Patent Publication Number: US-11384774-B2

Title: Rotor and centrifugal compressor including the same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a rotor and a centrifugal compressor including the rotor. 
     BACKGROUND 
     In a centrifugal compressor of a turbocharger, when the natural frequency of an impeller is equal to the frequency of excitation caused by a fluid flowing in the centrifugal compressor, resonance may occur and increase the vibration of the impeller, which may lead to damage to the impeller. In order to improve the safety against such resonance, it is conceivable to partially decrease the blade thickness at the portion corresponding to the anti-node of the eigenmode and increase the blade thickness at the portion corresponding to the node of the eigenmode. For achieving such a shape, it is necessary to three-dimensionally define the blade thickness distribution of the blade. 
     In Patent Document 1, not for improving the safety against resonance but for extending the operating range of the centrifugal compressor at the high flow rate side, the blade of the impeller is divided in the blade height direction into a tip portion on the tip side, a root portion on the hub side, and a connection portion between the tip portion and the root portion, with the blade thickness of the tip portion constant and thinner than the blade thickness of the root portion, the blade thickness of the connection portion gradually decreasing from the root portion toward the tip portion, and the blade thickness of the root portion gradually decreasing toward the connection portion. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP2016-17461A 
     SUMMARY 
     Problems to be Solved 
     However, as can be seen from  FIG. 4  showing results of eigenvalue analysis of the blade by the present inventors, the anti-node portion of the first eigenmode of the blade  100  is located in a range of 50 to 100% of the blade height from the hub-side edge  102  to the tip-side edge  103  of the blade  100  on the leading edge  101  side of the blade  100 . Accordingly, in the blade thickness distribution of the blade described in Patent Document 1, although the blade thickness can be partially decreased at the portion corresponding to the anti-node of the eigenmode, the blade thickness cannot be appropriately increased at the portion corresponding to the node of the eigenmode, so that it may not be possible to improve the safety against resonance. Further, due to the portion where the blade thickness distribution is concave from the hub side to the tip side, the machining method for forming the blade surface is limited. 
     In view of the above, an object of at least one embodiment of the present disclosure is to provide a rotor and a centrifugal compressor including the rotor whereby it is possible to improve the safety against resonance. 
     Solution to the Problems 
     (1) A rotor according to at least one embodiment of the present invention comprises: a hub; and a plurality of blades disposed on the hub. Each of the plurality of blades includes a suction surface, a pressure surface, a leading edge, a trailing edge, a tip-side edge, and a hub-side edge. In a cross-section of each blade at a given chord position between the leading edge and the trailing edge, an angle of at least one of the suction surface or the pressure surface with respect to a blade height direction of the blade increases in a direction from the hub-side edge to the tip-side edge over a region from the hub-side edge to the tip-side edge, in at least a range from the leading edge to a chord position away from the leading edge toward the trailing edge. 
     With the above configuration (1), since, in a cross-section of each blade at a given chord position between the leading edge and the trailing edge, the angle of at least one of the suction surface or the pressure surface with respect to the blade height direction of the blade increases in the direction from the hub-side edge to the tip-side edge over the region from the hub-side edge to the tip-side edge, in at least a range from the leading edge to a chord position away from the leading edge toward the trailing edge, the blade thickness of the portion corresponding to the anti-node of the eigenmode is partially decreased, and the blade thickness of the portion corresponding to the node of the eigenmode is increased. Thus, it is possible to improve the safety against resonance. 
     (2) In some embodiments, in the above configuration (1), the at least one of the suction surface or the pressure surface includes a first region from the leading edge to a chord position away from the leading edge toward the trailing edge, and a second region on a trailing edge side of the first region. In the first region, the angle increases continuously from the hub-side edge to the tip-side edge. 
     With the above configuration (2), although the first region requires point cutting which may increase the processing time and manufacturing cost of the blade, since the first region is a partial region in the vicinity of the leading edge, it is possible to suppress an increase in processing time and manufacturing cost of the blade, as compared with the case where the entire blade surface is formed by point cutting. 
     (3) In some embodiments, in the above configuration (2), the second region is composed of at least two line segments between the tip-side edge and the hub-side edge. 
     With the above configuration (3), since the second region can be machined by line cutting, even when the configuration in which the angle with respect to the blade height direction of the blade increases in the direction from the hub-side edge to the tip-side edge over the region from the hub-side edge to the tip-side edge is formed on the trailing edge side of the first region, it is possible to suppress an increase in processing time and manufacturing cost of the blade. 
     (4) In some embodiments, in the above configuration (2) or (3), the first region is in a range between the leading edge and a 5% to 15% chord position from the leading edge. 
     Generally, the range between the leading edge and the 5% to 15% chord position requires point cutting to round the leading edge of the blade. With the above configuration (4), by machining the blade surface shape of the first region at the time of rounding the leading edge of the blade, it is possible to suppress an increase in processing time and manufacturing cost of the blade, as compared with the case where the point cutting process is performed only for machining the blade surface shape of the first region. 
     (5) In some embodiments, in any one of the above configurations (1) to (4), the angle of one of the suction surface or the pressure surface with respect to the blade height direction of the blade increases in the direction from the hub-side edge to the tip-side edge over the region from the hub-side edge to the tip-side edge, in at least the range between the leading edge and the chord position away from the leading edge toward the trailing edge, and the other of the suction surface or the pressure surface forms a line segment connecting the hub-side edge and the tip-side edge. 
     With the above configuration (5), since only one of the suction surface or the pressure surface is machined so that the angle with respect to the blade height direction of the blade increases in the direction from the hub-side edge to the tip-side edge over the region from the hub-side edge to the tip-side edge, it is possible to suppress an increase in processing time and manufacturing cost of the blade, as compared with the case where both the suction surface and the pressure surface are machined as described above. Further, since the other of the suction surface or the pressure surface is a flat surface connecting the hub-side edge and the tip-side edge, it is possible to reliably achieve the blade thickness distribution in which the blade thickness of the portion corresponding to the anti-node of the eigenmode is partially decreased, and the blade thickness of the portion corresponding to the node of the eigenmode is increased. 
     (6) A centrifugal compressor according to at least one embodiment of the present invention comprises: the rotor described in any one of the above (1) to (5). 
     With the above configuration (6), it is possible to improve the safety against resonance. 
     Advantageous Effects 
     According to at least one embodiment of the present disclosure, since, in a cross-section of each blade at a given chord position between the leading edge and the trailing edge, the angle of at least one of the suction surface or the pressure surface with respect to the blade height direction of the blade increases in the direction from the hub-side edge to the tip-side edge over the region from the hub-side edge to the tip-side edge, in at least a range from the leading edge to a chord position away from the leading edge toward the trailing edge, the blade thickness of the portion corresponding to the anti-node of the eigenmode is partially decreased, and the blade thickness of the portion corresponding to the node of the eigenmode is increased. Thus, it is possible to improve the safety against resonance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a centrifugal compressor including a rotor according to an embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view taken along line II-II in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line in  FIG. 1 . 
         FIG. 4  is a diagram showing results of eigenvalue analysis of a blade by the present inventors. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the scope of the present invention is not limited to the following embodiments. It is intended that dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention. 
     A rotor according to some embodiments of the present disclosure will be described by taking a rotor (impeller) provided in a centrifugal compressor of a turbocharger as an example. However, the centrifugal compressor of the present disclosure is not limited to a centrifugal compressor of a turbocharger, and may be any centrifugal compressor which operates alone. Further, although not described specifically, the rotor of the present disclosure includes a rotor used for a turbine or an axial-flow pump. 
     As shown in  FIG. 1 , the centrifugal compressor  1  includes a housing  2  and an impeller  3  rotatably disposed around the rotational axis L within the housing  2 . The impeller  3  has a plurality of blades  4  (only one blade  4  is depicted in  FIG. 1 ) of streamlined shape arranged on the hub  5  at a predetermined interval in the circumferential direction. Each blade  4  includes a leading edge  4   a , a trailing edge  4   b , a tip-side edge  4   c  facing the housing  2 , and a hub-side edge  4   d  connected to the hub  5 . 
     The suction surface  10  of the blade  4  is divided into a first region  11  ranging from the leading edge  4   a  to a chord position away from the leading edge  4   a  toward the trailing edge  4   b  and a second region  12  on the trailing edge  4   b  side of the first region  11 . Although not depicted in  FIG. 1 , the pressure surface of the blade  4  is also divided into the first region  11  and the second region  12 . 
       FIG. 2  shows a cross-section obtained by cutting the blade  4  at a given chord position in the first region  11  of each of the suction surface  10  and the pressure surface  20  of the blade  4  (hatching is omitted). Both the suction surface  10  and the pressure surface  20  are curved convexly with respect to line segments L 10  and L 20  which connects the tip-side edge  4   c  and the hub-side edge  4   d  in the cross-section. 
     In the cross-section shown in  FIG. 2 , the convex curve in the first region  11  of the suction surface  10  is shaped such that the angle with respect to the blade height direction of the blade  4  increases in a direction from the hub-side edge  4   d  to the tip-side edge  4   c  over a region from the hub-side edge  4   d  to the tip-side edge  4   c . That is, θ 1 &lt;θ 2  is established, where θ 1  is an angle with respect to the blade height direction of the blade  4  at the position A closer to the hub-side edge  4   d  than the tip-side edge  4   c , and  02  is an angle with respect to the blade height direction of the blade  4  at the position B closer to the tip-side edge  4   c  than the position A. 
     In the cross-section shown in  FIG. 2 , similarly, the convex curve in the first region  11  of the pressure surface  20  is shaped such that the angle with respect to the blade height direction of the blade  4  increases in a direction from the hub-side edge  4   d  to the tip-side edge  4   c  over a region from the hub-side edge  4   d  to the tip-side edge  4   c . That is, θ 3 &lt;θ 4  is established, where θ 3  is an angle with respect to the blade height direction of the blade  4  at the position C closer to the hub-side edge  4   d  than the tip-side edge  4   c , and θ 4  is an angle with respect to the blade height direction of the blade  4  at the position D closer to the tip-side edge  4   c  than the position C. 
       FIG. 3  shows a cross-section obtained by cutting the blade  4  at a given chord position in the second region  12  of each of the suction surface  10  and the pressure surface  20  of the blade  4  (hatching is omitted). The suction surface  10  has a shape composed of three line segments L 11 , L 12 , L 13  sequentially connected in the cross-section. Similarly, the pressure surface  20  has a shape composed of three line segments L 21 , L 22 , L 23  sequentially connected in the cross-section. As a result, the suction surface  10  and the pressure surface  20  protrude from the line segments L 10  and L 20 , respectively 
     In the cross-section shown in  FIG. 3 , the second region  12  of the suction surface  10  is shaped so as to satisfy θ 11 &lt;θ 12 &lt;θ 13 , where θ 11 , θ 12 , and θ 13  are angles between each line segment L 11 , L 12 , L 13  and the blade height direction of the blade  4 . That is, the second region  12  of the suction surface  10  is also shaped such that the angle with respect to the blade height direction of the blade  4  increases in the direction from the hub-side edge  4   d  to the tip-side edge  4   c  over the region from the hub-side edge  4   d  to the tip-side edge  4   c , not continuously but stepwise. 
     In the cross-section shown in  FIG. 3 , the second region  12  of the pressure surface  20  is shaped so as to satisfy θ 21 &lt;θ 22 &lt;θ 23 , where θ 21 , θ 22 , and θ 23  are angles between each line segment L 21 , L 22 , L 23  and the blade height direction of the blade  4 . That is, the second region  12  of the pressure surface  20  is also shaped such that the angle with respect to the blade height direction of the blade  4  increases in the direction from the hub-side edge  4   d  to the tip-side edge  4   c  over the region from the hub-side edge  4   d  to the tip-side edge  4   c , not continuously but stepwise. 
     As described with reference to  FIGS. 2 and 3 , since the angles of both the suction surface  10  and the pressure surface  20  with respect to the blade height direction of the blade  4  increase in the direction from the hub-side edge  4   d  to the tip-side edge  4   c  over the region from the hub-side edge  4   d  to the tip-side edge  4   c , the blade thickness of the portion in the vicinity of the tip-side edge  4   c  corresponding to the anti-node of the eigenmode is decreased to ensure an eigenvalue, and the blade thickness of about 50% blade height from the hub-side edge  4   d  to the tip-side edge  4   c  is increased to improve the strength of the portion corresponding to the node of the eigenmode. Thus, it is possible to improve the safety against resonance that may occur during operation of the centrifugal compressor  1  (see  FIG. 1 ). 
     As shown in  FIG. 3 , the blade surface shape of the second region  12 , whose cross-section obtained by cutting the blade  4  at a given chord position is composed of a plurality of line segments, can be formed by line cutting. Meanwhile, as shown in  FIG. 2 , the blade surface shape of the first region  11 , whose cross-section obtained by cutting the blade  4  at a given chord position is composed of a continuous curve, cannot be formed by line cutting but requires point cutting. Although the point cutting process requires a longer processing time and a higher cost than the line cutting process, the first region  11  is limited to a partial region in the vicinity of the leading edge  4   a . Thus, it is possible to suppress an increase in processing time and manufacturing cost of the blade  4 , as compared with the case where the entire blade surface has the shape of the first region  11 . 
     The first region  11  is preferably in a range between the leading edge  4   a  and a 5% to 15% chord position from the leading edge  4   a . Generally, the range between the leading edge  4   a  and the 5% to 15% chord position from the leading edge  4   a  requires point cutting to round the leading edge  4   a  of the blade  4 . By machining the blade surface of the first region  11  at the time of rounding the leading edge  4   a  of the blade  4 , it is possible to suppress an increase in processing time and manufacturing cost of the blade  4 , as compared with the case where the point cutting process is performed only for machining the blade surface of the first region  11 . 
     In the above embodiment, the second region  12  has a shape such that three line segments are sequentially connected in the cross-section obtained by cutting the blade  4  at a given chord position, but the embodiment is not limited thereto. The second region  12  may have shape such that two or four or more line segments are sequentially connected. 
     In the above embodiment, the suction surface  10  and the pressure surface  20  have the blade surface shapes of the first region  11  and the second region  12  according to the same embodiment, but the embodiment is not limited thereto. The first region  11  of the suction surface  10  and the first region  11  of the pressure surface  20  may have different ranges. In this case, it is preferred that the range of the first region  11  of the suction surface  10  is larger than the range of the first region  11  of the pressure surface  20 . This is because the pressure surface  20  has a thinner boundary layer than the suction surface  10 , and separation is less likely to occur in response to a change in curvature of the wall surface, so that performance improvement can be expected. 
     In the above embodiment, the suction surface  10  and the pressure surface  20  both have the blade surface shapes of the first region  11  and the second region  12 , but the embodiment is not limited thereto. Either one of the suction surface  10  or the pressure surface  20  may have the blade surface shapes of the first region  11  and the second region  12 , and the other may be a flat surface connecting the hub-side edge  4   d  and the tip-side edge  4   c  (corresponding to line segment L 10  or L 20  in  FIGS. 2 and 3 ). In this case, it is preferred that the pressure surface  20  have the blade surface shape of the second region  12 , and the suction surface  10  is a flat surface connecting the hub-side edge  4   d  and the tip-side edge  4   c . This is because the pressure surface  20  has a thinner boundary layer than the suction surface  10 , and separation is less likely to occur in response to a change in curvature of the wall surface. 
     When the blade surface shapes of the first region  11  and the second region  12  are formed on one of the suction surface  10  or the pressure surface  20 , it is possible to suppress an increase in processing time and manufacturing cost of the blade  4 , as compared with the case where the blade surface shapes are formed on both the suction surface  10  and the pressure surface  20 . Further, since the other of the suction surface  10  or the pressure surface  20  is a flat surface connecting the hub-side edge  4   d  and the tip-side edge  4   c , it is possible to reliably achieve the blade thickness distribution in which the blade thickness of the portion corresponding to the anti-node of the eigenmode is partially decreased and the blade thickness of the portion corresponding to the node of the eigenmode is increased. 
     In the above embodiment, each of the suction surface  10  and the pressure surface  20  includes both the first region  11  and the second region  12 , but each may include at least the first region  11 . In the case where the second region  12  is included, the second region  12  may not extend in the entire region from the first region  11  to the trailing edge  4   b , but may extend in a region from the first region  11  to a chord position away from the first region  11  toward the trailing edge  4   b.    
     Although in the above embodiment, the blade  4  is a full blade, the blade is not limited thereto. The blade  4  may be a splitter blade disposed between two full blades. 
     REFERENCE SIGNS LIST 
     
         
           1  Centrifugal compressor 
           2  Housing 
           3  Impeller (Rotor) 
           4  Blade 
           4   a  Leading edge 
           4   b  Trailing edge 
           4   c  Tip-side edge 
           4   d  Hub-side edge 
           5  Hub 
           10  Suction surface 
           11  First region 
           12  Second region 
           20  Pressure surface 
         L Rotational axis 
         L 10  Line segment 
         L 11  Line segment 
         L 12  Line segment 
         L 13  Line segment 
         L 20  Line segment 
         L 21  Line segment 
         L 22  Line segment 
         L 23  Line segment 
         θ 1  Angle 
         θ 2  Angle 
         θ 3  Angle 
         θ 4  Angle 
         θ 11  On Angle 
         θ 12  Angle 
         θ 13  Angle 
         θ 21  Angle 
         θ 22  Angle 
         θ 23  Angle