VARIABLE DIFFUSER
United States Patent 3799694
A variable diffuser for a centrifugal compressor has a set of fixed vanes remote from the compressor rotor and a set of movable vanes nearer the rotor. There is one movable vane for each two fixed vanes, and the movable vanes are swingable about axes adjacent their leading edges between a position in which the trailing edges of these vanes block the passage between two adjacent fixed vanes and a position in which the trailing edges of the movable vanes are substantially spaced from the fixed vanes.
US Patent References:
Split guide blade for centrifugal pumps
Hahn - July 1930 - 1771711
Centrifugal compressor
Thompson - January 1946 - 2392200
Gaseous fluid compressor
Bauger et al. - July 1953 - 2645410
Gas turbine construction
Schwarz - December 1964 - 3162421
Supersonic compressors of the centrifugal or axial flow and centrifugal types
Plotkowiak - December 1967 - 3356289
Split guide blade for centrifugal pumps
Hahn - July 1930 - 1771711
Centrifugal compressor
Thompson - January 1946 - 2392200
Gaseous fluid compressor
Bauger et al. - July 1953 - 2645410
Gas turbine construction
Schwarz - December 1964 - 3162421
Supersonic compressors of the centrifugal or axial flow and centrifugal types
Plotkowiak - December 1967 - 3356289
Application Number:
05/308160
Publication Date:
03/26/1974
Filing Date:
11/20/1972
View Patent Images:
Export Citation:
Assignee:
General Motors Corporation (Detroit, MI)
Primary Class:
Other Classes:
415/149.100, 415/163, 415/148
International Classes:
F04D29/46; F04D27/00; F04D29/60
Field of Search:
415/160,161,162,163,164,165
US Patent References:
| 3588270 | July 1969 | Boeles |
Primary Examiner:
Raduazo, Henry F.
Attorney, Agent or Firm:
Fitzpatrick, Paul
Claims:
I claim
1. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced set of generally radially and circumferentially extending fixed vanes bridging the passage in a radially outer zone and defining diverging passages between adjacent vanes; and a circumferentially spaced set of generally radially and circumferentially extending movable vanes bridging the passages in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis generally parallel to the axis of rotation of the compressor; the movable vanes diverging in thickness from the leading edge and each having a trailing edge movable to engage the leading edge of two mutually adjacent fixed vanes so as to close the passage between the fixed vanes so engaged and provide a continuous diffusing passage through the vanes of the two sets to a diffuser exit at the outer end of the fixed vanes; the trailing edges being movable away from the fixed vanes upon rotation of the movable vanes toward the axis of rotation of the compressor to reduce the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser for small flow between the movable vanes, and open the passages between all of the fixed vanes for unimpeded flow of the diffused gas; and common actuating means operable to rotate the movable vanes concurrently.
2. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced set of generally radially and circumferentially extending fixed vanes bridging the passage in a radially outer zone and defining diverging passages between adjacent vanes; and a circumferentially spaced set of generally radially and circumferentially extending movable vanes bridging the passage in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis adjacent to its leading edge generally parallel to the axis of rotation of the compressor; the movable vanes diverging in thickness from the leading edge and each having a trailing edge movable to engage the leading edge of two mutually adjacent fixed vanes so as to close the passage between the fixed vanes so engaged and provide a continuous diffusing passage through the vanes of the two sets to a diffuser exit at the outer end of the fixed vanes; the trailing edges being movable away from the fixed vanes upon rotation of the movable vanes toward the axis of rotation of the compressor to reduce the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser for small flow between the movable vanes, and open the passages between all of the fixed vanes for unimpeded flow of the diffused gas; and common actuating means operable to rotate the movable vanes concurrently.
3. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced annular set of generally radially and circumferentially extending movable vanes bridging the passage in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis adjacent to its leading edge; common actuating means operable to rotate the movable vanes concurrently to vary the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser adjustable for small and large flows between the movable vanes; the movable vanes diverging in thickness from the leading edge and each having a thick trailing edge; and a circumferentially spaced annular set of generally radially and circumferentially extending fixed walls bridging the passage in a zone radially outward of the movable vanes, the walls being in sets of two adjacent walls, one set corresponding to each movable vane, the walls defining an outlet passage between the walls of each set and defining a diverging continuing diffusing passage between each two adjacent sets; the movable vanes in the large flow position each engaging the radially inner ends of the walls of one set to block flow through the outlet passage and to deliver the flow from each diffusing passage through the movable vanes into a continuing diffusing passage between walls sets, and the movable vanes in the small flow position being spaced from the walls to open the outlet passage.
4. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced annular set of generally radially and circumferentially extending movable vanes bridging the passage in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis adjacent to its leading edge; common actuating means operable to rotate the movable vanes concurrently including a unison ring rotatable about the axis of rotation of the compressor and pins on the unison ring engaging in slots in the movable vanes remote from the axis of vane rotation to vary the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser adjustable for small and large flows between the movable vanes; the movable vanes diverging in thickness from the leading edge and each having a thick trailing edge; and a circumferentially spaced annular set of generally radially and circumferentially extending fixed walls bridging the passage in a zone radially outward of the movable vanes, the walls being in sets of two adjacent walls, one set corresponding to each movable vane, the walls defining an outlet passage between the walls of each set and defining a diverging continuing diffusing passage between each two adjacent sets; the movable vanes in the large flow position each engaging the radially inner ends of the walls of one set to block flow through the outlet passage and to deliver the flow from each diffusing passage through the movable vanes into a continuing diffusing passage between wall sets, and the movable vanes in the small flow position being spaced from the walls to open the outlet passages.
1. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced set of generally radially and circumferentially extending fixed vanes bridging the passage in a radially outer zone and defining diverging passages between adjacent vanes; and a circumferentially spaced set of generally radially and circumferentially extending movable vanes bridging the passages in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis generally parallel to the axis of rotation of the compressor; the movable vanes diverging in thickness from the leading edge and each having a trailing edge movable to engage the leading edge of two mutually adjacent fixed vanes so as to close the passage between the fixed vanes so engaged and provide a continuous diffusing passage through the vanes of the two sets to a diffuser exit at the outer end of the fixed vanes; the trailing edges being movable away from the fixed vanes upon rotation of the movable vanes toward the axis of rotation of the compressor to reduce the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser for small flow between the movable vanes, and open the passages between all of the fixed vanes for unimpeded flow of the diffused gas; and common actuating means operable to rotate the movable vanes concurrently.
2. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced set of generally radially and circumferentially extending fixed vanes bridging the passage in a radially outer zone and defining diverging passages between adjacent vanes; and a circumferentially spaced set of generally radially and circumferentially extending movable vanes bridging the passage in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis adjacent to its leading edge generally parallel to the axis of rotation of the compressor; the movable vanes diverging in thickness from the leading edge and each having a trailing edge movable to engage the leading edge of two mutually adjacent fixed vanes so as to close the passage between the fixed vanes so engaged and provide a continuous diffusing passage through the vanes of the two sets to a diffuser exit at the outer end of the fixed vanes; the trailing edges being movable away from the fixed vanes upon rotation of the movable vanes toward the axis of rotation of the compressor to reduce the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser for small flow between the movable vanes, and open the passages between all of the fixed vanes for unimpeded flow of the diffused gas; and common actuating means operable to rotate the movable vanes concurrently.
3. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced annular set of generally radially and circumferentially extending movable vanes bridging the passage in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis adjacent to its leading edge; common actuating means operable to rotate the movable vanes concurrently to vary the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser adjustable for small and large flows between the movable vanes; the movable vanes diverging in thickness from the leading edge and each having a thick trailing edge; and a circumferentially spaced annular set of generally radially and circumferentially extending fixed walls bridging the passage in a zone radially outward of the movable vanes, the walls being in sets of two adjacent walls, one set corresponding to each movable vane, the walls defining an outlet passage between the walls of each set and defining a diverging continuing diffusing passage between each two adjacent sets; the movable vanes in the large flow position each engaging the radially inner ends of the walls of one set to block flow through the outlet passage and to deliver the flow from each diffusing passage through the movable vanes into a continuing diffusing passage between walls sets, and the movable vanes in the small flow position being spaced from the walls to open the outlet passage.
4. An annular diffuser for a radial-flow gas compressor comprising, in combination, front and back walls extending substantially radially from the axis of rotation of the compressor, the walls defining between them a diffusing passage for the gas; a circumferentially spaced annular set of generally radially and circumferentially extending movable vanes bridging the passage in a radially inner zone and defining diverging passages between adjacent vanes; each movable vane being mounted so as to be rotatable about an axis adjacent to its leading edge; common actuating means operable to rotate the movable vanes concurrently including a unison ring rotatable about the axis of rotation of the compressor and pins on the unison ring engaging in slots in the movable vanes remote from the axis of vane rotation to vary the entrance and discharge areas of the passages between the movable vanes and thus define a diffuser adjustable for small and large flows between the movable vanes; the movable vanes diverging in thickness from the leading edge and each having a thick trailing edge; and a circumferentially spaced annular set of generally radially and circumferentially extending fixed walls bridging the passage in a zone radially outward of the movable vanes, the walls being in sets of two adjacent walls, one set corresponding to each movable vane, the walls defining an outlet passage between the walls of each set and defining a diverging continuing diffusing passage between each two adjacent sets; the movable vanes in the large flow position each engaging the radially inner ends of the walls of one set to block flow through the outlet passage and to deliver the flow from each diffusing passage through the movable vanes into a continuing diffusing passage between wall sets, and the movable vanes in the small flow position being spaced from the walls to open the outlet passages.
Description:
SPECIFICATION
My invention is directed to variable diffusers for radial-flow compressors and is particularly intended to permit efficient operation of such a compressor over a wide range of flow.
As is well known, a centrifugal compressor is a device in which a rotating rotor or impeller delivers air at relatively high velocity by the effect of centrifugal force on the gas within the impeller. Such a compressor also includes a diffuser, which normally is an annular space surrounding the periphery of the impeller and which usually is provided with vanes to guide the gas flow and minimize turbulence and frictional losses in the diffuser. The air or other gas (which will be referred to hereafter as air) is delivered from the impeller with a substantial radial component of velocity and ordinarily a substantially greater tangential component. The function of the diffuser is to decelerate the air smoothly and to recover as static head the dynamic head of the air due to its velocity. The vanes usually provided in the diffuser divide the air into a number of streams flowing circumferentially and radially of the diffuser, each stream flowing through a passage which diverges gradually so as to facilitate the efficient conversion of the dynamic head to static head.
My invention is particularly directed to providing a diffuser efficient over a wide range of flows. This involves changing the geometry of the diffuser, and should effect such a change in a manner to preserve as far as possible the efficiency of diffusion over a considerable range of operating conditions.
It will be obvious that the direction of flow of the air from the rotor will vary with the rotational speed of the rotor and with the amount of air flow, which also generally depends upon the speed of the rotor. In a typical application of a centrifugal compressor to a gas turbine engine, the compressor discharges through combustion apparatus to a turbine nozzle which may be of fixed or variable area. In some sorts of service it is highly desirable that the gas turbine operate efficiently over a normal operating range to deliver power and also in idling operation in which the rotation speed and air flow of the engine are greatly reduced. This is particularly the case in automotive vehicles in which the engine may be idling during standstill of the vehicle or may be operating at relatively low power during non-accelerating low-speed cruising of the vehicle.
My invention is directed to the provision of a diffuser in which the diffuser vanes are movable so that the vanes may be aligned with the direction of flow from the impeller and thus minimize disturbances of flow caused by off-design incidence of the flow on the leading edge of the vanes.
It also provides for varying the area of the effective part of the diffuser between a relatively large area condition for high air flow and a relatively small area condition for low flow, while minimizing undesirable variations in the ratio between entrance and exit areas of the effective part of the diffuser. This is effected by the provision of an outer row of fixed vanes and an inner row of movable vanes, with the angle of the inner row vanes being variable, and with the inner row of vanes serving to block flow through alternate passages in the outer row of vanes in one condition or setting of the diffuser vanes. This may be viewed alternatively as a diffuser in which there is an inner row of movable vanes and an outer row of hollow vanes and in which there is a diffusing passage between adjacent hollow outer vanes, as well as a passage through the interior of each hollow vane which may be closed by the movable vanes.
I recognize that various proposals for variable diffusers for compressors have been proposed and may call attention as examples to those shown in U.S. Pats. as follows: Elling, No. 908,227, Dec. 29, 1908; Birmann, No. 2,428,830, Oct. 14, 1947; and Bauger et al., No. 2,645,410, July 14, 1953. However, so far as I am aware, my type of variable diffuser described above is not suggested by the prior art.
The nature of my invention and its advantages will be clearly apparent to those skilled in the art from the succeeding detailed description and accompanying drawings of the preferred embodiment of the invention.
Referring to the drawings;
FIG. 1 is a sectional view of a centrifugal compressor taken on a plane containing the axis of rotation thereof.
FIG. 2 is a partial elevation view, with parts cut away and in section, taken on the plane indicated by the line 2--2 in FIG. 1.
The drawings illustrate a centrifugal compressor which is intended to be a part of a gas turbine engine which, as is well known, includes a combustion apparatus to which the compressor delivers compressed air and a turbine to which the combustion apparatus delivers motive fluid, the turbine driving the compressor. The combustion apparatus and turbine are not illustrated, since the structure of these is not material to an understanding of my invention.
As shown in FIG. 1, the installation includes a case or housing 2, an upper wall 3 and front wall 4 of which are illustrated. The front wall has a circular opening at 6 within which is piloted an annular mounting plate 7. An annular diffuser front plate 8 is fixed to the mounting plate 7 by a ring of bolts 10. A fixed impeller forward shroud 11 is mounted on the front plate 8 by a cap screw 12. A diffuser outer ring 14 is fixed to plate 8 by a ring of studs 15 welded to the diffuser ring and secured by nuts. A diffuser rear plate 16 of annular form is fixed to the outer ring 14 by a ring of cap screws 18. The diffuser rear plate is fixed by a ring of cap screws 19 to a flange 20 at the forward end of a shaft housing 22.
An annular compressor inlet outer wall 23 is fixed to mounting plate 7 by a ring of cap screws 24. An annular compressor inlet inner wall 26 is joined by struts 27 to a ring secured by cap screws 28 to an annular plate 29. Plate 29 is fixed to the mounting plate 7 by a ring of cap screws 30 which also mount the housing 31 of an air cleaner (not illustrated). Walls 23 and 26 define between them a converging air inlet 32 into the compressor. The swirl or circumferential velocity component of air entering the compressor through the inlet 32 may be varied by variable setting inlet vanes 34 each of which is connected by an arm 35 to some suitable mechanism for actuating the inlet vanes 34 in unison which is not illustrated, since it is not material to my invention. This actuating mechanism may be mounted on a plate 36 bolted to the inner wall 26. While the adjustable inlet guide vanes 34 are a desirable part of the overall compressor or engine, they are not relevant to my invention which has to do with the diffuser of the compressor rather than its inlet.
Leading now into the rotating structure of the compressor, a drive shaft 38 which may be connected to the turbine is mounted in the shaft housing 22 and supported by a fixed bearing or journal block 39 within which a journal 40 of the shaft rotates. Bearing 39 is fixed to an inwardly extending flange 42 of the shaft housing. Thrust bearings 43 and 44 on the shaft 38 engage the faces of journal block 39. These are located on the shaft by abutments at which the shaft changes diameter. Oil is supplied to the bearings from a line 46. The lubrication of the bearing will now be further described as the details are immaterial.
A seal ring 47 abuts the thrust bearing 44 through a washer and is in turn abutted by the impeller 48 of the compressor which is piloted upon and splined to an extension 50 of shaft 38 and secured thereto by nut 51 and sleeve 52. Seal ring 47 cooperates with a seal mounted in a ring 53 bolted to the forward end of the shaft housing 22.
The impeller 48 comprises a disk 55 and radially extending vanes 56, and may follow standard practice in the design of such impellers. Details are immaterial to my invention. Air entering the compressor through the inlet 32 is driven outwardly and circumferentially by the vanes 56 into a diffuser 58 bounded by plate 8, ring 14, and plate 16, the diffuser having an outlet at 59.
All of the stationary parts of the compressor are fixed to the shaft housing 22, which is suitably located, by means not illustrated, in the case 2. Thus, the mounting plate 7 is located axially of the case and may slide relative to the front wall 4 to accommodate differential expansion of the parts as required.
A heat insulating ring 60 is mounted on the rear face of the mounting plate 7. Having described the general structure of the compressor in which the invention is embodied, we may now consider more particularly the variable diffuser with reference also to FIG. 2.
The outer diffuser ring 14 is a brazed structure made up of a forward part and a rear part. The forward part comprises a ring 62 (FIG. 1) from which vanes or walls 63 and 64 extend axially of the compressor. These vanes or walls are thin sheets of metal provided by machining grooves across ring 62. The rear edges of the vanes are brazed to a rear ring 66. The diffuser outer ring 14, as previously pointed out, is fixed to the diffuser front plate 8 by studs 15 and to the rear plate 16 by cap screws 18. Constantly open diffusing passages 67 are defined between vanes 64 and 63 adjacent in the direction of rotation of the impeller and closable diffuser passages 68 are defined between vanes 63 and 64 adjacent in the direction of rotation of the impeller.
The movable diffuser vanes 70 are shown most clearly in FIG. 2. Each vane comprises a wedge-shaped body 71 having a thin leading edge 72 and a broad trailing edge 74. The leading edge portion of each vane is brazed to a cylindrical pivot 75, each of which is inserted in a socket or journal 76 in the diffuser rear plate 16. A chordwise-extending slot 78 in each vane accommodates an actuating pin 79 fixed in a unison ring 80. This unison ring is radially located by engagement with the inner surface of diffuser rear ring 66 and a shoulder 83 on plate 16, and is axially located by its mounting between vanes 70 and the rear diffuser plate 16. Vanes 70 in turn bear against the diffuser front plate 8.
A bearing surface 82 is disposed on the rear face of the unison ring 80. When the unison ring 80 is rotated about the axis of rotation of the compressor, the actuating pins 79 swing the vanes 70 about their pivots as will be obvious from FIG. 2, in which the five right-hand vanes shown are illustrated in the high flow position and the two vanes to the left are illustrated as being in the minimum flow position.
The unison ring 80 is in turn rotated by an actuating ring 84 mounted on the rear side of rear plate 16 and supported by three rollers 86 disposed at 120° intervals and rotatably supported on bolts 87 fixed in the plate 16. The ring 84 may be rotated by any suitable actuating mechanism such as a pneumatic or oil servo or electromechanical servo, and the mechanism for rotating this is not illustrated. Actuating ring 84 is coupled to unison ring 80 by six posts 88 extending rearwardly from the unison ring through circumferential slots 90 (see also FIG. 2) in the rear plate 16. Ring 84 is fixed to these posts by cap screws 91. Referring again to FIG. 2, it will be noted that the trailing edge 74 of each movable diffuser vane 70 is terminated at an angle such as to fit against the leading edges of the vanes 63 and 64 with which it cooperates. Also, a small abutment 92 on each movable vane engages a vane 63 to limit and fix the open position of the movable vanes.
The operation should be clear from the foregoing description but may be gone through briefly. Any suitable actuator rotates ring 84 which rotates ring 80 through posts 88. The pins 79 on ring 80 moves the vanes 70 about their pivots 75, with the pins moving in the slots 78 of the vanes. The position for maximum flow is that illustrated at the right of FIG. 2 in which the opening between adjacent movable vanes is a maximum and the succeeding vanes or walls 63 and 64 of the outer set continue the diffusing passages which may be considered to be the passage indicated at 94 in FIG. 2 and continuing through passage 67.
In the closed or low flow condition of the vanes as illustrated at the left of FIG. 2, a more constricted diffusing passage 95 is defined between the vane bodies 71. In this condition of operation, the walls or vanes 63 and 64 perform no particular diffusing function, the smaller diffuser having sufficient area ratio between vanes 70. The diffuser may operate over a range between minimum and maximum area, being varied as air flow varies by any suitable control. The diffuser works well over the intermediate range as well as at the extremes.
Of course, the dimensions and details of the structure are subject to variation, but it may be pointed out that the particular structure shown to scale here was designed for an engine which was intended to operate efficiently at 100 percent speed with 100 percent airflow (three pounds per second) and also at 70 percent speed with 22 percent or 0.66 lbs. per second airflow. This is, of course, a very wide range. It may be pointed out again that the vanes 63 and 64 define the walls of diffusing passages for the higher flow condition and are immaterial to the diffusion in the minimum flow condition in which the smaller diffuser area between the closed vanes 70 is sufficient for diffusion. In intermediate conditions, some diffusion occurs in passages 67 and 68 in the outer ring.
It should be clear to those skilled in the art from the foregoing that I have devised a wide range diffuser structure of singular utility and practicality for handling wide flow ranges in a radial-flow compressor, and in such a compressor which forms an element of a gas turbine engine.
The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.
My invention is directed to variable diffusers for radial-flow compressors and is particularly intended to permit efficient operation of such a compressor over a wide range of flow.
As is well known, a centrifugal compressor is a device in which a rotating rotor or impeller delivers air at relatively high velocity by the effect of centrifugal force on the gas within the impeller. Such a compressor also includes a diffuser, which normally is an annular space surrounding the periphery of the impeller and which usually is provided with vanes to guide the gas flow and minimize turbulence and frictional losses in the diffuser. The air or other gas (which will be referred to hereafter as air) is delivered from the impeller with a substantial radial component of velocity and ordinarily a substantially greater tangential component. The function of the diffuser is to decelerate the air smoothly and to recover as static head the dynamic head of the air due to its velocity. The vanes usually provided in the diffuser divide the air into a number of streams flowing circumferentially and radially of the diffuser, each stream flowing through a passage which diverges gradually so as to facilitate the efficient conversion of the dynamic head to static head.
My invention is particularly directed to providing a diffuser efficient over a wide range of flows. This involves changing the geometry of the diffuser, and should effect such a change in a manner to preserve as far as possible the efficiency of diffusion over a considerable range of operating conditions.
It will be obvious that the direction of flow of the air from the rotor will vary with the rotational speed of the rotor and with the amount of air flow, which also generally depends upon the speed of the rotor. In a typical application of a centrifugal compressor to a gas turbine engine, the compressor discharges through combustion apparatus to a turbine nozzle which may be of fixed or variable area. In some sorts of service it is highly desirable that the gas turbine operate efficiently over a normal operating range to deliver power and also in idling operation in which the rotation speed and air flow of the engine are greatly reduced. This is particularly the case in automotive vehicles in which the engine may be idling during standstill of the vehicle or may be operating at relatively low power during non-accelerating low-speed cruising of the vehicle.
My invention is directed to the provision of a diffuser in which the diffuser vanes are movable so that the vanes may be aligned with the direction of flow from the impeller and thus minimize disturbances of flow caused by off-design incidence of the flow on the leading edge of the vanes.
It also provides for varying the area of the effective part of the diffuser between a relatively large area condition for high air flow and a relatively small area condition for low flow, while minimizing undesirable variations in the ratio between entrance and exit areas of the effective part of the diffuser. This is effected by the provision of an outer row of fixed vanes and an inner row of movable vanes, with the angle of the inner row vanes being variable, and with the inner row of vanes serving to block flow through alternate passages in the outer row of vanes in one condition or setting of the diffuser vanes. This may be viewed alternatively as a diffuser in which there is an inner row of movable vanes and an outer row of hollow vanes and in which there is a diffusing passage between adjacent hollow outer vanes, as well as a passage through the interior of each hollow vane which may be closed by the movable vanes.
I recognize that various proposals for variable diffusers for compressors have been proposed and may call attention as examples to those shown in U.S. Pats. as follows: Elling, No. 908,227, Dec. 29, 1908; Birmann, No. 2,428,830, Oct. 14, 1947; and Bauger et al., No. 2,645,410, July 14, 1953. However, so far as I am aware, my type of variable diffuser described above is not suggested by the prior art.
The nature of my invention and its advantages will be clearly apparent to those skilled in the art from the succeeding detailed description and accompanying drawings of the preferred embodiment of the invention.
Referring to the drawings;
FIG. 1 is a sectional view of a centrifugal compressor taken on a plane containing the axis of rotation thereof.
FIG. 2 is a partial elevation view, with parts cut away and in section, taken on the plane indicated by the line 2--2 in FIG. 1.
The drawings illustrate a centrifugal compressor which is intended to be a part of a gas turbine engine which, as is well known, includes a combustion apparatus to which the compressor delivers compressed air and a turbine to which the combustion apparatus delivers motive fluid, the turbine driving the compressor. The combustion apparatus and turbine are not illustrated, since the structure of these is not material to an understanding of my invention.
As shown in FIG. 1, the installation includes a case or housing 2, an upper wall 3 and front wall 4 of which are illustrated. The front wall has a circular opening at 6 within which is piloted an annular mounting plate 7. An annular diffuser front plate 8 is fixed to the mounting plate 7 by a ring of bolts 10. A fixed impeller forward shroud 11 is mounted on the front plate 8 by a cap screw 12. A diffuser outer ring 14 is fixed to plate 8 by a ring of studs 15 welded to the diffuser ring and secured by nuts. A diffuser rear plate 16 of annular form is fixed to the outer ring 14 by a ring of cap screws 18. The diffuser rear plate is fixed by a ring of cap screws 19 to a flange 20 at the forward end of a shaft housing 22.
An annular compressor inlet outer wall 23 is fixed to mounting plate 7 by a ring of cap screws 24. An annular compressor inlet inner wall 26 is joined by struts 27 to a ring secured by cap screws 28 to an annular plate 29. Plate 29 is fixed to the mounting plate 7 by a ring of cap screws 30 which also mount the housing 31 of an air cleaner (not illustrated). Walls 23 and 26 define between them a converging air inlet 32 into the compressor. The swirl or circumferential velocity component of air entering the compressor through the inlet 32 may be varied by variable setting inlet vanes 34 each of which is connected by an arm 35 to some suitable mechanism for actuating the inlet vanes 34 in unison which is not illustrated, since it is not material to my invention. This actuating mechanism may be mounted on a plate 36 bolted to the inner wall 26. While the adjustable inlet guide vanes 34 are a desirable part of the overall compressor or engine, they are not relevant to my invention which has to do with the diffuser of the compressor rather than its inlet.
Leading now into the rotating structure of the compressor, a drive shaft 38 which may be connected to the turbine is mounted in the shaft housing 22 and supported by a fixed bearing or journal block 39 within which a journal 40 of the shaft rotates. Bearing 39 is fixed to an inwardly extending flange 42 of the shaft housing. Thrust bearings 43 and 44 on the shaft 38 engage the faces of journal block 39. These are located on the shaft by abutments at which the shaft changes diameter. Oil is supplied to the bearings from a line 46. The lubrication of the bearing will now be further described as the details are immaterial.
A seal ring 47 abuts the thrust bearing 44 through a washer and is in turn abutted by the impeller 48 of the compressor which is piloted upon and splined to an extension 50 of shaft 38 and secured thereto by nut 51 and sleeve 52. Seal ring 47 cooperates with a seal mounted in a ring 53 bolted to the forward end of the shaft housing 22.
The impeller 48 comprises a disk 55 and radially extending vanes 56, and may follow standard practice in the design of such impellers. Details are immaterial to my invention. Air entering the compressor through the inlet 32 is driven outwardly and circumferentially by the vanes 56 into a diffuser 58 bounded by plate 8, ring 14, and plate 16, the diffuser having an outlet at 59.
All of the stationary parts of the compressor are fixed to the shaft housing 22, which is suitably located, by means not illustrated, in the case 2. Thus, the mounting plate 7 is located axially of the case and may slide relative to the front wall 4 to accommodate differential expansion of the parts as required.
A heat insulating ring 60 is mounted on the rear face of the mounting plate 7. Having described the general structure of the compressor in which the invention is embodied, we may now consider more particularly the variable diffuser with reference also to FIG. 2.
The outer diffuser ring 14 is a brazed structure made up of a forward part and a rear part. The forward part comprises a ring 62 (FIG. 1) from which vanes or walls 63 and 64 extend axially of the compressor. These vanes or walls are thin sheets of metal provided by machining grooves across ring 62. The rear edges of the vanes are brazed to a rear ring 66. The diffuser outer ring 14, as previously pointed out, is fixed to the diffuser front plate 8 by studs 15 and to the rear plate 16 by cap screws 18. Constantly open diffusing passages 67 are defined between vanes 64 and 63 adjacent in the direction of rotation of the impeller and closable diffuser passages 68 are defined between vanes 63 and 64 adjacent in the direction of rotation of the impeller.
The movable diffuser vanes 70 are shown most clearly in FIG. 2. Each vane comprises a wedge-shaped body 71 having a thin leading edge 72 and a broad trailing edge 74. The leading edge portion of each vane is brazed to a cylindrical pivot 75, each of which is inserted in a socket or journal 76 in the diffuser rear plate 16. A chordwise-extending slot 78 in each vane accommodates an actuating pin 79 fixed in a unison ring 80. This unison ring is radially located by engagement with the inner surface of diffuser rear ring 66 and a shoulder 83 on plate 16, and is axially located by its mounting between vanes 70 and the rear diffuser plate 16. Vanes 70 in turn bear against the diffuser front plate 8.
A bearing surface 82 is disposed on the rear face of the unison ring 80. When the unison ring 80 is rotated about the axis of rotation of the compressor, the actuating pins 79 swing the vanes 70 about their pivots as will be obvious from FIG. 2, in which the five right-hand vanes shown are illustrated in the high flow position and the two vanes to the left are illustrated as being in the minimum flow position.
The unison ring 80 is in turn rotated by an actuating ring 84 mounted on the rear side of rear plate 16 and supported by three rollers 86 disposed at 120° intervals and rotatably supported on bolts 87 fixed in the plate 16. The ring 84 may be rotated by any suitable actuating mechanism such as a pneumatic or oil servo or electromechanical servo, and the mechanism for rotating this is not illustrated. Actuating ring 84 is coupled to unison ring 80 by six posts 88 extending rearwardly from the unison ring through circumferential slots 90 (see also FIG. 2) in the rear plate 16. Ring 84 is fixed to these posts by cap screws 91. Referring again to FIG. 2, it will be noted that the trailing edge 74 of each movable diffuser vane 70 is terminated at an angle such as to fit against the leading edges of the vanes 63 and 64 with which it cooperates. Also, a small abutment 92 on each movable vane engages a vane 63 to limit and fix the open position of the movable vanes.
The operation should be clear from the foregoing description but may be gone through briefly. Any suitable actuator rotates ring 84 which rotates ring 80 through posts 88. The pins 79 on ring 80 moves the vanes 70 about their pivots 75, with the pins moving in the slots 78 of the vanes. The position for maximum flow is that illustrated at the right of FIG. 2 in which the opening between adjacent movable vanes is a maximum and the succeeding vanes or walls 63 and 64 of the outer set continue the diffusing passages which may be considered to be the passage indicated at 94 in FIG. 2 and continuing through passage 67.
In the closed or low flow condition of the vanes as illustrated at the left of FIG. 2, a more constricted diffusing passage 95 is defined between the vane bodies 71. In this condition of operation, the walls or vanes 63 and 64 perform no particular diffusing function, the smaller diffuser having sufficient area ratio between vanes 70. The diffuser may operate over a range between minimum and maximum area, being varied as air flow varies by any suitable control. The diffuser works well over the intermediate range as well as at the extremes.
Of course, the dimensions and details of the structure are subject to variation, but it may be pointed out that the particular structure shown to scale here was designed for an engine which was intended to operate efficiently at 100 percent speed with 100 percent airflow (three pounds per second) and also at 70 percent speed with 22 percent or 0.66 lbs. per second airflow. This is, of course, a very wide range. It may be pointed out again that the vanes 63 and 64 define the walls of diffusing passages for the higher flow condition and are immaterial to the diffusion in the minimum flow condition in which the smaller diffuser area between the closed vanes 70 is sufficient for diffusion. In intermediate conditions, some diffusion occurs in passages 67 and 68 in the outer ring.
It should be clear to those skilled in the art from the foregoing that I have devised a wide range diffuser structure of singular utility and practicality for handling wide flow ranges in a radial-flow compressor, and in such a compressor which forms an element of a gas turbine engine.
The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.