Abstract:
Methods and apparatus for conveying fluids (e.g., liquids, gases, and mixtures thereof) are disclosed. A turbopump in accordance with an exemplary implementation of the present invention comprises an impeller defining at least one flow channel and a shroud defining an opening communicating with the at least one flow channel. In certain advantageous implementations, at least one inlet partial of the impeller extends into the opening defined by the shroud. The at least one inlet partial may advantageously be capable of supporting the opening in the shroud. In some cases, the impeller may include a plurality of these inlet partials.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to methods and apparatus for conveying fluids (e.g., liquids, gases, and mixtures thereof). More particularly, the present invention relates to pumps (e.g., pumps capable of providing propellant to a rocket engine). 
   BACKGROUND OF THE INVENTION 
   Today, turbopumps are used in a wide variety of applications. One example of such an application is rocket propulsion systems. Many rocket propulsion systems include turbopumps as part of a propellant feed system. Turbopumps may be used, for example, to convey various fluids (e.g., fuels and oxidizers) to a combustor of the rocket engine. Turbopumps consist of turbine and pump components. The pump typically increases these incoming fluids to a higher pressure. 
   The rotational seal is typically formed between a rotating portion of the pump (e.g., centrifugal pump impeller) and a stationary portion of the pump. High rotational speeds can cause the rotating member forming this seal to bow outwardly or scallop. One approach for restricting the amount of scalloping is to increase the thickness of the rotating member of the seal. Another approach, is to provide a larger seal clearance to accommodate the scalloping. However, the larger seal clearances tend to reduce the efficiency of the pump. In other words, pump impeller efficiency usually decreases with increases in seal clearances. 
   SUMMARY OF THE INVENTION 
   The present invention relates generally to methods and apparatus for conveying fluids. More particularly, the present invention relates to pumps (e.g., pumps capable of providing propellant to a rocket engine). An impeller in accordance with an exemplary embodiment of the present invention may advantageously include a plurality of inlet partials. The inlet partials may be positioned and dimensioned to reduce scalloping in a rotating seal member. When this is the case, strain in the rotating seal member is reduced. The likelihood that rubbing will occur between the rotating seal member and a stationary seal member is also reduced. Additionally, reduced scalloping allows for the use of relatively small seal clearances, thus boosting efficiency. 
   A turbopump in accordance with an exemplary implementation of the present invention comprises an impeller defining at least one flow channel and a shroud defining an opening communicating with the at least one flow channel. In certain advantageous implementations, at least one inlet partial of the impeller extends into the opening defined by the shroud. The at least one inlet partial may advantageously be capable of supporting the opening in the shroud. In some cases, the impeller may include a plurality of these inlet partials. 
   In one aspect of the present invention, the inlet partials are capable of precluding a change of shape in the opening during operation of a turbopump including the shroud. The inlet partials may, for example, be capable of providing supporting forces that are substantially equal and opposite to deformation forces acting on the shroud. The deformation forces may be, for example, centrifugal forces acting on the shroud during rotation of the shroud. The deformation forces may also be, for example, deformation forces produced by a working fluid passing through the at least one flow channel. 
   In some implementations, the opening is defined by an annular ring of the shroud. When this is the case, the at least one inlet partial may be capable of decreasing the radial deformation of the annular ring. In certain implementations, a second annular ring is disposed about the first annular ring so that a rotary seal is formed therebetween. A gap may, in some cases, be defined by the first annular ring and the second annular ring. The inlet partials supporting the first annular ring may be adapted so that the gap remains more constant when the first ring is rotating than would be the case if the first annular ring was not reinforced. The second annular ring may be formed by a pump casing in some implementations. 
   The opening defined by the shroud may have a first shape when the shroud is stationary and a second shape when the shroud is rotating at a working speed. In one aspect of the present invention, a difference between the first shape and the second shape is smaller than a difference in shape occurring when the shroud is not supported by the inlet partials. When this is the case, the first shape may have generally circular cross section. 
   In one aspect of the present invention, the inlet partials are capable of precluding a change in the shape of the opening during rotation of the shroud. For example, the inlet partials may be capable of preventing the opening from assuming a non-circular shape. A deflection of the shroud during rotation of the shroud is advantageously smaller than a deflection occurring when the shroud is not supported by the inlet partials. The presence of the inlet partials may also cause the second shape to be more circular than would be the case without the inlet partials. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified diagrammatic representation of a rocket engine. 
       FIG. 2  is a cross sectional view of a turbopump in accordance with an exemplary embodiment of the present invention. 
       FIG. 3  is a perspective view of an impeller in accordance with an exemplary embodiment of the present invention. 
       FIG. 4  is an isometric view of an impeller in accordance with an exemplary embodiment of the present invention. 
       FIG. 5  is a cross sectional view of a turbopump in accordance with an exemplary embodiment of the present invention. 
       FIG. 6  is an axial view of an impeller in accordance with the present invention. 
       FIG. 7  is an additional axial view of impeller shown in the previous figure. 
       FIG. 8  is an additional axial view of impeller shown in the previous figure. 
       FIG. 9  is an axial view of an impeller comprising a hub and a shroud. 
       FIG. 10  is an additional axial view of assembly shown in the previous figure. 
   

   DETAILED DESCRIPTION 
   The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. All other elements employ that which is known to those of skill in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that can be utilized. 
     FIG. 1  is a simplified diagrammatic representation of a rocket engine  122 . Rocket engine  122  of  FIG. 1  includes a nozzle  124 , a combustor  126  and a propellant supply system  128 . In the embodiment of  FIG. 1 , propellant supply system  128  includes a first turbopump  130  and a second turbopump  132  that both fluidly communicate with combustor  126  of rocket engine  122 . During operation of rocket engine  122 , first turbopump  130  and second turbopump  132  may provide fuel and oxidizer to combustor  126  of rocket engine  122 . 
   First turbopump  130  comprises a casing  134  that is disposed about an impeller  104 . Casing  134  defines a chamber  136  that fluidly communicates with combustor  126  via a conduit  138 . In the embodiment of  FIG. 1 , impeller  104  comprises a body  140  and a shroud  142  overlaying a front face  144  of body  140 . Impeller  104  also includes a plurality of blades  146  that are shown extending between body  140  and shroud  142  in  FIG. 1 . With reference to  FIG. 1 , it will be appreciated that blades  146  define a plurality of flow channels  148 . 
   Shroud  142  defines an opening  120  that fluidly communicates with flow channels  148 . Impeller  104  of  FIG. 1  includes a plurality of inlet partials  106  extending into opening  120  defined by shroud  142 . In some useful embodiments of the present invention, inlet partials  106  are capable of supporting shroud  108  in a manner that precludes undesirable changes in the shape of opening  120 . 
     FIG. 2  is a cross sectional view of a pump  350  in accordance with an exemplary embodiment of the present invention. An impeller  304  of pump  350  comprises a body  340 , a shroud  342  and a plurality of blades  346  extending between body  340  and shroud  342 . Each blade  346  of impeller  304  has a leading edge  343  and a trailing edge  345 . Shroud  342  defines an opening  320  fluidly communicating with a plurality of flow channels  348  of impeller  304 . In the embodiment of  FIG. 2 , opening  320  is defined by a first annular ring  352  of shroud  342 . 
   A second annular ring  354  is disposed about first annular ring  352  so that a seal  356  is formed between first annular ring  352  and second annular ring  354  in the embodiment of  FIG. 2 . In  FIG. 2 , seal  356  is illustrated using a gap  358  that is shown disposed between first annular ring  352  and second annular ring  354 . In some useful embodiments of the present invention, seal  356  comprises a labyrinth seal. With reference to  FIG. 2 , it will be appreciated that seal  356  has a length L. In  FIG. 2 , length L is shown extending between a distal end  366  of seal  356  and a proximal end  368  of seal  356 . In the embodiment of  FIG. 2 , distal end  366  of seal  356  is disposed in an upstream location relative to proximal end  368  of seal  356 . 
   With reference to  FIG. 2 , it will be appreciated that impeller  304  also includes a plurality of inlet partials  306  extending into opening  320  defined by shroud  342 . In  FIG. 2 , inlet partials  306  can be seen extending between an inner surface  360  of first annular ring  352  and a hub  362  of impeller  304 . In some useful embodiments of the present invention, inlet partials  306  of impeller  304  are capable of decreasing the radial deformation of first annular ring  352 . When this is the case, the dimensions of gap  358  are likely to remain more constant when first annular ring  352  is rotating than would be the case if first annular ring  352  was not reinforced. In some applications, this consistency reduces the likelihood that rubbing will occur between the first ring and the second ring, while at the same time allowing the gap between the first ring and the second ring to be relatively small. A smaller gap provides for less leakage and greater pump efficiency. 
   In the embodiment of  FIG. 2 , it will be appreciated that a distal extent  370  of each inlet partial  306  is disposed distally of proximal end  368  of seal  356 . The distal extent  370  of each inlet partial  306  is also disposed distally of a proximal surface  378  of shroud  342  in the embodiment of  FIG. 2 . Each inlet partial  306  also has a proximal extent  380  that is disposed distally of a front surface  382  of body  340  of impeller  304  in the embodiment of  FIG. 2 . With reference to  FIG. 2 , it will be appreciated that the proximal extent  380  of each inlet partial  306  is disposed in a spaced apart relationship with front surface  382  of body  340 . 
   In some useful embodiments of the present invention, each inlet partial  306  is capable of directing the flow of a working fluid in a desired direction. In the embodiment of  FIG. 2 , each inlet partial  306  comprises a flow directing surface  384 . In the embodiment of  FIG. 2 , flow directing surface  384  of each inlet partial  306  is positioned and dimensioned so as to direct a working fluid in a direction that is non-parallel with a rotational axis  386  of impeller  304 . Impeller  304  is fixed to a drive shaft  244  so that impeller  304  rotates about rotational axis  386 . 
     FIG. 3  is a perspective view of an impeller  404  in accordance with an exemplary embodiment of the present invention. Impeller  404  of  FIG. 3  comprises a body  440 , a shroud  442  and a plurality of blades  446  extending between body  440  and shroud  442 . In some embodiments of the present invention body  440 , shroud  442  and blades  446  are all formed from a single piece of material. 
   With reference to  FIG. 3 , it will be appreciated that body  440 , shroud  442  and blades  446  define a plurality of radially disposed outlets  488 . Shroud  442  defines an opening  420  that preferably communicates with outlets  488 . When this is the case, a working fluid may pass through opening  420  while traveling in an axial direction  492  and may exit outlet  488  while traveling in a radial direction  490 . 
   In the embodiment of  FIG. 3 , opening  420  is defined by a ring  494  of shroud  442 . With reference to  FIG. 3 , it will be appreciated that impeller  404  also includes a plurality of inlet partials  406  extending into opening  420  defined by shroud  442 . In  FIG. 3 , inlet partials  406  can be seen extending between an inner surface  460  of shroud  442  and a hub  462  of impeller  404 . 
     FIG. 4  is an isometric view of an impeller  1104  in accordance with an exemplary embodiment of the present invention. In the embodiment of  FIG. 4 , impeller  1104  comprises a hub  1162 , a ring  1194  and a plurality of blades. Impeller  1104  of  FIG. 4  may also comprise a body and a shroud that are not shown in  FIG. 4  for purposes of illustration. 
   With reference to  FIG. 4 , it will be appreciated that the blades of impeller  1104  define a plurality of flow channels. More particularly, a first blade  1196  and a second blade  1198  of impeller  1104  define a first flow channel  1200 . Likewise, second blade  1198  and a third blade  1202  define a second flow channel  1204 . Similarly, third blade  1202  and a fourth blade  1206  of impeller  1104  define a third flow channel  1208 . With reference to  FIG. 4 , it will be appreciated that fourth blade  1206  and a fifth blade  1220  of impeller  1104  define a fourth flow channel  1222 . A fifth flow channel  1224  is defined by fifth blade  1220  and a sixth blade  1226  of impeller  1104 . Finally, sixth blade  1226  and first blade  1196  define a sixth flow channel  1228 . 
   Ring  1194  defines an opening  1120  that communicates with the flow channels of impeller  1104 . In the embodiment of  FIG. 4 , a hub  1162  of impeller  1104  is disposed within opening  1120  of ring  1194 . With reference to  FIG. 4 , it will be appreciated that a plurality of inlet partials  1106  extend between hub  1162  and ring  1194 . In some useful embodiments of the present invention, inlet partials  1106  are capable of decreasing the radial deformation of ring  1194 . 
   In the embodiment of  FIG. 4 , a first inlet partial  1106 A is disposed between a first leading edge  1230  of first blade  1196  and a second leading edge  1232  of second blade  1198 . Additionally, a second inlet partial  1106 B is shown disposed between second leading edge  1232  of second blade  1198  and a third leading edge  1234  of third blade  1202 . 
   In the embodiment of  FIG. 4 , a third inlet partial  1106 C is disposed between third leading edge  1234  of third blade  1202  and a fourth leading edge  1236  of fourth blade  1206 . In  FIG. 4 , a fourth inlet partial  1106 D is shown disposed between fourth leading edge  1236  of fourth blade  1206  and a fifth leading edge  1240  of fifth blade  1220 . A fifth inlet partial  1106 E can also be seen disposed between fifth leading edge  1240  of fifth blade  1220  and a sixth leading edge  1242  of sixth blade  1226  in  FIG. 4 . Finally, a sixth inlet partial  1106 F is disposed between sixth leading edge  1242  of sixth blade  1226  and first leading edge  1230  of first blade  1196 . 
   Although the impeller shown in  FIG. 4 , comprises six blades and six inlet partials it will be appreciated that this is an exemplary embodiment and that additional configurations are possible without deviating from the spirit and scope of the present invention. For example, impellers having more than six blades or fewer than six blades are possible without deviating from the spirit and scope of the present invention. By way of a second example, impellers having more than six inlet partials or fewer than six inlet partials are possible without deviating from the spirit and scope of the present invention. 
     FIG. 5  is a cross sectional view of a pump  2150  in accordance with an exemplary embodiment of the present invention. An impeller  2104  of turbopump  2150  comprises a body  2140 , a shroud  2142  and a plurality of blades  2146  extending between body  2140  and shroud  2142 . Each blade  2146  of impeller  2104  has a leading edge  2143  and a trailing edge  2145 . Shroud  2142  defines an opening  2120  fluidly communicating with a plurality of flow channels  2148  of impeller  2104 . In the embodiment of  FIG. 5 , opening  2120  is defined by a first annular ring  2152  of shroud  2142 . 
   A second annular ring  2154  is disposed about first annular ring  2152  so that a seal  2156  is formed between first annular ring  2152  and second annular ring  2154  in the embodiment of  FIG. 5 . In  FIG. 5 , seal  2156  is illustrated using a gap  2158  that is shown disposed between first annular ring  2152  and second annular ring  2154 . With reference to  FIG. 5 , it will be appreciated that seal  2156  has a length L. In  FIG. 5 , length L is shown extending between a distal end  2166  of seal  2156  and a proximal end  2168  of seal  2156 . In the embodiment of  FIG. 5 , distal end  2166  of seal  2156  is disposed in an upstream location relative to proximal end  2168  of seal  2156 . In some useful embodiments of the present invention, seal  2156  comprises a labyrinth seal. 
   With reference to  FIG. 5 , it will be appreciated that impeller  2104  also includes a plurality of inlet partials  2106  extending into opening  2120  defined by shroud  2142 . In  FIG. 5 , inlet partials  2106  can be seen extending between an inner surface  2160  of first annular ring  2152  and a hub  2162  of impeller  2104 . In some useful embodiments of the present invention, inlet partials  2106  of impeller  2104  are capable of decreasing radial deformation of first annular ring  2152 . When this is the case, the dimensions of gap  2158  are likely to remain more constant when first annular ring  2152  is rotating than would be the case if first annular ring  2152  was not reinforced. In some applications, this consistency reduces the likelihood that rubbing will occur between the first ring and the second ring, while at the same time allowing the gap between the first ring and the second ring to be relatively small. A smaller gap provides for less leakage and greater pump efficiency. 
   In the embodiment of  FIG. 5 , it will be appreciated that a distal extent  2170  of each inlet partial  2106  is disposed distally of proximal end  2168  of seal  2156 . The distal extent  2170  of each inlet partial  2106  is also disposed distally of a proximal surface  2178  of shroud  2142  in the embodiment of  FIG. 5 . Each inlet partial  2106  also has a proximal extent  2180  that is disposed distally of a front surface  2182  of body  2140  of impeller  2104  in the embodiment of  FIG. 5 . 
   In some useful embodiments of the present invention, each inlet partial  2106  is capable of directing the flow of a working fluid in a desired direction. In the embodiment of  FIG. 5 , each inlet partial  2106  comprises a flow directing surface  2184 . In the embodiment of  FIG. 5 , flow directing surface  2184  of each inlet partial  2106  is positioned and dimensioned so as to direct a working fluid in a direction that is non-parallel with a rotational axis  2186  of impeller  2104 . Impeller  2104  is fixed to a drive shaft  2244  so that impeller  2104  rotates about rotational axis  2186 . 
     FIG. 6  is an axial view of an impeller  3104  in accordance with an exemplary embodiment of the present invention. In the embodiment of  FIG. 6 , a shroud  3142  is shown overlaying a front face  3144  of a body  3140  of impeller  3104 . Impeller  3104  includes a plurality of blades  3146  defining a plurality of flow channels  3148 . For purposes of illustration, each flow channel of impeller  3104  is filled with a distinctive pattern in  FIG. 6 . 
   In the embodiment of  FIG. 6 , a first flow channel  3200  is shown extending between a first leading edge  3230  of first blade  3196  and a second leading edge  3232  of second blade  3198 . Additionally, a second flow channel  3204  is shown extending between second leading edge  3232  of second blade  3198  and a third leading edge  3234  of third blade  3202 . 
   In the embodiment of  FIG. 6 , a third flow channel  3208  is shown extending between third leading edge  3234  of third blade  3202  and a fourth leading edge  3236  of fourth blade  3238 . In  FIG. 6 , a fourth flow channel  3246  is shown extending between fourth leading edge  3236  of fourth blade  3238  and a fifth leading edge  3240  of fifth blade  3220 . A fifth flow channel  3224  can also be seen extending between fifth leading edge  3240  of fifth blade  3220  and a sixth leading edge  3242  of sixth blade  3226  in  FIG. 6 . Finally, a sixth flow channel  3228  is extending between sixth leading edge  3242  of sixth blade  3226  and first leading edge  3230  of first blade  3196 . 
   Shroud  3142  of  FIG. 6  includes a ring  3194  defining an opening  3120 . With reference to  FIG. 6 , it will be appreciated that opening  3120  communicates with first flow channel  3200 , second flow channel  3204 , third flow channel  3208 , fourth flow channel  3246 , fifth flow channel  3224  and sixth flow channel  3228 . 
   In  FIG. 6 , a plurality of inlet partials  3106  are shown extending between an inner surface  3160  of ring  3194  and a hub  3162  of impeller  3104 . In some useful embodiments of the present invention, inlet partials  3106  of impeller  3104  are capable of supporting in locations proximate opening  3120 . In some useful embodiments of the present invention, the presence of inlet partials  3106  inside opening  3120  reduces the likelihood that undesirable changes in the shape of opening  3120  will occur during operation of a pump including shroud  3142 . 
     FIG. 7  is an additional axial view of impeller  3104  shown in the previous figure. In the embodiment of  FIG. 7 , shroud  3142  of impeller  3104  has been removed so that additional portions of the blades can be seen. Impeller  3104  comprises a hub  3162  defining a bore  3250 . Bore  3250  is preferably adapted to receive a drive shaft of a turbopump. A plurality of inlet partials  3106  are shown extending away from bore  3250  in  FIG. 7 . 
   In the embodiment of  FIG. 7 , impeller  3104  includes a first inlet partial  3172 A, a second inlet partial  3172 B, a third inlet partial  3172 C, a fourth inlet partial  3172 D, a fifth inlet partial  3172 E and a sixth inlet partial  3172 F. In some useful embodiments of the present invention, inlet partials  3106  are dimensioned so as to support an opening defined by a shroud that is not shown in  FIG. 7 . In the embodiment of  FIG. 7 , each of these inlet partials  3106  extend to an inner surface  3160  defining an opening  3120 . Inner surface  3160  is illustrated using a phantom line in  FIG. 7 . 
   In the embodiment of  FIG. 7 , inner surface  3160  defines a cylinder having a first diameter  3252 . With reference to  FIG. 7 , it will be appreciated that body  3140  of impeller  3104  has a second diameter  3254 . In the embodiment of  FIG. 7 , each inlet partial  3106  extends to a first radius  3256  and each blade extends to a second radius  3258 . With reference to  FIG. 7 , it will be appreciated that second radius  3258  is generally larger than first radius  3256 . 
   Impeller  3104  comprises a body  3140  having a front face  3144  and a plurality of blades  3146  extending beyond front face  3144 . Front face  3144  of body  3140  may have various shapes without deviating from the spirit and scope of the present invention. For example, front face  3144  may comprise a generally conical surface. By way of a second example, front face  3144  may comprise a generally toroidal surface. 
   Impeller  3104  of  FIG. 7  includes a first blade  3196 , a second blade  3198 , a third blade  3202 , a fourth blade  3238 , a fifth blade  3220  and a sixth blade  3226 . In the embodiment of  FIG. 7 , each blade has a somewhat arcuate shape. A leading edge  3262 , a trailing edge  3264 , and a top edge  3266  of each blade can be seen in  FIG. 7 . 
   In the embodiment of  FIG. 7 , each inlet partial  3106  is disposed between a pair of blades  3146 . First inlet partial  3172 A, for example, is disposed between first blade  3196  and second blade  3198 . Additionally, second inlet partial  3172 B is disposed between second blade  3198  and third blade  3202 . 
   In the embodiment of  FIG. 7 , third inlet partial  3172 C is disposed between third blade  3202  and fourth blade  3238 . In  FIG. 7 , fourth inlet partial  3172 D is shown disposed between fourth blade  3238  and fifth blade  3220 . Fifth inlet partial  3172 E can also be seen disposed between fifth blade  3220  and sixth blade  3226  in  FIG. 7 . Finally, sixth inlet partial  3172 F is disposed between sixth blade  3226  and first blade  3196 . 
   In some useful embodiments of the present invention, each inlet partial  3106  is capable of directing the flow of a working fluid in a desired direction. In the embodiment of  FIG. 7 , each inlet partial  3106  comprises a flow directing surface  3184 . In the embodiment of  FIG. 7 , flow directing surface  3184  of each inlet partial  3106  is positioned and dimensioned so as to direct a working fluid in a direction that is non-parallel with a rotational axis  3186  of impeller  3104 . 
   Although the impeller shown in  FIG. 7 , comprises six full blades, six inlet partials, six long discharge partials, and  12  short discharge partials it will be appreciated that this is an exemplary embodiment and that additional configurations are possible without deviating from the spirit and scope of the present invention. For example, impellers having more than six blades or fewer than six blades are possible without deviating from the spirit and scope of the present invention. By way of a second example, impellers having more than six inlet partials or fewer than six inlet partials are possible without deviating from the spirit and scope of the present invention. 
     FIG. 8  is an additional axial view of impeller  3104  shown in the previous figure. With reference to  FIG. 8 , it will be appreciated that impeller  3104  defines a plurality of flow channels  3148 . For purposes of illustration, each flow channel of impeller  3104  is filled with a distinctive pattern in  FIG. 8 . The patterns filling each flow channel may represent, for example, a working fluid that is being conveyed by impeller  3104 . First blade  3196 , second blade  3198  and front face  3144  define a first flow channel  3200  that is filled with hatch lines in  FIG. 8 . Likewise, second blade  3198  third blade  3202 , and front face  3144  of body  3140  define a second flow channel  3204  that is filled with a pattern of “+” symbols. Similarly, third blade  3202 , fourth blade  3238  and front face  3144  define a third flow channel  3208  that is filled with a houndstooth pattern. 
   With reference to  FIG. 8 , it will be appreciated that fourth blade  3238 , fifth blade  3220  and front face  3144  define a fourth flow channel  3222  that is filled with a honeycomb pattern. A fifth flow channel  3224  is defined by fifth blade  3220 , sixth blade  3226  and front face  3144 . In  FIG. 8 , fifth flow channel  3224  is filled with a pattern of squares. Finally, sixth blade  3226 , first blade  3196  and front face  3144  define a sixth flow channel  3228  that is filled with a pattern of triangles in  FIG. 8 . 
   Impeller  3104  of  FIG. 8  also includes a plurality of splitters  3268  extending beyond front face  3144  of body  3140 . Impeller  3104  comprises a plurality of outlets  3190  disposed between the trailing portions of splitters  3268  and the trailing portions of blades  3146 . 
     FIG. 9  is an axial view of an impeller  4104  comprising a hub  4162  and a shroud  4142 . With reference to  FIG. 9 , it will be appreciated that impeller  4104  does not include inlet partials like those shown in the previous figure. Impeller  4104  includes a first blade  4196 , a second blade  4198 , a third blade  4202 , a fourth blade  4238 , a fifth blade  4220 , and a sixth blade  4226 . With reference to  FIG. 9 , it will be appreciated that impeller  4104  defines a plurality of flow channels  4148 . For purposes of illustration, each flow channel of impeller  4104  is filled with a distinctive pattern in  FIG. 9 . More particularly, a first flow channel  4200 , a second flow channel  4204 , and a third flow channel  4208  of impeller  4104  are filled with hatch lines, “+” symbols, and a houndstooth pattern, respectively. The patterns filling each flow channel may represent, for example, a working fluid that is being conveyed by impeller  4104 . In  FIG. 9 , a fourth flow channel  4222 , a fifth flow channel  4224 , and a sixth flow channel of impeller  4104  are filled with a honeycomb pattern, a pattern of squares, and a pattern of triangles, respectively. 
   Shroud  4142  of  FIG. 9  includes a ring  4194  defining an opening  4120 . With reference to  FIG. 9 , it will be appreciated that opening  4120  communicates with first flow channel  4200 , second flow channel  4204 , third flow channel  4208 , fourth flow channel  4246 , fifth flow channel  4224  and sixth flow channel  4228 . In the embodiment of  FIG. 9 , shroud  4142  is shown in a relaxed state in which opening  4120  has a generally circular shape. As impeller  4104  rotates, deformation forces may act on shroud  4142 . During operation of a pump including impeller  4104 , forces may act on shroud  4142  so as to cause shroud  4142  to assume a radially deflected shape. For example, shroud  4142  may assume a radially deflected shape when it is rotated at high speed. 
     FIG. 10  is an additional axial view of impeller  4104  shown in the previous figure. In  FIG. 10 , shroud  4142  is shown in a radially deflect state in which opening  4120  has a second, deflected shape. In the exemplary embodiment of  FIG. 10 , opening  4120  of shroud  4142  is shown having a shape that may be generally described as a hexagon having a plurality rounded corners. The state of shroud  4142  depicted in  FIG. 10  may be generally referred to as a scalloped state. Various forces may act on shroud  4142  may cause scalloping. For example, centrifugal forces acting on the mass of the shroud when it is rotating. The level of scalloping depicted in  FIG. 10  has been exaggerated for purposes of illustration. Shroud  4142  of  FIG. 10  opening  4120  is defined by ring  4194 . 
   Numerous characteristics and advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size and ordering of steps without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.