US2843354A

US2843354A - Turbine and like blades

Info

Publication number: US2843354A
Application number: US171263A
Authority: US
Inventors: Austin G Smith
Original assignee: Power Jets Research and Development Ltd
Current assignee: Power Jets Research and Development Ltd
Priority date: 1949-07-06
Filing date: 1950-06-30
Publication date: 1958-07-15
Anticipated expiration: 1975-07-15
Also published as: BE496812A; NL73916C; GB728834A; GB680118A; FR1022398A; CH286626A; FR66874E

Description

y 1958 A. cs. SMITH 2,843,354-

' TURBINE AND LIKE BLADES Filed June 30. 1950 2 Sheets-Sheet 1 FIG. 3 A

Invenfor, y" WM [M4, 4 AL; Attorney;

y 5, 1958 A. G. SMITH 2,843,354

TURBINE AND LIKE BLADES Filed June 30, 1950 2 Shets-Sheet 2 FIG.8. '4.

2 y In vensor mwmtw TURBINE AND LIKE BLADES Austin G, dnilth, iilaby, England, assignor to Power Jets (Research and Development) Limited, London, England, a hrlitish company Application June 30, 195% Serial No. 171,263 Claims priority, application Great Britain July 6, 1949 9 Claims. (Cl. Edd -39.15)

This invention relates to cooling arrangements for tun bine and like blades required to operate at high tern peratures (e. g. above 700 C.), and is concerned with that class of cooling arrangement in which a blade is provided with an internal passage through which, in the operation of the blade, flows a coolant fluid.

The present invention resides in the realisation that in such a cooling arrangement it is advantageous to vary the internal conductance from place to place along the length of the passage, co iductance, being defined as ocS, where a is the coefilcient of heattransfer and S the surface area per unit length'of the passage. It is envisaged that the manner of such variation should be determined on the basis of either or both of two con siderations: firstly, the need to, vary the cooling provision along the length of the passage in the general sense required by variation of the gas temperature and/ or mechanical stress; secondly, the desirability of effecting the requisite cooling with maximum economy in the use of coolant, which implies a close correspondence between the cooling required at any station in the passage and that actually provided. For example when the coolant is discharged into the turbine working fluid it should, from the point of view of plant efficiency, be at the maximum practicable temperature when it emerges into the working fluid flow, which implies limitation of the rate of flow of coolant and a high coolant temperature at the outlet end of the coolant passage resulting in correspondingly reduced cooling capacity in that region. The former consideration would indicate on the one hand that the internal heat transfer surface should be designed on the basis of securing maximumconductance in the region at which the most onerous stress-temperature combination occurs (which might be, for example, in the case of an axial flow turbine,- at about on third of the blade height from the root), and on'the other that the conductance should increase progressively in the direction of coolant flow to compensate for the rising temperature of the coolant. The second factor implies the formulation of some method of determining cooling requirements. Such a method will be described more fully hereafter with referenceto. theaccompanying drawings. We have found that generally speaking, from a structural point of view, it is not difiicult at the inlet end of a passage, where the coolant provides a considerable temperature difference, to achieve a conductance suflicient to result in an acceptable stress-temperature relationship, even though at that region the stress may rise to its maximum value; depending,.therefore, upon the manner of variation of the stress-temperature relationship over the length of thepassage, it may happen that, having chosen a suitable variation of conductance to satisfy the temperature factor, the stress factor will be incidentally dealt with. The fact that adequate conductance at the entry end of the passage is readily achievable, however, necessitates caution if unnecessary overcooling at that regionis to be avoided, with consequent premature heating of the coolant, to the detriment of its subsequent efiectiveness. This danger maybe avoided by selecting the manner of variation of conductance by the method described hereafter with reference to the accompanying drawings.

There are a number of possible methods by which the internal conductance OLS can be varied, namely by varying or by changing the form of the heat conducting surface while keeping S constant, or varying the value of S while keeping a constant, or by varying both these quantities, as by varying the cross sectional area of the passage and hence the coolant velocity.

it is, however, difficult, using a smoothed walled passage in the conditions of operation normallylencountered in a gas turbine, to achieve an internal heat conductance sufficiently high to produce an adequate cooling effect, and, moreover, in such a case, change of cross sectional area has to be relied upon in order to vary the conductance. In order to mitigate this difiiculty it has already been proposed in copending application Serial No. 62,813 filed October 5, 1948, now Patent No. 2,750,147 in the name of the present inventor, to provide within the passage and in heat conducting relationship with a blade body, heat conducting structure of such form as to increase the area of the heat transfer surface per unit length as compared with a smooth walled passage and, hence, the overall or aggregate internal conductance of the passage, the structure in these. particular prior proposals being fabricated separately from the blade for insertion into the passage.

In its preferred practice, form, the present invention also makes use within the blade cooling passage of an extended heat conducting formation to increase the aggregate internal conductance of the passage, but additionally proposes to vary the conductance by varying from place to place the form or distribution of the heat exchange surface provided by said formation.

In the practical execution of the invention it is preferred, in further accordance with the invention, to make up an inserted heat conducting structure from a plurality of discrete, elements mounted in succession along the length of and Within the. coolant passage as an assembly unitary with the blade and in heatconducting relation therewith, each element being gapped to permit the flow of coolant through or around it and along the passage. By the use of discrete elements in this way it is readily possible to vary their spacing along the length of the passage and hence to obtain a variation of the amount of heat exchange surface available per unit of that length.

The discrete elements making up the heat conducting insert may take a variety of forms such as to affordv a succession of partitions or similar obstructions across or in the coolant passage, the flow of coolant being permitted by passages altorded either by the shape of or by holes in the elements, and successive elements may be designed to provide for a tortuous coolant path either by the use of diiferent combinations of holes therein or by diiferentlyarranging successive similar elements with respect to the axis of the passage.

The elements may also be either separately introduced into the blade passage and subsequently secured therein, in which case their location can readily be controlled by the use of a rarnrod whose penetration into the passage is accurately controlled, or may be previously as sembled'on acarrier and inserted into and secured in the blade passage as a group. In either case the final ses curing of the elements in the passage may be achieved by brazing,vthe efiectiveness of which may be aided by the use of elements having an extended rim, and in the second case the carrier (e. g. a central rod) may remain as a partof the finished unit.

it may be advantageous to shape the inserted elements,

' 3 for example by dishing, so that the elements have lateral flexibility to minimize any tendency for differential expansion to weaken the attachment between an element and the inner wall of the passage.

The passages into which the elements are positione may be formed in various ways. Thus, for example, the blade may be solid and the passages drilled out from the solid blade; or the blade may be cast with preformed passages which may be subsequently suitably worked to the required dimensions; or (more particularly in the case when it is desired that the elements should be noncircular) the blade may be formed from a number of laminae each having an aperture whose section corresponds to that ofthe required passage, these laminae being subsequently brazed together to form a block from which the blade may be machined.

By way of example, various forms of the invention are illustrated in the accompanying drawings in which:

, Figure 1 is a transverse section through a turbine blade having a number of internal passages.

Figure 2 is a fragmentary longitudinal section on the line IIII in Figure 1 and to an enlarged scale showing in perspective the arrangement of inserted elements.

Figure 3 is a side view of a blade partly in longitudinal section showing the general arrangement of a coolant p-assage therein and a possible distribution of inserted elements in said passage.

Figure 4 is a view similar to that of Figure 2 showing an alternative form of element.

Figures 5 and 6 are respectively a face view and axial section of an alternative form of insert element.

Figure 7 is a side view of a spacer for use therewith.

Figure 8 is a fragmentary section to an enlarged scale of the insert elements and spacers of Figures 5 to 7 assembled in a blade passage.

Figure 9 shows curves illustrating a method of choosing the manner of variation of the internal conductance of a passage.

Figure 10 shows a modification of the arrangement shown in Figure 8.

In Figure 1, a blade 1 is provided with

longitudinal passages

2a, 2b, 2c, 2d and 2e. The

passages

2a, 2b, and 2c are circular or the passage 2d is approximately rectangular and the passage 2e is approximately triangular. Within these passages are placed a number of thin sheet elements extending transversely across the passage and acting as an assemblage of cooling fins. The elements in the passage 2a take the form of perforated discs 3 having a number of apertures 3a which are arranged in a regular pattern over the entire surface of the disc in simulation of wire mesh, those in passage 2b are gauze discs 4 having any number of wires, and those in

passages

2d and 2c are perforated plates 5, 6. In the passage 2c, the elements, as shown in Figure 2, comprise a number of perforated discs 7 alternating with imperforate discs 8. Each disc 7 has a central aperture 7a, while each disc 8 is larger than the aperture 7a andis secured to the inner wall of the passage 2 by means of radial arms 9.

Figure 3 shows a blade 1 having a longitudinal passage 2, in which a number of elements are arranged at varied spacing along the passage, being closer at the region 19 intermediate the root and tip ends of the passage 2 than at other regions along the passage 2,, this distribution typifying one arrived at solely on the assumed basis that 10 is the region of most onerous stresstemperature relationship. The elements may be entered into and located in the passage by the use of a ramrod and secured by copper or other high melting point brazing. a

Figure 4 shows a. perforated disc element 11, which is dished in order to enable centrifugal force to assist the attachment of the element to the inner wall of the passage 2.

In all the above described arrangements, the inserted elements are in good heat conducting contact at their edges with the inner wall of the passage in which they are inserted. Further they have surfaces exposed to the flow of coolant fluid through the passages, which surfaces constitute heat exchange surfaces for transferring heat from the elements and hence from the blade to the coolant fluid.

The elements so far described are intended to be manufactured by stamping from metal sheet or gauze; the alternative form illustrated in Figures 5 to 8 is intended for manufacture by machining. In the latter case, to simplify production, it is proposed that the inserted structure should be made up of any required number of identical elements 12 of the form shown in Figures 5 and 6, each machined from solid blanks and mounted as a unitary assembly (Figure 8) on a support rod 13, the individual elements being differentially spaced by the use of spacers 15 (Figure 7) of different sizes. In manufacture, the blanks for the elements 12, aftr drilling, may be mounted on the rod 13 without spacers and milled to form their radial arms, the group being thereafter dismantled and reassembled with appropriate spacers and with their radial arms out of phase, and the whole group inserted into a. blade passage and copper brazed in position. The elements 12 may then be thought of as cooling fins extending from the rod 13. It may be contrived that at this stage any securing nuts, if used, and possibly also the carrier rod, are dispensed with, leaving the elements and spacers secured to each other and the blade solely by brazing.

In this arrangement, the heat exchange surfaces are constituted by the side and end surfaces of the radial arms of the elements 12. As shown in Figure 8, the spacing of the elements is varied along the length of the passage 2, the spacing decreasing from one end to the other, and so the area of the heat exchange surface per unit length of the passage and the internal conductance of the passage varies in a corresponding manner.

In the embodiment of Figure 10, the area of the heat exchange surface per unit length of passage is further varied by making the elements 12 of different axial lengths.

The preferred method of choosing the manner of variation of the conductance, whether by varying the spacing of the inserted elements or otherwise, is'as follows,

assuming an axial flow blade with a straight longitudinal passage discharging into the turbine working fluid, and using the following symbols:

2: temperature azcoeflicient of heat transfer S :surface area per unit length L:total blade length lzlength along the blade K tspecific heat mzmass flow per unit time subscripts b:blade czcoolant g:gas (turbine working fluid) i:internal (of the passage) oaexternal (of the passage) rzroot t:tip

It has been found that in such a blade the variation of the maximum permissible blade temperature T along the blade length, taking into account the varitation of centrifugal stress, can be taken as being approximately linear as typified by the curve T in Figure 9. Having decided upon an attainable conductance at the blade tip one can calculate the coolant exit temperature T from the ratio of internal to external conductance Having thus obtained the coolant. exit temperature, the coolant flow quantity can be determined byequating The conductance ratio then necessary at each part of the blade may be calculated from the following This gives conductance ratios as typified by the curve Cr in Figure 9, which curve serves as a basis of design which may be departed from to satisfy minor refinements.

i claim:

1. In a combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, and a plurality of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of said fluid along the passageway, being in good heat conducting contact at their edges with the passagewaydefining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being variably spaced along at least part of the passageway so that the area of said heat exchange surfaces per unit length of the passageway varies along at least this part of the passageway.

2. In combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, and a plurality of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of said fluid along the passageway, being in good heat-conducting contact at their edges with the passageway-defining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being variably spaced along the passageway and being closer together at the region intermediate the root and tip ends of the blade than at the root and tip ends.

3. In combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, and a plurality of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of said fluid along the passageway, being in good heat-conducting contact at their edges with the passage-defining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being variably spaced along the passageway, the spacing decreasing from one end of the passageway to the other.

4. In a combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, a central support extending lengthwise of the passageway and a plurality of elements mounted on said support within saidpassageway and, extending transversely, with respect theretoand axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of saidfiuid along the passageway, being in good heatconducting contact at their edges with the passageway-defining portion of the blade and having heat exchange; surfaces exposed to the flow of said fluid, said, elements being variably spacedqalong at least partof the passageway so that the area of said heat exchange surfaces per unitlength of thepassageway varies along at least this parttofthe assageway.

5. In a combination, aturbine blade having-root and tip ends and a portion, defining; an internal passageway extending lengthwiseof the blade from the rootend to the tip end to permit the flow'of coolant fluid,.and;a .plurality of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along thelongitudinal axisythereof, said elements being apertured to permit the flow of said fluid, along the passageway, being in good heat-conducting contact at their edges with the passageway-defining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being of different dimensions along at least part of the passageway so that the area of said heat exchange surfaces per unit length of the passageway varies along at least this part of the passageway.

6. In combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, and a plnraiity of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of said fluid along the passageway, being in good heat-conducting contact at their edges with the passageway-defining portion of the blade and having heat exchange surfaces exposed to the flow or" said fluid, said elements being of different lengths along at least part of the passageway, so that the area of said heat exchange surfaces per unit length of the passageway varies along at least this part of the passageway.

7. In a combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, and a plurality of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of said fluid along the passageway, being in good heat-conducting contact at their edges with the passageway-defining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being of different lengths with the greater length elements being at the region intermediate the root and tip ends of the blade.

8. In a combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, and a plurality of elements within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said ele ments being apertured to permit the flow of said fluid along the passageway, being in good heat-conducting contact at their edges with the passageway-defining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being of different lengths and positioned along the longitudinal axis of the passageway with the lengths of said elements decreasing from one end of the passageway to the other.

9. In combination, a turbine blade having root and tip ends and a portion defining an internal passageway extending lengthwise of the blade from the root end to the tip end to permit the flow of coolant fluid, a central support extending lengthwise of the passageway and a plurality of elements mounted on said support within said passageway and extending transversely with respect thereto and axially spaced from one another along the longitudinal axis thereof, said elements being apertured to permit the flow of said fluid along the passageway, being in good heat-conducting contact at their edges with the passageway-defining portion of the blade and having heat exchange surfaces exposed to the flow of said fluid, said elements being of different lengths along at least part of the passageway so that the area of said heat exchange surfaces per unit length of the passageway varies along at least this part of the passageway.

References Cited in the file of this patent UNITED STATES PATENTS OWin Sept. 13,

'2?) Koch June 28, Schaper Sept. 26, 1 Young 1, June 9, Zellbeck et a1 Sept. 29, Birmann Sept. 10, Price Aug. 29, Franz Sept. 25, Goetzel Jan. 1, Smith Ian. 12,

FOREIGN PATENTS Switzerland May 1, Great Britain Apr. 11, Great Britain July 1,