US2657901A

US2657901A - Construction of turbine rotors

Info

Publication number: US2657901A
Application number: US674229A
Authority: US
Inventors: Mcleod Roderick Cristall
Original assignee: Power Jets Research and Development Ltd
Current assignee: Power Jets Research and Development Ltd
Priority date: 1945-06-08
Filing date: 1946-06-04
Publication date: 1953-11-03
Anticipated expiration: 1970-11-03

Description

CONSTRUCTION OF TURBINE ROTORS Filed June 4, 1946 4 Sheets-Sheet l lnvenlor MRI (7/5??? McLEOO,

Q QW

Attorney Nov. 3, 1953 R. c. McL o 2,657,901

CONSTRUCTION OF TURBINE ROTORS Filed June 4, 1946 4 Sheets-Sheet 2 mac-010v 01 455 77414 McL 00,

lnvenl y Attorney Nov. 3, 1953 R. c. MOLEOD 2,657,901

CONSTRUCTION OF TURBINE. ROTORS Filed June 4, 1946 4 Sheets-Sheet 3 Inventor IPODfP/C/f AS72 44 MCLEOD,

Nov. 3, 1953 R. 1c. MCLEOD CONSTRUCTION OF TURBINE ROTORS 4 Sheets-Sheet 4 Filed June 4, 1946 v OI In van or W44 MCLIOO) A Itorney Patented Nov. 3, 1953;

UNITED STATES iiATENT OFFICE CONSTRUGTION F TURBINE BOT-OBS Roderick 'Cr'ista'll McLeod, Leicester, England, as-

signer to Power-Jets (Research '62Development) Limited, London, England Application June '4, 1946, Serial No. 574,229 "Claims priority, application Great Britain 'June 8, 1945 7 Claims. (01. 253-39.-15)

This invention relates to the "construction of multistage turbine rotors and whilst it isdeemed to be especially applicable to gas turbines in which certain special problems of design may arise it is capableof being applied to other turbines also.

In turbines generally and in gas turbinesin particular there are 'difii'culti'es of design in relation to the appropriate disposition of stresscarrying structure in a multistage rotor, particularly if the rotor is required to operate -at high speeds and is subject -to marked temperature gradients and high temperatures at least locally. These design problems are particularly acute if it be required to minimize "the-weight of the turbine rotor as for example in the case of a gas turbine for aircraft use.

The invention accordingly has two main objects in View; firstly, to provide'a multistage rotor whose stress-carrying structure is designed and arranged to afford adequate mechanical strength with economy in total mass; secondly, to provide adequate cooling to enable the temperature gradients-as between difi'erent parts of the rotor to be kept within acceptable limits.

The invention is based upon an appreciation of the fact that the attaimnentof these objects can be facilitated by the use of a composite rotor built up from a plurality of individual bladecarrying discs or wheels, "and-hasa number "of aspects concerned with givingfpractical form to this basic conception.

Considered from one aspect, the inventicn provides a multistage turbine rotor "consisting of or comprising two coaxial bladed wheel-type rotor elements axially abutting with a non-bladed intermediate wheel-type rotor element, whose -rim preferably forms thelrotor surface between {said bladed elements, said intermediate and bladed elements having between them radially interengaging connecting means by which they are mutually located "and "supported in :the radial sense relatively to one another.

In a further aspect of the invention, thetwo coaxial bladed rotor "elements 'haveb'etween them an annular space-which is divided by the intermediate rotor element against which they abut to define separate ."annular cavitiesfithese cavities being associated with ducting at an inner'radius for the entry of cooling air and with ducting :at a greater .radius, (preferably in the region of the blade roots/for the .egressof such air.

According to .a further feature of the lastmentioned aspect of the invention, theinternal cooling of the rotor is associated with cooling of its external faces and bearing, for which purpose the upstream and downstream external races have adjacent thereto stationary structure defining with each face a narrow annular cav ity having a supply-of cooling air entering at aradially inner diameter and "leaving at a greater diamiter, preferably in the region or the blade roo s.

It is necessary that provision should "be :made

for holding all the elements together in the axial sense and this, according to a further feature (of the invention, is achieved by providing "an axial extension on the hub of the bladed element at one end of the rotor which passes through the hub of the bla'ded element oreach fiurther hl'aded element and *the' spacing element or 1 each spacing element and has "a nut or other retaining means at its free end.

According to a' further'ieatu-reof the invention, some, but not all the elements :of :the motor are self-supporting in relation to :centrifugal load, and such self-supporting elements are used to give centrifugal support to those which are not self-supporting.

"The invention in its various aspects vmay :he applied either to an overhung multistage vturbine rotor '(-that is, "one which has a bearingssupport at one endonly), or to one :havingaabeaning support at each end, and a number .of further features of the invention arising from :these two applications thereof will appear :from the following description of the two examples :of nonstruct'ion, one an overhung rotor and the :other not, illustrated "in the accompanying drawings in which:

Figure 1 is a longitudinal half'section .of part of an aircraft gas turbine power xnnit embodying an overhung two stage -rotor :constructed according to the invention, sullicient :parts .of the unit being shownto illustrate the relation of the iturbine rotor tothe other elements cofthe unit;

Figure'2 =is=a section on a larger scale of the rotor illustrated inFigure l, and its beaizingr-supp Figure 8 is a viewgenerajlly similar to Figure 2, but illustrates the *inveniton applied to a three stage rotor supported at both ends and suitable for "inclusion "in a powernnit of the general form illustrated in "Figure "1*;

Figure 14 is a detail'view of'therotors-shown in Figures? and 3; and

Figure '5 is an end view of the arrangement shown in Figure '4.

The small arrows throughout the drawings represent the direction of flow of cooling air,

Referring first to Figure l, the power unit to which the rotor according to the invention is shown as being applied comprises a compressor (of which only thet last stage is shown) supplying air to an annular air casing afforded by inner and

outer annuli

2, 3, and containing an annularly disposed set of flame tubes 4 into which fuel is injected by burners 5. The products of combustion are discharged through blading 8 of a two stage axial flow turbine whose rotor is mounted on and drives the compressor I through a shaft 1. It will be noted that the turbine rotor is overhung, that is to say, it is supported only at one end, in this case by the shaft bearing 8 at its upstream end,

The inner annulus 2, together with its associated end structure 2a, forms an enclosed chamber 9 whose atmosphere is maintained under pressure by air taken from the aircasing by connections l through cooler 60, whilst the shaft 'l is hollow to form an air duct and is ported at H to communicate with the chamber 9.

The features so far described and illustrated are intended merely to give the general background or framework of a power unit to which the invention may be applied and do not in themselves form a part of the invention except in so far as they afford a means of supplying air for cooling purposes to the turbine rotor and its bearing,

to which function further reference is made below.

Considering now in more detail the rotor and rotor mounting construction illustrated in Figure 2, the first stage blading is carried, preferably by serrated roots l2, in complementary axial slots by a first rotor element in the form of a wheel |3 which has a relatively massive hub l4 bolted to an end flange on the turbine shaft 1. This hub l4 has a coaxial extension l5 towards the downstream side, i. e. away from the shaft 1. The second stage blading is similarly carried on a second rotor element or wheel i6 which has a somewhat less massive hub l1 centrally bored so as to surround the extension l5 of the first hub and to leave an annular a coolant duct. The axial extension I5 is radially ported at IQ for the passage of coolant air from within its hollow interior (to which compressed air is supplied from the chamber 9 by the ports I|) into the annular duct spaced axially to form radial coolant ducting at in continuation of the annular duct. Between the two blade-carrying wheels l3, IS, a third much lighter intermediate rotor element or wheel 2| is situated. This third wheel has at its inner margin a thickened hub or rim 22 provided with accurately machined radially facing steps or surfaces 23 which are fitted in engagement with complementary inwardly facing circular surfaces formed on flanges 24 projecting axially from the mutually facing sides of the first two wheels l3, IS. The fit between these respective surfaces is preferably a shrink fit and the object of the construction at this point is to afford radially locating engagement between the two blade carrying wheels l3, l5, whereby the wheel I6 is radially located relative to the wheel l3, whilst simultaneously the third wheel 2| is radially located relatively to both. The third wheel 2| extends outwardly and preferably with a tapered section to the region of the blade roots and at a radius just less than the minimum root radius has on each of its sides flanges 25 extending axially which are serrated to engage corresponding flanges 26 extending inwardly from the blade clearance at l8 forming IS. The two hubs are carrying wheels l3, It. This engagement is for the transmission of torque between the two blade-carrying wheels and does not take part in their radial location relatively to the wheel 2|. Still further outwardly the third wheel extends to its periphery at which it has a T sectioned rim 21 to form a peripheral cylindrical surface which forms the inner fluid guiding surface of the turbine annulus between the two rotor blade stages. This rim may incidentally serve as the inward abutment of the turbine blade roots l2, preventing their shifting axially in that sense.

The third wheel 2| partitions the interior space enclosed by the first two wheels l3, l6, into upstream and

downstream cavities

28, 29, of annular form, the air ducting at 20 previously referred to being thus split into two by the hub 22. Passages 30 are formed through the locating flanges 24 for the passage of air outwards through the two

cavities

28, 29. These passages may be differently proportioned to act as restricttions controlling the pressure of the air in the

cavities

28, 29. For example it may be arranged that the cavity 28 will be maintained at a pressure of approximately twice that of the cavity 29 for a reason mentioned later. The torque-transmitting flanges 26 are also provided with air passages 3| by appropriate clearances between their serrations, and still further passages are provided in or in the region of the fitting of the blade roots to the wheels, for example beneath the roots as shown. The coolant air is therefore passed from the

cavities

28, 29, over the somewhat extensive areas of the structure formed by the serrations Or dogs and thence through the root passages. The air from the upstream cavity 28 emerges on the upstream side of the first wheel I3 and escapes radially outwardly into the turbine annulus; the reason that the pressure at which this air is delivered is maintained high, is in order to avert any possibility of reversal of flow, i. e. from the turbine annulus into the turbine rotor chamber. The air pressure is of course selected to ensure airfiow in the desired sense. The air from the cavity 29 emerges by a similar route to be discharged on the downstream side of the turbine where it leaks outwardly to join the exhaust from the turbine.

The wheels I3, l6, 2| are kept together axially by a lock nut arrangement 32 on the hub extension l5 of the wheel l3.

It will be appreciated from the foregoing that although the first wheel I3 is fixed in both the axial and the radial sense on the shaft 1, the relative positioning of all the wheels, I3, l6, 2|, in the radial sense is determined solely by the complementary interengagement of the flanges 24 on the wheels |3, IS, with the surfaces 23 on the wheel 2|, by means of which the wheels l6, 2|, are mutually located in the radial sense relatively to one another and upon the wheel |3.

It is a further feature of the construction that the hubs l4, H, are made self-supporting in relation to centrifugal load and are used to give centrifugal support through the flanges 24 and faces 23 to the hub 22 which, accordingly, is not made to be centrifugally self-supporting. By this means, use is made of the relatively large mass of the hubs l4, H, to afford adequate anchorage for the hub 22. Further, as the

interengaging parts

23, 24, are at a small radius there is an advantageous concentration of mass near the centre of rotation. With such an arrangement the hub 22 would be more highly stressed than the hubs I4, l'l, so that under running conditions of the intermediate wheels 2|, 43. Due to their direct exposure to the hot working gas stream, these rims are necessarily at the temperature of the latter, and since they are not interrupted, as are the rims of the wheels [3, I6, 42, by blade root mountings which will usually allow a sufiicient degree of thermal expansion to avoid unacceptable thermal stresses, special provision is necessary to avoid such stresses therein. To this end the rims 21 of the wheels 2|, 43, may have applied thereto the subject matter of our co-pending patent application number 665,106 filed April 26, 1945, now Patent No. 2,623,727 of December 30, 1952, in the name of the inventor in the present application, in accordance with which the rims 21 of the wheels 2|, 43, have radially extending slits as at 51 which are peripherally closed by lips susceptible of crushing when expansion of the rims takes place. Where it is necessary, owing to the existence of difierential air pressures on opposite sides of the wheels 2|, 53, to limit leakage in an undesired direction through the slits 51, the latter are sealed as by loosely fitting plugs 58 and screws 59.

I claim:

1. A multistage turbine rotor designed for overhung mounting, comprising a rotary bearer member, a first bladed rotor element of substantially disc-form fixed in both the axial and the radial sense on said rotary bearer member, a further coaxial and substantially disc-form bladed rotary element, a non-bladed substantially disc-form intermediate rotor element arranged between said bladed elements, said intermediate element having a peripheral portion on t either side thereof in axial abutment with the bladed elements to permit relative sliding movement in a radial direction due to thermal expansion and contraction, and said intermediate and further rotor elements each having anaxial bore, means providing between said intermediate element and both the bladed elements complementary interengagment by which alone said intermediate element and the further bladed element are mutually located and supported in the radial sense relatively to one another and upon the first bladed element, and tensioning means extending from said first element through said axial bores with radial clearance therein to retain said intermediate and further elements against axial displacement.

2. A multistage turbine rotor designed for bearing support at each end, comprising a first rotary bearer member, a first bladed rotor element of substantially disc form fixed in both the axial and the radial sense on said rotary bearer member, at least one further coaxial and substantially disc-form bladed rotor element, a non-bladed and substantially disc-form intermediate spacing rotor element arranged between any one of said bladed elements and the one adjacent to it, said intermediate element having a peripheral portion on either side thereof in axial abutment with said bladed elements, and said intermediate and further elements each having an axial bore, means providing between such intermediate element and its abutting bladed elements complementary interengagement by which it and said elements are mutually located and supported in the radial sense relatively to one another, tensioning means extending from said first element through said axial bores with radial clearance therein to retain said intermediate and further elements against axial displacement, and a second rotary bearer mem- 8 her nominally coaxial with but separate from the bearer member of the first bladed element and from said tensioning means and upon which the last bladed element in the succession is fixed in both the axial and the radial sense.

3. A multistage turbine rotor as defined in claim 2, wherein said tensioning means comprises, for holding all the elements together in the axial sense, an axial extension from the hub of the bladed element at one end of the rotor which passes with a radial clearance through the hub of each further bladed element and each spacing element, and retaining means at the free end of said extension.

4. A multistage turbine rotor designed for bearing support at each end, comprising a first rotary bearer member, a first bladed rotor element of substantially disc-form fixed in both the axial and the radial sense on said rotary bearer member, at least one further coaxial and substantially disc-form bladed rotor element, a nonblacled and substantially disc-form intermediate spacing rotor element arranged between and in axially abutting relationship at both its central and peripheral regions with any one of said bladed elements and the one adjacent to it, said intermediate and further elements each having an axial bore, means providing between such intermediate element and its abutting bladed elements complementary interengagement by which it and said elements are mutually located and supported in the radial sense relatively to one another, tensioning means extending from said first element through said axial bores with radial clearance therein to retain said intermediate and further elements against axial displacement, said tensioning means comprising an axial extension from the hub of the bladed element at one end of the rotor and passing with a radial clearance through the hub of each further bladed element and each spacing element, and retaining means at the free end of said extension, a second rotary bearer member nominally coaxial with but separate from the bearer member of the first bladed element and from said tensioning means and upon which the last bladed element in the succession is fixed in both the axial and the radial sense, and means for passing coolant fluid through said axial extension into said radial clearance and thence into the space on either side of said intermediate elements.

5. A multistage turbine rotor designed for overhung mounting, comprising a rotary bearer member, a first bladed rotor element of substantially disc-form fixed in both the axial and the radial sense on said rotary bearer member, a further coaxial and substantially disc-form bladed rotor element, a non-bladed substantially disc-form intermediate rotor element arranged between and in axially abutting relationship at its peripheral regions with said bladed elements, said intermediate and further elements each having an axial bore, means providing between said intermediate element and both the bladed elements complementary interengagement by which alone said intermediate element and said further bladed element are mutually located and supported relative to one another and upon the first bladed element, an axial extension from the hub of said first-mentioned bladed element which passes with a radial clearance through the axial bores of said intermediate and further elements and retaining means at the free end of the extension to retain said intermediate and further elements against axial displacement.

6. A multistage turbine rotor comprising a first and second bladed rotor element of substantially disc-form having between them an annular space, a non-bladed substantially disc-form intermediate rotor element lying between said bladed elements to divide said annular space into separate annular cavities and abutting with said bladed elements at both its central and peripheral regions, said second and intermediate elements each having an axial bore, a shaft extending from said first rotor element through said axial bores with radial clearance and retaining means at the end of said shaft to retain said intermediate and second rotor elements against axial displacement, and means for the entry of air to the cavities of said rotor, said last named means including ducting aflorded in the shaft and by spaces between the hubs of the rotor elements.

7. A multistage turbine rotor designed for overhung mounting, comprising a rotary bearer member, a first bladed rotor element of substantially disc-form fixed in both the axial and the radial sense on said rotary bearer member. a further coaxial and substantially disc-form bladed rotary element, a non-bladed substantially disc-form intermediate rotor element arranged between said bladed elements, said intermediate element having a peripheral portion on either side thereof in axial abutment with the bladed elements, and said intermediate and further rotor elements each having an axial bore, means providing between said intermediate element and both the bladed elements complementary interengagement by which alone said intermediate element and the further bladed element are mutually located and supported in the radial sense relatively to one another and upon the first bladed element, an axial extension from the hub of the first bladed element extending through said axial bores with radial clearance therein, retaining means at the free end of said extension to retain said intermediate and further elements against axial displacement, and means for passing coolant fluid through said axial extension into said radial clearance and thence in to the space on either side of said intermediate element.

RODERICK CRISTALL MCLEOD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,399,816 Spiess Dec. 13, 1921 2,117,131 Auger May 10, 1938 2,173,489 Voight Sept. 19, 1939 2,200,287 Lysholm May 14, 1940 2,356,605 Meininghaus Aug. 22, 1944 2,393,963 Berger Feb. 5, 1946 2,401,826 Halford June 11, 1946 2,427,614 Meier Sept. 16, 1947 2,440,069 Bloomberg Apr. 20, 1948 2,452,782 McLeod et al Nov. 2, 1948 2,461,243 Soderberg Feb. 8, 1949 2,532,721 Kalitinski et a1 Dec. 5, 1950 FOREIGN PATENTS Number Country Date 103,746 Sweden Dec. 18, 1941 402,525 Germany Sept. 20, 1924 876,194 France July 20, 1942