US2956733A

US2956733A - Fluid turning wheels for compressors

Info

Publication number: US2956733A
Application number: US458912A
Authority: US
Inventors: Edward A Stalker
Original assignee: Stalker Corp
Current assignee: Stalker Corp
Priority date: 1954-09-28
Filing date: 1954-09-28
Publication date: 1960-10-18
Anticipated expiration: 1977-10-18

Description

Oct. 1-8, 1960 E. A. STALKER mum TURNING WHEELS FOR COMPRESSORSI 2 sheets-sheet 1 I Filed Sept. 28, 1954 INVENTOR. I

FLUID TURNING WHEELS FOR COMPRESSORS Edward A. Stalker, Bay City, Mich., assignor to The Stalker Corporation, a corporation of Michigan Filed Sept 28, 1954, Ser. No. 458,912

6 Claims. (Cl. 230122) My invention relates to blade constructions for compressors.

It is important to reduce the weight and cost of compressors for aircraft and turbines. These can be reduced if the overall length of the compressor can be shortened. This would entail a reduction in the chord lengths of the blades for a given radial or spanwise length. Such reductions have not been employed because the vibrating characteristics of each blade becomes unsatisfactory and the blades tend to fail after a relatively short period of operation.

An object of this invention is to provide a bladed wheel structure wherein the blades and other parts are adapted to resist vibrations.

Another object is to provide an axially short wheel with sheet metal blades.

Still another object is to provide an axially short wheel with a novel shroud construction.

Other objects will appear from the description, drawings and claims.

The above objects are accomplished by the means illustrated in the accompanying drawings in which Fig. 1 is an axial section through a compressor according to this invention;

Fig. 2 is a fragmentary axial view of a rotor from the front thereof;

Fig. 3 is a fragmentary view of the rotor blading on line 33 in Fig. 1;

Fig. 4 is a fragmentary side view of a blade;

Fig. 5 is a tip view of the blade of Fig. 4;

Fig. 6 is a fragmentary radial view of a shroud; and

Fig. 7 is an axial view of a blade showing the angle of tilt D relative to a radial line.

Referring now to the drawings the compressor is indicated generally as 10. It comprises the case 12 and rotor assembly 14.

Air or other fluid enters the annular inlet 16 and is discharged from the annular exit 18.

The rotor assembly 14 is mounted in the case for rotation about the axis of shaft 22 which is supported in bearings 24 and 26.

The rotor assembly comprises the wheels 30-33 fixed on the shaft 22 for rotation with it. Stators 34-37 are alternated with the rotors.

The wheels are similarly constructed so that it will sufiice to describe only wheel 31. This wheel has the blades 40 carried on the hub 41 peripherally spaced about the rim surface 42 of the hub and extending radially outward therefrom.

The blades are preferably sheet metal blades but the invention is applicable to any type of blade. Each sheet metal blade has a constant thickness along a major portion of its chord length with faired leading and trailing edges. The leading edge may be either sharp or rounded.

The blades have a short chord length relative to their span, that is radial length providing an aspect ratio greater than 2.4, and are joined at their tips by the shroud 50. It comprises a front ring 52 and a complementary rear Patented Oct. 18, 1960 ice ring 53 suitably secured together. A support ring 54 having a peripherally open channel 54a is fixed to bothfront and rear rings on opposite sides of the joint between the two. See Fig. l. A seal ring 55 is fixed to the case with its radial leg cooperating with the channel 54a of the support ring to form a labyrinth seal.

As shown particularly in Figs. 4, 5 and 6 each blade has a tongue 56 which is positioned in a slot 60 in the shroud 50. Preferably the tongue is just long enough radially to equal the thickness of the shroud, so that its outer surface is substantially flush with the outer surface of the shroud. Each shroud ring 52 and 53 is formed with a cooperating pattern of slots, and each complete ring is slid into place over the blades with the two slot sections matching to receive the tongues 56. Thereafter the complete support ring 54 is slid over the assembled shroud rings. Thus the supporting ring 54 fays the surfaces of the front and rear rings 52, 53 and the tip surfaces of the tongues 56, and is brazed to them.

At high tip speeds such as those of axial flow compressors a shroud at the tips of the blades tends to elongate peripherally to such an extent that it moves away from radial blades which do not elongate under centrifugal stress sufficiently to retain contact with the shroud. Consequently the shroud tends to leave the blade tips, or if restrained by them, bends outward between blades. In order to overcome this condition, preferably each blade is tilted backward at the tip relative to the direction of rotation as shown in Fig. 7 where the line 70 through the centers of gravity 71 of each cross section of the blade is tilted by the angle D relative to the radial line 72. When the wheel rotates centrifugal force tends to deflect the blade into the radial position pressing the tip end of the blade more firmly against the shroud. This action will relieve the joint between each blade and the shroud of any tendency of the shroud to move radially outward from the blade.

a For aerodynamic and structural reasons the blades should overlap at the mean radius as seen in axial view, preferably with the leading edge of the following blade of a pair of adjacent blades at least as far forward as the mid chord point of the leading blade of the pair.

Preferably the solidity of the rotor (defined as the ratio of the length of a blade chord to the peripheral distance between said chord and a similarly located chord of an adjacent blade) is sufficiently great that the shroud is supported at three axially spaced points about in the same axial plane. This usually means a solidity greater than about 2. A solidity as high as 4 does not impair the efiiciency of the rotor if the blades are thin and/or of substantially constant thickness chordwise, or if they are substantially cambered. Preferably the camber is greater than 8 percent of the chord length or the aft portion of the blade is more nearly parallel to the axis of rotation than to the fore portion of the blade. The direction of the fore portion is to be determined by the direction of the mean line 76 and that of the aft portion by the mean line 75. The angle of incidence 0 is defined between line 76 and the plane or rotation.

The maximum thickness of the root section of each blade is preferably small, less than 12 percent of the chord length and preferably between 5 and 10 percent of the chord length. These proportions facilitate placing the blades close together while retaining a high efficiency. Close spacing is also facilitated by the constant thickness along the chord of each blade by eliminating throats in the passage between blades.

It is important to have a portion of the blade substantially parallel to the axis of rotation to offer additional resistance to a tendency of the blades and shroud to vibrate along the axial direction. Thus in Fig. 3 theaft portions 90 of the blades 40 restrain any axial component of vibration.

The force acting along the axial direction can attain a significant magnitude from gyroscopic action of the shroud arising from tilting the axis of rotation of the wheel.

The diagonal or forward portions 91 of the blades cooperate with the aft portions to restrain any peripheral component of vibration.

The blade section proportions cooperate with the shroud to make practicable the employment of very short root chords, less than one-half the blade span, that is one-half the radial length of the blade and preferably in the range of 0. 3 to 0.45 of the maximum span.

This invention refers to compressor wheels for increasing .the static pressure and density of an elastic fluid. In order to achieve a significant change in density with an axial flow compressor each wheel must be operated at a speed high enough to effect a significant change in density, that is a change which in magnitude is outside the usual order of engineering accuracy in industry. Thus machines are considered to be compressors as distinguished from fans or blowers at tip speeds of about 400 feet per second or more. At such a speed the average change in density along the blade length is about 3% which is just about the common order of accuracy of measurement of the density. Such compressors are expected also to operate at blade tip speeds close to the velocity of sound. At such speeds the change in pressure may be more than 70% or more than 10 pounds per square inch for air inducted at atmospheric pressure.

Since in a compressor wheel there is a substantial pressure variation from front to rear the ratio of the hub radius to the blade tip radius is relatively large of a value of the order of 0.5 and preferably greater so that the pressure difference between front and rear sides can be sustained without a return flow at the hub such as occurs in a fan. For the same reason the blades are spaced peripherally close together, preferably about one chord length or less apart.

Commonly half to all the pressure rise occurs in the wheel between the leading and trailing edges. To sustain such an increase in pressure along the wheel passages from leading to trailing edges of the blades the hub rim between adjacent blades and from leading to trailing edges is a fair and continuous surface. Also at all rotative speeds the case must fit closely about the blade tips which are contoured to the cylindrical surface of the case along substantially the whole length of the blade tip chord.

To diffuse the fiow between blades to achieve a pressure rise the flow should follow the blade surfaces without eddies. Accordingly the blades should have rounded leading edges. They should have sharpened trailing edges to be efiicient.

While I have illustrated specific forms of the invention, it is to be understood that variations may be made therein and that I intend to claim my invention broadly as indicated by the appended claims.

I claim:

1. .In combination in an axial flow compressor wheel adapted for rotation about an axis, a hub structure, a plurality of axial flow blades carried on said hub and peripherally spaced thereabout, each said blade having faired leading and trailing edge portions adapting them for efiicient compressing action at high tip speeds, each said blade having an aspect ratio greater than 2.4 to provide a short axial length to said rotor and tending to permit undue vibrations of said blades, a shroud means encircling said blades at the tips thereof and being fixed thereto to exclude said tendency to undue vibrations, said shroud means comprising a front ring portion and a rear ring portionhaving openings on .their adjacent edges for receiving the tips of said, blades, said ring portions being joinedalong peripherallines between blades, and a pcripherally continuous support ring encircling said shroud means and overlapping and brazed to both said portions of said shroud means on opposite sides of said lines and to the tips of said blades.

2. In combination in an axial flow wheel defining an axis of rotation, a hub means having a rim surface, a plurality of axial flow blades peripherally spaced about said means and carried thereon with fluid flow passages between said blades, a continuous annular shroud encircling said blades at the tips thereof, said shroud comprising complementary front and rear rings positioned in tandem with a joint therebetween, said shroud having openings therein each receiving a tip end of a said blade thereinto and fixed to the sides thereof, and a peripherally continuous support ring encircling said shroud and faying the external surfaces of said front and rear portions across said joint and being fixed to said portions and to the tip ends of said blade by brazing material.

3. In combination in an axial flow wheel defining an axis of rotation, a hub means having a rim surface, a plurality of axial flow blades peripherally spaced about said means and carried thereon with fluid flow passages between said blades, a continuous annular shroud encircling said blades at the tips thereof, said shroud comprising complementary front and rear rings positioned in tandem with a joint therebetween, said shroud having openings therein each receiving a tip end of a said blade thereinto and fixed to the sides thereof, and a support ring encircling said shroud and faying the external surfaces of said front and rear portions continuously across the periphery of said joint and being fixed to said portions and to the tip ends of said blades bybrazing material, said support ring having a circular leg extending radially outward therefrom.

4. In combination in an axial flow wheel defining an axis of rotation, a case, a hub means having a rim surface, a plurality of axial flow blades peripherally spaced about said means and carried thereon with fluid flow passages between said blades, a continuous annular shroud encircling said blades at the tips thereof, said shroud comprising complementary front and rear rings positioned in tandem with a joint therebetween, said shroud having openings therein each receiving a tip end of a said blade thereinto and fixed to the sides thereof, and a support ring encircling said shroud and faying the external surfacesof said front and rear portions continuously across the periphery of said joint and being fixed to said portions and to the tip ends of said blades by brazing material, said support ring having a circular leg extending radially outward therefrom, and a seal ring supported on said case and projecting toward said shroud adjacent to said leg.

5. In combination in an axial flow rotor defining an axis of rotation, a hub means having a rim surface, a plurality of axial flow blades of limited chord length peripherally spaced about said means and carried thereon, said blades being rotatable about said axis at tip speeds at least as great as 400 feet per second causing a substantial change in density and pressure in said fluid, each said blade having a root section at the radial location of said rim surface and having leading and trailing edges extendingoutward from said surface with a line through the center of gravity of each chordwise section being tilted at a substantial anglerelative to a radial line passingradially outward through the center of gravity of said foot section of each said blade, each said blade having a front portion set at a substantial angle relative to said axisand a curved rear portion, each said blade having a-limited chord length for said root section less than 0.45 of the span of said blade, said limited chord length tending to permit each said blade to vibrate unduly when rotated at said tip speeds, and a peripherally continuous shroud ring encircling said blades at the tips thereof and fixed thereto to restrain said tendency, said tilt of each said blade causing saidblades to press against said shroud ring under the action of centrifugal forces.

6. In combination in an axial flow compressor wheel adapted for rotation about an axis, a hub structure, a plurality of axial flow blades carried on said hub and peripherally spaced thereabout, each said blade having faired leading and trailing edge portions adapting them for efiicient compressing action at high tip speeds, each said blade having a root chord length less than 0.45 of the maximum length of the span of said blade to provide a short axial length to said rotor and tending to permit undue vibrations of said blades, a continuous annular shroud encircling said blades at the tips thereof and being fixed thereto to exclude said tendency to undue vibrations, each said blade at the tip thereof extending through said shroud to substantially the outer periphery thereof, a peripherally continuous support ring having axially spaced legs bonded to said shroud and to the tips of said blades on the outer surface thereof extending radially outward therefrom and from one blade to another to support said shroud between said blades.

References Cited in the file of this patent UNITED STATES PATENTS Green Nov. 23, Hanzlik Sept. 7, Herr Dec. 21, Steenstrup Oct. 9, Dahlstrand May 30, Whittle June 12, Bodger June 6, Bachle July 22, Stalker Aug. 11, McDowall et a1. Apr. 13,

FOREIGN PATENTS Great Britain Dec. 1, Great Britain May 4, Germany Oct. 30, Germany Apr. 9,