Abstract:
A radial compressor impeller having a wheel disc, a cover disc arranged at a distance from the wheel disc, and blades arranged therebetween and connecting the wheel disc and the cover disc. The blades have an end portion, which is arranged at a distance from the radial outer end of the wheel disc and the cover disc towards the inside and has a reduced thickness with respect to an adjoining section.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2015/071174 filed Sep. 16, 2015, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102014219058.4 filed Sep 22, 2014. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a radial compressor impeller with a wheel disk, a cover disk spaced apart from said wheel disk, and blades arranged therebetween and connecting the wheel disk and the cover disk. 
       BACKGROUND OF INVENTION 
       [0003]    Impellers of this type are used, for example, in compressors or ventilators. 
         [0004]    The wheel disk of such a radial compressor impeller has blades which are, for example, milled from solid material, and a cover disk is then fastened onto the blades, thereby forming the radial compressor impeller. 
         [0005]    A conventional radial compressor impeller is arranged on a driven shaft. The radial compressor impeller is surrounded by a housing and, as a result of the rotation of the radial compressor impeller, a gas which flows axially into the space between the wheel disk and cover disk can be accelerated radially and circumferentially and consequently compressed. After it has passed the radial compressor impeller, the flowing gas passes into a duct of the housing. 
         [0006]    The flow at the impeller outlet of a rotating radial compressor impeller is coupled interactively with the flow at the sides of the impeller. This interaction influences the performance, in particular the achievable pressure increase and the efficiency of a compressor stage. Pressure losses occur in the wake depression in the region of the rotating trailing edge of an impeller blade and this causes displacement and constriction effects in the flow at the impeller outlet as a result of gas flowing from the sides of the impeller into the impeller flow. The pressure increase of the radial compressor impeller is thereby undesirably reduced. 
         [0007]    These interactions between the flow at the impeller outlet and the flow at the sides of the impeller are visualized by complex 3D flow simulations. 
       SUMMARY OF INVENTION 
       [0008]    An object of the invention is therefore to provide a radial compressor impeller which is designed such that a desired pressure increase in a compressor stage occurs. 
         [0009]    In order to achieve this object, in a radial compressor impeller of the type mentioned at the beginning it is provided according to the invention that the blades have an end portion, spaced apart inward from the radial outer end of the wheel disk and the cover disk, with a reduced thickness compared with an adjoining portion. 
         [0010]    In contrast to a conventional radial compressor impeller, in which the blades extend as far as the outer circumference of the wheel disk and cover disk, the blades of the radial compressor impeller according to the invention are “shortened”, i.e. they have a shortened design and extend radially not as far as the outer end of the wheel disk and cover disk but instead they have an end portion which is offset or arranged radially inward from the outer end. Furthermore, the radially outer end portions of the blades also have a reduced thickness compared with the thickness of the adjacent portion of the blades. The reduced thickness is here advantageously provided only in the region of the end portion of the blades, whereas the blades do not have a reduced thickness in the adjoining portion. As a result of this adapted design of the impeller outlet, the interaction of the impeller flow and the flow at the sides of the impeller can be desirably influenced, and hence the pressure increase in the compressor stage, at a specified speed. Furthermore, mixture losses at the impeller outlet are reduced, as a result of which the efficiency of the stage is increased. 
         [0011]    The “shortening” of the blades, i.e. their reduced diameter, can be 1% to 15%, compared with the “unshortened” diameter d of the wheel and/or cover disk. 
         [0012]    A development of the invention provides that the end portions of the blades in each case have a rounded edge on the suction side. It has been noted that a thick blade trailing edge causes clear pressure losses with correspondingly pronounced wake depressions in the impeller downstream flow, and additionally mixing takes place of the gas flowing through the radial compressor impeller and the gas at the sides of the impeller. 
         [0013]    The rounded edge and the profile of the blade on the suction side advantageously gradual merge into each other. This means that the rounded edge and the profile of the blade on the suction side, i.e. the suction side contour, merge progressively into each other, i.e. the rounded edge and the profile of the blade have the same tangent at the point of contact. 
         [0014]    In the radial compressor impeller according to the invention, it is advantageous that the rounded edge has a radius R which corresponds at least approximately to the equation R≈−a.d, where d is the diameter of the cover disk or the wheel disk, and a is a factor between 0.1 and 0.3, which is advantageously 0.2. 
         [0015]    In a further embodiment of the invention it can be provided that approximately one third of the width of the radial outer end of the blades is designed to be approximately parallel to the outer circumference of the wheel disk and the cover disk, and that the rounded edge adjoins said third. Accordingly, the rounded edge does not extend over the whole width of the radial outer end of the blades and instead only over approximately two thirds of the width. The radial outer end of the blades is designed to be parallel to the outer circumference of the wheel disk and the cover disk, or alternatively can also be designed as a tangent. 
         [0016]    It is also within the scope of the invention that the end portions of the blades in each case have a rounded edge on the pressure side. Similarly or contrary to the rounded edge on the suction side, the pressure side thus has a rounded edge. Accordingly, the aerodynamic properties of the radial compressor impeller according to the invention can be influenced in a targeted fashion by modifying the profile on the suction side and/or the pressure side. Usually either the suction side or the pressure side is rounded, because both effects counteract each other. 
         [0017]    On the pressure side too it is advantageous that the rounded edge and the profile of the blade merge gradually into each other, i.e. the tangents are identical at the contact point. 
         [0018]    In the radial compressor impeller according to the invention, the rounded edge can have a radius R which corresponds at least approximately to the equation R≈b.d, where d is the diameter of the cover disk or the wheel disk, and b is a factor between 0.1 and 0.3, which is advantageously 0.2. 
         [0019]    A variant of the radial compressor impeller according to the invention provides that approximately one third of the width of the radial outer end of the blades is designed to be approximately parallel to the outer circumference of the wheel disk and the cover disk, and that the rounded edge adjoins said third. 
         [0020]    Additionally, the invention relates to a radial compressor which has a radial compressor impeller of the type described which is accommodated in a housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention is described in detail below with the aid of exemplary embodiments and with reference to the drawings. The drawings are schematic representations in which: 
           [0022]      FIG. 1  shows a view in section of a detail of a radial compressor impeller according to the invention; 
           [0023]      FIG. 2  shows a cross-section through the blade shown in  FIG. 1 , along the line II-II; 
           [0024]      FIG. 3  shows a similar view in section to that in  FIG. 2  according to a further exemplary embodiment; 
           [0025]      FIG. 4  shows a detail from  FIG. 3  in the region of the end portion of the blade; 
           [0026]      FIG. 5  shows a similar view in section of the blade to that in  FIG. 2  according to a further exemplary embodiment; and 
           [0027]      FIG. 6  shows a detail of the blade shown in  FIG. 5  in the region of the end portion of the blade. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0028]    The view in section in  FIG. 1  shows part of a radial compressor impeller  1  which comprises a wheel disk  2  which is fastened on a shaft (not shown). The radial compressor impeller  1  additionally comprises a cover disk  3  spaced apart from the wheel disk  2 . Blades  4 , arranged distributed around the circumference, are arranged in the space between the wheel disk  2  and the cover disk  3 . The radial compressor impeller  1  is surrounded externally by a housing  5  which is shown only partially in  FIG. 1 . When the radial compressor impeller  1 , fastened on a shaft, is set in rotation, a gas which flows in axially in the direction shown by an arrow  6  can be accelerated and hence compressed radially and circumferentially. The gas passes over the radial compressor impeller  1  and flows into a flow duct  7  formed in the housing  5 . 
         [0029]      FIG. 2  is a view in section of the radial compressor impeller  1  in  FIG. 1  along the line II-II. In  FIG. 2 , only the section through the blade  4  and a part of the wheel disk  2  is shown, which is designed integrally with the blade  4 . The blade  4  has an aerodynamic profile and comprises a suction side  8  and a pressure side  9 . The blade  4  has an approximately uniform thickness over its length. 
         [0030]    It can be seen in  FIG. 2  that the blade  4  has an end portion  10  which is spaced apart inward from the radial outer end  11  of the wheel disk  2  and from the cover disk  3  arranged approximately parallel thereto. Accordingly, the blade  4  has a shortened radially outer end, compared with a conventional blade. The shortened blade end, which can be produced for example by machining, in particular by boring, effects a reduction in the pressure increase of the radial compressor impeller  1 . A radial compressor impeller can thus, for example after a bench test has been performed, be modified by boring in such a way that a predetermined pressure increase is obtained. As part of the production of a new radial compressor impeller, the end portion of the blade can of course also be formed directly, as shown in  FIG. 2 , i.e. with an end portion spaced apart from the outer end of the wheel disk. On the other hand, a pre-existing radial compressor impeller can be machined as described by boring in order to shorten the blades in the impeller outlet region. 
         [0031]      FIGS. 3 and 4  show a further exemplary embodiment of a radial compressor impeller, wherein—similarly to  FIG. 2 —only a cross-section through a blade is shown, and in  FIG. 4  a detail of the view in  FIG. 3 . 
         [0032]    The blade  12  shown in  FIG. 3  corresponds in principle to the blade  4  shown in  FIG. 2 . In particular, the blade  12  has an end portion  13  which is spaced apart inward from the radial outer end of the wheel disk  2 . As can be seen best in the enlarged view in  FIG. 4 , the end portion  13  of the blade  12  has a rounded edge  14  on the suction side  8 . The rounded edge  14  and the profile of the blade  12  on the suction side  8  merge gradually into each other, and at this point the tangential condition is fulfilled, i.e. the edge  14  and the edge of the profile of the blade  12  have the same tangent at the contact point. 
         [0033]    The rounded edge  14  is a segment of a circle with a radius R which corresponds to approximately 0.2 times the diameter d of the wheel disk  2 . 
         [0034]    It can be seen in  FIG. 4  that approximately one third of the (unrounded) width of the radial outer end portion  13  of the blade  12  is designed to be approximately parallel to the outer circumference of the wheel disk  2 , and that the rounded edge  14  adjoins said third. The outer edge of the end portion  13  and the rounded edge  14  enclose an angle which is somewhat greater than 90°. 
         [0035]    The end portion  13  having the rounded edge  14  can be formed directly during the production of the blade  12  or the wheel disk  12  formed integrally with the blades, or alternatively the end portion  13  can also be produced subsequently by shaping a conventional blade on a lathe. The production of the rounded edge  14  can thus be viewed as “rounding off”, i.e. the edge usually present at this point is provided with a radius. 
         [0036]      FIGS. 5 and 6  show a further exemplary embodiment of a radial compressor impeller in the region of a blade, wherein  FIG. 5  shows a similar view to that in  FIGS. 2 and 3 , and  FIG. 6  shows an enlarged detail of the blade shown in  FIG. 5 . 
         [0037]    The blade  15  shown in  FIGS. 5 and 6  has, in conformity with the exemplary embodiment shown in  FIG. 2 , an end portion  16  which is spaced apart from the radial outer end 
         [0038]      11  of the wheel disk  2 . The end portion  16  of the “shortened” blade  15  has a rounded edge  17  on the pressure side  9 . As can best be seen in  FIG. 6 , the rounded edge  17  and the outer contour of the blade  15  on the pressure side  9  merge gradually into each other. The tangential condition is fulfilled at the contact point. 
         [0039]    It is moreover shown in  FIG. 6  that the rounded edge  17  takes the form of a segment of a circle, the radius of which corresponds to approximately 0.2 times the diameter d of the wheel disk  2 . In other embodiments, a different radius can be provided and this can be, for example, between 0.15 d and 0.25 d. 
         [0040]    Approximately one third of the width of the radial end portion  16  of the blade  15  is designed so that it is parallel to the outer circumference of the wheel disk  2 , and the rounded edge  17 , which thus extends over approximately two thirds of the (notional) width, adjoins said third. 
         [0041]    A conventional radial compressor impeller can be machined by boring the radial end portion of the blades and by rounding off on the pressure side in such a way that the radial compressor impeller shown in  FIGS. 5 and 6  results. On the other hand, the shape of the blade  15  shown in  FIGS. 5 and 6  can be formed, during the production of a new radial compressor impeller, directly by milling or a different manufacturing method. 
         [0042]    The different methods shown in the exemplary embodiments for influencing the flow conditions cause a reduction in pressure losses and reduction or prevention of undesired mixing of fluid in the region of the sides of the impeller with fluid in the region of the impeller outlet. In this way, the efficiency of the impeller stage is increased. The measures shown in the different described exemplary embodiments can also be combined with each other. In order to obtain a radial compressor impeller with defined properties, the modifications performed in the region of the end portion of the blades can also be modified. For example, a rounded edge can be provided on both the suction side and the pressure side. Additionally, the remaining length of the blades in the radial direction or the distance from the outer edge of the wheel disk can also be adapted. 
         [0043]    Although the invention has been illustrated and described in detail via the preferred exemplary embodiments, the invention is not limited by the disclosed examples and other variations can be derived by a person skilled in the art without going beyond the protective scope of the invention.