Patent Publication Number: US-9404506-B2

Title: Impeller and rotary machine

Description:
TECHNICAL FIELD 
     The present invention relates to an impeller and a rotary machine, and particularly, to a flow passage shape thereof. 
     Priority is claimed on Japanese Patent Application No. 2009-164782 filed on Jul. 13, 2009, the contents of which are incorporated herein by reference. 
     BACKGROUND ART 
     In centrifugal or mixed-flow compressors used for rotary machines, such as an industrial compressor, a turbo refrigerator, and a small gas turbine, improvements in performance are required, and particularly, improvements in the performance of the impeller that is a key component of the compressors are required. Thus, in recent years, in order to improve the performance of an impeller, an impeller in which a recess is provided at a leading edge between tip and hub of the blades to effectively suppress secondary flow or flaking has been proposed (for example, refer to PTL 1). 
     Additionally, there are impellers (for example, refer to PTLs 2 and 3) in which turbulence is caused in a flow along the hub surface by forming a plurality of grooves in the hub surface between blades such that a boundary layer of the flow along the hub surface is not expanded, in order to improve the performance of a centrifugal or mixed-flow impeller, and in which a plurality of small blades is provided between blades in order to prevent local concentration of a boundary layer. 
     RELATED ART DOCUMENT 
     Patent Literature 
     [PTL 1] JP-A-2006-2689 
     [PTL 2] JP-A-2005-163640 
     [PTL 3] JP-A-2005-180372 
     SUMMARY OF INVENTION 
     Technical Problem 
       FIG. 9  shows the vicinity of a leading edge of a blade in a related-art impeller. As shown in  FIG. 9 , in an inlet hub surface of a related-art impeller, in order to maintain a throut area at an inlet  206  of a fluid flow passage  210 , a blade angle of a blade  203  at an inlet  206  is designed so as to approach to a radial direction of the impeller relative to an entry angle (entry flow angle) of fluid to inlet  206  at a designed flow rate. Therefore, the entry flow angle (hereinafter called entry angle θ) of the fluid with respect to the blade angle becomes large. Since the entry angle θ of the 4444 fluid tends to increase depending on decreases in the inflow, a boudary layer notably grows on the hub surface near a suction surface n of the blade, where the flow rate is lowest in the vicinity of the inlet  206 , due to decreases in the inflow. Thus, problems arise in that the efficiency is decreased and the fluid stall. 
     The invention has been made in view of the above circumstances, and the object thereof is to provide an impeller and a rotary machine that can suppress a decrease in efficiency and a stall of the fluid by growing of a boundary layer on the hub surface near a suction surface n at the inlet when inflow decreases. 
     Solution to Problem 
     The invention adopts the following configurations in order to solve the above problems to achieve the object concerned. 
     An impeller (for example, the impeller  1  in the embodiment) related to the invention is an impeller of a rotary machine in which the direction of flow gradually changes from an axial direction to a radial direction as it goes from the inside in the radial direction of a fluid flow passage (for example, the impeller flow passage  10  in the embodiment) to the outside in the radial direction thereof. The impeller includes a hub surface (for example, the hub surface  4  in the embodiment) constituting at least a portion of the fluid flow passage; a blade surface (for example, the pressure surface p or the suction surface n in the embodiment) constituting at least a portion of the fluid flow passage; and a bulge (for example, the bulge b in the embodiment) that bulges toward the inside of the fluid flow passage at a corner (for example, the corner  12  in the embodiment) where a pressure surface of the blade surface comes in contact with the hub surface in the vicinity of an inlet (for example, the inlet  6  in the embodiment) of the fluid flow passage. 
     According to the impeller of the rotary machine related to the invention, since the bulge is provided at the corner where the hub surface comes in contact with the pressure surface in the vicinity of the inlet, the leading edge of the blade on the hub surface side is thickly formed and a radius of a round portion, which is formed of the bulge at the leading edge of the blade, becomes large substantively. Therefore, even when the entry angle of the fluid with respect to the blade angle becomes large because the inflow velocity on the hub surface is low, the fluid flows along the round portion, which is formed of the bulge at the leading edge of the blade and increases radius thereof, at a slow pace. Thus, since enlarging a boundary layer at the leading edge in the suction surface side is suppressed, growing the boundary layer on the hub surface near suction surface can be suppressed. Moreover, since the bulge is provided at the corner near the hub surface (that is, local only), and the amount of decrease in the throat area can be minimally suppressed. 
     Additionally, the strength of the portion contacting the blade with the hub, where a force by the fluid applies to and centrifugal stress is generated by rotating the impeller, can be increased by providing a bulge at the corner in the vicinity of the inlet. Moreover, an increase in the number of parts can be suppressed by being formed integrally with the hub and the blade. 
     In the impeller of the rotary machine of the above invention, the impeller may further include a second bulge that bulges toward the inside of the fluid flow passage at a corner where a suction surface of the blade comes in contact with the hub surface in the vicinity of the inlet of the fluid flow passage. 
     In this case, since the second bulge is provided at the corner where the suction surface of the blade comes in contact with the hub surface in addition to the bulge that is provided at the corner where the pressure surface of the blade surface comes in contact with the hub surface, the thickness of the leading edge of the blade near the hub surface can be larger. Therefore, it is possible to further suppress growing of a boundary layer due to decreases in the flow rate, and the strength of the portion contacting the blade with the hub in the vicinity of the inlet can be further increased. 
     Advantageous Effects of Invention 
     According to the impeller of the rotary machine related to the invention, even when the entry angle of the fluid with respect to the blade angle becomes large when the flow rate is low, enlarging a boundary layer at the inlet (in particular, on the hub surface near the suction surface) can be suppressed, depending on the increase in the radius of the leading edge of the blade, by providing the bulge thereon. Therefore, there is an advantage that a decrease in the efficiency of the low flow rate and the stall of the fluid can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a centrifugal compressor in the embodiment of the invention. 
         FIG. 2  is an enlarged front view showing chief parts of the impeller in the embodiment of the invention. 
         FIG. 3  is a sectional view taken along a line A-A of  FIG. 2 . 
         FIG. 4  is a sectional view along a line B-B of  FIG. 3 . 
         FIG. 5  is an enlarged cross-sectional view showing leading edge of a blade in the embodiment of the invention. 
         FIG. 6  is a graph showing efficiency characteristics with respect to the flow rate of the impeller in the embodiment of the invention. 
         FIG. 7  is graph showing head characteristics with respect to the flow rate of the impeller in the embodiment of the invention. 
         FIG. 8  is a cross-sectional view equivalent to  FIG. 4  in another example of the embodiment of the invention. 
         FIG. 9  is a front view showing vicinity of a leading edge of a blade in a related-art impeller. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, an impeller and a rotary machine in the embodiment of the invention will be described, referring to the drawings. The impeller of this embodiment will be described taking an impeller of a centrifugal compressor that is a rotary machine as an example. 
     A centrifugal compressor  100  that is a rotary machine of the present embodiment, as shown in  FIG. 1 , is mainly constituted by, as an example, a shaft  102  that is rotated around an axis O, an impeller  1  that is attached to the shaft  102  and compresses process gas (gas) G using a centrifugal force, and a casing  105  that rotatably supports the shaft  102  and is formed with a flow passage  104  that allows the process gas G to pass from the upstream to the downstream. 
     A casing  105  is formed so as to form a substantially columnar outline, and the shaft  102  is arranged so as to pass through a center. Journal bearings  105   a  are provided at both ends of the shaft  102  in an axial direction, and a thrust bearing  105   b  is provided at one end. The journal bearings  105   a  and the thrust bearing  105   b  rotatably support the shaft  102 . That is, the shaft  102  is supported by the casing  105  via the journal bearings  105   a  and the thrust bearing  105   b.    
     Additionally, a suction port  105   c  into which the process gas G is made to flow from the outside is provided on the side of one end of the casing  105  in the axial direction, and a discharge port  105   d  through which the process gas G flows to the outside is provided on the side of the other end. An internal space, which communicates with the suction port  105   c  and the discharge port  105   d , respectively, and repeats diameter enlargement and diameter reduction, is provided in the casing  105 . This internal space functions as a space that accommodates the impeller  1 , and also functions as the above flow passage  104 . 
     That is, the suction port  105   c  and the discharge port  105   d  communicate with each other via the impeller  1  and the flow passage  104 . 
     A plurality of the impellers  1  is arranged at intervals in the axial direction of the shaft  102 . In addition, although six impellers  1  are provided in the illustrated example, it is only necessary that at least one or more impellers are provided. 
       FIGS. 2 to 3  show the impeller  1  of the centrifugal compressor  100 , and the impeller  1  includes a hub  2  and a plurality of blades  3 . 
     The hub  2  is formed in a substantially round shape in front view, and is made rotatable around the axis with the axis O as a center. In the hub  2 , as shown in  FIG. 3 , a hub surface  4  is formed so as to be curved toward the outside in the radial direction from a predetermined position S on the inside in the radial direction slightly separated radially outward from the axis O. This curvedly formed hub surface  4  is formed such that a surface located on the inside in the radial direction is formed along the axis O, and runs along the radial direction gradually as it goes to the outside in the radial direction. That is, the hub  2  is formed such that the axial thickness thereof decreases from one (upstream) of the axial end surfaces as it goes to the outside in the radial direction from the position S on the inside in the radial direction slightly separated from the axis O, and this axial thickness becomes larger near the inside and becomes smaller near the outside. In addition, in  FIG. 3 , an arrow indicates the radial direction of the hub  2 . 
     A plurality of blades  3  is substantially radially arranged on the above-described hub surface  4  as shown in  FIG. 2 , and is erected substantially perpendicularly (in normal direction) to the hub surface  4  as shown in  FIG. 4 . The blade  3  is formed such that the thickness thereof is substantially uniform from a hub end h up to a tip end t, and shows a curved shape that slightly becomes a convex surface toward the rotational direction (shown by an arrow in  FIG. 2 ) of the hub  2  from the hub end h (refer to  FIG. 3 ) to the tip end t. As the impeller  1  rotates, a blade surface on a convex side of respective blade surfaces on a convex side and the convex side of the curved blade  3  becomes a pressure surface p, and a blade surface on the concave side that is a back side of the convex surface becomes the suction surface n. 
     Additionally, as shown in  FIG. 3 , the tip end t of a blade  3  is formed so as to be curved from the inside in the radial direction of the hub  2  to the outside in the radial direction thereof. More specifically, similarly to the above-described hub surface  4 , the blade is formed in a concave shape that runs along the axis O nearer the inside in the radial direction and runs along the radial direction gradually as it goes to the outside in the radial direction. 
     If the hub surface  4  is taken as a reference, the blade  3  is formed so as to be higher near the inside in the radial direction of the hub  2  and lower near the outside in the radial direction thereof. 
     In the above-described impeller  1 , the tip end t side of the blade  3  is covered with the casing  105  (refer to  FIG. 1 ), and an impeller flow passage  10  of the impeller  1  is constituted by a shroud surface  5  constituted by the casing  105 , the pressure surface p and suction surface n of adjacent blades  3  described above, and the hub surface  4  between the pressure surface p and the suction surface n. As the impeller  1  rotates, a fluid flows in along the radial direction from an inlet  6  of the impeller flow passage  10  located on the inside in the radial direction of the hub  2 , and the fluid flows out to the outside along the radial direction from an outlet  7  located on the outside in the radial direction due to a centrifugal force. 
     The impeller flow passage  10  having the configuration described above is formed so as to be curved from the above-described inlet  6  toward the outlet  7 , and the direction of flow of the flow passage gradually changes from the axial direction to the radial direction as it goes from the inside in the radial direction of the hub  2  to the outside in the radial direction thereof. 
     A bulge b that bulges toward the inside of the impeller flow passage  10  is formed at a corner  12  where the hub surface  4  comes in contact with the pressure surface p of the blade  3  in the vicinity of an inlet  6 . The bulge b is formed integrally with the hub surface  4  and the pressure surface p (refer to  FIGS. 2 to 4 ). In addition, a cross-sectional shape of the leading edge  20  of the blade  3  is formed in a substantially semicircular shape (refer to  FIG. 5 ). The bulge b is formed at the corner  12  in the vicinity of the inlet  6  in the above-described corner  12  (that is, a part of the corner  12  nearby the leading edge  20 ). 
     The maximum width of the bulge b, is set to about 20% of the width of the impeller flow passage  10 , and to about 20% of the height of the blade  3 . The bulge b has a maximum width and a maximum height at a position where the bulge b smoothly bulges as it goes along a flow direction from a vicinity of the inlet  6  to downstream in a curved surface protruding toward the inside of the impeller flow passage  10 . The bulge b gradually decreases in the curved surface same as the above from the position having the maximum width and the maximum height, and smoothly connects to the hub surface  4  and the pressure surface p at a position of about 10% of the flow passage length from the inlet  6  to the outlet  7  of the impeller flow passage  10 . The thickness of the leading edge  20  of the blade  3  near the hub surface  4  is increased by forming the bulge b in this manner, and the radius r 1  of the leading edge of the blade practically increases to the radius r 2  of the leading edge of the blade as shown in  FIG. 5 . 
       FIG. 6  is a graph showing the efficiency characteristics of rotary machines using the impeller  1  and a related-art impeller. In this graph, the vertical axis represents efficiency η, and the horizontal axis represents flow rate Q. In addition, in  FIG. 6 , a solid line shows the efficiency of a rotary machine including an impeller that is not provided with the bulge b, and a broken line shows the efficiency of a rotary machine including the above-described impeller  1  that is provided with the bulge b. 
     As shown in  FIG. 6 , it is apparent that the efficiency is improved in a case where the bulge b is provided at the same flow rate Q, as compared to a case where the bulge b is not provided. Particularly, it is apparent that the efficiency on the side of a small flow rate is improved greatly. 
     Additionally,  FIG. 7  is a graph showing the head (work) characteristics of the rotary machines using the impeller  1  and the related-art impeller, and the vertical axis represents head (work), and the horizontal axis represents the flow rate Q. In addition, in  FIG. 7 , a solid line shows the head of a rotary machine including an impeller that is not provided with the bulge b, and a broken line shows the head of a rotary machine including the above-described impeller  1  that is provided with the bulge b. 
     As shown in  FIG. 7 , it is apparent that a surge point (shown by an open circle in the drawing) of the rotary machine including the above-described impeller  1  that is provided with the bulge b is displaced toward a lower flow rate side more than a surge point of the rotary machine including the impeller that is not provided with the bulge b (shown by a filled circle in the drawing), and a surge margin is expanded. 
     As shown in these  FIGS. 6 and 7 , the reason why the efficiency characteristics of the impeller  1  is improved and the surge point is displaced toward a lower flow rate side in comparison with the impeller without the bulge b is that it is difficult to grow a boundary layer on the suction surface n by partial increasing of the radius of the leading edge of the blade at the inlet  6  in a case where the entry angle of the fluid as shown in  FIG. 2  becomes large when a flow rate is low. In addition, the surge point is a minimum flow rate at which a rotary machine is required to operate normally without surging. 
     Accordingly, according to the impeller  1  of the rotary machine of the above-described embodiment, the thickness of the leading edge  20  of the blade  3  near the hub surface  4  is partially increased by providing the bulge b at the corner  12  where the hub surface  4  comes in contact with the pressure surface p in the vicinity of the inlet  6 . Therefore, the radius r 1  of the leading edge of the blade near the hub surface  4  practically increases to the radius r 2  of the leading edge of the blade, and growing of a boundary layer on the suction surface near the hub at a designed flow rate can be suppressed. 
     In addition, since the radius r 1  of the leading edge of the blade practically increases to the radius r 2  of the leading edge of the blade by forming the leading edge  20  of the blade  3  near the hub surface  4  to be thick with the bulge b, even when the entry angle of the fluid with respect to the blade angle (refer to  FIG. 2 ) becomes large, enlarging a boundary layer on the hub surface  4  near the suction surface n can be suppressed. Thus, suppressing a decrease in the efficiency at low flow rate and preventing from the stall of the fluid can be achieved, and the surge margin can be expanded. 
     Moreover, since the bulge b is provided at the corner  12  near the hub surface  4  (that is, local only), amount of decrease in the throat area at the inlet  6  of the impellar flow passage  10  can be minimally suppressed. 
     Additionally, the strength of the portion contacting the blade  3  with the hub  2 , where a force by the fluid applies to and centrifugal stress is generated by high-speed rotating the impeller  1 , can be increased by providing the bulge b at the corner  12  in the vicinity of the inlet  6 . Moreover, an increase in the number of parts can be suppressed by being formed integrally with the hub  2  and the blade  3 . 
     In addition, in the impeller  1  of the above-described embodiment, the case where the bulge b is provided at the corner  12  where the pressure surface p comes in contact with the hub surface  4  has been described in the vicinity of an inlet  6  of the fluid flow passage  10 ; however, the invention is not limited to this configuration. For example, as another example, as shown in  FIG. 8 , the bulge b′ may be provided at the corner  22  where the suction surface n comes in contact with the hub surface  4  in the vicinity of an inlet  6  of the fluid flow passage  10 . In a case where the bulge b′ is provided at the corner  22  in this manner, since the thickness of the leading edge  20  of the blade  3  near the hub surface  4  can be larger, the radius of the leading edge of the blade can further become large. Therefore, it is possible to further suppress growing of a boundary layer due to decreases in the flow rate. Moreover, the strength of the portion contacting the blade  3  with the hub  2  at the corner  12  in the vicinity of the inlet  6  can be further increased. 
     Additionally, the shape and position of the bulge b of the above-described embodiment are examples, and shape and position are not limited thereto. 
     Additionally, although the impeller of the centrifugal rotary machine has been described in the above embodiment, the impeller is not limited to this, and may be an impeller of a mixed-flow rotary machine. Additionally, the invention may be applied to an impeller of a blower, a turbine, or the like without being limited to the compressor. Additionally, although the so-called open impeller in which the facing side of the hub surface  4  is covered with the shroud surface  5  has been described as an example in the above-described embodiment, the invention may be applied to a closed impeller including a wall that covers the tip end t side integrally formed in the blade  3 . In the case of this closed type impeller, it is only necessary to substitute the shroud surface  5  of the above-described embodiment with the inner surface side of the wall that covers the tip end t. In addition, as in the related art, a fillet R formed by the tip roundness of a cutting cutter tool is slightly given to a boundary portion between the hub surface  4  other than the bulge b, and a blade surface (the suction surface n or the pressure surface p). 
     INDUSTRIAL APPLICABILITY 
     According to the impeller of the rotary machine related to the invention, even when the entry angle of the fluid with respect to the blade angle becomes large when the flow rate is low, enlarging a boundary layer at the inlet (in particular, on the hub surface near the suction surface) can be suppressed, depending on the increase in the radius of the leading edge of the blade, by providing the bulge thereon. Therefore, there is an advantage that a decrease in the efficiency of the low flow rate and the stall of the fluid can be suppressed. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 : IMPELLER 
               4 : HUB SURFACE 
               6 : INLET 
               7 : OUTLET 
               10 : IMPELLER FLOW PASSAGE (FLUID FLOW PASSAGE) 
               12 : CORNER 
               22 : CORNER 
               100 : CENTRIFUGAL COMPRESSOR 
             p: PRESSURE SURFACE (BLADE SURFACE) 
             n: SUCTION SURFACE (BLADE SURFACE) 
             b: BULGE 
             b′: BULGE (SECOND BULGE)