Mounting for a ceramic scroll in a gas turbine engine

Abstract: In a gas turbine engine, an annular flange (82) of a ceramic scroll (70) is clamped to an annular shoulder (36) of a gas turbine engine housing by a plurality of nuts (130) on threaded rods (118) extending perpendicular to the annular shoulder (36). A metal sleeve (98) around each rod (118) co-operates therewith in defining a coolant passage (120) which is connected at one end to a source of compressed air and which discharges at the other end into a cooling chamber (136) around the nuts (130) through grooves (132) in a surface of each nut (130). Air circulating in the coolant passages (120) and through the cooling chamber (136) cools and thermally shields the rods (118) and the nuts (130).

Description: This invention relates to a mounting for an annular ceramic member on a metal engine block or housing of a gas turbine engine as specified in the preamble of claim 1, for example as disclosed in US-A-4,326,835. In hot sections of gas turbine engines where gas temperatures may exceed 1371°C (2500 degrees F), ceramic material, which does not require air-cooling for acceptable durability, is preferable to alloy metal which does. A scroll, for example, defining the transition from a discharge of a combustor can to an annular nozzle is an ideal candidate for substitution of ceramic material for alloy metal. Mounting a ceramic scroll on a metal engine block, however, is challenging because of the different physical properties, including thermal expansion characteristics, of the two materials. A mounting according to this invention affords a relatively simple and effective connection between a ceramic scroll and a metal engine block in a gas turbine engine. A mounting between a metal engine block of a gas turbine engine and an annular ceramic member according to the present invention is characterised by the features specified in the characterising portion of claim 1. This invention is a new and improved mounting for a ceramic scroll on a metal engine block of a gas turbine engine. The scroll mounting according to this invention includes an annular shoulder on the engine block and an annular ceramic flange on the scroll having a plurality of clearance slots therein. The ceramic flange is clamped against the annular shoulder with a crushable member between the two for cushioning. The clamping apparatus includes a plurality of steel sleeves extending through respective slots in the ceramic flange and bolt-like fasteners within the sleeves which screw into thread holes in the annular shoulder. In each sleeve, an annulus between the sleeve and the fastener therein defines a passage for cooling air which flows from the threaded end of the fastener to the head end thereof. The head ends are relieved to permit flow of the cooling air out of the passages into a cooling chamber around the fastener heads, which cooling air thermally shields the heads. The cooling chamber is vented to the hot gas flow path of the engine for discharge of the cooling air into the hot gas stream therein. In a preferred embodiment, zirconia thermal barriers are provided to minimize heat transfer from the annular ceramic flange to the sleeves and to the engine block. The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings in which: Figure 1 is a fragmentary elevational view of a hot section of a gas turbine engine having a ceramic scroll mounting according to this invention and taken on a longitudinal centreline of the engine; Figure 2 is an enlarged view of a portion of Figure 1; and Figure 3 is a reduced, fragmentary sectional view taken generally along the plane indicated by lines 3-3 in Figure 2. Referring to Figure 1, a partially-illustrated hot section 10 of a gas turbine engine includes a single stage gasifier turbine rotor 12 which may be as described in US Patent 4639194, issued 27 June 1987 to A.H. Bell III, et al. The gasifier turbine rotor includes a ceramic turbine wheel 14 and an alloy steel shaft 16. A tubular end 18 of the alloy steel shaft 16 is shrink-fitted on a tubular stem 20 of the ceramic turbine wheel 14. The turbine wheel 14 has a stage 22 of turbine blades around its circumference. The hot section 10 further includes a power turbine rotor 24 having a pair of turbine wheels 26A, 26B. Each of the turbine wheels 26A, 26B has a stage of turbine blades 28A, 28B, respectively, around its circumference. The power turbine rotor 24 is supported on a fragmentarily-illustrated engine block 30 of the gas turbine engine for rotation about a primary axis 32 of the engine. A representative arrangement for mounting the power turbine rotor on the engine block is described in US Patent 4825645, issued 2 May 1989 to A.H. Bell III. The engine block is made of alloy metal and has a structurally rigid cylindrical wall 34 aligned on the primary axis 32. The cylindrical wall terminates at an annular shoulder 36 in a plane perpendicular to the primary axis. A substantially tubular, cast-iron carrier 38 is disposed in the cylindrical wall 34 with a radial annular flange 40 of the carrier seating against the annular shoulder 36. A sleeve bearing 42 between the carrier 38 and the alloy steel shaft 16 supports the gasifier turbine rotor 12 on the engine block 30 for rotation about the primary axis 32. A pair of high-temperature seal rings 44A, 44B are disposed between the carrier 38 and the alloy steel shaft 16 and are separated by a tubular spacer 46. A schematically-illustrated plenum 48 in the engine block is connected to a source of cooling air, not shown, such as the compressor of the engine. Circumferentially-spaced holes 50 in the carrier 38 conduct cooling air from the plenum 48 to the high-temperature seal rings 44A, 44B. An interior structural wall 52 of the engine defines a radial outer side of an annular hot gas motive fluid flow path 54 in which the turbine blades 22, 28A, 28B are all disposed. A first stage of stator vanes 56 connected to the wall 52 is disposed upstream of the power turbine blades 28A and a second stage of stator vanes 58 connected to the wall 52 is disposed between the power turbine blades 28A, 28B. Downstream of the stator vane stage 56, the radial inner side of the hot gas flow path 54 is defined by respective platforms 60, 62 and 64A, 64B on the stator vanes 56, 58 and turbine blades 28A, 28B, respectively. Upstream of the stator vane stage 56, the inside of the hot gas flow path is defined by a shield 66 on the engine block and by platforms 68 on the gasifier turbine blades 22. A fragmentarily-illustrated ceramic scroll 70 of the gas turbine engine includes a volute chamber 72 centred around the primary axis 32. The volute chamber 72 is in fluid communication with a combustor, not shown, of the engine which discharges hot gas motive fluid into the volute chamber 72 generally at a tangent to a circle around the primary axis 32 in a plane perpendicular thereto so that a circular flow of motive fluid is established in the volute chamber 72. The scroll 70 further includes an annular nozzle 74 defined between a substantially cylindrical outer wall 76 of the scroll 70 and a substantially cylindrical inner wall 78 of the scroll 70. The nozzle 74 is centred around the primary axis 32 and discharges motive fluid from the volute chamber 72 into the annular hot gas flow path 54 upstream of the gasifier turbine blades 22. The ceramic scroll 70 is connected to the cylindrical wall 34 of the engine block by a mounting 80 according to this invention. The scroll mounting 80 includes an annular ceramic flange 82 in a plane perpendicular to the primary axis 32. The flange 82 is integral with or bonded to the cylindrical inner wall 78 of the scroll 70 and has a first side 84 facing an opposing and parallel surface 86 of the flange 40 on the carrier 38 and a second side 88 facing the gasifier turbine wheel 14. The ceramic flange 82 has a plurality of inwardly-opening, angularly-spaced radial notches in the form of slots 90 and is relieved between respective pairs of slots so that pads 92, see Figure 3, are defined on the ceramic flange 82. The ceramic flange 82 is disposed around a cylindrical surface 94 of the carrier 38 with the pads 92 radially spaced from the surface 94. Arcuately-shaped ceramic spacers 96 are disposed between the surface 94 and the pads 92 and effectively centre the ceramic flange 82, and hence the scroll 70, around the primary axis 32. The mounting 80 further includes tubular alloy steel sleeves 98 projecting through respective slots 90 perpendicular to the annular shoulder 36 and to the ceramic flange 82. As seen best in Figure 2, each sleeve has an outside surface 100, an inside surface 102, an annular inner end 104, and an annular outer end 106. The outside surface 100 of each sleeve has a thermal barrier coating layer 107 of zirconia or other suitable insulating material to a depth of about 0.508 mm (0.020 inch). A pair of annular alloy metal plates 108A, 108B on opposite sides of the ceramic flange 82 are perforated to receive therethrough respective sleeves 98. Each of the plates 108A, 108B has a thermal barrier coating layer 109A, 109B, see Figure 2, of zirconia or other suitable insulating material to depth of about 1.016 mm (0.040 inch) on the side thereof facing the ceramic flange 82. An annular crushable member 110 is disposed between the annular plate 108A and the flange 40 on the carrier 38 and is perforated to receive therethrough the respective sleeves 98. The inside surfaces 102 of the sleeves 98 register with corresponding holes 112 in the carrier flange 40. The holes 112, in turn, register with corresponding threaded bores 114 in the cylindrical wall 34 of the engine block perpendicular to the plane of the annular shoulder 36. Respective notches 116 in an inner side of the carrier flange 40 afford communication between the plenum 48 and the inside surfaces 102 of the sleeves 98 through the corresponding holes 112 in the carrier flange 40. Threaded rods 118 extend through respective sleeves 98 and the aligned holes 112 in the carrier flange 40 and are screwed into respective threaded bores 114 in the cylindrical wall 34 of the engine block 30. The diameter of each rod 118 is less than the diameter of the corresponding hole 112 and less than the diameter of the inside surface 102 of the corresponding sleeve 98. Accordingly, an annular passage 120, see Figure 2, is defined inside each sleeve 98 around the corresponding threaded rod 118 extending from the plenum 48 towards an outer end 122 of the rod 118. As seen best in Figures 1-2, the gas turbine engine includes an annular end assembly 128 in which an annular metal end plate 124 positioned outwards of the plate 108B is perforated to receive therethrough respective rods 118. The end plate 124 has a thermal barrier coated layer 125 of zirconia or the like on the side facing the plate 108B to a depth of about 1.016 mm (0.040 inch). The end plate 124 abuts the outer ends 106 of the sleeves 98 and the plate 108B. The holes in the end plate 124 are about the same diameter as the inside surfaces 102 of the sleeves 98 so that the passages 120 extend through the end plate 124. Nuts 130 are threaded on the respective outer ends 122 of the rods 118 outwards of the end plate 124. Each nut 130 has an inner surface abutting the end plate 124 and a plurality of grooves 132 in the inner surface, each of which grooves intersects the threaded hole in the centre of the corresponding nut 130. It is contemplated that bolts having heads with grooves corresponding to the grooves 132 could be substituted for the rods 118 and nuts 130. An annular metal cover 134 attaches to the end plate 124 at a plurality of interfitting tangs, not shown, or the like, whereby an annular cooling chamber 136 is defined between the cover 134 and the end plate 124. The cooling chamber 136 envelops the nuts 130 and communicates with the hot gas flow path 54 through a plurality of bleed orifices 138 in the end plate 124 and through a clearance between the gasifier turbine wheel 14 and the annular nozzle 74. The grooves 132 in the inner surfaces of the nuts 130 open into the cooling chamber 136. The sleeves 98 function as spacers when the nuts 130 are tightened on the rods 118 to clamp the ceramic flange 82 to the annular shoulder 36 of the engine block 30. That is, as the nuts 130 are tightened, the stack consisting of the ceramic flange 82, the annular plates 108A, 108B and the crushable member 110 are progressively more tightly clamped between the nuts 130 and the annular shoulder 36. Simultaneously, the inner ends 104 of the sleeves 98 are urged towards the carrier flange 40. Normally, the nuts 130 are tightened to a predetermined torque level corresponding to a clamping load on the ceramic flange 82 that is sufficient to operatively mount the scroll on the engine block but not so great as to damage the ceramic flange 82. In that condition, the inner ends 104 of the sleeves 98 are separated from the surface 86 of the carrier flange 40. If the nuts are over-torqued, the inner ends 104 of the sleeves are driven against the surface 86. In that condition, further tightening of the nuts 130 is effectively prevented and the clamping load on the ceramic flange 82 thus limited. Accordingly, the integrity of the ceramic flange 82 is protected by careful control of the lengths of the sleeves 98, a relatively simple manufacturing technique. Regarding cooling and thermal insulation, the thermal barrier coats deposited on the sleeves 98, the annular plates 108A, 108B, and the end plate 124 minimize direct conduction of heat from the scroll 70 to the metal parts of the gas turbine engine such as the carrier 38 and the cylindrical wall 34 of the engine block 30. In addition, air flowing in the passages 120 around the rods 118 from the plenum 48 to the chamber 136 thermally shields and cools the rods 118 and the nuts 130 to limit the temperatures thereof to levels compatible with long-term structural reliability of the gas turbine engine.

Claims: A mounting between a metal engine block (30) of a gas turbine engine and an annular ceramic member (70) aligned on a primary axis (32) of said engine block (30), which mounting comprises: an annular shoulder (36) on said engine block (30) extending in a plane perpendicular to and centred around said primary axis (32), an annular ceramic flange (82) on said annular ceramic member (70) centred on said primary axis (32), and a clamp means for clamping said annular ceramic flange (82) to said annular shoulder (36), characterised in that said an annular ceramic member is an annular ceramic scroll (70); said clamp means includes: a metal sleeve (98) extending perpendicular to said annular shoulder (36) and having an inner end (104) facing said annular shoulder (36) and in spaced relation thereto, and an outer end (106) opposite said inner end (104); a slot (90) in said annular ceramic flange (82) through which said metal sleeve (98) projects; a crushable member (110) positioned around said metal sleeve (98) between said annular shoulder (36) and said ceramic flange (82); and fastener means including a rod (118) extending through said metal sleeve (98) for rigid attachment to said engine block (30) perpendicular to said annular shoulder (36) and a head (130) connected to said rod (118) outwards of both said ceramic flange (82) and said outer end (106) of said metal sleeve (98) whereby rotation of said head (130) relative to said annular shoulder (36) urges said ceramic flange (82) towards said crushable member (110) and said inner end (104) of said metal sleeve (98) towards said annular shoulder, until said inner end (104) of said metal sleeve (98) engages said annular shoulder (36) to prevent further rotation of said head (130) of said fastener means so as to limit clamping forces applied to said ceramic flange (82); there is an annular passage (120) defined by a clearance between said rod (118) and said metal sleeve (98); there are coolant means (50,112,116) conducting coolant to said annular passage (120) adjacent said inner end (104) of said metal sleeve (98), and there is a coolant discharge (132) connected to said annular passage (120) and located between said ceramic flange (82) and said head (130) of said fastener means. A mounting according to claim 1, in which the mounting also includes: a cooling chamber (136) around said head (130) of said fastener means having a bleed orifice (138) therein, and said coolant discharge (132) is connected to said cooling chamber (136) so that coolant from said annular passage (120) circulates through said cooling chamber (136) and out through said bleed orifice (138) so as to cool and to thermally shield said rod (118) and said head (130) of said fastener means. A mounting according to claim 2, in which said coolant is pressurized air. A mounting according to claim 2, in which the mounting also includes: a first perforated metal plate (108A) positioned around said metal sleeve (98) between said ceramic flange (82) and said crushable member (110), a second perforated metal plate (108B) positioned around said metal sleeve (98) between said ceramic flange (82) and said head (130) of said fastener means, and a thermal barrier coat (107) on an outside surface of said metal sleeve (98) and thermal barrier coats (109A,109B) on respective surfaces of each of said first and said second metal plates which face said ceramic flange (82) for minimizing heat transfer from said ceramic flange (82) to said metal sleeve (98) and to each of said first and said second metal plates (108A,108B). A mounting according to claim 4, in which each of said thermal barrier coats (107,109A,109B) is a layer of zirconia.

Inventors: BELL III ALBERT HARVEY, COFFEY DAN, BELL III, ALBERT HARVEY, COFFEY, DAN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1991
Main classification: F01D25
IPC codes: F01D25, F02C7, F16B31, F16B1