US2727716A - Bladed body - Google Patents

Description

Dec. 20, 1955 G. B. R. FEILDEN ETAL BLADED BODY 3 Sheets-Sheet 1 Filed Dec. 18, 1946 FIG.2.

tlzhitforneys Dec. 20, 1955 G. B. R. FEILDEN ET AL BLADED BODY 3 Sheets-Sheet 2 Filed Dec. 18, 1946 FIG. 8

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a. B. R. FEILDEN ETAL BLADED BODY Dec. 20, 1955 Filed Dec. 18, 1946 5 Sheets-Sheet I5 Altar/1e yr United States Patent to Power" Jets (Research and Development)" Limited,

London, England, a' British company Application December 18, 1946,- SerialNo. 716530 Claims priority, application Great Britain December 21, 1945 4 Claims. (Cl. 253-47) This invention relates to improvements in the mounting of rotor blades in axial flow compressors, turbines, or similarly bladed fluid flow machines and has particular although not exclusive application to the case of axial flow units of this kind,,when used to deal with gaseous fluids in gas turbine engines for aircraft.

In high speed axial flow rotor blading for dealing with gaseous fluid'at high mass flows (as in aircraft gas turbine units) it has hitherto been the general practice to compensate the total load on each blade by oflsetting the centre of gravity of the blade sections in a direction such that the centrifugal force produces a bending moment on the blade equal and opposite to that produced by the gas load. This compensationcan, however, be correct at only one particular gas loading so that when this loading varies, for example with a change of air density or altitude there remains a residual stress on the blade. Furthermore, since the blade stresses are generally high it is necessary for the blades to be of relatively substantial chord and thickness, which adds to the weight and costof the whole structure.

The present invention aims at enabling compensation of the kind indicated, in an axial flow compressor, turbine or similarly bladed machine, to be effectivelover a range of operating conditions, with the consequent advantage of also enabling the blades to be of much smaller chord than otherwise would be the case so long as this range is not exceeded, since the fluid loading may then be disregarded, or with a correspondingly smaller advantage if the range is exceeded.-

The invention accordingly provides, in an axial flow compressor, turbine, or similarly bladed fluid flow ma- Chine having axial flow rotor blades so arranged that in the co'nditions of operation the centrifugal and fluid loads impose opposing bending moments thereon, and especially in a high speed machine of this kind operating with 4 more" specifically, each blade may have a pivot extending in the axial sense of the rotor, although notnecessarily in the. plane of the rotor axis; or each blade may be mounted for tilting by means of a guide bearing of arcuate cross section and preferably (in order to allow tilting in more than one plane) part spherical form; or again each blade may be rendered tiltable by being anchored by means of a flexible radially extending tension element in the natureof a strip or arod or wire.

Where relatively moving bearing surfaces are involved either rolling antifriction elements or, according to a furtherfeature of the-invention, in suitable cases a yield- 2,727,716 Patented Dec. 20, 1955 2 ing laminar element such as is described hereinaftcr'mafy be interposed therebetween the latter again, in some degree, permitting tilting in more than one plane. 7

In another general form of the invention, which will not necessarily involve that the tilting should be a pivoting movement always taking place about the same point or axis, but which is subject to limitations as to the temperature at which it may be employed, tilting is provided for by the inclusion in each blade mounting of a pad of a material capable of yielding locally under stress by undergoing displacement analogous to hydraulic flow. Materials such as rubber are suitable for this purpose, but in this connection a further feature of the invention consists in the use of a material which, though resilient, has a low response rate so that it does not respond to high frequency vibrations; that is, its acts to damp such vibrations. Synthetic rubber is found to be better for this purpose than the natural variety.

It follows that in each case clearance is provided between each tiltable blade (and any parts moving therewith) and adjacent abutment faces either of the rotor or other blades sufficient to allow in the requisite direction the desired amount (which need be only quite small); it is a further feature of the invention, however, that in those cases where the nature of the support is suitable this clearance may be arranged to allow tilting of the blade in more than one plane. These clearances should, of course, be kept to a minimum to avoid fluid flow losses, and in practice can be very small, but are exaggerated in the accompanying drawings for the sake of clarity. 7 p p Axial flow rotor blades which are tiltably mounted in conformity with the invention, espec'iallyin the case of a multistage arrangement may, with advantage from the point of view of constructional design, be so combined with a rotor built up from axially separate circular sections held together axially that the blade root mounting means permitting the tilting of. the blades are located between the adjacent peripheral portions of the said sections by mutual interengagernent therewith, and a number of constructional examples employing this combination are illustrated inthe accompanying drawings, which are as follows: 7

Figure l is a view in axial section of the rotor,

' Figure 2 an enlargement on section 2-2 of Figure 1 and Figure 3 a sectionon line 3-3 of Figure 2 showing one form of the invention.

Figures 4, 5 and 6 are views in axial, peripheral, and plan section respectively of a second form of the invention,

Figures 7, 8 and 9 are an axial, peripheral and plan section respectively of a third form of the invention,

Figure 10 is-a fragmentary perspective'view of the blade" root of yet another form of the invention and Figure ll is a detail of Figure 10.

Figures 1' to 3 illustrate'a case in which rotor blades are rendered tiltable by being mounted on an axially extending pivot pin. In a multistage axial flow rotor, the complete rotor is built up from a plurality of discs 1, which are presumed to be held together axially by means which for the purposes of the present invention need not beconsidered. Each disc 1 has a peripheral flange 2 and the axially successive rows or stages of blades 3 have their roots 4 located between and by the adjacent flanges 2 of successive discs. In this instance the blades 3 are pivotally mounted through needle roller bearings 5 on pins 6 extending axially of the rotor and' passing through appropriate bores" of the blade roots 4, the ends of thepins' 6 being held in recesses in the flanges" 2 of the respective discs 1. As shown in Figure 2, a periprs eral clearance is left. between adjacent blades is the same stage, so that each blade is capable! of tilting peripherally to adjust itself to variations in the relationship between gas and centrifugal load. As a modification, the pins 6 could be skewed with reference to the axial plane instead of being parallel with the axis of rotation. Since the needle rollers tend when under load to be distorted into an arcuate form, the centre portion of the bore may be provided, as shown, with a widened part at 7 so that the mid point of the arc formed by each needle roller does not come into contact with the wall of the bore and thus foul the root. Part of the root may also be cut away as shown at the left hand side of Figure 1 and in Figure 3, in order to economise in material and weight.

Figures 4 and 5 illustrate in axial and peripheral section, and Figure 6 in section on line 6-6 of Figure 4, a modification in which the blade root 4 is anchored by means of a flexible radial tension strip 8 which for securing purposes is bent at one end round a pin 9 within the body of the root and at the other round a pin 10; As in the previous case, this pin extends axially, but may alternatively be skewed, and enters recesses in the adjacent flanges 2 of successive discs 1. Tilting of each blade is limited by the clearance between it and the one adjacent, as seen in Figure 3.

The constructional forms so far described permit tilting of each blade in only one plane. Figures 7, 8, and 9 illustrate in fragmentary axial section, circumferential section, and plan respectively an arrangement in which the pivot about which tilting takes place is defined by a spherical guide bearing, so that tilting may take place in more than one plane. In the example given, the spherical guide bearing is defined on the one hand by'a part-spherical head 11 screwed or otherwise secured to a shank 12 on the blade root, and on the other by part-spherical recesses formed in the members 14 which lie between the rotor discs 1 and provide a hole for the passage of the blade shanks 12. A ball race 15 is disposed in the spherical bearing space between the head 11 and each member 14, and tilting of the blades both circumferentially and axially is permitted by appropriate clearances as indicated between each blade and adjacent blades and the rotor parts. The clearance between adjacent blades, in principle, also allows rotation of the blades about radial axes, but by keeping the clearances low and the interengaging faces long in the axial direction such rotation can be rendered negligible.

Instead of employing a form of fixed or defined mechanical pivot as in the foregoing embodiments, each blade may be bedded on a pad of yielding material as illustrated in the fragmentary perspective view of Figure 10. In this case the blade root consists of a rectangular base 16 having a channel 17 running round its sides in which is accommodated a pad 18 of yielding material (separately shown in Figure 11), the shaping and dimensioning of which is such as to leave in the channel 17 at the upstream and downstream sides of the base 16 a recess into which fit correspondingly shaped lips 19 on the adjacent rotor discs 1. In that tilting may take place in the peripheral direction a clearance is left between the blades, but it will be apparent that the direction of tilt can also have a component in the axial plane. The yielding material should be one such as rubber which is enabled to yield locally by undergoing displacement analogous to hydraulic flow and preferably also, whilst being resilient, should be selected to have a low response and recovery rate so that it does not yield under the influence of high frequency vibrations such as may be encountered in compressor and like blading, but does yield to a sustained load. In this way, not only is the desired compensating tilt obtainable when there is a change in the gas load/centrifugal force ratio, but also the mounting acts as a vibration damper. For this purpose synthetic rubber is found to have better characteristics than the natural variety.

We claim:

1. An axial flow compressor, turbine or similarly bladed fluid flow machine in which the blades are short in length compared with the diameter of the rotor comprising a rotor having in its peripheral surface blade retaining recesses, each formed with a pair of tongues projecting towards one another from opposite faces of said recess, a plurality of blades distributed in uniformly spaced relationship around said rotor surface in said recesses, each blade and blade root being spaced from its adjacent blade and blade root and with the root mounting of each of said blades formed with a pair of grooves on opposite sides thereof for reception and engagement therein on said pair of tongues with radial clearance between said tongues and grooves and a plurality of shaped pads of rubber or similar material capable of yielding locally under load with displacement of material and capable of returning to shape on removal of load located with said tongues in said grooves to fill said radial clearance completely and hold said blades securely mounted individually and independently of any other support on said rotor for tilting movement under centrifugal and fluid loads and render each self positionmg.

2. An axial flow compressor, turbine or similarly bladed fluid flow machine in which the blades are short in length compared with the diameter of the rotor comprising a rotor having at least one blade retaining recess circumferentially arranged around the periphery of said rotor with a pair of tongues projecting towards one another from opposite faces of said recess, a plurality of blades distributed in uniformly spaced relationship around said rotor in said recess and with their root mountings of rectangular form, each blade and blade root being spaced from its adjacent blade and blade root, and provided with a groove formed'thereon disposed around the four sides and with portions on opposite sides formed for reception of and engagement therein of said pair of tongues with radial clearance, and a plurality of shaped pads of rubber or similar material capable of yielding locally under load with displacement of material and capable of returning to shape on removal of load, each formed as a thin rectangular body with a rectangular hole for location in a said groove on each side of said rectangular root mountings to fill said radial clearance completely and hold said blades securely mounted individually and independently of any other support on said rotor for tilting movement under centrifugal and fluid loads and render each self positioning.

3. An axial flow compressor, turbine or similarly bladed fluid flow machine in which the blades are short in length compared with the diameter of the rotor comprising a rotor having at least one blade retaining recess circumferentially arranged around the periphery of said rotor with a pair of tongues projecting towards one another from opposite faces of said recess, a plurality of blades distributed in uniformly spaced relationship around said rotor in said recess, each blade and blade root being spaced from its adjacent blade and blade root mounting and having its root mounting formed with an annular groove for reception and engagement of said pair of tongues with radial clearance and a plurality of annular pads of rubber or similar material capable of yielding locally under load with displacement of material and capable of returning to shape on removal of load, each located in a said annular groove on each of said root mountings to fill said radial clearance completely and hold said blades securely mounted individually and independently of any other support on said rotor for tilting movement vunder centrifugal and fluid loads and render each self positioning.

4. An axial flow compressor, turbine or similarly bladed fluid flow machine comprising a rotor having in its peripheral surface blade retaining recesses each formedwith tongues projecting towards one another from opposite faces of said recesses, a plurality of blades distributed in uniformly spaced relationship around the periphery of said rotor, each of said blades terminating in a root located in one of said recesses, each blade and blade root being spaced from its adjacent blade and blade root, each of said roots being formed with grooves to receive said tongue with clearance, each said groove being deeper than the said tongue therein by a distance which would allow the root to move radially outward for some distance through a radial clearance space, and a plurality of resilient pads of rubbery material each shaped to fit in and fill one of said radial clearance spaces completely and to clamp said blade root between the pad and said tongue and hold said blade securely individually and independently of any other support of said rotor for tilting movement under centrifugal and fluid loads on each blade.

References Cited in the file of this patent UNITED STATES PATENTS 1,802,648

Heath Apr. 28, 1931 20 6 Levasseur Aug. 8, 1933 Avery Oct. 29, 1940 Bugatti Mar. 18, 1941 Thomas May 6, 1941 Rydmark Apr. 20, 1943 Reissner Mar. 14, 1944 Broders July 18, 1944 Martinotti Feb. 5, 1946 Kearns, Ir. Feb. 18, 1947 Benson Feb. 17, 1948 Murphy June 21, 1949 Dean May 6, 1952 FOREIGN PATENTS Great Britain Dec. 21, 1928 Germany Nov. 3, 1941

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