JP2016084730A - Axial flow turbine and supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial flow turbine capable of effectively suppressing loss resulting from leak flow in a chip clearance with a simple structure, and a supercharger.SOLUTION: An axial flow turbine includes a rotor having a plurality of moving blades on its outer periphery, and a stationary member provided on the outer peripheral side of the rotor and having an annular wall surface opposite to the chip surface of the moving blade. In stop of the axial flow turbine, a clearance between the chip surface on the rear edge side of the moving blade and the annular wall surface is made larger than a clearance between the chip surface on the front edge side of the moving blade and the annular wall surface.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to an axial turbine and a supercharger in which a plurality of rotor blades are arranged on the outer periphery of a rotor.

  In general, in an axial flow turbine, a rotor to which a moving blade is attached is rotated by a fluid flowing in an axial direction in a casing.

  In such an axial-flow turbine, the leak flow in the tip clearance between the stationary member on the casing side and the moving blade is a major factor of performance degradation. The tip clearance is usually set so that the stationary member and the moving blade do not contact each other in consideration of the effects of thermal deformation, centrifugal deformation, vibration and backlash during turbine operation.

Therefore, in order to improve the performance of the axial turbine, it is required to reduce the tip clearance.
For example, in Patent Document 1, a stationary member that faces the tip of a moving blade includes a functionally gradient material, and the functionally gradient material is thermally deformed so as to maintain the tip clearance at a predetermined value regardless of the temperature rise of the fluid. The structure which was made to be described is described. The functionally gradient material is a composite of a material having a low linear expansion coefficient and a material having a high linear expansion coefficient, and has a property that the linear expansion coefficient increases as the thickness direction position x increases.

Japanese Patent Laid-Open No. 6-1599099

By the way, in recent years, for the purpose of further improving the turbine performance, the axial flow turbine tends to have a higher working fluid temperature or a higher rotational speed. Therefore, thermal deformation and centrifugal deformation of the moving blades in the axial flow turbine become significant. Since the rotor blades of an axial flow turbine have a complicated curved surface shape, the amount of deformation of the rotor blades is not uniform, and the tip clearance is set to prevent rubbing in consideration of the amount of deformation of the rotor blades. When set, it is necessary to provide an excessive tip clearance depending on the part. As a result, the leak flow partially increases, and the loss due to the leak flow increases.
In this respect, in Patent Document 1, although the tip clearance during operation can be reduced by the functionally gradient material, it is necessary to add a new member, the structure becomes complicated, and there is a possibility that the cost may be significantly increased. .

  In view of the above circumstances, at least one embodiment of the present invention provides an axial turbine and a supercharger that can effectively suppress a loss due to a leak flow in a tip clearance with a simple structure. For the purpose.

(1) An axial turbine according to at least one embodiment of the present invention includes:
A rotor having a plurality of rotor blades on the outer periphery;
A stationary member provided on the outer peripheral side of the rotor and having an annular wall surface facing the tip surface of the rotor blade,
When the axial turbine is stopped, a clearance between the tip surface and the annular wall surface on the trailing edge side of the moving blade is larger than that on the leading edge side of the moving blade.

As a result of intensive studies by the present inventors, it has been found that the change in the tip clearance in the axial flow turbine is greatly influenced by thermal deformation and centrifugal deformation of the rotor blades. As a result of the deformation analysis performed by the present inventors in consideration of these, it has been found that, in particular, the deformation amount on the trailing edge side of the moving blade is larger than the deformation amount on the front edge side.
Therefore, the axial flow turbine according to the above-described embodiment is configured such that the clearance between the tip surface and the annular wall surface on the trailing edge side of the moving blade is larger than that on the leading edge side of the moving blade when the axial flow turbine is stopped. For this reason, when the rotor blade is deformed by heat or centrifugal force during the operation of the axial turbine, the trailing edge side, which has been set larger in advance, is closer to the annular wall surface than the leading edge side when the rear edge side is larger in deformation. The clearance becomes narrower and approaches the clearance on the front edge side where the deformation is small. As a result, the tip clearance can be maintained properly, and the loss due to the leak flow in the tip clearance can be effectively suppressed with a simple structure.

(2) In some embodiments, in the configuration of (1) above, the difference between the clearance on the front edge side and the clearance on the rear edge side during rated operation of the axial flow turbine is such that the axial flow turbine is stopped. Smaller than.
Thereby, the clearance between the tip surface and the annular wall surface during operation can be made uniform with respect to the fluid flow direction. In this specification, “uniformizing” the clearance not only means that the clearance is uniform, but also means that the clearance is brought close to a uniform state.

(3) In some embodiments, in the above configuration (1) or (2), the tip surface is zero with respect to the annular wall surface facing the tip surface at least when the axial turbine is stopped. The inclined surface has a larger inclination angle and gradually increases the clearance from the front edge side to the rear edge side of the moving blade.
Thereby, it is possible to easily realize a structure in which the clearance between the tip surface and the annular wall surface on the trailing edge side of the moving blade is larger than that on the leading edge side of the moving blade. Further, the above-described structure can be realized without changing the stationary member side on which the annular wall surface is provided from the existing structure, and in that case, application to an existing axial flow turbine is facilitated.

(4) In some embodiments, in any one of the configurations (1) to (3), the annular wall surface is at least the tip surface facing the annular wall surface when the axial turbine is stopped. On the other hand, the inclined surface has an inclination angle larger than zero, and the clearance gradually increases from the front edge side to the rear edge side of the moving blade.
Thereby, it is possible to easily realize a structure in which the clearance between the tip surface and the annular wall surface on the trailing edge side of the moving blade is larger than that on the leading edge side of the moving blade. Further, the above structure can be realized without changing the moving blade from the existing structure. In this case, the moving blade can be easily manufactured.

(5) In some embodiments, in the configuration according to any one of (1) to (4), the annular wall surface has a space between a leading edge and a trailing edge of the blade in the axial direction of the rotor. A step is formed at the position, and the annular wall surface is located on the outer side in the radial direction of the axial flow turbine on the rear edge side with respect to the step than on the front edge side with respect to the step.
(6) In one embodiment, in the configuration of (5) above, the annular wall surface has a recess formed in an axial range including the position of the trailing edge of the moving blade, and the leading edge side that forms the recess The wall surface constitutes the step.
According to the configuration of (5) or (6) above, a structure is realized in which the clearance between the tip surface and the annular wall surface on the trailing edge side of the moving blade is larger than that on the leading edge side of the moving blade due to the step of the annular wall surface. can do. Further, the above structure can be realized only by the step of the annular wall surface without providing a minute inclination angle. In this case, processing for providing a minute inclination angle becomes unnecessary, and the processing of the annular wall surface is easy. .

(7) The supercharger according to at least one embodiment of the present invention is:
An axial turbine according to any one of (1) to (6) configured to be driven by exhaust gas from an internal combustion engine;
A compressor driven by the axial turbine and configured to compress intake air supplied to the internal combustion engine.
Thereby, since the loss resulting from the leak flow in an axial turbine can be suppressed, it leads also to the efficiency improvement in a supercharger.

  According to at least one embodiment of the present invention, the clearance on the trailing edge side that has been set large in advance is narrowed, and the clearance during operation can be made uniform in the fluid flow direction.

It is sectional drawing which shows the whole structure of the supercharger which concerns on one Embodiment. It is a fragmentary sectional view showing a bucket and a stationary member of an axial flow turbine concerning one embodiment. It is a fragmentary sectional view which shows the moving blade and stationary member of the axial flow turbine which concern on other embodiment. It is a fragmentary sectional view which shows the moving blade and stationary member of the axial flow turbine which concern on other embodiment. It is a fragmentary sectional view which shows the moving blade and stationary member of the axial flow turbine which concern on other embodiment. It is a figure which shows an example of the blade type | mold of a moving blade. (A) is a view showing the blade before deformation when the axial turbine is stopped, and (b) is a view showing the blade during deformation during operation of the axial turbine. is there.

  Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.

Initially, with reference to FIG. 1, the supercharger 1 provided with the axial flow turbine 2 which concerns on this embodiment is demonstrated. FIG. 1 is a cross-sectional view (longitudinal cross-sectional view) showing an overall configuration of a supercharger 1 according to an embodiment, and shows a marine exhaust turbine supercharger as an example. In addition, the kind and application destination of the supercharger 1 are not limited to this.
As shown in FIG. 1, a supercharger 1 according to an embodiment includes an axial flow turbine 2 configured to be driven by exhaust gas from an internal combustion engine (for example, a marine diesel engine), and the axial flow turbine 2. And a compressor 3 configured to compress intake air that is driven and supplied to the internal combustion engine.

  As a specific configuration example, a bearing stand 4 is provided between the axial turbine 2 and the compressor 3. The turbine casing 21 of the axial flow turbine 2, the bearing stand 4, and the compressor casing 31 of the compressor 3 are integrally configured by connecting means such as a fastening member (for example, a bolt). A thrust bearing 41 and radial bearings 42 and 43 are accommodated in the bearing stand 4. The rotor 5 is rotatably supported by the thrust bearing 41 and the radial bearings 42 and 43. The rotor blade 10 of the axial turbine 2 is connected to one end side of the rotor 5, and the impeller 32 of the compressor 3 is connected to the other end side.

The axial turbine 2 includes a rotor 5 (actually one end side of the rotor 5), a plurality of moving blades 10 implanted on the outer periphery of the rotor 5, and a turbine provided on the outer peripheral side of the rotor 5 and the moving blades 10. A casing 21. A stationary member 22 is attached to the turbine casing 21 via a support member 26. By a stationary system member including the turbine casing 21 and the stationary member 22, an inlet passage 27, an axial passage 28, and an outlet passage 29 through which exhaust gas flows are sequentially formed in the exhaust gas flow direction. The axial passage 28 is located between the inlet passage 27 and the outlet passage 29 and extends along the rotation axis O of the rotor 5. The moving blade 10 is provided in the axial passage 28. A turbine nozzle (static blade) 25 is provided on the inlet side of the moving blade 10.
In the axial flow turbine 2, exhaust gas from an internal combustion engine (not shown) is introduced from the inlet passage 27 so that the rotor 5 connected to the moving blade 10 is rotated by the exhaust gas flowing through the axial passage 28. It has become. The exhaust gas that has passed through the moving blade 10 is discharged through the outlet passage 29. A specific configuration of the axial turbine 2 will be described later.

The compressor 3 is a centrifugal compressor, and is arranged on the rotor 5 (actually the other end side of the rotor 5), the impeller 32 provided on the outer periphery of the rotor 5, and the outer periphery side of the rotor 5 and the impeller 32. A compressor casing 31 provided. An air inlet 37 and an outlet scroll 38 are formed by a stationary member including the compressor casing 31. Between the air inlet 37 and the outlet scroll 38, an impeller 32 and a diffuser 36 are sequentially arranged in the air flow direction. The impeller 32 includes a disk-shaped hub 33 fixed to the outer periphery of the rotor 5, and a plurality of blades (vanes) 34 fixed to the hub 33 and arranged radially with respect to the hub 33.
In the compressor 3, the air introduced from the air inlet 37 is pressurized when passing through the impeller 32, the diffuser 36 and the outlet scroll 38. The air compressed by the compressor 3 is sent to an internal combustion engine (not shown).

  Here, the axial flow turbine 2 according to the present embodiment will be described in detail with reference to FIGS. 2 to 5 are partial cross-sectional views respectively showing the moving blade 10 and the stationary member 22 of the axial turbine 2 according to each embodiment. FIG. 6 is a diagram illustrating an example of the blade shape of the moving blade 10. FIG. 7 is a diagram illustrating deformation of a moving blade by analysis. 2 to 5, the moving blade 10 indicated by a solid line indicates a state when the axial flow turbine 2 is stopped, and the moving blade 10 ′ indicated by a dotted line indicates that the axial flow turbine 2 is in operation (for example, during rated operation). ). 6 and 7 show a moving blade 10 of an axial flow turbine 2 applied to a supercharger 1 as shown in FIG. 1 as an example. However, the axial turbine 2 according to the present embodiment is not limited to this type.

As shown in FIGS. 2 to 5, the axial turbine 2 according to some embodiments includes a plurality of blades 10 implanted on the outer periphery of the rotor 5 (see FIG. 1) and the outer peripheral side of the rotor 5. And a stationary member 22 having an annular wall surface 23 facing the tip surface 11 of the rotor blade 10. In these drawings, a base (not shown) below the rotor blade 10 is attached to the rotor 5, and a tip surface 11 is provided above the rotor blade 10.
A plurality of moving blades 10 are provided at equal intervals in the circumferential direction along the outer peripheral surface of the rotor 5. The moving blade 10 is arranged so as to extend radially outward from the rotor 5 side. In the present embodiment, the radially outward direction refers to the radial direction inner side (rotor 5 side) to the outer side (stationary member 22 side) of the axial turbine 2 around the rotation axis O (see FIG. 1) of the rotor 5. The direction to go.
A tip clearance (hereinafter simply referred to as a clearance) 20 is provided between the annular wall surface 23 of the stationary member 22 and the tip surface 11 of the rotor blade 10. Usually, the clearance 20 is set so that the moving blade 10 and the stationary member 22 do not come into contact with each other when the axial flow turbine 2 is operated.

  As shown in FIG. 6, in one embodiment, the airfoil of the moving blade 10 has a leading edge 12 located on the upstream side in the flow direction of the working fluid and a trailing edge 13 located on the downstream side. Between the front edge 12 and the rear edge 13, an abdominal surface (pressure surface) 14 is formed on one side, and a back surface (negative pressure surface) 15 is formed on the other side. The airfoil is curved so that the angle formed by the camber line (airfoil center line) and the flow direction of the working fluid gradually increases.

  In such an airfoil, the thickness of the trailing edge 13 of the moving blade 10 is usually reduced for the purpose of reducing loss due to wake. On the other hand, in the axial turbine 2, the working fluid tends to increase in temperature or the rotational speed tends to increase. Therefore, thermal deformation and centrifugal deformation of the moving blade in the axial flow turbine 2 become significant. Further, since the moving blade 10 is formed by a curved surface having a complicated shape, the amount of deformation at each part is also non-uniform. Therefore, when the clearance 20 shown in FIGS. 2 to 5 is set so that rubbing does not occur in consideration of the deformation amount of the moving blade 10, it is necessary to provide the clearance 20 excessively depending on the part. Thereby, the loss resulting from the leak flow in the clearance 20 increases.

For the purpose of reducing the loss caused by the leak flow, the present inventors have studied the deformation of the moving blade 10, and as a result, the change of the clearance 20 in the axial turbine 2 mainly causes the thermal deformation of the moving blade 10 and the deformation of the moving blade 10. It has been clarified that it occurs due to centrifugal deformation. Further, as a result of the deformation analysis of the moving blade 10, the inventors obtained the analysis result shown in FIG. In this deformation analysis, the centrifugal force acting on the moving blade 10 (centrifugal deformation) and the temperature of the moving blade 10 (thermal deformation) are included in the analysis conditions as factors affecting the shape of the moving blade 10. . FIG. 7A shows the moving blade 10 before deformation when the axial flow turbine 2 is stopped, and FIG. 7B shows the moving blade 10 ′ when deforming during operation of the axial flow turbine 2. ing.
Comparing these figures, it can be seen that the rear edge 13 side of the moving blades 10 and 10 'has a larger deformation amount than the front edge 12 side. Therefore, for example, when the clearance 20 is set so that the rear edge 13 side does not contact the stationary member 22, the margin of the clearance 20 is larger on the front edge 12 side than on the rear edge 13 side during operation of the axial turbine 2. As a result, the leak flow increases accordingly, and the turbine performance deteriorates.

Therefore, as shown in FIGS. 2 to 5, in the present embodiment, when the axial turbine 2 is stopped, the clearance 20 between the tip surface 11 and the annular wall surface 23 on the trailing edge 13 side of the moving blade 10 is the moving blade. The moving blade 10 is formed so as to be larger than the clearance 20 between the tip surface 11 and the annular wall surface 23 on the front edge 12 side.
Specifically, the clearance _{d 2} at the trailing edge 13, the relationship between the clearance _{d 1} at the leading edge _12, and has a d 2> _{d 1.} Incidentally, FIGS. 2 In 5, the clearance _{d 2} at the trailing edge 13, front is exemplified respectively as compared with the clearance _{d 1} at the edge 12, two clearance _d 1 to be compared, _{d 2} The position of is not limited to these. That is, the clearance d ₂ at any position in the region on the trailing edge 13 side of the moving blade 10 and the clearance d ₁ at any position in the region on the front edge 12 side of the moving blade 10 are related to each other (d ₂ > D ₁ ). For example, in the case where the tip surface 11 of the rear edge 13 is provided with an edge (squealer or the like) that protrudes radially outward assuming that it contacts the annular wall surface 23, the clearance 20 at this edge is Although previous smaller than the edge 12 of the clearance 20, the clearance d ₂ at other sites of the trailing edge 13 side is contained in the larger if the present embodiment than the clearance d ₁ of the leading edge 12 side.

According to the above embodiment, when the axial turbine 2 is stopped, the clearance 20 (d ₂ ) between the tip surface 11 and the annular wall surface 23 on the trailing edge 13 side of the moving blade 10 is on the leading edge 12 side of the moving blade 10. The clearance is made larger than 20 (d ₁ ). For this reason, when the axial turbine 2 is operated, in the moving blade 10 ′ deformed by heat or centrifugal force, the rear edge 13 side having a larger deformation amount is closer to the annular wall surface 23 than the front edge 12 side. The set clearance 20 (d ₂ ) on the rear edge 13 side narrows, and approaches the clearance 20 (d ₁ ) on the front edge 12 side with a small deformation amount. Thereby, the clearance 20 can be maintained appropriately, and the loss due to the leak flow in the clearance 20 can be effectively suppressed with a simple structure.

In this case, the difference in the clearance 20 between the front edge 12 side and the rear edge 13 side during rated operation of the axial flow turbine 2 is the clearance 20 between the front edge 12 side and the rear edge 13 side when the axial flow turbine 2 is stopped. Smaller than the difference. Specifically, the absolute value of the difference between the clearance 20 during rated operation of the axial turbine 2 _(d 2 -d ₁₎ is the difference in the clearance 20 at the time of stopping axial turbine 2 _(d 2 -d ₁₎ Less than absolute value.
When the axial flow turbine 2 reaches the rated operation, a centrifugal force close to the maximum acts on the moving blade 10 ', and a temperature increase close to the maximum temperature is observed on the moving blade 10'. Therefore, the axial flow turbine 2 is configured so that the difference (d ₂ −d ₁ ) in the clearance 20 between the leading edge 12 side and the trailing edge 13 side of the moving blade 10 ′ is reduced during rated operation of the moving blade 10 ′. The clearance 20 between the tip surface 11 ′ and the annular wall surface 23 during operation of the flow turbine 2 can be made uniform with respect to the fluid flow direction. In the present embodiment, “uniformizing” the clearance 20 not only means that the clearance 20 is uniform, but also means that the clearance 20 is brought close to a uniform state.

Hereinafter, each embodiment of FIGS. 2 to 5 will be described in detail.
As shown in FIG. 2, in one embodiment, the tip surface 11 of the rotor blade 10 has an inclination angle θ ₁ larger than zero with respect to the annular wall surface 23 at least when the axial turbine 2 is stopped, It is an inclined surface in which the clearance 20 gradually increases from the front edge 12 side toward the rear edge 13 side. For example, when the annular wall surface 23 is formed parallel to the rotation axis O (see FIG. 1) of the rotor 5, the tip surface 11 of the rotor blade 10 is inclined more than zero with respect to the rotation axis O of the rotor 5. θ ₁ . The annular wall surface 23 may be inclined with respect to the rotation axis O of the rotor 5. In this case, the angle of the chip surface 11 with respect to the rotation axis O of the rotor 5 does not coincide with the inclination angle θ ₁ .

Even if the annular wall surface 23 is formed in such a manner that there is no unevenness or step and the cross section along the flow direction is linear in the range in which the tip surface 11 of the rotor blade 10 extends in the fluid flow direction. Good. Alternatively, although not shown, the annular wall surface 23 is formed to be curved with a minute curvature (for example, in a curved shape in which the center of curvature is located radially inward or radially outward from the annular wall surface 23). May be.
On the other hand, the chip surface 11 formed by the inclined surface may be formed so that the cross section along the fluid flow direction is linear as shown in the figure. Alternatively, although not shown, the chip surface 11 may be formed to be curved with a small curvature (for example, in a curved shape along the annular wall surface 23). That is, in the present embodiment, the inclined surface in the chip surface 11 includes a curved surface.

Thereby, a structure in which the clearance 20 between the tip surface 11 and the annular wall surface 23 on the trailing edge 13 side of the moving blade 10 is larger than that of the tip surface 11 on the leading edge 12 side of the moving blade 10 can be easily realized. For this reason, in the moving blade 10 ′ during operation of the axial turbine 2, the tip surface 11 ′ on the rear edge 13 side having a large deformation amount is closer to the annular wall surface 23 than the front edge 12 side. The loss can be effectively suppressed and the loss due to the leak flow in the clearance 20 can be effectively suppressed with a simple structure.
Further, the above structure can be realized without changing the stationary member 22 side on which the annular wall surface 23 is provided from the existing structure, and in that case, application to the existing axial turbine 2 is facilitated.

As shown in FIG. 3, in another embodiment, the annular wall surface 23 has an inclination angle θ ₂ larger than zero with respect to the tip surface 11 at least when the axial turbine 2 is stopped, and the leading edge 12. This is an inclined surface in which the clearance 20 gradually increases from the side toward the rear edge 13 side. For example, when the tip surface 11 of the rotor blade 10 is formed in parallel to the rotation axis O (see FIG. 1) of the rotor 5, the annular wall surface 23 is inclined more than zero with respect to the rotation axis O of the rotor 5. Has an angle θ ₂ . The tip surface 11 of the rotor blade 10 may be inclined with respect to the rotation axis O of the rotor 5. In this case, the angle of the annular wall surface 23 with respect to the rotation axis O of the rotor 5 does not coincide with the inclination angle θ ₂ .

The tip surface 11 of the moving blade 10 may be formed so that the cross section along the fluid flow direction is linear. Alternatively, although not shown, the chip surface 11 is formed to be curved with a small curvature (for example, in a curved shape in which the center of curvature is located radially inward or radially outward from the chip surface 11). May be.
On the other hand, as shown in the figure, the annular wall surface 23 formed by the inclined surface does not have irregularities or steps in the range in which the tip surface 11 of the moving blade 10 extends in the fluid flow direction, and follows the flow direction. Alternatively, the cross section may be formed in a straight line. Or although not shown in figure, the cyclic | annular wall surface 23 may be formed so that it may have a very small curvature (for example, the curve shape which follows the chip surface 11). That is, in this embodiment, the inclined surface in the annular wall surface 23 includes a curved surface.

Thereby, a structure in which the clearance 20 between the tip surface 11 and the annular wall surface 23 on the trailing edge 13 side of the moving blade 10 is larger than that of the tip surface 11 on the leading edge 12 side of the moving blade 10 can be easily realized. For this reason, in the moving blade 10 ′ during operation of the axial turbine 2, the tip surface 11 ′ on the rear edge 13 side having a large deformation amount is closer to the annular wall surface 23 than the front edge 12 side. The loss can be effectively suppressed and the loss due to the leak flow in the clearance 20 can be effectively suppressed with a simple structure.
Further, the above structure can be realized without changing the moving blade 10 from the existing structure. In this case, the moving blade 10 can be easily manufactured.

  As shown in FIG. 4, in another embodiment, the annular wall surface 23 has a position between the leading edge 12 and the trailing edge 13 of the rotor blade 10 in the axial direction of the rotor 5 (or the fluid flow direction). A step 23a is formed. In the annular wall surface 23, the annular wall surface 23 c closer to the trailing edge 13 than the step 23 a is positioned on the radially outer side of the axial turbine 2 as compared to the annular wall surface 23 b closer to the front edge 12 than the step 23 a. Further, the step 23 a is formed in an annular shape in the circumferential direction around the rotation axis O of the rotor 5. In the example shown in the figure, a step 23 a is provided at one location in the axial direction of the rotor 5. However, at least one step 23 a may be provided in the axial direction of the rotor 5. For example, a plurality of steps 23 a may be provided in the axial direction of the rotor 5. In that case, in each of the plurality of steps 23a, the annular wall surface 23c on the trailing edge 13 side with respect to the step 23a is more radially outward of the axial turbine 2 than the annular wall surface 23b on the front edge 12 side with respect to the step 23a. You may make it locate in. That is, the annular wall surface 23 may be stepped up from the front edge 12 side toward the rear edge 13 side.

According to the above configuration, the clearance 20 between the tip surface 11 on the trailing edge 13 side of the moving blade 10 and the annular wall surface 23 is larger than the tip surface 11 on the leading edge 12 side of the moving blade 10 due to the step 23 a of the annular wall surface 23. A large structure can be realized. For this reason, in the moving blade 10 ′ during operation of the axial turbine 2, the tip surface 11 ′ on the rear edge 13 side having a large deformation amount is closer to the annular wall surface 23 than the front edge 12 side. The loss can be effectively suppressed and the loss due to the leak flow in the clearance 20 can be effectively suppressed with a simple structure.
Further, the above-described structure can be realized only by the step 23a of the annular wall surface 23 without providing a minute inclination angle. In this case, the processing for providing the minute inclination angle becomes unnecessary, and the annular wall surface 23 can be processed. Easy.

  As shown in FIG. 5, in another embodiment, the annular wall surface 23 has a position between the leading edge 12 and the trailing edge 13 of the rotor blade 10 in the axial direction of the rotor 5 (or the fluid flow direction). A step 23a is formed. In the annular wall surface 23, the rear edge 13 side of the step 23 a is positioned on the radially outer side of the axial turbine 2 as compared to the front edge 12 side of the step 23 a. The annular wall surface 23 is formed with a recess 23d in the axial range including the position of the trailing edge 13 of the rotor blade 10. The annular wall surface 23 on the front edge 12 side forming the recess 23d has the step 23a. It is composed. The recess 23 d is formed in an annular shape along the circumferential direction around the rotation axis O of the rotor 5. Specifically, in the axial direction of the rotor 5 (or the fluid flow direction), the step 23a on the front edge side that forms the recess 23d is located between the front edge 12 and the rear edge 13, and the rear surface that forms the recess 23d. The step 23e on the edge side is located downstream of the rear edge 13. Further, the annular wall surface 23 between the step 23a on the front edge side and the step 23e on the rear edge side has a shape recessed outward in the radial direction. The annular wall surface 23b on the upstream side in the flow direction from the recess 23d and the annular wall surface 23f on the downstream side in the flow direction from the recess 23d may be formed on the same straight line in the cross section along the fluid flow direction. However, they may be formed on different straight lines.

According to the above configuration, the clearance 20 between the tip surface 11 on the trailing edge 13 side of the moving blade 10 and the annular wall surface 23 is smaller than the tip surface 11 on the leading edge 12 side of the moving blade 10 by the recess 23 d of the annular wall surface 23. A large structure can be realized. For this reason, in the moving blade 10 ′ during operation of the axial turbine 2, the tip surface 11 ′ on the rear edge 13 side having a large deformation amount is closer to the annular wall surface 23 than the front edge 12 side. The loss can be effectively suppressed and the loss due to the leak flow in the clearance 20 can be effectively suppressed with a simple structure.
Further, the above structure can be realized only by the concave portion 23d of the annular wall surface 23 without providing a minute inclination angle. In this case, processing for providing a minute inclination angle becomes unnecessary, and the annular wall surface 23 can be processed. Easy.

  As described above, according to the embodiment of the present invention, when the moving blade 10 is deformed by heat or centrifugal force during the operation of the axial turbine 2, the leading edge 12 has a larger deformation amount on the rear edge 13 side. Since it is closer to the annular wall surface 23 than on the side, the clearance 20 on the rear edge 13 side, which has been set in advance, is narrowed, and the clearance 20 during operation can be made uniform in the fluid flow direction. Thereby, the loss resulting from the leak flow in the clearance 20 can be effectively suppressed with a simple structure.

The present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.
In the above embodiment, as an example, the supercharger 1 has been described as the application destination of the axial turbine 2 according to this embodiment, but the application destination of the axial turbine 2 according to this embodiment is limited to the supercharger 1. It is not a thing. For example, the rotary turbine 2 according to the embodiment can be applied to other rotating machines such as a turbine such as a gas turbine or a steam turbine.

For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
On the other hand, the expression “comprising”, “including”, or “having” one constituent element is not an exclusive expression that excludes the presence of the other constituent elements.

DESCRIPTION OF SYMBOLS 1 Supercharger 2 Axial flow turbine 3 Compressor 4 Bearing stand 5 Rotor 10, 10 'Rotor blade 11, 11' Tip surface 12 Front edge 13 Rear edge 20 Clearance 21 Turbine casing 22 Stationary member 23 Annular wall 23a Step 23d Recess 26 Support member 27 Inlet passage 28 Axial passage 29 Outlet passage 31 Compressor casing 32 Impeller 33 Hub 36 Diffuser 37 Air inlet 38 Outlet scroll O Rotor rotation axis d ₁ , d ₂ Tip clearance θ ₁ , θ ₂ Inclination angle

Claims (7)

A rotor having a plurality of rotor blades on the outer periphery;
A stationary member provided on the outer peripheral side of the rotor and having an annular wall surface facing the tip surface of the rotor blade,
The axial flow turbine characterized in that, when the axial flow turbine is stopped, a clearance between the tip surface and the annular wall surface on the trailing edge side of the moving blade is larger than that on the leading edge side of the moving blade.   2. The axial turbine according to claim 1, wherein a difference between the clearance on the leading edge side and the clearance on the trailing edge side during rated operation of the axial turbine is smaller than when the axial turbine is stopped.   The tip surface has an inclination angle larger than zero with respect to the annular wall surface facing the tip surface at least when the axial turbine is stopped, and the tip surface moves from the leading edge side toward the trailing edge side. The axial-flow turbine according to claim 1, wherein the clearance is an inclined surface with gradually increasing clearance.   The annular wall surface has an inclination angle larger than zero with respect to the tip surface facing the annular wall surface at least when the axial flow turbine is stopped, and from the leading edge side of the moving blade toward the trailing edge side. The axial flow turbine according to any one of claims 1 to 3, wherein the clearance is an inclined surface with a gradually increasing clearance. In the annular wall surface, a step is formed at a position between the leading edge and the trailing edge of the rotor blade in the axial direction of the rotor,
5. The annular wall surface according to claim 1, wherein a rear edge side of the annular flow wall is positioned on a radially outer side of the axial turbine as compared with a front edge side of the step. An axial flow turbine described in 1. A concave portion is formed in the annular wall surface in an axial range including a position of a trailing edge of the moving blade,
The axial flow turbine according to claim 5, wherein a wall surface on a front edge side forming the concave portion constitutes the step. An axial turbine according to any one of claims 1 to 6, configured to be driven by exhaust gas from an internal combustion engine;
And a compressor driven by the axial turbine and configured to compress intake air supplied to the internal combustion engine.

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