Abstract:
An inducer having a hub and a plurality of blades is provided. In one embodiment, the thickness of the blades is defined such that during the operation of the inducer each of the blades is positioned underneath a cavitation vapor line so as to improve the performance of the inducer. In another embodiment, the hub is contoured or ramped according to a fifth order polynomial to provide improved performance. In another embodiment, the flow passage area of the inducer, as taken normal to the flow of fluid, is varied according to a fifth order polynomial to provide improved performance.

Description:
TECHNICAL FIELD 
     The present invention relates generally to pumps and more particularly to the geometry of the inducer blades of a pump to improve performance and prevent cavitation damage. 
     BACKGROUND OF THE INVENTION 
     Background Art 
     As is well known in the art, inducer blade design is a compromise between various considerations for performance, structural integrity and manufacturability. For example, in considering the aspects of an inducer to arrive at maximum performance, the inducer blade thickness ideally approaches zero. Unfortunately, construction in this manner is extremely difficult and severely compromises the structural integrity of the inducer. In considering the aspects of structural integrity, a large inducer blade thickness is preferable. However, construction in this manner results in an inducer with extremely poor performance. In considering the aspects which affect the ease with which an inducer may be manufactured, it is highly desirable to simplify the geometry of the inducer blade using a single angle to define the cant of the blade. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide a simplified inducer blade design which may be more easily manufactured but which has a high degree of structural integrity and provides improved performance. 
     It is another object of the present invention to provide an inducer having a plurality of blades whose thickness does not exceed the height of a cavitation cavity. 
     It is a further object of the present invention to provide an inducer having a hub which is ramped according to a fifth order polynomial. 
     It is yet another object of the present invention to provide an inducer whose flow passage area as taken normal to the flow of fluid varies according to a fifth order polynomial. 
     In one form, the present invention provides an inducer having a hub and a plurality of blades with the thickness of the blades being defined such that during the operation of the inducer each of the blades is positioned underneath a cavitation vapor line so as to improve the performance of the inducer. In another form, the present invention provides an inducer with a hub that is contoured or ramped according to a fifth order polynomial to provide improved performance. In still another form, the present invention provides an inducer having a flow passage area, as taken normal to the flow of fluid, which varies according to a fifth order polynomial to provide improved performance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of an inducer constructed in accordance with the teachings of the present invention; 
     FIG. 2 is a plot of the blade of the inducer of FIG. 1; 
     FIG. 3 is a plot of the cavitation cavity height and blade thickness along a streamline adjacent the inducer hub; 
     FIG. 4 is a plot of the cavitation cavity height and blade thickness along a mean streamline; 
     FIG. 5 is a plot of the cavitation cavity height and blade thickness along a streamline adjacent the tip; 
     FIG. 6 is a longitudinal cross-section of the inducer of FIG. 1 illustrating the variation in the hub contour; 
     FIG. 7 is a perspective view similar to that of FIG. 1 illustrating the area distributions of the flow passages; and 
     FIG. 8 is an exemplary plot of the flow passage area distribution indicating various relationships with respect to the cavity termination locations. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1 of the drawings, an inducer constructed in accordance with the teachings of the present invention is generally indicated by reference numeral  10 . With brief reference to FIG. 6, inducer  10  is shown to cooperate with housing  11   a  to form a pump  11 . Returning to FIG.  1 , inducer  10  is shown to include a hub portion  12  and a plurality of blades  14  which cooperate to define a plurality of flow passages  16 . Each of the plurality of blades  14  includes a suction side  18  and a pressure side  20 . The cant angle of the pressure side  20  of the blade  14  is illustrated to be constant to render inducer  10  easier to manufacture and reduce machining costs. 
     FIG. 2 shows a polar plot of four distinct regions on the suction side  18  of inducer  10 . Each region is defined by a constant cant angle which improves the ease with which inducer  10  may be manufactured. The suction side  18  includes a plurality of fairing blend lines ( 22 ,  24 ,  26 ) between each of the regions. 
     In designing blade  14 , the thickness of the blade  14  in the area between the leading edge  28  of the blade and the second fairing blend line  24  is controlled so that the blade  14  does not extend beyond a cavitation vapor line for a predetermined flow incidence angle. The cavitation vapor line defines the maximum blade thickness for the predetermined flow incidence angle. 
     In the region between the leading edge  28  of the blade  14  and the first fairing blend line  22 , the blade thickness is designed to counter the stress loading produced by high fluid pressures at the leading edge  28  while remaining below the cavitation vapor line. In the region between the second and third fairing blend lines  24  and  26 , the blade thickness distribution is controlled to produce no diffusion and constant relative velocity. 
     In FIGS. 3 through 5, the thickness of blade  14  and the cavitation cavity is illustrated along various streamlines. As mentioned above, the predictions of the cavitation vapor line  32  are used to define the maximum blade thickness allowed for a given flow incidence angle at the leading edge  28  of blade  14 . FIG. 3 illustrates the height of the cavitation cavity and the thickness of the blade  14  along a streamline nearest to hub  12 . FIG. 4 illustrates the height of the cavitation cavity and the thickness of the blade  14  along a mean streamline. FIG. 5 illustrates the height of the cavitation cavity and the thickness of the blade  14  along a streamline at the tip of the blade  14 . Note that in all cases the blade thickness is controlled such that the blade remains within the cavitation cavity. In so doing, blade passage blockage is minimized, permitting higher suction performance. 
     FIGS. 6,  7  and  8  illustrate another aspect of the present invention, namely the control of the angular variation of the blades  14  and the ramp of the hub  12  to maintain a flow passage  16  having a constant area before the cavity termination. As shown in FIG. 7, the area of the flow passages  16  is taken normal to the flow of fluid through the inducer  10 , as indicated by areas A 1 , A 2 , A 3 , A 4  and A 5 . The area of flow passages  16  as taken normal to the flow of fluid through the inducer  10  preferably varies in a manner similar to that shown in FIG.  8 . Construction in this manner minimizes the length of the cavitation cavity and improves the performance of the inducer  10 . 
     The blade normal area at the constant pressure side cant line is preferably controlled pursuant to equation (1): 
     
       
           A   x =2 ×π×r   t   2 ×tan(β x )×{sqrt[1+tan 2 (β x )]+sqrt[ x   2 +tan 2 (β x )]} 
       
     
     where: 
     A x  is the normal blade area at any predetermined location x, where x is the axial distance from the tip of the leading edge; 
     r t  is the inducer tip radius; 
     β x  is the tip blade angle at a predetermined location x, where x is the axial distance from the tip of the leading edge; 
     sqrt is the square root of the indicated quantity; 
     tan is the trigonomic tangent function of the indicated quantity; and 
     h x  is the hub and tip radius ratio as a function of x, where x is the axial distance from the tip of the leading edge. 
     The tangential blade angle distribution extended from any constant cant line at any x is preferably controlled pursuant to equation (2): 
     
       
           r ×tan(β r )= r   t ×tan(β x ) 
       
     
     Where: 
     r is any radius along the constant cant line extended from the tip; 
     β r  is the tangential blade angle at any radius on the constant cant line; 
     r t  is the inducer tip radius; and 
     β x  is the tip blade angle at a predetermined location x, where x is the axial distance from the tip of the leading edge. 
     The normalized blade passage normal area variation is preferably controlled pursuant to equations (3), (4) and (5): 
     
       
           AR   x =1  Equation (3) 
       
     
     
       
           AR   x =1+( AR −1)×(10−15 ×y +6 ×y   2 )× y   3   Equation (4) 
       
     
     
       
           y =( X−X   tm )/( X   t   −X   tm )  Equation (5) 
       
     
     where: 
     AR x  is the normalized blade passage normal area at any predetermined location x, where x is the axial distance from the tip of the leading edge; 
     AR is the area ratio at the inducer tip leading and trailing edge location (final area); once AR is determined, 
     y is an intermediate variable defined by Equation 5; 
     X is the axial distance from the tip of the leading edge; 
     X t  is the inducer tip trailing edge distance from the inducer tip leading edge; and 
     X tm  is the distance for tip cavity termination location from the inducer tip leading edge. 
     Equation (3) is employed to calculate the normalized blade passage normal area in situations where (X) is less than or equal to (X tm ). Equation (3) is designed to closely simulate a Stripling-Acosta flat plate (constant blade area) cavitation model to optimize the suction performance of the inducer  10 . Equation (4) is employed to calculate the normalized blade passage normal area in situations where (X) is greater than (X tm ). Equation (5) is employed to calculate the intermediate variable (y) used in Equation (4). 
     The hub  12  includes a first portion  40 , a second portion  44  and a third portion  48 . The first portion  40  has a constant radius and terminates at the constant tip leading edge cant line intercept point  52  shown in FIG.  6 . The radius of the second portion  44  is defined by a smooth function governing the degree of increase from leading edge cant line intercept point  52  and the trailing edge cant line intercept point  56 . The second portion  44  terminates at the trailing edge cant line intercept point  56 . The third portion  48  begins at the trailing edge cant line intercept point  56  and has a constant radius. 
     The radius of the second portion  44  may be produced according to a fifth order polynomial to define the hub profile, an example of which is provided by equations (6) and (7): 
     
       
           r   h   =r   h1 +( r   h2   −r   h1 )×(10−15 ×Z +6 ×Z   2 )×z 3   Equation (6) 
       
     
     
       
           X   h   =X +( r   t   −r   h )×tan(β cant )  Equation (7) 
       
     
     where: 
     r h  is the radius of the hub at a predetermined point in the second portion  44 ; 
     r h1  is the radius of the hub at the first portion  40 ; 
     r h2  is the radius of the hub at the third portion  48 ; 
     Z is an intermediate variable equaling the quantity of X/X t ; 
     X is the axial distance from the tip of the leading edge; 
     X t  is the inducer tip trailing edge distance from the inducer tip leading edge; 
     X h  is the hub axial location; 
     r t  is the is the inducer tip radius; and 
     β cant  is the pressure cant angle. 
     Note that the fifth order polynomial has first and second derivatives equal to zero at the leading edge cant line intercept point  52  and the trailing edge cant line intercept point  56 . By employing equations (6) and (7), the blade angle distributions can be defined through equations (1) through (5). 
     The radius of the second portion  44  may also be produced by with a fifth order polynomial to define the tip tangential blade angle, such as the one provided in equation (8): 
     
       
         β x =β 1 +(β 2 −β 1 )×(10−15 ×Z +6 ×Z   2 )×Z 3   
       
     
     where: 
     β x  is the tip tangential blade angle at a predetermined location x; 
     β 1  is the tip tangential blade angle at the leading edge; 
     β 2  is the tip tangential blade angle at the trailing edge; 
     Z is an intermediate variable equaling the quantity of X/X t ; 
     X is the axial distance from the tip of the leading edge; and 
     X t  is the inducer tip trailing edge distance from the inducer tip leading edge. 
     Construction of inducer  10  in a manner which incorporates the above equations provides a gradually increasing tip discharge tangential angle which causes the final area of the flow passage  16  and the area of blade  14  to provide the desired blade area ratio (AR). Designing the inducer discharge blade angle closer to the area ratio (AR) yields a discharge area that provides the design or target inducer head. 
     While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.