US2696345A - Method of controlling supercharger to avoid pulsation - Google Patents

Description

P. S. HOPPER Dec. 7, 1954 METHOD OF CONTROLLING SUPERCHARGER TO AVOID PULSATION Filed Oct. 14, 1949 SOURCE POWER I WORM DH/ VE MPL/F/ER luo yuew' ATTORNEY Pad ALL Jun arms 31 33g; TEMPE/mum:-

70 ENE/ME United States Patent METHOD OF CONTROLLING SUPERCHARGER TO AVOID PULSATION Philip S. Hopper, Manchester, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application October 14, 1949, Serial No. 121,342 8 Claims. (Cl. 230115) curve in the surging range is not the same for all compressors and can be different in different installations. Operation within this range is undesirable because of the detrimental effects on compressor loading and on compressor efficiency. Various effects of surging which have been noted in tests include a definite increase in inlet-air temperature, a high degree of turbulence and definite prerotation at the compressor inlet annulus, and a large radial temperature gradient at the compressor inlet. 7

The remedy for surging is to alter the operating characteristics of the compressor. This can be done by varying the angle of attack of vanes mounted adjacent the compressor impeller inlet, or by the use of a bleed in the delivery conduit of the compressor through which a portion of the discharge flow is dissipated, or recirculated to the compressor inlet.

Surging is a cycle of events in which there is a recirculation of air through the compressor. The mixing of the heated air flowing back through the compressor with the cooler inlet air results in a temperature gradient in the air stream adjacent to the impeller, being particularly large at the compressor inlet annulus. It has been ob-, served that any major surging is preceded by an initial recirculation, and by observing the temperature gradient at some point in the air stream adjacent to the compressor impeller it is possible to anticipate detrimental conditions of operation in time to alter the compressor operating characteristics and avoid these'conditions.

An object of this invention is to extend the operating range of a compressor.

. Another object of this invention is to provide a control which will assure surge-free operation of a compressor.

A further object of this invention is to provide a control which is responsive to changes in the radial temperature gradient existing in the air stream adjacent to a compressor impeller and will prevent detrimental operation of the compressor.

Although the novel features which are characteristics of this invention are set forth more in detail in the claims appended hereto, the nature and scope of the invention may be better understood by referring to the following description, taken in connection with the accompanying drawing forming a part thereof, in which a specific embodiment has been set forth for purposes of illustration.

In the drawing:

Fig. 1 is a vertical section through a centrifugal compressor utilizing the control apparatus.

Fig. 2 is a fragmentary view of an alternate arrangement of the control apparatus.

Fig. 3 is a vertical section through an axial flow compressor showing the thermocouples mounted on the inlet side of the first compressor stage.

Fig. 4 is .a modification of Fig. 3, showing the thermo-v 2,696,345 Patented Dec. 7, 1954 "ice couples mounted on the delivery side of the first compressor stage.

Referring to Fig. 1 in detail, the compressor includes bladed impeller 10 mounted on drive shaft 12, inlet casing 14, and outlet casing 20. Casing 14 defines inlet conduit 16 and inlet annulus 18 and surrounds impeller 10 to define therewith a continuation of the inlet conduit. Casing 20 defines delivery conduit 22 and is connected to an aircraft engine, not shown. The outer casing includes diffuser vanes 24 mounted within the delivery conduit adjacent to the delivery side of the impeller, and port 26 for bleeding air from the delivery conduit.

A pair of thermocouples 28 and 30 are mounted within the inlet annulus 18. These thermocouples are located adjacent to and at approximately an equal distance from the impeller inlet face, and radially spaced apart so as to be responsive to a radial temperature gradient across the impeller inlet. The thermocouples are balanced, being wired in series and having opposed polarity, and their leads 32 are connected to a common junction box 34 in order that the three junctions 36, 38 and 40 can be maintained at the same temperature. Junction 38 is common to the two thermocouples and junctions 36 and 40 are connected by leads 42 and 44, respectively, to servo amplifier 46 which in turn is connected to a power source, not shown.

Servo amplifier 46 is connected by leads 48 to reversing motor 50 which operates worm drive 52 to regulate the position of bleed valve 54 within port 26, the valve 22mg drivingly connected to the worm drive by shaft An alternative arrangement is shown in Fig. 2 in which the reversing motor 50 and worm drive 52 of Fig. 1 function to vary the angle of attack of vane 58 located within the inlet annulus 18. This vane is drivingly connected to the worm drive by shaft 60. While only one vane is. shown for simplicity, it is to be understood that, as is common in the art, a series of such vanes would be provided around the inlet annulus.

When recirculation occurs within the vicinity of the impeller inlet indicating the onset of surge, the temperature of thermocouple 28 mounted adjacent the outer wall of the inlet annulus, will increase with respect to that of thermocouple 30, mounted adjacent the inner wall of the inlet annulus, creating a potential difference between the thermocouples and causing a signal to be relayed to servo amplifier 46. The servo amplifier in turn will respond to this signal by operating reversing motor 50 so as either to open bleed valve 54 or change the angle of attack of vanes 58, Whichever system is used. In either case the result is to alter. the operating characteristics of the compressor, thus anticipating surge and avoiding its detrimental effects. When stable operating conditions have been established, and the radial temperature gradient at the impeller has become normal, the servo amplifier will function in response to'this signal to restore either the bleed valve or the vanes to their original position.

Fig. 3 illustrates the use of the control apparatus in connection with an axial flow compressor, 62 indicating a bladed impeller mounted on drive shaft 66. The inlet annulus is defined by inner casing 68 and outer casing 70, the outer casing carrying stationary vanes 71. pair of balanced thermocouples 72 and 74 are mounted in a radial plane within the inlet annulus adjacent to the impeller and are connected to junction box 76. These thermocouples function in the same manner as those described in connection with Fig. 1 to operate a bleed on'the delivery side of the impeller or to vary the angle of attack of vanes mounted within the inlet annulus. Fig. 3 shows neither a bleed nor vanes, but it is understood that either arrangement could be used as taught in Fig. l and Fig. 2.

Rather than using temperature responsive elements mounted adjacent the impeller inlet, it would be possible to place these elements on the delivery side of the impeller. In Fig. 4, balanced thermocouples 78 and 80 are shown mounted downstream of impeller 62, as on the stationary vanes 71. These thermocouples are connected to junction box 82 and can be arranged to vary the operating characteristics of the compressor in response to a potential difference therebetween.

It is to be understood that the invention is not limited to the specific embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1 A compressor including a rotatable impeller having an inlet side and a delivery side and casing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, in combination with a surge control comprising essentially a plurality of temperature sensing elements mounted in said conduit adjacent to one of said impeller sides, said elements being spaced apart transversely of the conduit, substantially equally spaced from the impeller longitudinally of the conduit, with at least one of said elements being located adjacent said inner Wall and at least one of said elements being located adjacent said outer wall of said casing, means cooperating with said conduit to aflect the flow of air therethrough thereby altering the operating characteristics of said compressor, and anoperative connection between said temperature sensing elements and said operating characteristic altering. means including means responsive to a temperature difference between said elements for actuating said operating characteristic altering means.

2. A compressor including a rotatable impeller having an inlet side and a delivery side and easing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, in combination with a surge control comprising essentially a pair of temperature sensing elements mounted in said conduit adjacent to one of said impeller sides, said elements being spaced apart transversely of the conduit, substantially equally spaced from the impeller longitudinally of the conduit, with one of said elements being located adjacent said inner wall and the other of said elements being located adjacent said outer wall of said casing, means cooperating with said conduit to affect the flow of air therethrough thereby altering the operating characteristics of said compressor, and an operative connection between said temperature sensing elements and said operating characteristic altering means including means responsive to a temperature difference between said elements for actuating said operating characteristic altering means.

3. A compressor including a rotatable impeller having an inlet side and a delivery side and casing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, in combination with a surge control comprising essentially a pair of balanced thermocouples mounted in said conduit adjacent to one of said impeller sides, said thermocouples being substantially equally spaced from the impeller longitudinally of the conduit with one of said thermocouples being located adjacent said inner wall and the other of said thermocouples being located adjacent said outer wall of said casing, means cooperating with said conduit to affect the flow of air therethrough thereby altering the operating characteristics of said compressor, and an operative connection between said thermocouples and said operating characteristic altering means including means responsive to a potential difference between the thermocouples for actuating said operating characteristic altering means.

4. A compressor including a rotatable impeller having an inlet side and a delivery side and easing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, in combination with a surge control comprising essentially a pair of thermocouples wired in series and of opposed polarity mounted in said conduit adjacent to one of said impeller sides, said thermocouples being substantially equally spaced from the impeller longitudinally of the conduit with one of said thermocouples being located adjacent said inner wall and the other of said thermocouples being located adjacent said outer wall of said casing, a servo amplifier operatively connected to the thermocouples and responsive to a potential difference therebetween, means cooperating with said conduit to affect the flow of air therethrough thereby altering the operating' characteristics'of' said compressor, and a reversing motor operatively connected to the servo amplifier and to said operating characteristic altering means, said amplifier actuating said reversing motor whenever a radial temperature gradient across said conduit creates a potential difference between said thermocouples.

5. A compressor including a rotatable impeller having an inlet side and a delivery side and casing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, in combination with a surge control comprising essentially a pair of thermocouples wired in series and of opposed polarity mounted in said conduit adjacent to the inlet side of said impeller, said thermocouples being substantially equally spaced from the impeller longitudinally of the conduit with one of said thermocouples being located adjacent said inner wall and the other of said thermocouples being located adjacent said outer Wall of said casing, means cooperating with said conduit to affect the flow of air therethrough thereby altering the operating characteristics of said compressor, and an operative connection between said'thermocoupl'es and said operating characteristic altering means including means responsiveto a temperature difference between said thermocouples for actuating said operating characteristic altering means.

6. A compressor including a rotatable impeller having an inlet side and a delivery side and easing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, in combination with a surge control comprising essentially a pair of thermocouples wired in series and of opposed polarity mounted in said" conduit ad'- jacent to the delivery side of said impeller, said thermocouples being substantially equally spaced from the impeller longitudinally of the conduit with one of said thermocouples being located adjacent said. inner wall and the other of said thermocouples being located adjacent said outer wall of said casing, means cooperating with said conduit to affect the flow of air therethrough thereby altering the operating characteristics of said compressor, and an operative connection between said thermocouples and said operating characteristic altering means including means responsive to a temperature difference between said thermocouples for actuating said operating characteristic altering means.

7. A compressor including a rotatable impeller having an inlet side and a delivery side, casing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, at least one bleed port located in said casing means ad'- jacent to the delivery side of said impeller and valve means controlling the area of said bleed port, in combination with a surge control comprising essentially a pair of thermocouples mounted in said conduit adjacent to one of said impeller sides, said thermocouples being substantially equally spaced from the impeller longitudinally of the conduit with one of said thermocouples being located adjacent said inner wall and the other of said thermocouples being located adjacent said outer wall of said casing, and an operative connection between said thermocouples and said bleed port valve means including means responsive to a temperature difference between said thermocouples for actuating said valve means.

8. A compressor including a rotatable impeller having an inlet side and a delivery side, casing means having inner and outer walls defining an annular conduit for the flow of air through said compressor, said walls extending upstream and downstream of said impeller, a plurality of guide vanes mounted within said casing means adjacent to the inlet side of said impeller and means controlling the angle of attack of said guide vanes, in combination with a surge control comprising essentiallya pair of thermocouples mounted in said conduit adjacent to one of said impeller sides, said thermocouples being substantially equally spaeed from the impeller longitudinally of the conduit with one of said thermocouples being located adjacent'said innerwall and the other of said thermocouples being located adjacent said tauter wall 03 said casing, and andoperiative (fonnec- References Cited in the file of this patent tion etween sai t ermocoup es an sai gui e vane angle of attack controlling means including means re- UNITED STATES PATENTS sponsive to a temperature difference between said therrno- Number Name Date couples for actuating said angle of attack controlling 5 1,281,216 Schellens Oct. 8, 1918 means. 2,000,721 Standerwick May 7, 1935 2,442,049 Lee May 25, 1948 2,455,292 Borden Nov. 30, 1948

Images