Abstract:
A centrifugal rotor includes a hub ( 10 ) having a longitudinal axis ( 8 ), a fluid inlet ( 20 ), a first flange referred to as upstream flange ( 12 ) and having an opening ( 22 ) around the hub ( 10 ), a second flange referred to as downstream flange ( 14 ) separated from the first flange by blades ( 16 ) thus forming ducts each delimited by the first flange ( 12 ), the second flange ( 14 ) and two blades ( 16 ) and extending from the fluid inlet ( 20 ) to a peripheral outlet ( 26 ), near the peripheral outlet ( 26 ) the first flange ( 12 ) having a concave zone ( 32 ) facing towards the ducts whereas the second flange ( 14 ) has a convex zone ( 34 ) facing towards the ducts.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a centrifugal rotor. 
         [0002]    The technical field of this invention is that of the fluid, liquid or gaseous compression. The invention therefore relates to both pumps as well as compressors which make a supply of liquid or gas respectively possible, from a given pressure to a higher pressure. 
         [0003]    There are many techniques to increase the pressure of a fluid. A common technique consists in centrifuging the fluid upon which stress is exerted which in turn causes an increase in its pressure. For the implementation of this technique, there are many different structures of pumps and compressors depending upon many parameters including the related fluid, the environment (size, etc.) and desired performance (compression rate, etc.). Subsequently, we will focus on pumps and compressors comprising at least one centrifugal rotor associated with an axial diffuser. 
         [0004]    A centrifugal rotor is a rotor having an axis of rotation. It is designed to compress a fluid flowing in a direction parallel to its axis of rotation, the compressed fluid leaving the rotor in a radial direction outwardly. When the compressed fluid must flow axially, one solution is to direct the fluid exiting the rotor so that it changes the direction of flow. The element used for this purpose is a fixed part called an axial diffuser and it has at least one duct to direct the compressed fluid. The downstream end of the duct, that is to say the end which is remote from the centrifugal rotor, is axially oriented in accordance with the direction that one wishes to direct the compressed fluid. The purpose of the axial diffuser is to then take a turn at about 90° to the outgoing fluid from the centrifugal rotor so as to guide it axially. 
         [0005]    Document FR-2874241 discloses a high-efficiency centrifugal rotor which uses truncated blades with a radial diffuser. The wake of the blade recloses in the diffuser and by working with the wakes of the other adjacent blades creates a stratified flow that gradually expands within the diffuser. We thus find in this document a rotor incorporating a diffuser. The very thick blades are located in the lower part of the rotor. 
         [0006]    U.S. Pat. No. 1,447,916 illustrates another embodiment of a rotor incorporating a diffuser. The latter may be a single piece with the rotor portion comprising blades or it may be a separate piece secured to the rotor portion comprising the blades. Although it is noted that in all the figures illustrating the vanes, they only extend over one part of the device (corresponding to the centrifugal rotor) and not to the peripheral output of the device and that the portion corresponding to the centrifugal rotor has a perfectly radial outlet upstream from the diffuser. 
         [0007]    One technical problem encountered with such a structure is that it is the source of pressure loss in the compressed fluid. It is indeed known that when a fluid flows, it undergoes pressure losses that depend on the conduit in which it is found, including any changes in direction undergone. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0008]    It is not possible to eliminate the pressure drop that are particularly related to the nature of the fluid itself (particularly its viscosity) but this invention is to provide the means to minimize as much as possible these losses. 
         [0009]    An object of this invention is thus, for a given compression stage, comprising a centrifugal rotor and an axial diffuser, to increase the performance of this stage, i.e., for example, obtaining a higher compression ratio for a given power or for a given compression reducing the mechanical power needed to be exerted on the rotor to make it turn. 
         [0010]    To this end, this invention proposes a centrifugal rotor including: 
         [0011]    a hub having a longitudinal axis, 
         [0012]    a fluid inlet, 
         [0013]    a first flange, upstream and having an opening around the hub, 
         [0014]    a second flange, separated downstream from said first flange by the vanes thereby forming channels each delimited by the first flange, the second flange and two vanes extending from the fluid inlet to a peripheral outlet. 
         [0015]    According to this invention, in the proximity of the peripheral outlet, the first flange has a concave area oriented towards the channels while the second flange has a convex area oriented towards the channels. 
         [0016]    Due to the form thus given to the outlet channels, the passage of a radial flow within the centrifugal rotor to an axial flow in the diffuser upstream from the rotor is performed less brusquely making it possible to limit the losses in pressure when the fluid changes direction. 
         [0017]    To have a rotor that is simple to produce, the first flange and the second flange advantageously have a circular shape around the longitudinal axis. 
         [0018]    For example it is anticipated that the surface tangent to the concave region of the first flange exiting the channel, forms an angle of between 1° and 45°, preferably between 10° and 30°, with a radial plane perpendicular to the longitudinal axis. Likewise, it is anticipated that the surface tangent to the convex region of the second flange exiting the channel, forms an angle of between 1° and 45°, preferably between 10° and 30°, with a radial plane perpendicular to the longitudinal axis. 
         [0019]    To better guide the fluid in a centrifugal rotor according to the invention, it is advantageously provided that the vanes extend to the outer peripheral exterior edge of the first flange and/or of the second flange. 
         [0020]    To easily create an acceleration of the fluid exiting the centrifugal rotor, the first flange advantageously has an outer peripheral edge adjacent to the channels which have a greater diameter than an outer peripheral edge adjacent to the channels of the second flange. At the edge with the greater diameter, which corresponds to the outside of the curved shape given to the outlet of the centrifugal rotor, the speed is therefore higher. This is preferable because the path to be traveled along the outside of a turn is greater than that of the inside of a turn. In this way, a more uniform distribution of the velocity is promoted when the fluid then moves in a substantially longitudinal direction. 
         [0021]    This invention further relates to a centrifugal compressor and/or a centrifugal pump comprising a centrifugal rotor as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Details and advantages of this invention will become more apparent from the following description with reference to the accompanying drawings in which: 
           [0023]      FIG. 1  illustrates a centrifugal rotor of the prior art with a cross sectional view of a half rotor mounted in a compressor, 
           [0024]      FIG. 2  is a view similar to that of  FIG. 1  for a centrifugal rotor according to a first embodiment of this invention, 
           [0025]      FIG. 3  is a view similar to the preceding views according to a second embodiment of this invention, and 
           [0026]      FIG. 4  is a cross-section view in perspective along the cut line IV-IV of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Those skilled in the art will recognize a centrifugal rotor  2  in  FIG. 1  mounted inside a housing  4 , for example a compressor housing, and a shaft  6  having a longitudinal axis  8 . The following description will be made with reference to a working air compressor (or more generally a gaseous fluid compressor), but this invention may also be applied to pumps for liquids. 
         [0028]    When the centrifugal rotor  2  is rotated by the shaft  6 , the air (or other gaseous fluid) is drawn into the centrifugal rotor  2  in a longitudinal direction relative to the longitudinal axis  8 , and is driven in a mixed flow motion in the centrifugal rotor  2  while rotating and appear radially with respect to the longitudinal axis  8 . 
         [0029]    The centrifugal rotor  2  is built in one piece and comprises a hub  10 , a first flange or upstream flange  12 , a second flange or downstream flange  14  and vanes  16 . 
         [0030]    The hub  10  enables a connection between the shaft  6  and the centrifugal rotor  2 . It has an overall circular, cylindrical, tubular shape and is provided with a means to fasten it to the shaft  6 . For example, a longitudinal groove is typically provided in the hub  10  and the shaft  6  to receive a longitudinal spline or even grooves, or any other type of connection. 
         [0031]    The downstream flange  14  is connected directly to the hub  10  and extends radially relative to the longitudinal axis  8 . The upstream/downstream direction is defined relative to the direction of the air flow in the centrifugal rotor  2 . Indeed, in  FIG. 1  (as well as in the other figures) air is drawn to the right of the rotor and then moves longitudinally to the left before being driven in a radial direction to be oriented finally, after leaving the centrifugal rotor  2  in a longitudinal direction back towards the left of the figure. Thus the upstream elements are arranged to the right of the downstream elements in the figures. 
         [0032]    The upstream flange  12  faces the downstream flange  14  and is connected thereto by the vanes  16  thereby defining the channels for the air between the two flanges. The air is thus introduced between the inner surfaces of the flanges and vanes in a centrifugal radial manner. 
         [0033]    The upstream flange  12  does not extend to the hub  10  but remains at a distance therefrom. A sealing bearing  18  faces the hub  10  in front. Towards the inside of the centrifugal rotor  2 , the front sealing bearing  18  with the hub  10  defines an inlet chamber  20  with an annular opening  22  upstream of the inlet chamber  20 . Towards the exterior, the front sealing bearing  18  is machined to enable it to create a seal of the centrifugal rotor  2  in rotation within the housing  4 . For example, a seal may be used, such as for example a labyrinth ring  24 , as an interface between the centrifugal rotor  2  and the housing  4 . As can be seen in the figures, the centrifugal rotor  2  also includes a further sealing bearing  18  on the downstream side, or a rear sealing bearing, which extends from the downstream flange  14  and receives another labyrinth ring  24 . 
         [0034]    The channels driving air between the upstream flange  12  and downstream flange  14 , each have an outlet  26  ( FIG. 1 ) radially oriented at the largest diameter of the flanges. The air then enters a diffuser  28  in which it is guided so that the air flow is more longitudinal than radial. The channels  30  in the diffuser  28  also make it possible to convert the helical movement of the air flow to a substantially straight movement. 
         [0035]      FIGS. 2 and 4  illustrate a first embodiment of a centrifugal rotor according to this invention. As shown in the drawing, the overall structure is substantially the same in  FIG. 1  and in  FIGS. 2 to 4 . Thus, the references in  FIG. 1  are used in  FIGS. 2 to 4  to designate similar elements. A centrifugal rotor is thus found  2  rotatably mounted in a housing  4  around a shaft  6  having a longitudinal axis  8 . The centrifugal rotor  2  is sealed off relative to the housing  4  thusly ensured in particular through the sealing bearings  18  working together with the labyrinth rings  24  (or other type of seal). A hub  10  enables a connection between the rotor and the shaft  6 , for example by means of a spline that is not shown. The centrifugal rotor  2  further comprises an upstream flange  12  and downstream flange  14  interconnected by vanes  16 . The upstream flange  12  has a sealing bearing  18  which with the hub  10  defines an inlet chamber  20  of the annular opening  22 . Again, when the centrifugal rotor  2  rotates around the longitudinal axis  8  of the air (or other fluid) is being drawn through the opening  22  (longitudinal suction) to be compressed in a helico-centrifugal motion and then again become longitudinally oriented within a diffuser  28  optionally provided with channels. 
         [0036]    The differences between a rotor of the prior art and a centrifugal rotor  2  according to this invention are essentially located at the outputs  26 , that is to say at the area having the greatest diameter of the upstream flange  12 , of the downstream flange  14  and the vanes  16 . 
         [0037]    Compared with centrifugal rotors of a compressor (or pump) known in the prior art, this invention proposes to provide an outlet for air flow in a centrifugal rotor (or other fluid) having an improved velocity vector to enter into the longitudinal diffuser. For this purpose, it is expected that the air channels will be slightly bent (defined by the flanges and the vanes) in the centrifugal rotor  2  close to the outlets  26 . A curvature is thus produced at the output of the centrifugal rotor which makes it possible to increase the speed of the air towards the outside of the curvature. 
         [0038]    While in the embodiment of  FIG. 1 , it is noted that the inner face of the upstream flange  12  and the surface of the downstream flange  14  are substantially plane (and slightly converging), the inner surface of the upstream flange  12  has, near the output  26 , a concave area  32  and the inner surface of the downstream flange  14  has, near the outlet  26 , opposite the concave area  32 , a convex area  34 . 
         [0039]    If we then consider a surface  36  tangent to the inner surface of the downstream flange  14  at the outlet  26 , this surface is substantially conical (cone axis of the longitudinal axis  8 ) and forms, with a radial plane illustrated by a dotted line, angle a. In the embodiment of  FIG. 2 , this angle is about 15° and it is about 30° in the embodiment of  FIG. 3 . Preferably, this angle will be comprised between 10° and 45°. In the centrifugal rotors of the prior art, as illustrated by  FIG. 1 , this angle is substantially zero. 
         [0040]    To avoid overloading the Figures, the surface tangent to the inner surface of the upstream flange  12  was not illustrated. A substantially conical surface is also found here, around the longitudinal axis  8 , which forms, with the radial plane illustrated, an angle which is preferably less than 45°, for example between 10 and 45°. 
         [0041]      FIG. 4  illustrates that the vanes  16  extend into the convex area  34  of the downstream flange  14 . Of course, they extend in a similar manner into the concave zone  32  of the upstream flange  12 . Preferably, as illustrated in this  FIG. 4 , the vanes  16  extend to the peripheral edge of the upstream flange  12  and the downstream flange  14 , that is to say, up to the output  26  of the rotor. 
         [0042]    In  FIG. 3 , H is referenced by the line having the greatest diameter of the inner surface of the downstream flange  14  and by S for the line having the greatest diameter of the inner surface of the upstream flange  12 . S and H are circles the center of which lies on the longitudinal axis  8 . R S  and R H  radius respectively. As is apparent from  FIG. 3  (this is also visible in  FIG. 2  but slightly less pronounced), R S &gt;R H . Thus, for a same average speed over the air outlet surface outside the centrifugal rotor  2 , the peripheral speed of the air in the vicinity of point S is greater than that of the air near the point H. This also applies to the absolute tangential velocity. The air is accelerated from the upstream side (exterior to the exiting “turn” of the rotor), thereby making it possible to have a more uniform speed at the input of a substantially longitudinal section of the diffuser. Therefore, the losses in pressure, if only within the diffuser, are reduced and therefore make it possible to increase the yield of the device. 
         [0043]    The shape of the centrifugal rotor according to this invention thus allows a more gradual transition from a radial air flow to a longitudinal flow. The distribution of fluid velocities through a passage section of the diffuser is more uniform and regular. The pressure drops are thus limited and again in terms of yield is obtained at a time when the fluid passes from an essentially radial flow to an axial flow as it flows into the axial diffuser. 
         [0044]    Note that the channels in the centrifugal rotor  2  have a passage in which the flow is substantially radial. The inner surfaces of the upstream flange and the downstream flange each have an inversion of curvature. And the inner surface of the upstream flange  12  has a convex area near the inlet chamber  20  and then it extends from the hub  10  after a curved area, said inner surface has a concave area as described above. And the inner surface of the upstream flange  14  has a convex area near the inlet chamber  20  and then it extends from the hub  10  after a curved area, said inner surface has a concave area as described above. The trajectory of the fluid in the channels defined by the flanges and the vanes in the centrifugal rotor  2  and thus has a curve. 
         [0045]    To better guide the fluid in the curved rotor, the vanes  16  extend into the curved region (that is to say up to the concave area of the inner surface of the upstream flange and to the convex area of the inner surface of the downstream flange) and guide the fluid preferably to the outlet  26 . The blades  16  thus are also curved. They preferably extend from the inlet chamber  20  to the line H and the line S. or for example up to the vicinity of these lines (to least 10 mm in these lines). 
         [0046]    Of course, this invention is not limited to the preferred embodiments described above as non-limiting examples, but it also relates to the variants within the reach of those skilled in the art. 
         [0047]    It also concerns variations on the embodiment that will be found within the scope of professionals in the field within the framework of the Claims below.