Patent Publication Number: US-4321008-A

Title: Wide range compressor

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to rotary mechanisms and more particularly to the class of mechanisms designated as turbomachinery. Still more particularly, the invention is concerned with the compressor portions of turbomachinery, especially wide range fans and compressors. 
     The present invention is directed to the class of rotary machines exemplified by the following U.S. Pat. Nos.: 483,394 Seelye Sept. 27, 1892, 1,748,768 Hofmann Feb. 25, 1930, 1,846,379 Anderson Feb. 23, 1932, 2,771,239 Moreillon Nov. 20, 1956, 2,797,044 Lovesey June 25, 1957, 3,066,488 Mock Dec. 4, 1962, 3,611,724 Kutney Oct. 12, 1971, 3,659,418 Poucher May 2, 1972. 
     The listed patents show rotary machines of various types for moving incompressible as well as compressible fluids, with a variety of mechanisms for controlling the volume, the pressure, and other characteristics of the output of the machines. While the machines shown in the listed patents may embody some of the elements of the present invention, none shows the complete combination nor do they show mechanisms for accomplishing the objectives of the present invention which include system requirements of fans and compressors for special air moving applications having a need for a wide range of pressure-flow deliveries with virtually constant discharge pressure. 
     SUMMARY OF THE INVENTION 
     The present invention resides in the provision of a wide range compressor having means for stabilizing the operation of the compressor while producing a wide range of volumes. 
     An object of the invention is to provide a compressor designed to produce a pressure-flow delivery over a wide flow range with virtually constant discharge pressure. 
     Still another object of the invention is to provide a compressor with variable components which may be controlled to produce the desired output; such variable components may include, but not be limited to, guide vanes, rotor blades, and throttle devices which may be used with varying degrees of effectiveness. 
     A further object of the invention is to provide a compressor having a casing in which a passage is formed, the passage having an inlet and receiving the blades of a rotor journalled in the casing, operation of the rotor causing the blades to draw air into the inlet and force it through the passage, means being disposed in the casing to vary the characteritics of the flow in the passage in a predetermined manner to produce desired results. 
     A still further object is to provide the compressor mentioned in the preceding object with stall ring means adjacent the inlet to promote stable recirculation of excess flow when the compressor is at low flow stage of operation and to supplement the stall ring with guide vanes which are located in predetermined regions and made variable to secure desired control characteristics. 
     Another object is to provide the compressor mentioned in the preceding paragraph with a stall ring disposed in the inlet to divide the fluid entering the passage into inner and outer flow annuluses and to dispose variable inlet guide vanes between the stall ring and the inner wall of the passage, means being provided in the casing to adjust the inlet guide vanes to vary the angle of flow of air admitted to the blades of the rotor for the purpose of controlling compressor pressure rise, capacity, and efficiency. 
     An object also is to provide a centrifugal compressor having variable geometry to improve the efficiency at low flow operation, an example of such variable geometry being a shroud section which is adjustable to control the area of flow of fluid to the rotor blades. 
     Other objects and advantages will become apparent to those skilled in the art from a reading of the following description of the forms of the invention selected for illustration in the accompanying drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a partial axial sectional view of a compressor formed in accordance with the present invention; 
     FIG. 2 is a graph with curves resulting from plotting the fan delivery pressure relative to the flow and indicating in solid, dotted, and dashed lines the results of predetermined adjustments of control mechanism provided in the compressor shown in FIG. 1; 
     FIG. 3 is a partial axial sectional view, similar to FIG. 1, of a modified form of the invention; 
     FIG. 4 is a graph with curves resulting from plotting the fan delivery pressure relative to the fan flow and indicating in solid and dashed lines the results of certain adjustments of geometry changing mechanisms shown in FIG. 3; 
     FIG. 5 is a fragmentary sectional view, similar to FIG. 3, showing a further modification; and 
     FIG. 6 is a sectional view taken on the line VI--VI of FIG. 5. 
    
    
     DESCRIPTION 
     More particular reference to FIG. 1 of the drawings shows that one form of the invention includes a compressor &#34;C&#34; of the axial type having casing means 10 and 11 providing a passage 12 with inner and outer walls 13 and 14. These walls are curved away from one another at the front of the casing to form an inlet 15 which communicates with an axially extending portion leading to an outlet or to other stages of compression. The compressor includes a rotor 16 mounted for rotation about an axis 17 extending substantially parallel to the passage 12, the rotor being provided with blades 18 which project into the passage 12. The blades are so shaped that when the rotor revolves under the action of a prime mover (not shown), fluid, such as ambient air, will be drawn into the inlet 15 and forced through the passage 12 to the outlet or succeeding stages of compression. Downstream from the rotor blades the passage 12 contains one or more rows of stator vanes 19 which extend betwen the inner and outer passage walls 13 and 14, respectively, and are disposed at suitable angles to diffuse the air flowing from the blades and cause a pressure increase. When the demand for air is low, the pressure increase causes a build up of fluid in the passage 12 and the air, or other fluid, tends to flow back toward the inlet or recirculate and result in a stall condition. 
     To combate such condition, it has heretofore been proposed to provide the inlet with a stall ring 20 which is relatively thin compared to its length axially and serves to split the fluid drawn in by the fan blades into inner and outer annuluses of flow. This stall ring tends to stabilize the operation of axial fans below normal stall by allowing recirculation of excess flow. 
     To facilitate control of the fan characteristics to match flow conditions, the compressor of this invention has partial span inlet guide vanes 21 in combination with the stall ring 20. As shown in FIG. 1, the inlet guide vanes 21 extend from the inner passage wall 13 substantially to the inner surface of the stall ring 20. The guide vanes 21 are mounted for pivotal adjustment about axes extending radially relative to the axis 17 of the rotor. Each vane 21 has a pinion or sector thereof secured thereto for meshing engagement with a ring gear 22 supported in the casing for rotary action in response to suitable control means (not shown) to effect adjustment of the guide vanes. In this manner the guide vanes may be moved to vary the angle at which the vanes direct the entering air against the rotating blades 18. It will be apparent that since the guide vanes are disposed between the stall ring and the inner wall of the passage, adjustment of such vanes will change predetermined characteristics of the inner annulus of flow. The control resulting from the mechanism of the invention provides a stable operating range of the fan. 
     At low flows, positions of the inlet guide vanes at minus settings will control the fan pressure rise and provide reduction of the recirculation flow as indicated by the dotted line &#34;A&#34; in FIG. 2. The use of &#34;plus&#34; inlet guide settings increases maximum capacity of a given size fan as indicated by the dot-dash line &#34;B&#34; in FIG. 2 and indirectly contributes to low-flow efficiency by allowing use of a smaller fan size for given flow requirements. 
     Similar results can be secured in the operation of fan of centrifugal configuration by providing the latter with means for varying the geometry thereof, as shown in FIG. 3. In this Figure, a centrifugal fan 25 is shown in axial section. Fan 25 has casing means 26 providing a passage 27 with an axial inlet 28 at the front and a radially directed outlet 29 at the side. The casing receives a rotor 30 which has a curved surface 31 constituting the inner wall of the fluid passage 27, circumferentially spaced blades 32 projecting from the surface 31 adjacent the periphery of the rotor. The blades 32 are curved in a radial direction so that when the rotor revolves about an axis 33, fluid, such as ambient air, will be drawn into the inlet 28 and discharged by centrifugal force through the outlet 29. The latter may be provided with suitably shaped blades 34, if desired, or found necessary. 
     In the fan shown in FIG. 3, means for varying the geometry includes a shouud secton 35 which is mounted for axial sliding movement into and out of the path of fluid flowing to the rotor blades 32. The shroud section 35 is, in the form of the invention shown in FIG. 3, shaped somewhat like a ring with a curved surface constituting a continuation of the outer passage wall when the shroud is withdrawn into a chamber 36 therefor formed in the casing. When the shroud is extended it reduces the area of the passage leading to the rotor blades. This positioning of the shroud provides a smooth blockage of flow to the fan and a consequent reduction of fan flow with little effect on pressure rise. It is contended that at a completely closed or zero flow position the pressure rise will be virtually unaffected. The shroud may be moved axially of the casing in any desired manner. 
     The variable inlet section may be modified to improve the performance by recess contouring the surface adjacent the fan blades, as at 37, see FIGS. 5 and 6, and providing curved guiding webs 38 in the recess and extending across it whereby fluid tending to flow backward into the passage from the fan will be recirculated thereinto at an optimum angle. 
     As in the first form of the invention illustrated, the centrifugal fan of FIG. 3 may be further modified by providing a stall ring 39 adjacent the inlet, see FIG. 3, to divide the fluid drawn into the passage into inner and outer annuluses of flow, one of which may have certain characteristics of flow varied by inlet guide vanes 40. These elements are arranged between the stall ring 39 and one wall of the passage. As in the first form of the invention illustrated, each inlet guide vane is mounted for rotary adjustment about an axis radiating from the axis of rotation 33 of the rotor 30. Each guide vane has a pinion or sector 41 meshing with a ring gear 42 movement of which simultaneously adjusts the angles of the guide vanes and consequently the direction of flow of air to the rotor blades. This adjustment of the guide vanes changes predetermined characteristics of the fluid flow in one of the annuluses of flow through the passage 27. 
     While the foregoing description is directed more particularly to several forms of the invention parts of which may be utilized either individually or collectively, other forms or modifications may be suggested therein without departing from the principles of the present invention as set forth in the accompanying claims.