Abstract:
A variable stator of a turbomachine with a profile skeleton line extending along a meridional flow line, with the stator being radially divided into at least three zones (Z 0 , Z 1 , Z 2 ) and with the respective radial inner and the radial outer profile skeleton line of each zone (Z 0 , Z 1 , Z 2 ) being designed such that it satisfies the following equations: 
     
       
         
           
             
               α 
               * 
             
             = 
             
               
                 
                   α 
                   1 
                 
                 - 
                 
                   α 
                   P 
                 
               
               
                 
                   α 
                   1 
                 
                 - 
                 
                   α 
                   2 
                 
               
             
           
         
       
       
         
           
             
               S 
               * 
             
             = 
             
               
                 S 
                 P 
               
               S 
             
           
         
       
       
         
           
             where:
           P is any point of the profile skeleton line,   α 1  is the angle of inclination at the stator leading edge,   α 2  is the angle of inclination at the stator trailing edge,   α* is the dimensionless, specific angle of the total curvature,   S* is the dimensionless, specific extension,   α P  is the angle of the tangent at any point P of the profile skeleton line to the central meridional flow line,   s P  is the extension of the profile skeleton line at any point P, and   S is the total extension of the profile skeleton line.

Description:
This application claims priority to German Patent Application DE 10 2005 060 699.7 filed Dec. 19, 2005, the entirety of which is incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to variable stator blades of turbomachines, such as blowers, compressors, pumps and fans of the axial, semi-axial or radial type. The working medium (fluid) may be gaseous or liquid. 
   More particularly, this invention relates to at least one variable stator blade of a turbomachine or to a variable inlet guide vane assembly, if applicable. The respective blading is situated within a casing, which confines the passage of fluid through at least one rotor and one stator in the outward direction. While a rotor comprises several rotor blades attached to a rotating shaft and transfers energy to the working medium, a stator consists of several stator blades mostly fixed in the casing. 
   The aerodynamic roadability and the efficiency of turbomachines, for example blowers, compressors, pumps and fans, is limited in particular by the growth and the separation of boundary layers in the area of the radial gaps between the blading and the casing or the hub, respectively, these gaps being necessary at the annulus rim for reasons of design. 
   In particular on rotatable variable stators, the radial gaps generated by the required recesses before and after the trunnion are pronounced and entail considerable flow losses. In order to limit these losses, rotary bases of max possible size are usually used on the inward and outward ends of the variable stators to keep small the extension of the recesses in flow direction. Preferably, the rotary bases are provided such that they are situated in the crucial profile leading edge zones of the blade peripheral sections. 
   However, due to failure provisions and design constraints, configurations of variable stators quite frequently exist which have only small size and where the rotary bases are not situated far enough upstream. In this case, a considerable radial gap exists both before and after the rotary base. The state of the art does not provide any aerodynamically favorable solutions to this fundamental problem. The general concept of boundary influencing of radial running gaps by changing the type of skeleton line along the blade height is provided in the state of the art, however, the known solutions are not adequate and, therefore, not effective, in particular for the flow conditions at a blade end with rotary base and two partial radial gaps. 
     FIG. 1  schematically shows two blade configurations in the meridional plane defined by the radial direction r and the axial direction x, these blade configurations corresponding to the state of the art. The representation is limited to a variable stator borne in the hub and the casing, a bearing only in the casing or the hub, with full radial gap at the respective (other) blade end is however also possible in individual cases. 
   On the left-hand side, a conventional variable stator without variation of the type of skeleton line is shown. In this simplest standard case, the blade consists of only one block (Z 0 ) in which the type of the skeleton line is specified according to fixed rules. This category includes the so-called CDA (controlled diffusion airfoils) according to U.S. Pat. No. 4,431,376. Aerodynamically, CDA aim at a moderate profile front load. 
   On the right-hand side, a conventional blade is shown whose rotating base extends up to the leading edge. In lieu of a completely uniform profile, the blade may also feature a continuous change of the profile type over the entire height according to the state of the art. Here, the entire blade is not represented by a block (Z 0 ) of uniform profile, but by only one large transition zone. This includes concepts from known publications providing for a transition from a CDA type of skeleton line to a type of skeleton line that aims more at a profile back load in the blade outer areas (R. F. Behike, Journal of Turbomachinery, Vol. 8, July 1986). 
   In addition, attempts exist to positively influence the peripheral zone flow by specially shaping the blade stacking axis, for example by imparting a bend, sweep or dihedral to the blading (see EP0661413A1, EP1106835A2, EP1106836A2). None of the existing solutions refers to variable stators. 
   DESCRIPTION OF THE INVENTION 
   The present invention relates to stators which are rotatably borne on at least one blade end and are variable around a fixed rotating axis by a trunnion. As in all representations shown herein, inflow to the respective blade row is from the left to the right in the direction of the bold arrow. 
   The state of the art is disadvantageous in that the respective blade forms are designed, often deliberately, with low complexity regarding the shape of the skeleton line. Where different types of skeleton lines along the blade height are used, the character of the skeleton lines lacks block-wise markedness which would allow the profile pressure distribution in wall vicinity to be stronger influenced to obtain the max. possible degree of gap and peripheral flow steadying. In particular with variable stators, there is a lack of blade concepts with skeleton line variations along the blade height which appropriately combine a profile front load favorable in the blade mid area with a type of load distribution favorable for the peripheral areas. 
   A broad aspect of the present invention is to provide a variable stator blade of the type specified above which, while avoiding the disadvantages of the state of the art, is characterized by exerting a highly effective influence on the peripheral flow due to a specific and problem-oriented block-wise definition of the profile skeleton lines along the blade height. 
   It is a particular object of the present invention to provide solutions to the above problems by a combination of the features described herein. Further advantageous embodiments of the present invention will become apparent from the description below. 
   The present invention provides for a variable stator blade for use in a turbomachine which features defined types of profile skeleton lines in different zones (blocks) of the blade height, limited by meridional flow lines, with the proviso that
     i) the distribution of the types of skeleton lines along the blade height advantageously combines a marked aerodynamic profile front load in the blade mid area with a specific profile load distribution in the peripheral areas,   ii) a specifically delimited type of skeleton line is provided throughout the defined peripheral zones Z 1  and Z 2 , in accordance with the definition given further below,   iii) the choice of the type of skeleton line in the transition zones T 1  and T 2  following Z 1  and Z 2  towards the blade center is optional,   iv) a specifically delimited type of skeleton line according to the definition given further below is provided throughout the defined blade mid zone Z 0 .   

   
     The present invention is more fully described in light of the accompanying drawings showing examples of embodiments. In the drawings, 
       FIG. 1  is a schematic representation of variable stators according to the state of the art, 
       FIG. 2  shows the definition of meridional flow lines and flow line profile sections, 
       FIG. 3   a  shows a variable stator (borne in casing and hub) “SGN” according to the present invention, 
       FIG. 3   b  shows a variable stator (borne in casing) “SG” according to the present invention, 
       FIG. 3   c  shows a variable stator (borne in hub) “SN” according to the present invention, 
       FIG. 3   d  provides the allocation of the blade zones Z 1 , Z 0 , Z 2  according to the present invention and of the defined types of skeleton lines PM and PR, 
       FIG. 4  provides the definition of the height-to-side ratio HSV and of the individual zone widths (block widths) WZ 1 , WT 1 , WZ 0 , WT 2 , WZ 2 , 
       FIG. 5  provides the definition of the rotating axis position at the blade ends, 
       FIG. 6   a  provides the definition of the skeleton line of a flow line profile section, 
       FIG. 6   b  provides the definition of the type of profile skeleton line “PM” for the blade mid zone, 
       FIG. 6   c  provides the definition of the type of profile skeleton line “PR” for the blade peripheral zone at a rotating axis position of D=0.3, 
       FIG. 6   d  provides the definition of the type of profile skeleton line “PR” for the blade peripheral zone at a rotating axis position of D=0.5. 
   

     FIG. 2  provides a precise definition of the meridional flow lines and the flow line profile sections. The central meridional flow line is established by the geometrical center of the annulus. If a normal is erected at any point on the central flow line, the annulus width W along the flow path and a number of normals are obtained, these enabling further meridional flow lines to be produced, with same relative division in the direction of the duct height. The intersection of a meridional flow line with a blade produces a flow line profile section. 
     FIG. 3   a  shows the variable stator blade borne in casing and hub “SGN” according to the present invention in the meridional plane defined by the axial coordinate x and the radial coordinate r. Here, the blade peripheral zones Z 1  and Z 2 , the transition zones T 1  and T 2  and the blade mid zone Z 0  are highlighted and limited by the respective meridional flow lines according to the definition in  FIG. 2 . A partial width WZ 1 , WT 1 , WZ 0 , WT 2 , WZ 2  is allocated to each of the five blade zones which is measured in the direction of the duct width W. 
   Analogically with this representation,  FIG. 3   b  and  FIG. 3   c  show the inventive stator blade borne in casing “SG” as well as the inventive stator blade borne in hub “SN”. 
     FIG. 3   d  shows in tabulated form the allocation according to the present invention of the three blade zones Z 1 , Z 0 , Z 2  and of the types of skeleton lines PM and PR specified below ( FIGS. 6   b - d ). For example, type PR is provided in zone Z 1 , type PM in zone Z 0  and type PR in zone Z 2  for the blade configuration “SGN”. Zone Z 1  in the case of blade configuration “SG” and zone Z 2  in the case of blade configuration “SN” are optional, as no rotary base exists at the respective blade end. 
   PM—Type of profile skeleton line for the blade mid zone, 
   PR—Type of profile skeleton line for the blade peripheral zone. 
     FIG. 4  shows the definition of the height-to-side ratio relevant for the determination of the respective zone width. The bottom right-hand half of the figure contains a sketch of a blade configuration with a number of meridional flow lines. Firstly, the central flow line, with the distance between the leading and the trailing edge being halved, defines the position for establishing the total blade height H (point G). Height H is established along a straight line normal to the central flow line in point G. Furthermore, five flow lines are defined at 10%, 30%, 50%, 70% and 90% of the duct width W (SL 10 , SL 30 , SL 50 , SL 70 , SL 90 ) along which the respective chord length L is to be determined. The definition of L for any meridional flow surface (u-m plane) is shown in the upper left-hand half of the figure. The chord length resulting at xy% of the duct width is designated with LSLxy here and in the formulas of  FIG. 4 . The height-to-side ratio is finally to be determined a follows:
   HSV= 5· H /( L   SL10   +L   SL30   +L   SL50   +L   SL70   +L   SL90 ) 
   The zone widths are determined in dependence of the height-to-side ratio in relative form (related to the total duct width W) according to the following rule:
 
 WZ 1 /W=WZ 2 /W =(0.06 ·HSV   0.65 )/ HSV 
 
 WT 1 /W=WT 2 /W =(0.30 ·HSV   0.80 )/ HSV 
 
 WZ 0 /W =1 −WZ 1 /W−WT 1 /W−WZT 2 /W−WZ 2/ W 
 
     FIG. 5  shows the definition of the rotating axis position which is co-determinant for the type PR of the profile skeleton line to be provided according to the present invention. The Figure schematically shows the flow line section through the variable stator blade at 5 percent or 95 percent duct width, respectively. Shown is the break-through point of the rotating axis in the plane of the flow line section, point D. This point need not necessarily lie within the profile, as shown here. The overall profile chord length is L. By dropping the perpendicular of point D on the profile chord, the distance d of the rotating axis from the leading edge measured in the same direction is obtained. The relative position of the rotating axis in the direction of the profile chord is designated d*=d/L. 
   The respective type of skeleton line is defined in relative representation by way of the specific angle of inclination α* and the specific extension s*, ref.  FIG. 6   a . The figure shows a flow line profile section of the blade on a meridional flow area (u-m plane). 
   For this, the angle of inclination α p  and the extension s p  covered so far are determined in all points of the skeleton line. For reference, the inclination angle at the leading and the trailing edge α1 and α2 and the skeleton-line total extension S are used. The following applies:
 
α*=(α 1 −α p) /(α 1 −α 2 ) and  s*=s   p   /S. 
 
     FIG. 6   b  shows the definition of the type “PM” of the skeleton line in the known relative representation. Skeleton line extensions according to the present invention are above the boundary line. Skeleton line extensions in the excluded area below and on the boundary line do not comply with the present invention. The boundary line for the type “PM” of the skeleton line is given by the following definition:
 α*=−3.8512520965( s *) 6 +14.6764714420( s *) 5 −21.6808727924( s *) 4 +16.3850592743( s *) 3 −6.9703863077( s *) 2 +2.4431236235( s *)−0.0060854622 
   A skeleton line distribution provided according to the present invention for the block at the blade center is delineated by way of example. 
     FIGS. 6   c  and  6   d  show the definition of the type “PR” of the skeleton line in the known relative representation for the rotating axis positions d*=0.3 and d*=0.5. Skeleton line extensions according to the present invention are below the continuous upper boundary line and above the lower boundary line given at a certain interval. Skeleton line extensions in the excluded area above and on the upper boundary line do not comply with the present invention. Skeleton line extensions below or on the lower boundary line do not comply with the present invention either. 
   Depending on the relative rotating axis positions d* the boundary lines for the type “PR” of the skeleton line are given by the following definitions: 
   Upper boundary line for d*=0.3:
 
α*=−15.1441661664( s *) 6 +52.8168915277( s *) 5 −67.2135203453( s *) 4 +35.9670881201( s *) 3 −6.8146566070( s *) 2 +1.3350483823( s *)+0.0535731815
 
   Upper boundary line for d*=0.5:
 
α*=3.6478453237( s *) 6 −5.6044881912( s *) 5 −5.3211690262( s *) 4 +11.7583720270( s *) 3 −4.3361971934( s *) 2 +0.8062070974( s *) +0.0502599068
 
   For rotating axis positions d* unequal to 0.3 and 0.5, the values of α* are to be determined by linear interpolation between those for d*=0.3 and d*=0.5.
 
α*( d *)=α*( d* =0.5)+[α*( d* =0.3)−α* ( d* =0.5)]*[0.5 −d* ]/0.2
 
   Lower boundary:
 
α*=2.0( s *)−2 d* 
 
   Applicable at the interval of s*: (d*+0.1; d*+0.3) 
   In  FIGS. 6   c  and  6   d  one each skeleton line distribution provided according to the present invention for the blade peripheral block is delineated by way of example. 
   With the blade for turbomachines, such as blowers, compressors, pumps and fans, according to the present invention, peripheral flow influencing is achieved which is capable of increasing the efficiency of each stage by approx. 1 percent, with stability remaining unchanged. In addition, a reduction of the number of blades of up to 20 percent is possible. The concept according to the present invention is applicable to different types of turbomachines and, depending on the degree of utilization of the concept, yields savings in cost and weight of the turbomachine of 2 to 10 percent. In addition, the overall efficiency of the turbomachine is increased by up to 1.5 percent, depending on the application.