US3661477A

US3661477A - Heat shield

Info

Publication number: US3661477A
Application number: US885139A
Authority: US
Inventors: Thorbjorn Westrum
Original assignee: Kongsberg Vapenfabrikk AS
Current assignee: Kongsberg Gruppen ASA
Priority date: 1968-12-17
Filing date: 1969-12-15
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09
Also published as: JPS4825683B1; NO123552B; DE1960693B2; DE1960693A1; GB1294675A

Abstract

A segmented annular heat shield for mounting between the turbine blade wheel and the compressor impeller of a radial gas turbine. Each segment is fixedly secured to a stationary structure at one point at its outer edge and also fastened to said structure at two further fastening points at its inner edge in such a manner that at these further fastening points the segment is restrained from movement in the axial direction of the shield but can move freely in the plane of the segment. The segments adjoin along joints of such a design as to admit of relative movement of the segments in the plane thereof due to heat expansion.

Description

United States Patent [151 3,661,477

Westrum 1 May 9, 1972 54] HEAT SHIELD FOREIGN PATENTS OR APPLICATIONS [72] Inventor: Thorbjorn Wes r m, K ng gy No y 679,916 9/1952 Great Britain 415/178 Assignec: Kongsberg vapenfabrikk KongsbergI 542,197 1 941 Great Britain 1 5/1 39 Norway 726,510 10/1942 Germany ..415/1 38 [22] Filed: Dec. 15, 1969 Appl. No.: 885,139

Primary E.\'aminer-Arthur l. McKeon Assistant Examiner-Richard E. Gluck Attorney-Holman & Stern [57] ABSTRACT A segmented annular heat shield for mounting between the turbine blade wheel and the compressor impeller of a radial gas turbine. Each segment is fixedly secured to a stationary structure at one point at its outer edge and also fastened to said structure at two further fastening points at its inner edge in such a manner that at these further fastening points the segment is restrained from movement in the axial direction of the shield but can move freely in the plane of the segment. The segments adjoin along joints of such a design as to admit of relative movement of the segments in the plane thereof due to heat expansion.

7 Claims, 6 Drawing Figures PATENTEDHAY 9 1972 5 77 SHEET 1 BF 2 INVENTOR 7'. 14/55 rflum/ BBM ATTORNEY PATENTEDMAY 9:972 ,55 7

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ATTORNEY HEAT SHIELD BACKGROUND OF THE INVENTION The present invention relates to an annular, stationary heat shield for mounting between two rotating members of different temperature for reducing the heat transfer between these members, which in particular may be the compressor impeller and the turbine blade wheel of a radial gas turbine.

In radial gas turbines, in which the compressor turbine and the turbine blade wheel are mounted closely together back to back, the cold air passing through the compressor and the hot gases passing through the turbine are kept apart by means of a stationary structure extending into a peripheral groove between the impeller and blade wheel and sealed against one of the rotating components, for instance by a labyrinth seal. In order to protect the compressor and prevent too large heat losses from the turbine, the insulating properties of this stationary structure can be enhanced by an annular, stationary heat shield located on the side facing the turbine, the hot gases in the latter moving along the heat shield, which is spaced from the remaining parts of the stationary structure so that a layer of comparatively stagnant gas acting as a heat insulation is provided between said structure and the heat shield, The temperature gradients in the heat shield are very large both in the radial direction and in the axial direction, since on its outer side, i.e., the side facing the turbine, the heat shield is hotter at its outer periphery than at its inner periphery, and at the same time the temperature on the inner side of the heat shield is of course substantially lower than that on the outer side.

Such previously known annular he'at shields have the disadvantage that they are subjected to very large stresses due to the radial temperature gradients. Further, the axial temperature gradients will cause the shield to curve and adopt approximately the same shape as a plate spring or a spherical calotte. The radius of curvature is dependent upon the difference between the temperatures on the outer side and the inner side, respectively, of the heat shield. With commonly existing temperature differences and thicknesses of the heat shield the radius of curvature is comparatively small, and the axial deflection of the heat shield in operation may therefore become very considerable. This of course increases the requirements with respect to the available room between the compressor blade wheel and the turbineimpeller, and the heat shields previously used cannot be used at all in turbines having a great radius.

SUMMARY OF THE INVENTION The object of the invention is to provide an annular heat shield of the type referred to, which requires considerably less room in the axial direction, is subjected to lower stresses than the known designs and can be used in radial gas turbines having a large diameter. 1

The shield according to the invention is primarily characterized in that it consists of segments. In order that the shield shall be tight and the gas masses behind the shield shall be substantially stagnant, the joints between the segments are so designed as to be substantially sealed, while at the same time admitting of heat expansion of each segment relatively to the adjacent segments. Thereby each segment can move independently of the other segments and will not be subjected to stresses of the same magnitude as an integral ring. Further, each of the segments is of course much smaller relatively to the radius of curvature than an integral shield, whereby the deflection in the axial direction will be substantially smaller. A heat shield consisting of separate segments according to the invention further makes mounting of the shield possible without the necessity of separating the compressor impeller and turbine blade wheel.

The sealing of the joints between the segments can be obtained by means of thin strips inserted in grooves in the opposed edges of the segments.

The invention also teaches a simple manner of securing the segments to the stationary structure behind them in a way that causes a minimum of stress in the segments and the fastening means. Thus, each segment'is fixedly secured at one point only and restrained from movement in the axial direction of the ring at two further points. The two points at which the segment is withheld in the axial direction only, are located at the inner edge of the segment, and the fastening means are so designed that they may be mounted in advance, so that the segments may be inserted radially between the compressor impeller and the turbine blade wheel without use of tools. This allows an especially compact assembly of the impeller and .blade wheel. At the outer edge the segment can be secured without using axially extending bolts or similar fastening means which would be difficult to insert and lock, in view of the small room available between the impeller and blade wheel. Thus, the segments may at their outer edge have an axially extending flange through which the fastening means used at the outer edge extends radially. Such a fastening means, for instance a bolt, can be inserted in the radial direction and tightened by means of simple tools.

Further features of the invention will be evident from the following specification, reference being had to the accompanying drawings, which illustrate a preferred embodiment of a heat shield according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section of a sectional view through the axis of a radial gas turbine and illustrates the assembly of the heat shield according to the invention,

FIG. 2 illustrates the segments of which the heat shield of the invention consists, as viewed from the rear,

FIG. 3 illustrates a segment viewed from the end, i.e., from the line III-III in FIG. 2,

FIG. 4 is a cross section through the heat shield in FIG. 2 on the line IV-IV,

FIG. 5 is a cross section on the line VV in FIG. 2 through the heat shield adjacent a joint and with a sealing strip inserted, and

FIG. 6 is a cross section similar to that in FIG. 4, but on the line VI-VI in FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS The outer ends of a compressor blade wheel I having vanes 2 and a turbine impeller 3 having vanes 4, respectively, are shown in FIG. 1. From the compressor impeller l the compressed air further passes through diffuser rings, which are indicated at 5 and 6 and which are secured to a diffuser plate 7. From the combustion chamber the hot combustion gases enter the turbine through an inlet nozzle ring 8.

The impeller 1 and 3 are clamped together and blade wheel abut each other in a position that is not shown in FIG. 1. However, between the outer portions of the impeller and blade wheel there is provided an annular groove 9 into which a stationary annular structure 10 extends. The structure 10 is secured to the diffuser plate 7 by bolts 11 and at its inner end carries sealing means 12 which together with the rear face of the rotating compressor impeller 1 forms a labyrinth seal. The stationary structure 10 further carries an annular heat shield made up of segments 13 and spaced from the stationary structure 10 so that between this structure and the heat shield there is formed a substantially closed chamber 14 containing virtually stagnant gas serving as a heat insulation.

The design of the heat shield segments according to the invention appears from the FIGS. 2 to 6. In the embodiment illustrated there are eight segments which are manufactured by cutting a ring in such a way that each gap or joint 17 will have a certain width, which for a ring having a diameter of about 600 mm may be approximately 3 mm. Each segment 13 is substantially flat having, however, an enlarged inner margin 15 and an axially extending flange 16 at the outer edge. An aperture 18 has been drilled in the flange I6 midway between the ends of the segment. In the corners between curved inner edge 19 and the edges 20 facing the adjacent segments there are provided recesses 21 which are best illustrated in FIGS. 2 and 5, and which open towards inner side 22 of the segment. Together with a corresponding recess in an adjacent segment each recess 21 provides an opening for a fastening bolt 23 that is illustrated in FIG. 1. Within the enlarged marginal portion 15 the recess 21 is enlarged as illustrated at 24 (FIG. to accommodate and provide an abutment for head 25 of the fastening bolt 23.

Further, grooves 26 extending in a common plane parallel to the plane of the segments are provided in the opposed edges 20.0f the segments; in these grooves there may be inserted thin strips 27 of a width that is equal to or less than twice the depth of each groove 26 and greater than the depth of one groove plus the maximum spacing of the segments when cold.

Thereby the strips 27 will not prevent heat expansion of the segments 13, and on the other hand they will always seal the joints 17 and thereby prevent the hot gases passing along the front of the segments from penetrating into the chamber 14 and induce undesired movements and exchanges of gas therein. g

The mounting of the segments 13 is best illustrated in FIG. 1, in which the outer end of the stationary structure and the segments 13 are illustrated in a sectional view corresponding to the line lV-lV in FIG. 2, whereas at their inner ends they are illustrated in a sectional view corresponding to the line Ill-ll] in H0. 2. The bolts 23 for fastening the segments at the inner edges thereof are common to two adjacent segments. The bolts maybe mounted in advance in the stationary structure 10 while inserting intermediate plate springs 28. Thereby it willbe possible to force the segments radially into position behind the bolt head 25, the recesses 21 surrounding the shaft of the bolts and the bolt head 25 being accommodated in the enlarged recess 24. The segments are forced down behind the bolt head 25 until the flange l6 abuts the upper end of the stationary structure 10. The segment 13 can now be secured to the stationary structure 10 also at its outer edge by means of a bolt 29 extending through the aperture 18 in the flange l6 and threadedly engaging the stationary structure 10. Thus, it will be seen that each segment 13 is secured at three points, viz. partly by the bolt 29, which secures the segment 13 in such a way that at the point of attachment the segment-can neither move in the axial direction nor in the radial direction relatively to the stationary structure 10, and partly by two bolts 23, which secure the segment against movement in the axial direction relatively to the stationary structure 10, but admit of movement in the radial direction. When the segments 13 are heated in operation they will expand radially inwards and tangentially, and this expansion is possible because of the joints l7 and the way of securing the segmentsat their inner edges.

The novel design of the heat shield of the invention has rendered it feasible to design radial gas turbines having a relatively large diameter and having a compressor impeller and a turbine blade wheel assembled very closely together back to back.

What I claim is:

1. In a turbo-compressor unit comprising a compressor impeller, a turbine blade wheel axially aligned with the compressor impeller and connected thereto to drive the same, and a stationary supporting structure located between the impeller and blade wheel; an annular heat shield structure located in a substantially radial plane between the impeller and blade wheel and secured to said supporting structure, one side of said shield structure being subjected to hot gases in the turbine blade wheel during operation of the unit, said shield structure comprising at least three segments, said segments being individually secured to ,said supporting structure and each of said segments being substantially smaller than the assembled at least three segments, said segments being interconnected to define a substantially gas-impervious annular shield by means of elastic and sealing connecting means allowing each segment to perform, substantially independently of the adjacent segments, the deformations due 0 the increase in temperature and the temperature gradients in the segments during operation of the unit.

2. The heat shield as claimed in claim 1, in which said elastic and sealing connecting means comprises a groove provided in each of the opposed edges of adjacent segments and a thin strip accommodated within the two grooves of each two opposed edges of adjacent segments, I and each strip having a width equal to or less'than twice the depth of each groove and greater than the depth of a groove plus the maximum distance between the opposed edges of adjacent segments when cold.

3. In a turbo-compressor unit comprising a compressor im peller, a turbine blade wheel axially aligned with the compressor impellerand connected thereto to drive same, anda stationary supporting structure located between the impeller and blade wheel; an annular heat shield structure, located in a substantially radial plane between the impeller and blade wheel and secured to said supporting structure, one side of such shield structure being subjected to hot gases in the turbine blade wheel during operation of the unit, said shield structure comprising segments, said segments being individually secured to said supporting structure and each of said segments being substantially smaller than the assembled segments, said segments being interconnected to define a substantially gasimpervious annular shield by means of elastic and sealing connecting means allow each segment to perform, substantially independently of the adjacent segments, the defonnations due to the increase in temperature and the temperature gradients in the segments during operation of the unit, and each segment being fixedly secured at one point only and restrained from substantial movement in the axial direction of the turbocompressor unit at two further points. i

4. The heat shield as claimed in claim 3, in which the fixed securing point is located at the radially outer edge of the segment, while the two further restraining points are located at the radially inner edge.

5. The heat shield as claimed in claim 4, in which the restraining points at the radially inner edge of each segment are located at either end of the segment, and fastening means for fastening the segment at each of such restraining points being common to two adjacent segments.

6. The heat shield as claimed in claim 4, in which fastening means for fastening a segment at each of the restraining points at the radially inner edge comprises a headed bolt extending at right angles to the plane of the segment and spring biased in its axial direction, and the inner edge of the segment being provided with a recess for the bolt.

7. The heat shield as claimed in claim 4, in which each segment at its radially outer edge has an axially extending flange, fastening means for fastening the segment at at the fastening point located at the radially outer edge of the segment extending radially through said flange.

t F I t t

Claims

1. In a turbo-compressor unit comprising a compressor impeller, a turbine blade wheel axially aligned with the compressor impeller and connected thereto to drive the same, and a stationary supporting structure located between the impeller and blade wheel; an annular heat shield structure located in a substantially radial plane between the impeller and blade wheel and secured to said supporting structure, one side of said shield structure being subjected to hot gases in the turbine blade wheel during operation of the unit, said shield structure comprising at least three segments, said segments being individually secured to said supporting structure and each of said segments being substantially smaller than the assembled at least three segments, said segments being interconnected to define a substantially gasimpervious annular shield by means of elastic and sealing connecting means allowing each segment to perform, substantially independently of the adjacent segments, the deformations due to the increase in temperature and the temperature gradients in the segments during operation of the unit.

2. The heat shield as claimed in claim 1, in which said elastic and sealing connecting means comprises a groove provided in each of the opposed edges of adjacent segments and a thin strip accommodated within the two grooves of each two opposed edges of adjacent segments, and each strip having a width equal to or less than twice the depth of each groove and greater than the depth of a groove plus the maximum distance between the opposed edges of adjacent segments when cold.

3. In a turbo-compressor unit comprising a compressor impeller, a turbine blade wheel axially aligned with the compressor impeller and connected thereto to drive same, and a stationary supporting structure located between the impeller and blade wheel, an annular heat shield structure, located in a substantially radial plane between the impeller and blade wheel and secured to said supporting structure, one side of such shield structure being subjected to hot gases in the turbine blade wheel during operation of the unit, said shield structure comprising segments, said segments being individually secured to said supporting structure and each of said segments being substantially smaller than the assembled segments, said segments being interconnected to define a substantially gas-impervious annular shield by means of elastic and sealing connecting means allow each segment to perform, substantially independently of the adjacent segments, the deformations due to the increase in temperature and the temperature gradients in the segments during operation of the unit, and each segment being fixedly secured at one point only and restrained from substantial movement in the axial direction of the turbo-compressor unit at two further points.