GB2076067A

GB2076067A - Axial-flow compressor or turbine outer casing

Info

Publication number: GB2076067A
Application number: GB8115226A
Authority: GB
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1980-05-16
Filing date: 1981-05-18
Publication date: 1981-11-25
Also published as: IT8121696A0; DE3018621C2; GB2076067B; FR2482662B1; IT1137477B; DE3018621A1; FR2482662A1; JPS5710714A

Abstract

The casing comprises at least one integral unit formed from an inner ring 5 fixedly connected to an outer ring 3 by means of radially-extending connecting webs 2 forming circumferentially-spaced air chambers 4 therebetween, wherein each web 2 has a radial gap 1 opening at the radially-inner surface of the inner ring 5, such that, in use, the gap between the casing and a rotor therein is kept constant and as small as possible. <IMAGE>

Description

SPECIFICATION An outer Casing for an Axial-flow Compressor or Turbine of a Turbomachine This invention relates to an outer casing for an axialflow compressor or a turbine 6f a turbomachine, particularly of a gas turbine engine.

It is known to provide a double-walled casing having air chambers therein. Such a casing is intended to compensate for prevailing thermal effects. The advantage afforded by effective compensation via the casing lies in the fact that radial expansion and shrinkage of thermallystressed stator casings is controlled-so as to affect advantageously the radial gap between the rotor and the stator.

Known compensating designs, comprising for example a segmented inner ring of a hook-type centering device and a control ring, suffer from considerabw functional deficiencies. In particular, the hooks tend to jam as a result of distortion suffered by the segments in operation.

This design also suffers from the disadvantage that important structural elements, such as the hook-tape centering device and segment seals are subject to wear at abutment points, so that the compensating action will suffer.

An object of the present invention is to overcome the above disadvantages and provide an outer casing which ensures optimum compensating action with a narrow and substantially constant blade tip clearance, although the design remains relatively simple and free of wear.

The invention provides an outer casing for an axial-flow compressor or a turbine of a turbomachine comprising an integral unit formed from an inner ring fixedly connected to an outer ring by means of radially-extending connecting webs forming a plurality of circumferentiallyspaced air chambers therebetween, wherein each connecting web has a radial gap extending between adjacent air chambers and opening at the radially-inner surface of the inner ring.

For the proper function of the device of the present invention the radial support elements constitute a focal point, and they are loaded, under thermal effect acting primarily on the inner wall and causing it to extend lengthwise, by compressive or tensile stresses, and under circumferential expansion of the inner wall they are loaded flexurally.

Parameters to govern the optimum configuration and the number of connecting webs and their recesses can be determined by adequate temperature estimates and stress analyses. They relate directly to actual radial and tangential casing expansions in service and to the attending flexural and compressive loads.

The optimum mass ration between inner and outer walls can be determined in a similar manner.

At the axial ends and outer rim zones of the integral ring, purely design-oriented measures are required to reduce the heat transfer at the air chambers and the control mass, where the intended seals and covers should preferably not impair the supporting elements and the inner ring in their proper function.

In use involving relatively high temperature gradients the transfer of heat at the inner rim zone can be alleviated by a suitable thermal insulation layer.

Said general system of an integral casing requires careful centering radially and fixation axially, where the connecting members leading to adjacent casing stages are variously designed to suit the use.

An embodiment of the invention will now be described with reference to the accompanying drawing, wherein: Fig. 1 is a fragmentary view in cross-section of casing unit in accordance with the present invention, Fig. 2 is an enlarged detailed view II from Fig. 1, Fig. 3 is an enlarged sectional view taken along the line Ill-Ill of Fig. 1, and Fig. 4 is a longitudinal section of part of a casing comprising two integral casing units four a multiple-stage, axial-flow compressor of a turbojet engine.

In Fig. 1, a double-walled integral casing unit comprising an outer ring 3 and an inner ring 5 interconnected by thin-walled, radially-extending connecting webs 2. Equally-spaced air chambers 4 between the webs 2 reduce heat transfer between the inner ring 5 and the outer ring 3.

This delays radial thermal expansion and contraction of the outer ring 3, and thus allows the radial expansion of the inner ring 5 to be controlled by the webs 2.

Fig. 2 and 3 provide a step-by-step description of the compensation principle and its sequence in time: When the inner ring 5 is heated, it remains briefly in its original radial position. As the webs 2 increasingly absorb heat, the inner ring 5 moves radially inwards by the amount of radial expansion 8 of the webs 2 and it will not begin to move radially outwards until the outer ring 3 is affected thermally. This radially-outward movement corresponds approximately to the amount of radial thermal expansion of the outer ring 3.

The difference in magnitude between the radial expansion of the inner ring 5 and the outer ring 3, resulting from the optimum shape of the webs 2, is a factor determining the effectiveness of compensation. The amount of tangential expansion 9 of the inner ring 5 is determined by a suitable selection of the width 7 and shape of the radial gap 1, and by an adequately selecting the pitch 6 of the inner ring.

As the inner ring 5 cools down, the above described procedure is reversed. It is here worth noting that the radius of the inner ring 5 increases briefly because of contraction of the webs 2 as the temperature drops. This is an advantage in jet engines, since when the engine is cooling or decelerating -rapidly, this effect will optimise the gap between the rotor blades and the stator casing.

The temperature drop should nevertheless be a consideration in the dimensioning of all construction elements involved.

Fig. 4 shows an alternative design for the outer casing 10 of a multiple-stage axial-flow compressor of a turbojet engine. At least one Tshaped (when viewed in longitudinal section) annularly-formed connecting member 11 is provided for centering the casing axially at 12 and radially at 13, and supporting it. A radiallyextending annular wall section 14 of the connecting element 11 rests in a frontal recess adjacent the outer ring of an integral unit, and at the other end abuts directly against a sealing member 1 5. The integral units are optionally bolted together by means of fitted bolts extending through the respective outer rings 3, sealing members 1 5 and radial wall sections 1 4 of the connecting members 11 in an axial direction along line 16.In Fig. 4, each inner ring 5 is provided with a thermal insulation 1 7 facing the compressor or turbine duct. This insulation is preferably combined with an abraidable coating for the adjoining tips of the rotor blades 1 8 of the turbine.

The insulation 7 can optionally be manufactured from a ceramic material.

As is also apparent from fig. 4, the outer casing 10 may be shaped as a gudie vane carrier at the - respectibe connecting point on the inner side of the casing between two adjacent integral units, e.g. as a circumferential slot 1 9 to accept the respective blade roots.

In Fig. 4, an annular flanged connection 20 is used to provide radial centering and sealing of the respective air chambers 4 relative to the turbine or compressor duct at the respective connecting point on the inner side of the casing between the two adjacent integral units.

Manufacturing materials and methods should be selected to best suit the intended applications and the prevailing operating conditions of the casing.

The integral components associated with the casing are preferably manufactured from, e.g., a highly heat-resistant nickel-base alloy.

Claims

1. An outer casing for an axial-flow compressor or a turbine of a turbomachine comprising an integral unit formed from an inner ring fixedly connected to an outer ring by means of radiallyextending connecting webs forming a plurality of circumferentially-spaced air chambers therebetween, wherein each connecting web has a radial gap extending between adjacent air chambers and opening at the radially-inner surface of the inner ring.

2. An outer casing as claimed in claim 1, comprising a plurality of axially-aligned said integral units, and a sealing member arranged between adjacent integral units for lateral and axial sealing of the air chambers and for covering the radial gaps.

3. An outer casing as claimed in claim 2, wherein a substantially T-shaped, in longitudinal section connecting member is provided for axial fixing and radial centering of the integral units, each connecting member having a radiallyextending annular wall portion which rests in a frontal recess of substantially the outer ring of one integral unit and abuts directly on the sealing element, the integral units being connected together by bolts extending through the respective outer rings, sealing elements and radial wall portions of the connecting members.

4. An outer casing as claimed in claim 3, wherein the radially inner surface of each inner ring has a thermal insulator.

5. An outer casing as claimed in claim 4, wherein the thermal insulator is combined with an abraidable coating.

6. An outer casing as claimed in claim 4 or 5, wherein the insulator is formed from a ceramic material.

7. An outer casing as claimed in any one of claims 2 to 6, wherein the inner surface of the inner rings at the join between two adjacent integral units are formed so as to be capable of receiving respective stator blade roots.

8. An outer casing as claimed in any one of claims 2 to 7, wherein the end of one inner ring at each join has an axially-extending annular flange for radially centering and sealing the respective air chambers at the join.

9. An outer casing for an axial-flow compressor on a turbine of a turbomachine, the outer casing being substantially as herein described with reference to any one of the embodiments shown in the accompanying drawing.