactured from such a material, reinforced by fibres of suitable material.

The platform edges however, could be un-reinforced so as to provide the necessary flexibility. An advantage given by'use of this latter material is lightness of weight.

Claims

1. A bladed rotor for a fluid flow propulsion engine comprising a disc supporting a peripherally arranged row of equi-angularly spaced blades, a re-entrant groove through the rim of the disc between each adjacent pair of blades for the receipt and retention of respective platforms, further grooving peripherally of the disc and platforms having tined roots which are complementary in profile with the re-entrant grooves and which can be inserted in the peripheral grooving in a direction radially inwardly of the disc and then in a direction longitudinally of the re-entrant grooves so as to locate therein.

2. A bladed rotor as claimed in claim 1 including at least two said peripheral grooves.

3. A bladed rotor as claimed in claim 1 or claim 2 and in which further grooves which have blade retention features therein are provided through the rim of the disc and the blades have root which in form are complementary thereto and fit therein.

4. A bladed rotor as claimed in claim 3 wherein the further grooves are re-entrant grooves of dovetail form.

5. A bladed rotor as claimed in claim 3 wherein the further grooves are vee grooves and have blade retention features in the form of serrations in their flanks.

6. A bladed rotor as claimed in any previous claim wherein the platforms are constructed from a thermo setting plastic.

7. A bladed rotor as claimed in claim 6 wherein the thermo setting plastic is polyetheretherketone.

8. A bladed rotor as claimed in claim 6 or claim 7 wherein all but the side edges of the platforms are fibre reinforced.

9. A bladed rotor substantiaily as described in this specification and with reference to the accompanying drawings.

10. A fluid flow propulsion engine including a blased rotor substantially asdescribed in this specification and with reference to the accompanying drawings.