Impeller and centrifugal fluid machine using the same

Abstract

This impeller comprises: a hub; a plurality of main blades provided on a peripheral surface of the hub; and intermediate blades provided between the main blades adjacent to each other on the peripheral surface of the hub, the intermediate blades having leading edges on the downstream side of the leading edges of the main blades. Each of the main blades is configured such that the blade thickness on the leading edge side is the largest and gradually decreases from the position where the blade thickness is the largest toward the trailing edge side. The main blades and the intermediate blades are provided with filets at connection parts with the hub and a shroud. Each of the main blades is configured such that the filet size on the leading edge side is the largest and the filet size on the trailing edge side is smaller than the filet size on the leading edge side.

Description

Impeller and centrifugal fluid machine using the same

[0001] The present invention relates to an impeller and a centrifugal fluid machine using the same, and is particularly suitable for centrifugal impellers operated at high peripheral speeds.

[0002] In a process centrifugal compressor, which is an example of a centrifugal fluid machine, sucked working fluid is discharged after passing through a flow path provided in a single-stage or multi-stage impeller. In the process where the working fluid passes through the flow path of the impeller, rotational energy of the impeller is imparted to the working fluid, and the working fluid is compressed.

[0003] A centrifugal compressor compresses fluid by rotation of an impeller provided with a plurality of radial blades, and is required to have increased capacity and higher pressure ratio. Since the capacity is defined by the minimum flow passage area (throat area) formed at the inlet of the impeller, the capacity can be increased by reducing the number of blades to expand the throat area. In contrast, the pressure ratio can be increased by increasing the number of blades at the outlet of the impeller.

[0004] Particularly when an increase in capacity is required, blades of the impeller are constituted by main blades (long blades) and intermediate blades (splitter blades), and by arranging an intermediate blade shorter than the main blades on the downstream side of the leading edge of the main blade between adjacent main blades, the number of blades at the inlet of the impeller is reduced to expand the throat area, thereby increasing the capacity, and the number of blades at the outlet of the impeller is increased to improve the pressure ratio. A prior art of this type is described in Japanese Patent Laid-Open No. 2019-152166 (Patent Document 1).

[0005] Japanese Patent Laid-Open No. 2019-152166

[0006] The technology disclosed in the above Patent Document 1 does not take into consideration achieving a high peripheral speed by rotating the impeller at a high speed. That is, if the impeller is rotated at a high speed to achieve a high peripheral speed, it becomes possible to impart the same amount of fluid energy as conventional impellers with an impeller having a smaller outer diameter than conventional ones. However, when the peripheral speed of the impeller is increased, the stress acting on the impeller increases, resulting in a problem that further increase in peripheral speed cannot be achieved.

[0007] The objective of the present invention is to obtain an impeller capable of achieving high peripheral speed and a centrifugal fluid machine using the same.

[0008] To achieve the above objective, the present invention provides an impeller comprising a hub, a plurality of main blades provided on the circumferential surface of the hub, and intermediate blades provided between adjacent main blades on the circumferential surface of the hub, the intermediate blades having their leading edges downstream of the leading edges of the main blades, wherein the main blades are configured to have the greatest blade thickness at the leading edge side, and the blade thickness gradually decreases toward the trailing edge side from the position where the blade thickness is greatest.

[0009] Another feature of the present invention is an impeller comprising a hub, a plurality of main blades provided on the circumferential surface of the hub, intermediate blades provided between adjacent main blades on the circumferential surface of the hub and having their leading edges downstream of the leading edges of the main blades, and a shroud provided to sandwich the main blades and the intermediate blades together with the hub, wherein the main blades and the intermediate blades are provided with fillets at the connection points with the hub and the shroud, and the main blades are configured such that the fillet size is largest on the leading edge side and the fillet size on the trailing edge side is smaller than the fillet size on the leading edge side.

[0010] Another feature of the present invention is a centrifugal fluid machine comprising a rotating shaft and a centrifugal impeller attached to the rotating shaft, wherein the impeller is one of the impellers described above.

[0011] According to the present invention, it is possible to obtain an impeller capable of achieving high peripheral speed and a centrifugal fluid machine using the same.

[0012] This is a longitudinal cross-sectional view of a single-shaft multi-stage centrifugal compressor according to Embodiment 1 of the present invention. This is a partial cross-sectional view of one of the impellers of the single-shaft multi-stage centrifugal compressor shown in Figure 1, viewed from the meridional direction. This is a front view of the impeller shown in Figure 2, with the shroud removed. This is a partial cross-sectional view of one of the impellers shown in Figure 1. This is an enlarged view of a part of the impeller shown in Figure 3. This is a line diagram illustrating the blade thickness of the main blades and intermediate blades of the impeller. This is a diagram illustrating the fillets provided on the main blades and intermediate blades of the impeller, illustrating the configuration of the leading edge of one main blade and one intermediate blade. This is a cross-sectional view taken along the line A-A in Figure 5. This is a cross-sectional view taken along the line B-B in Figure 5. This is a cross-sectional view taken along the line C-C in Figure 5.

[0013] By increasing the rotational speed of the impeller, the amount of fluid energy per unit weight (head) can be increased. For example, in a multi-stage centrifugal compressor, the number of impeller stages required to satisfy the necessary head can be reduced. Reducing the number of impeller stages reduces energy loss, which in turn improves the efficiency of the compressor.

[0014] Furthermore, by increasing the peripheral speed by rotating the impeller at high speed, it becomes possible to supply the same amount of fluid energy with an impeller that has a smaller outer diameter than conventional impellers. In order to increase the peripheral speed by rotating the impeller at high speed, it is necessary to improve the limit peripheral speed of the impeller. By improving the limit peripheral speed of the impeller, it becomes possible to reduce the number of stages in the impeller and reduce the outer diameter of the impeller, which can lead to miniaturization and increased efficiency of process centrifugal compressors, for example.

[0015] However, it was found that increasing the rotational speed of the impeller generates large local stresses on the impeller blades, and that suppressing the generation of local stresses is necessary to further increase the rotational speed.

[0016] The following describes specific embodiments of the impeller of the present invention, which can suppress the generation of local stress and achieve high peripheral speed, and a centrifugal fluid machine using the same, based on the drawings. In each figure, parts denoted by the same reference numerals indicate the same or corresponding parts.

[0017] Embodiment 1 of the present invention will be described using Figures 1 to 10. First, Figure 1 will be used to describe the single-shaft multi-stage centrifugal compressor as a centrifugal fluid machine of the present invention. Figure 1 is a longitudinal cross-sectional view of the single-shaft multi-stage centrifugal compressor according to Embodiment 1 of the present invention.

[0018] Figure 1 shows a single-shaft multi-stage centrifugal compressor 100, which is constructed by arranging compressor stages, each consisting of multiple impellers 1A to 1E, diffusers 2A to 2E, return bends (return passages) 3A to 3D, and guide vanes 4A to 4D, in the axial direction. Multiple impellers 1A to 1E are mounted on the rotating shaft 7 in an axial stack, and both ends of the rotating shaft 7 are rotatably supported by bearings 9.

[0019] Diffusers 2A to 2E are provided on the radially outward side, downstream of each impeller 1A to 1E. Diffusers 2A to 2D of each stage except the final stage are connected to return bends 3A to 3D that guide the working fluid to the next stage, and guide vanes 4A to 4D are formed downstream of the return bends 3A to 3D to guide the working fluid radially inward. Downstream of the diffuser 2E of the final stage, a scroll 5 is provided to collect the working fluid discharged from the final stage impeller and discharge it from a discharge pipe (not shown).

[0020] The diffusers 2A to 2E, return bends 3A to 3D, guide vanes 4A to 4D, and scroll 5 are stationary components formed in the compressor casing 6. The working fluid drawn in from the suction port 8 is pressurized by the first stage impeller 1A and diffuser 2A, then its flow direction is changed from radially outward to radially inward by the return bend 3A and guide vanes 4A, and it is guided to the second stage impeller 1B. This flow is repeated at each stage, gradually increasing the pressure, and after passing through the final stage diffuser 2E, it passes through the scroll 5 and is guided to the discharge piping.

[0021] Figure 2 is a partial cross-sectional view of one of the impellers of the single-shaft multi-stage centrifugal compressor shown in Figure 1, viewed from the meridional direction, and Figure 3 is a front view of the impeller shown in Figure 2 with the shroud removed. The impellers 1A to 1E shown in Figure 1 will be collectively referred to as impeller 1.

[0022] The impeller 1 shown in Figure 2 consists of a hub 11, a shroud 12, and blades 13 (main blades 13a, intermediate blades 13b) provided between the hub 11 and the shroud 12.

[0023] The hub 11 is formed in a flange shape and press-fitted onto the rotating shaft 7 (see Figure 1) by means of shrink-fitting or the like, and rotates integrally with the rotating shaft 7. As shown in Figure 3, main blades (long blades) 13a and intermediate blades (short blades) 13b, which are shorter in length than the main blades 13a, are arranged alternately in the circumferential direction on the circumferential surface of the hub 11. Furthermore, as shown in Figure 2, the shroud 12 is provided so as to sandwich the main blades 13a and intermediate blades 13b with the hub 11. 14 shown in Figure 3 is the throat position where the flow path area is smallest in the flow path formed between adjacent main blades 13a.

[0024] The leading edge 13ba of the intermediate blade 13b is positioned downstream of the throat position 14 shown in Figure 3, and the trailing edge 13bb of the intermediate blade 13b is positioned at the same location as the outer circumferential surface of the hub 11, similar to the trailing edge 13ab of the main blade 13a. Note that 13aa is the leading edge of the main blade 13a. Furthermore, 15 is a fillet (corner radius) provided at the connection between the main blade 13a and the hub 11 or shroud 12, and 16 is a fillet (corner radius) provided at the connection between the intermediate blade 13b and the hub 11 or shroud 12. These fillets 15 and 16 will be described in detail later.

[0025] Figure 4 is a partial cross-sectional view (partial longitudinal cross-section) of the impeller shown in Figure 1, and is a cross-sectional view obtained by cutting the impeller 1 through an axial plane passing through the center of the rotation axis 7. In Figure 4, 13aa indicates the vicinity of the leading edge of one main blade 13a. Also, the blade near the radial midpoint in Figure 4 is another main blade 13a adjacent to the main blade 13a located at the innermost diameter in Figure 4, and shows a cross-section of this other main blade 13a at approximately the midpoint in the longitudinal direction. The outermost blade in Figure 4 shows a cross-section of the intermediate blade 13b at approximately the midpoint in the longitudinal direction.

[0026] In conventional impellers, it has been found that increasing the impeller's rotational speed generates large local stresses in the impeller blades. Specifically, as shown in Figure 4, large local stresses S are generated on the pressure side and the negative pressure side, respectively, at the connection point between the leading edge of the main blade 13a and the hub 11, and at the connection point between the main blade 13a and the shroud 12. For this reason, it has been difficult to further increase the rotational speed of conventional impellers.

[0027] Therefore, in this embodiment, in order to suppress the generation of local stress even when further speeds are increased, the configuration described below is adopted. Below, the configuration of the impeller of the present invention, which can suppress the generation of local stress and achieve high peripheral speed, will be described with reference to Figures 5 to 10.

[0028] <Configuration of blade thickness of main and intermediate blades> Figure 5 is an enlarged view of a part of the impeller shown in Figure 3, and Figure 6 is a diagram illustrating the blade thickness of the main and intermediate blades of the impeller. In Figure 5, 17 is the camber line of the main blade 13a, and 18 is the camber line of the intermediate blade 13b. The camber line is a line (blade centerline) that connects points at equal distances from the upper surface (pressure surface) and lower surface (negative pressure surface) of the blade. The camber line 17 is the line that connects the leading edge 13aa, which is the suction side end of the main blade 13a, and the trailing edge 13ab, which is the discharge side end, and the camber line 18 is the line that connects the leading edge 13ba, which is the suction side end of the intermediate blade 13b, and the trailing edge 13bb, which is the discharge side end. Therefore, the camber line 18 of the intermediate blade 13b is shorter than the camber line 17 of the main blade 13a.

[0029] In this embodiment, the main blade 13a has a different blade thickness distribution relative to the camber line 17. Specifically, as shown by curve a in Figure 6, the blade thickness is greatest at the leading edge 13aa of the main blade 13a. In other words, the blade thickness gradually or monotonically increases from the leading edge (tip) of the main blade 13a, and then gradually or monotonically decreases from the point of maximum thickness (maximum thickness position) towards the trailing edge 13ab. Furthermore, the position where the blade thickness of the main blade 13a reaches its maximum value is located closer to the leading edge than 10% of the total length of the camber line.

[0030] Furthermore, as shown in Figure 6, the curve showing the blade thickness distribution relative to the camber line of the main blade 13a is an upward-convex curve or approximately straight line from the tip position of the leading edge 13aa until the blade thickness reaches its maximum value, and from near the position where the blade thickness reaches its maximum value toward the trailing edge, the curve showing the blade thickness distribution becomes downward-convex.

[0031] Furthermore, a configuration in which the blade thickness gradually or monotonically decreases from near the position of the maximum blade thickness toward the trailing edge refers to a configuration in which the blade thickness gradually or monotonically decreases from the leading edge to at least 50% of the length of the camber line 17 of the main blade 13a toward the trailing edge, or toward the trailing edge 13ab.

[0032] On the other hand, with respect to the intermediate blade 13b, the blade thickness distribution relative to the camber line 18 is as shown by curve b in Figure 6. At the leading edge of the blade, the blade thickness increases monotonically from the front end (tip), and from the point where the blade thickness reaches its maximum value to the trailing edge 13bb, the blade thickness does not increase or decrease, but remains constant. In other words, the blade thickness of the intermediate blade 13b is configured to be approximately constant except at the leading edge.

[0033] Furthermore, the thickness (maximum thickness) of the intermediate blade 13b is set to be 60% or less of the maximum thickness of the main blade 13a. Preferably, the maximum thickness of the intermediate blade 13b is in the range of 50 to 60% of the maximum thickness of the main blade 13a. Similarly, with respect to the main blade 13a, the blade thickness at the trailing edge of the main blade is 60% or less of the maximum thickness of the main blade, preferably in the range of 50 to 60%.

[0034] At the connection point between the leading edge of the main blade 13a and the hub 11, and the connection point with the shroud 12, large local stresses S are generated at high peripheral speeds due to the effects of centrifugal force. However, in this embodiment, as described above, regarding the blade thickness distribution with respect to the camber line of the main blade 13a, the blade thickness gradually or monotonically increases from the leading edge 13aa of the blade, reaches a maximum value, and then gradually or monotonically decreases toward the trailing edge 13ab of the blade. In this way, the blade thickness is made largest at the leading edge 13aa side of the main blade 13aa where local stress is large, and after the blade thickness reaches a maximum value, it is configured to gradually or monotonically decrease toward the trailing edge 13ab side.

[0035] Therefore, since the blade thickness is configured to correspond to the local stress generated in the main blade 13a when the impeller 1 is increased in peripheral speed, local stress can be suppressed even when the impeller is increased in peripheral speed, and the peripheral speed of the impeller can be further increased.

[0036] Furthermore, the position where the blade thickness of the main blade 13a reaches its maximum value is located closer to the leading edge than 10% of the total length of the camber line. The curve showing the blade thickness distribution becomes convex downwards from near the position where the blade thickness is maximum toward the trailing edge, while keeping the blade thickness at the trailing edge of the main blade to 60% or less of the maximum blade thickness. Consequently, the weight of the main blade 13a can be reduced, and the resulting local stress can be further minimized.

[0037] With respect to the intermediate blade 13b, even when the impeller 1 is increased in peripheral speed, the effect of the centrifugal force acting on it is small, so the blade thickness is kept approximately constant from the leading edge 13ba to the trailing edge 13bb. Furthermore, since the thickness of the intermediate blade 13b is set to be 60% or less of the maximum thickness of the main blade 13a, the manufacturing of the impeller can be made easier, and the weight of the intermediate blade 13b can also be reduced. Therefore, from this point of view as well, it is possible to further reduce the local stress generated in the impeller. Thus, according to this embodiment, since the local stress generated in the impeller can be suppressed, it is possible to further increase the peripheral speed of the impeller.

[0038] <Configuration of Fillet Size of Main and Intermediate Blades> In this embodiment, as shown in Figures 3 and 5, each main blade 13a and each intermediate blade 13b are provided with fillets (corner radius sections) 15 and 16 at the connection points with the hub 11 and shroud 12. The specific configuration of these fillets 15 and 16 will be explained using Figures 7 to 10. Figure 7 is a diagram illustrating the fillets provided on the main and intermediate blades of the impeller, illustrating the configuration of the leading edge of one main blade and one intermediate blade. Figure 8 is a cross-sectional view taken along the line A-A in Figure 5, Figure 9 is a cross-sectional view taken along the line B-B in Figure 5, and Figure 10 is a cross-sectional view taken along the line C-C in Figure 5. Note that a fillet is sometimes called a corner radius section because the corner of the connection point is rounded.

[0039] As shown in Figure 7, fillets 15 are provided at the connection points between the main blade 13a and the hub 11 and shroud 12, and fillets 16 are also provided at the connection points between the intermediate blade 13b and the hub 11 and shroud 12. Furthermore, as shown in Figures 3 and 5, fillets 15 and 16 are also provided on the pressure side and negative pressure side of the main blade 13a and the intermediate blade 13b, respectively. The fillets 15 and 16 are provided on both the main blade 13a and the intermediate blade 13b from their leading edges 13aa and 13ba to their trailing edges 13ab and 13bb.

[0040] Furthermore, as shown in Figures 5 and 8 to 10, in the A-A section of Figure 5, which is the leading edge side of the main blade 13a, the size of the fillet 15 (e.g., radius R1) is largest, as shown in Figure 8. The size of the fillet refers to the size of the radius R of the fillet, but the fillet is not limited to a circular arc, and also includes curved shapes other than circular arcs that have been rounded. The larger the fillet size, the more the local stress generated at the connection between the main blade 13a and the hub 11 or shroud 12 can be reduced.

[0041] In the B-B cross-section shown in Fig. 5, which is approximately the center position of the camber line of the main blade 13a, as shown in Fig. 9, the size of the fillet 15 is smaller than that on the leading edge 13aa side (for example, the radius R2). In addition, in the C-C cross-section of Fig. 5 on the trailing edge 13ab side of the main blade 13a, as shown in Fig. 10, the size of the fillet 15 is even smaller than the approximate center position shown in Fig. 9 (for example, the radius R3).

[0042] As described above, in this embodiment, the fillet size is changed according to the magnitude of local stress generated at the connection between the main blade 13a and the hub 11 or the shroud 12. That is, in consideration of the generated local stress, the size of the fillet (for example, the radius R of the fillet) is changed in accordance with the position of the camber line, which is the blade center line connecting the leading edge 13aa, which is the suction side end of the main blade 13a, and the trailing edge 13ab, which is the discharge side end of the main blade 13a.

[0043] As described with reference to Fig. 4, at the leading edge 13aa of the main blade 13a, the local stress S at the connection between the main blade 13a and the hub 11 or the shroud 12 is particularly large due to the influence of the applied centrifugal force and the like. Therefore, in this embodiment, as shown in Fig. 7, the size of the fillet 15 at the leading edge 13aa of the main blade 13a is configured to be the largest, and the size of the fillet on the trailing edge 13ab side of the main blade 13a is configured to be smaller than the size of the fillet on the leading edge 13aa side.

[0044] In addition, the size of the fillet (the radius R of the fillet) relative to the camber line 17 of the main blade 13a is configured to gradually or monotonically decrease from the leading edge 13aa toward the trailing edge 13ab of the blade.

[0045] It should be noted that the configuration in which the fillet size gradually or monotonically decreases from the leading edge 13aa toward the trailing edge 13ab of the blade refers to a configuration in which the fillet size gradually or monotonically decreases from the leading edge to at least a position of 50% of the length of the camber line 17 of the main blade 13a toward the trailing edge, or to the position of the trailing edge 13ab.

[0046] In the present embodiment, the size (radius R3) of the fillet 15 at the trailing edge 13ab of the main blade 13a is 60% or less, preferably in the range of 50 to 60%, of the size (radius R1) of the fillet 15 on the leading edge 13aa side where the fillet size is maximum.

[0047] Further, as shown in FIGS. 3 and 5, the size (for example, radius Rm) of the fillet 16 in the intermediate blade 13b is formed substantially constant from the leading edge 13ba to the trailing edge 13bb, and furthermore, the size of the fillet of the intermediate blade 13b is formed smaller than the fillet size (radius R1) on the leading edge 13aa side of the main blade 13a. For example, the size (radius Rm) of the fillet 16 of the intermediate blade 13b is 60% or less, preferably in the range of 50 to 60%, of the size (radius R1) of the fillet 15 on the leading edge 13aa side where the fillet size of the main blade 13a is maximum.

[0048] As described above, when the impeller 1 is operated at a high circumferential speed, large local stress S occurs at the connection portion between the leading edge of the main blade 13a and the hub 11, and the connection portion between the leading edge of the main blade 13a and the shroud 12, due to the influence of centrifugal force and the like. Therefore, in the present embodiment, as described above, the size (for example, radius R) of the fillet 15 at the connection portion between the leading edge of the main blade 13a and the hub 11, and the connection portion between the leading edge of the main blade 13a and the shroud 12 is configured to be largest at the leading edge 13aa of the main blade 13a with respect to the camber line of the main blade 13a. Further, the size (radius R) of the fillet with respect to the camber line 17 of the main blade 13a is configured to gradually or monotonically decrease from the leading edge 13aa toward the trailing edge 13ab.

[0049] As described above, in the present embodiment, the fillet size is configured to correspond to the local stress generated in the main blade 13a when the impeller 1 is operated at a high circumferential speed. Further, the fillet size at the leading edge 13aa of the main blade 13a where the local stress is maximum is configured to be the largest. Therefore, even when the impeller 1 is operated at a high circumferential speed, the local stress generated in the main blade 13a can be suppressed, which has the effect of enabling further increase in the circumferential speed of the impeller.

[0050] With respect to the intermediate blade 13b, even when the impeller 1 is driven at a high speed, the effect of the centrifugal force acting on it is small. Therefore, the fillet size is kept approximately constant from the leading edge 13ba to the trailing edge 13bb, which makes it easy to manufacture the impeller.

[0051] Furthermore, the size of the fillet on the main blade 13a relative to the camber line 17 is configured to gradually or monotonically decrease from the leading edge 13aa to the trailing edge 13ab, and the size of the fillet 15 at the trailing edge 13ab of the main blade 13a is configured to be 60% or less of the size of the fillet 15 on the leading edge 13aa side. Also, the size of the fillet on the intermediate blade 13b is formed to be smaller than the size of the fillet on the leading edge 13aa side of the main blade 13a, and the size of the fillet 16 on the intermediate blade 13b is configured to be 60% or less of the size of the fillet 15 on the leading edge 13aa side of the main blade 13a. As a result, it is possible to configure a larger flow area between the blades in the impeller 1.

[0052] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, in the above embodiments, one intermediate blade 13b is provided between adjacent main blades 13a, but the present invention can be similarly applied to a system in which multiple intermediate blades are provided between adjacent main blades 13a. Furthermore, although the application of the present invention to a single-shaft multi-stage centrifugal compressor having a centrifugal impeller has been described, it is not limited to single-shaft multi-stage centrifugal compressors, but can be similarly applied to single-stage centrifugal compressors, centrifugal pumps equipped with centrifugal impellers, or turbo expanders. Moreover, it is not limited to centrifugal impellers, but can also be applied to mixed-flow turbo impellers. In addition, in cases where a material with relatively low strength is used as the material constituting the impeller, large local stresses are generated even at relatively low peripheral speeds of the impeller, so similar effects can be obtained by applying the present invention to such an impeller.

[0053] Furthermore, in the impeller of the above-described embodiment, an example was described in which the blade thickness of the main blade is greatest at the leading edge and gradually decreases towards the trailing edge, and the fillet size of the main blade is larger at the leading edge and smaller at the trailing edge, simultaneously having both feature 1 and feature 2. However, a configuration having either feature 1 or 2 is also acceptable. Moreover, the above-described embodiment is described in detail for the purpose of explaining the present invention in an easy-to-understand manner, and is not necessarily limited to having all the configurations described.

[0054] 1, 1A-1E...Impeller, 2A-2E...Diffuser, 3A-3D...Return bend, 4A-4D...Guide vanes, 5...Scroll, 6...Compressor casing, 7...Rotating shaft, 8...Inlet, 9...Bearing, 11...Hub, 12...Shroud, 13...Vandals, 13a...Main vane, 13aa...Leading edge, 13ab...Trailing edge, 13b...Intermediate vane, 13ba...Leading edge, 13bb...Trailing edge, 14...Throat position, 15, 16...Fillet, 17, 18...Camber line, 100...Single-shaft multi-stage centrifugal compressor, a...Curve showing the blade thickness distribution of the main vane, b...Curve showing the blade thickness distribution of the intermediate vane, S...Local stress, R, R1, R2, R3, Rm...Fillet size.

Claims

1. An impeller comprising a hub, a plurality of main blades provided on the circumferential surface of the hub, and intermediate blades provided between adjacent main blades on the circumferential surface of the hub, wherein the main blades are configured to have the greatest blade thickness at the leading edge and gradually decrease toward the trailing edge from the position where the blade thickness is greatest.

2. An impeller according to claim 1, characterized in that the main blades are provided so as to extend from the inlet to the outlet of the impeller, and the intermediate blades are provided so as to extend from downstream of the leading edge of the main blades in the impeller to the outlet.

3. An impeller according to claim 1, characterized in that the leading edge of the intermediate blade is positioned downstream of the throat position formed between adjacent main blades.

4. An impeller according to claim 1, characterized in that the blade thickness distribution with respect to the camber line, which is the blade centerline connecting the leading edge and trailing edge of the main blade, is monotonically increasing from the leading edge, reaching a maximum value, and then monotonically decreasing toward the trailing edge.

5. An impeller according to claim 1, characterized in that the blade thickness distribution with respect to the camber line, which is the blade centerline connecting the leading edge and trailing edge of the intermediate blade, is configured to be substantially constant in thickness, except for the tip of the leading edge, and the camber line of the intermediate blade is shorter than the camber line, which is the blade centerline connecting the leading edge and trailing edge of the main blade.

6. An impeller according to claim 1, characterized in that the position where the blade thickness of the main blade reaches its maximum value is located on the leading edge side of 10% of the total length of the camber line, which is the blade centerline connecting the leading edge and trailing edge of the main blade.

7. An impeller according to claim 6, characterized in that the curve showing the blade thickness distribution with respect to the camber line of the main blade is an upwardly convex curve or substantially straight line from the tip position of the leading edge until the blade thickness reaches its maximum value, and the curve showing the blade thickness distribution becomes downwardly convex from near the position where the blade thickness reaches its maximum value toward the trailing edge.

8. An impeller according to claim 1, characterized in that the thickness of the intermediate blades is configured to be substantially constant except for the leading edge, and the thickness of the intermediate blades is configured to be 60% or less of the maximum thickness of the main blades.

9. An impeller comprising a hub, a plurality of main blades provided on the circumferential surface of the hub, intermediate blades provided between adjacent main blades on the circumferential surface of the hub and having their leading edges downstream of the leading edges of the main blades, and a shroud provided to sandwich the main blades and the intermediate blades together with the hub, wherein the main blades and the intermediate blades are provided with fillets at the connection points with the hub and the shroud, and the main blades are configured such that the fillet size is largest on the leading edge side and the fillet size on the trailing edge side is smaller than the fillet size on the leading edge side.

10. An impeller according to claim 9, characterized in that the size of the fillets of the main blades is configured to gradually decrease from the leading edge side to the trailing edge side.

11. An impeller according to claim 9, characterized in that the size of the fillet of the intermediate blade is substantially constant from the leading edge to the trailing edge.

12. An impeller according to claim 11, characterized in that the size of the fillet on the leading edge side of the main blade is larger than the size of the fillet of the intermediate blade.

13. An impeller according to claim 9, characterized in that the size of the fillet with respect to the camber line, which is the blade centerline connecting the leading edge and trailing edge of the main blade, is configured to gradually decrease from the leading edge to the trailing edge, and the size of the fillet at the trailing edge is configured to be 60% or less of the size of the fillet at the leading edge where the fillet size is maximum.

14. An impeller according to claim 9, characterized in that the size of the fillet of the intermediate blade is set to 60% or less of the maximum size of the fillet of the main blade.

15. A centrifugal fluid machine comprising a rotating shaft and a centrifugal impeller attached to the rotating shaft, characterized in that the impeller is the impeller described in any one of claims 1 to 14.

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