GB1605191A - Hollow aerofoil rotor blade for a gas turbine engine - Google Patents

Description

(54) A HOLLOW AEROFOIL ROTOR BLADE FOR A GAS TURBINE ENGINE (71) We, ROLLS-ROYCE LIMITED formerly ROLLS-RoYCE (1971) LIMITED, a British Company of Norfolk House, St. James's Square, London, SWlY 4JR, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a hollow aerofoil rotor-blade suitable for use in a gas turbine engine and in particular to such a blade provided with an insert.

It is usual to provide at least some of the aerofoil rotor blades present in a gas turbine engine with internal cooling. At present this cooling is restricted to the turbine but it could become necessary in future to cool the compressor rotor blades. One convenient method of providing such cooling is by the use of an insert. An insert normally consists of a hollow tube which is adapted to be supplied with a cooling fluid, usually air, and which is provided with numerous small holes over at least part of its surface. Such an insert is adapted to be located within a hollow aerofoil rotor blade in such a manner that cooling air blowing through the small holes impinges on the internal suface of the blade, therby providing blade cooling.

Inserts of this type are usually fixedly located within the hollow aerofoil rotor blade by brazing or welding so as to constitute an integral part of the blade. However bladelinsert assemblies of this type suffer from several disadvantages if the blade is one which is mounted for rotation: a) The combined mass of the aerofoil rotor blade and its insert results in higher centrifugal forces being exerted by the rotating bladelinsert assembly than would be exerted by a similar aerofoil rotor blade not provided with an insert. As a result, the mounting root of the aerofoil rotor blade provided with an insert has to be more substantial than the root of a corresponding aerofoil rotor blade not provided with an insert.

b) If the means attaching the insert to the aerofoil rotor blade should fail, the insert could be thrown from the blade and cause considerable engine damage.

c) The mating surfaces at the joint between the aerofoil rotor blade and its insert must be extremely accurate and in fact take precedence over the objective of providing close proximity surfaces required for impingement and cooling air flow.

d) Heating of the finished or part-finished aerofoil rotor blade is required.

e) Bladelinsert materials have to be identical or compatible for jointing.

According to the present invention, a hollow aerofoil rotor blade suitable for use in a gas turbine engine has an insert located therein, said insert being adapted to be supplied with cooling fluid and to direct that cooling fluid onto at least part of the internal surface or surfaces of said hollow aerofoil rotor blade, each of said hollow aerofoil rotor blade and said insert being provided with respective means for the direct attachment thereof to a rotor disc, said insert attaching means being independent of and additional to said hollow aerofoil rotor blade attaching means.

Said insert attaching means and said hollow aerofoil rotor blade attaching means are preferably of the same type.

Each of said insert attaching means and said hollow aerofoil rotor blade attaching means preferably comprises a fir tree root.

Said fir tree root on said insert is preferably adapted so as to locate in the same fir tree root receiving feature on a rotor disc as that in which said hollow aerofoil rotor blade fir tree root is adapted to locate.

Said insert and said hollow aerofoil rotor blade may be adapted so that said fir tree root on said insert is arranged to be in superposed relationship with said fir tree root on said hollow aerofoil rotor blade.

Alternatively said insert and said hollow aerofoil rotor blades may be adapted so that said fir tree root on said insert is arranged to be aligned with at least one portion of said fir tree root on said hollow aerofoil rotor blade. Thus said fir tree root on said hollow aerofoil rotor blade may be bifurcated and said fir tree root on said insert adapted to be interposed between, and aligned with, said fir tree root portions on said bifurcations.

The invention will now be described, merely by way of example, with reference to the accompanying drawings in which: Fig. 1 is a partially sectioned side view of part of a gas turbine engine turbine rotor disc provided with a hollow turbine aerofoil rotor blade in accordance with the present invention, Fig. 2 is a sectional view taken on the plane indicated by the line A-A in Fig. 1. Part of the drawing has been omitted in the interests of clarity, Fig. 3 is a sectional view taken on the plane indicated by the line B-B in Fig. 4, and Fig. 4 is an exploded sectional perspective view of a further embodiment of a hollow turbine aerofoil rotor blade and insert in accordance with the present invention.

With reference to Fig. 1, a turbine disc 10 of a gas turbine engine (not shown) is provided with a hollow interior 11 adapted to be supplied with cooling air through a plurality of radially extending passages, one of which can be seen at 12. The cooling air may be derived from any convenient source of cool compressed air, for instance the compressor of the gas turbine engine in which the turbine disc 10 is located. The periphery of the turbine disc 10 is provided with a plurality of equi-angularly spaced apart turbine blade roots receiving features, one of which can be seen at 13. Each feature 13 is adapted to be supplied with cooling air from the hollow disc interior 11 by a radially extending passage 14. In each feature 13, there is located the bifurcated fir tree root 15 of a hollow turbine aerofoil rotor blade 16.

Each hollow turbine aerofoil rotor blade 16 has an insert 17 located therein.

The construction of a typical insert can be seen in Figs. 2 and 3. The insert 17 consists of a tube 18 which extends throughout the whole length of and corresponds in cross-sectional contour to the interior wall 19 of the hollow turbine aerofoil rotor blade 16. The crosssectional contour of the tube 18 is slightly smaller than that of the interior wall 19 of the hollow turbine blade 16 such that a narrow uniform gap 20 is defined therebetween. A plurality of projections 21 are provided on the interior wall 19 to space the tube 18 therefrom and consequently maintain the gap 20. The radially inner end of the insert 17 is provided with a fir tree root 22 which is adapted to locate in that portion of the turbine blade root receiving feature 13 defined by the bifurcation of the fir tree root of the hollow turbine blade 16.It will be seen therefore that the insert 17 is radially constrained only by the feature 13 in the turbine disc 10.

Accordingly upon rotation of the turbine disc 10, centrifugal forces resulting from the mass of the insert 17 are transferred directly to the disc 10, not to any portion of the hollow turbine blade 16.

A radially extending passage 23 is provided at the radially inner end of the insert 17 to connect the interior thereof with the root receiving feature 13. The radially extending insert passage 23 is positioned so as to be approximately aligned with the radially extending passage 14 provided in the turbine disc 10 such that a portion of the cooling air exhausted from the disc passage 14 passes through the insert passage 23 and into the interior of the insert 17. The radial depth of the insert fir tree root 22 is less than that of the bifurcated blade fir tree root 15 so that a partially enclosed compartment is defined by the fir tree roots 15 and 22 together with the disc 10. The so defined compartment ensures the free passage of cooling air from the disc passage 14 into the interior of the insert 17.A plurality of holes 24 are provided in that portion of the insert 17 adjacent the leading edge area 25 of the hollow turbine blade 16 so that cooling air exhausted therefrom impinges upon the leading edge area 25 to provide cooling. The radially outer end of the insert 17 is blocked at 26 so as to ensure that substantially all of the cooling air which enters the insert 17 is exhausted therefrom via the holes 24. After the cooling air which has been exhausted from the holes 24 has impinged the leading edge area 25, it passes along the gap 20 between the insert 17 and the interior wall 19 of the hollow turbine blade 16 to the trailing edge 27 of the blade where a slit 28 is provided to exhaust the cooling air into exhaust gases passing through the turbine of the gas turbine engine (not shown).A plurality of pillars 29 are provided in that part of the hollow turbine blade 16 between the region of the trailing edge 26 and the insert 17 to interconnect and support both flanks 30 and 31 of the hollow turbine blade 16.

A further embodiment of the present invention is shown in Fig. 4. All features of this embodiment which are common with the previously described embodiment have like numerals suffixed by the letter a.

With reference to Fig. 4, a hollow turbine aerofoil rotor blade 1 6a is provided with a fir tree root 15a for attaching the blade to a turbine disc (not shown) similar to the turbine disc 10 shown in Fig. 1. An insert 17a is adapted to locate inside the hollow turbine blade 16a in a similar manner to that described with reference to the previous embodiment i.e. with a narrow, uniform gap defined between the insert 1 7a and the interior wall 19a of the hollow turbine blade 16a. A plurality of projections (not shown) are provided on the interior wall 19a so as to maintain the above mentioned narrow, uniform gap.

The insert 1 7a is provided with its own fir tree root 22a which is adapted when the insert 17a is in position, to abut the blade fir tree root 15a in superposed relationship. Thus the radially outer faces 32 and 33 on the fir tree root 22a are adapted to respectively abut the radially inner faces 34 and 35 on the fir tree root 15a. The faces 32 and 33, and 34 and 35 may be brazed together. This results in a more rigid blade/insert structure and avoids the possibility of the wrong insert being located in a particular hollow turbine aerofoil blade during assembly or overhaul.

The insert fir tree root 22a is provided with a passage (not shown) which is adapted to be supplied with compressed air in a similar manner to that described with reference to the previous embodiment, and to direct that air into the interior of the insert 17a.

The tube 18a portion of the insert 1 7a is provided with a plurality of holes 36 over a major portion of its surface so as to provide impingement cooling over virtually the whole of the interior wall 19a of the hollow turbine blade 16a. Whether impingement cooling is provided over the whole or just a part of the interior wall 1 9a is determined by the temperatures which the hollow turbine blade 16a is likely to encounter during service. The cooling air is exhausted from the interior of the hollow turbine blade 16a through a slit (not shown) provided in the trailing edge of the blade in a similar manner to that described with reference to the previous embodiment of the present invention.

Cooling air is prevented from escaping from the radially outer end of the insert 1 7a by a sealing member 37 positioned at the radially outer end of the hollow turbine aerofoil blade 16a. The sealing member 37 is adapted to both seal the radially outer end of the hollow turbine blade 1 6a and to provide a surface against which the radially outer end of the insert 1 7a engages in sealing relationship.

As a result of their mode of construction, blade/insert assemblies in accordance with the present invention are simple to assemble. Moreover, except in the case of blade/insert assemblies which are brazed together, should either of the blade or insert be damaged then only the damaged member need be replaced and not the complete bladelinsert assembly as is necessary with previous hollow turbine aerofoil blades provided with integral inserts.

As the insert of a blade/insert assembly in accordance with the present invention is adapted to be attached directly to the disc on which the hollow turbine blade is mounted, then in addition to providing cooling, the insert may also act as a vibration damper and consequently could advantageously alter the vibration characteristics of the hollow turbine aerofoil blade in which it is located.

Since the insert 17 is located in an environment which, under engine operating conditions, is cooler than that in which the turbine blade 16 is located, it may be manufactured from a material which is not as thermally resistant as that from which the blade 16 must be manufactured. Moreover differential thermal expansion between the hot blade and relatively cool insert poses no problem as the blade and insert are independently mounted.

Other advantages which may be achieved with blade/insert assemblies in accordance with the present invention are as follows: a) The insert is readily removable and replaceable, this being a particularly useful facility for developmental purposes when cooling hole sizes or patterns are being evaluated.

b) Long-life blade/insert assemblies can be parted and independently cleaned, de-coked and flow tested for hole blockage.

c) De-rated or rig test engines could run with timeexpired blades with blanked inserts if cooling was not required.

Although the present invention has been described with reference to a blade and an insert having attachment means in the form of fir tree roots, it will be appreciated that they could be attached to a turbine disc by other means. Thus for instance, they could be attached by means of one or more pins.

WHAT WE CLAIM IS: 1. A hollow aerofoil rotor blade suitable for use in a gas turbine engine and having an insert located therein, said insert being adapted to be supplied with cooling fluid and to direct that cooling fluid on to at least part of the internal surface or surfaces of said hollow aerofoil rotor blade, each of said hollow aerofoil rotor blade and said insert being provided with respective means for the direct attachment thereof to a rotor disc, said insert attaching means being independent of and additional to said hollow aerofoil blade attaching means.

2. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 1 wherein said insert attaching means and said hollow aerofoil rotor blade attaching means are of the same type.

3. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 2 wherein each of said insert attaching means and said hollow aerofoil rotor blade attaching means comprises a fir tree root.

4. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 3 wherein said fir tree root on said insert is adapted so as to locate in the same fir tree root receiving feature on a rotor disc as that in which said hollow aerofoil rotor blade fir tree root is adapted to locate.

5. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 3 or claim 4 wherein said insert and said hollow aerofoil rotor blade are adapted so that said fir tree root on said insert is arranged to be in superposed relationship with said fir tree root on said hollow aerofoil rotor blade.

6. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 3 or claim 4 wherein said insert and said hollow aerofoil rotor blade are adapted so that said fir tree root on said insert is arranged to be aligned with at least one portion of said fir tree root on said hollow aerofoil rotor blade.

7. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 6 wherein said fir tree root on said hollow aerofoil rotor blade is bifurcated and said fir tree

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   a particular hollow turbine aerofoil blade during assembly or overhaul.

   The insert fir tree root 22a is provided with a passage (not shown) which is adapted to be supplied with compressed air in a similar manner to that described with reference to the previous embodiment, and to direct that air into the interior of the insert 17a.

   The tube 18a portion of the insert 1 7a is provided with a plurality of holes 36 over a major portion of its surface so as to provide impingement cooling over virtually the whole of the interior wall 19a of the hollow turbine blade 16a. Whether impingement cooling is provided over the whole or just a part of the interior wall 1 9a is determined by the temperatures which the hollow turbine blade 16a is likely to encounter during service. The cooling air is exhausted from the interior of the hollow turbine blade 16a through a slit (not shown) provided in the trailing edge of the blade in a similar manner to that described with reference to the previous embodiment of the present invention.

   Cooling air is prevented from escaping from the radially outer end of the insert 1 7a by a sealing member 37 positioned at the radially outer end of the hollow turbine aerofoil blade 16a. The sealing member 37 is adapted to both seal the radially outer end of the hollow turbine blade 1 6a and to provide a surface against which the radially outer end of the insert 1 7a engages in sealing relationship.

   As a result of their mode of construction, blade/insert assemblies in accordance with the present invention are simple to assemble. Moreover, except in the case of blade/insert assemblies which are brazed together, should either of the blade or insert be damaged then only the damaged member need be replaced and not the complete bladelinsert assembly as is necessary with previous hollow turbine aerofoil blades provided with integral inserts.

   As the insert of a blade/insert assembly in accordance with the present invention is adapted to be attached directly to the disc on which the hollow turbine blade is mounted, then in addition to providing cooling, the insert may also act as a vibration damper and consequently could advantageously alter the vibration characteristics of the hollow turbine aerofoil blade in which it is located.

   Since the insert 17 is located in an environment which, under engine operating conditions, is cooler than that in which the turbine blade 16 is located, it may be manufactured from a material which is not as thermally resistant as that from which the blade 16 must be manufactured. Moreover differential thermal expansion between the hot blade and relatively cool insert poses no problem as the blade and insert are independently mounted.

   Other advantages which may be achieved with blade/insert assemblies in accordance with the present invention are as follows: a) The insert is readily removable and replaceable, this being a particularly useful facility for developmental purposes when cooling hole sizes or patterns are being evaluated.

   b) Long-life blade/insert assemblies can be parted and independently cleaned, de-coked and flow tested for hole blockage.

   c) De-rated or rig test engines could run with timeexpired blades with blanked inserts if cooling was not required.

   Although the present invention has been described with reference to a blade and an insert having attachment means in the form of fir tree roots, it will be appreciated that they could be attached to a turbine disc by other means. Thus for instance, they could be attached by means of one or more pins.

   WHAT WE CLAIM IS: 1. A hollow aerofoil rotor blade suitable for use in a gas turbine engine and having an insert located therein, said insert being adapted to be supplied with cooling fluid and to direct that cooling fluid on to at least part of the internal surface or surfaces of said hollow aerofoil rotor blade, each of said hollow aerofoil rotor blade and said insert being provided with respective means for the direct attachment thereof to a rotor disc, said insert attaching means being independent of and additional to said hollow aerofoil blade attaching means.
2. 2. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 1 wherein said insert attaching means and said hollow aerofoil rotor blade attaching means are of the same type.
3. 3. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 2 wherein each of said insert attaching means and said hollow aerofoil rotor blade attaching means comprises a fir tree root.
4. 4. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 3 wherein said fir tree root on said insert is adapted so as to locate in the same fir tree root receiving feature on a rotor disc as that in which said hollow aerofoil rotor blade fir tree root is adapted to locate.
5. 5. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 3 or claim 4 wherein said insert and said hollow aerofoil rotor blade are adapted so that said fir tree root on said insert is arranged to be in superposed relationship with said fir tree root on said hollow aerofoil rotor blade.
6. 6. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 3 or claim 4 wherein said insert and said hollow aerofoil rotor blade are adapted so that said fir tree root on said insert is arranged to be aligned with at least one portion of said fir tree root on said hollow aerofoil rotor blade.
7. 7. A hollow aerofoil rotor blade having an insert located therein as claimed in claim 6 wherein said fir tree root on said hollow aerofoil rotor blade is bifurcated and said fir tree

   root on said insert is adapted to be interposed between, and aligned with, said fir tree root portions on said bifurcations.
8. 8. A hollow aerofoil rotor blade having an insert located therein substantially as hereinbefore described with reference to and as shown in Figs. 1-3 of the accompanying drawings.
9. 9. 9. A hollow aerofoil rotor blade having an insert located therein substantially as hereinbefore described with reference to and as shown in Fig.

   4 of the accompanying drawings.