Impeller wheel and centrifugal compressor having impeller wheel

An impeller wheel according to an embodiment includes a hub, a plurality of long blades disposed on a circumferential surface of the hub, the plurality of long blades extending from an inlet portion to an outlet portion of fluid and a plurality of short blades each disposed on the circumferential surface of the hub, the plurality of short blades extending from a downstream side of leading edges of the plurality of the long blades to the outlet portion in a flow passage formed between adjacent long blades of the plurality of long blades.In the impeller wheel, an expression β2s,full<β2s,spl is satisfied, where β2s,full and β2s,spl are respectively blade angles on tip side edges of the plurality of long blades and the plurality of short blades at the outlet portion.

TECHNICAL FIELD

The present disclosure relates to an impeller wheel and a centrifugal compressor having the impeller wheel.

BACKGROUND ART

A centrifugal compressor used for industrial compressors, turbochargers, and the like compresses a fluid by rotating an impeller wheel radially installed a plurality of blades and is required to have a high efficiency, a high pressure ratio, and a large capacity. The capacity is defined by the minimum flow path area, which is a throat area, formed at an inlet of the impeller wheel, then it is possible to increase the flow capacity by reducing the number of blades and increasing the throat area. In contrast, it is possible to increase pressure ratio by increasing the number of the blades at an outlet portion of the impeller wheel.

In particular, when the large capacity is required, the throat area is expanded by decreasing the number of long blades, which are full blades, and the number of blades at the outlet portion of the impeller wheel is increased by disposing each of short blades, which are splitter blades, which are shorter than the full blades, between adjacent full blades on downstream of leading edges of the full blades, which increases the pressure ratio.

Generally, it is a basic design that the splitter blades are the same shape with the full blades. However, since the fluid flowing a fluid passage between the adjacent full blades does not necessarily flow along a surface of the full blades, a mismatch, which is a coincidence, between a direction which the fluid flows and a blade angle occurs at a leading edge of the splitter blades. In a case when a load at the leading edge of the splitter blades is increased, a strong pressure distribution occurs. When the coincidence is large, peeling occurs and causes deterioration in efficiency.

Further, a gap, which is a clearance, exists between the impeller wheel and a casing covering the impeller wheel. Since a flow leaking from the clearance, which is a tip leakage flow, becomes an unintentional direction flow, which is a secondary flow, a shear layer is generated for a flow flowing the fluid passage, which is a main flow, and reduces efficiency. A pressure drop is incurred by forming a region in which the fluid hardly flows, which is a blockage area. Furthermore, the tip leakage flow forms a leakage vortex that is a vortex of a swirling flow, which is a longitudinal vortex, which causes deterioration in efficiency.

In contrast, in Patent Document 1, the coincidence at the leading edge is reduced by making the blade angle at the leading edge of the splitter blades larger than the blade angle of the full blades at the same position in a meridian plane, which improves efficiency. Further, in Patent Document 2, the splitter blades are not disposed on a line connecting between the leading edges of the full blades and the middle of the throat, which improves efficiency.

CITATION LIST

Patent Literature

SUMMARY

According to the patent Documents 1 and 2, the cause of loss directly related to the leading edge of the splitter blades is solved. However, the present inventors analyzed the loss structure in detail and found that the following two mechanisms exist as a cause of efficiency reduction by disposing the splitter blades.

As shown inFIG. 14, a pressure gradient in which a pressure rises toward a flow direction A of a fluid is present in a flow passage103of an impeller wheel having full blades100and a splitter blade101. A tip leakage flow102does not withstand the pressure gradient and flows back toward the upstream side of the flow path103. The tip leakage flow flowing back further leaks through clearance between a next blade, which is one of the full blades100or the splitter blade101, and a casing and further flows back. The tip leakage flow102which repeatedly leaks next blades, which is a multiple tip leakage flow, accumulates losses every time the leakage is repeated.

As shown inFIG. 15, when a leading edge101aof a splitter blade101works, that is, when a load is applied to the leading edge101aof the splitter blade101, in a vicinity of the leading edge101a,a high-pressure region104is generated on a pressure surface101bof the splitter blade101and a low pressure region105is generated on a suction surface101c.The tip leakage flow102reaches near the leading edge101aof the splitter blade101, wraps around the leading edge101aof the splitter blade101so as to avoid the high-pressure region104, and further flows back progressively. Then a blockage area is formed, which reduces efficiency.

As far as the clearance exists and the blade works, it is difficult to avoid the tip leakage flow102. The configurations of Patent Documents 1 and 2 are not sufficient to decrease the two mechanisms. In contrast, according to the detailed analysis by present inventors, when a load to the splitter blade101is less than a load to the full blades100, although the tip leakage flow leaking from the clearance between the full blades100and the casing cannot be reduced, the tip leakage flow106leaking from the clearance between the splitter blade101and the casing is weakened and flows toward downstream of the flow passage103(in the direction of Arrow B) by the fluid107flowing the flow passage103. Then it has been found that the multiple tip leakage flow is suppressed and the mechanisms can be reduced.

In view of the above, an object of at least one embodiment of the present disclosure is to provide an impeller wheel which can improve efficiency of centrifugal compressors and a centrifugal compressor with the impeller wheel.

(1) An impeller wheel according to at least one embodiment of the present invention comprises:

a hub;

a plurality of long blades disposed on a circumferential surface of the hub, the plurality of long blades extending from an inlet portion to an outlet portion of fluid; and

a plurality of short blades each disposed on the circumferential surface of the hub, the plurality of short blades extending from a downstream side of leading edges of the plurality of the long blades to the outlet portion in a flow passage formed between adjacent long blades of the plurality of long blades,

wherein an expression β2s,full<β2s,splis satisfied, where β2s,fulland β2s,splare respectively blade angles on tip side edges of each long blade and each short blade at the outlet portion.

The larger the blade angle at the outlet portion, the smaller the total load, which is a total work amount, of the blades. According to the above configuration (1), the blade angle on the tip side edge of each short blade at the outlet portion is larger than the blade angle on the tip side edge of each long blade at the outlet portion, which can reduce the load of the short blade in comparison with the load of the long blade. As a result, although the tip leakage flow leaking across the tip side edge of each long blade may not be reduced, the tip leakage flow leaking across the tip side edge of each short blade is reduced. Since the tip leakage flow which does not cross the tip side edge of each short blade flows toward the downstream of the flow passage by the fluid flowing through the flow passage. Thus, the multiple tip leakage flow is suppressed so as to improve efficiency of the centrifugal compressor.

(2) In some embodiments, in the above configuration (1),

an expression β2s,spl−β2s,full≥5° is satisfied.

According to the above configuration (2), the difference between the blade angle on the tip side edge of each short blade at the outlet portion and the blade angle on the tip side edge of each long blade at the outlet portion is 5° or more. Since the load of each short blade can be reliably reduced in comparison with the load of each long blade, the multiple tip leakage flow is suppressed, which can improve efficiency of the centrifugal compressor.

(3) In some embodiments, in the above configuration (1),

an expression βs,full<βs,splis satisfied over an entire length of each short blade, where βs,fulland βs,splare respectively blade angles on the tip side edges of each long blade and the short blade at the same position when the impeller wheel is viewed from a meridian plane direction.

According to the above configuration (3), the multiple tip leakage flow is suppressed in the whole area of each short blade, which can further improve efficiency of the centrifugal compressor.

(4) In some embodiments, in any one of the above configurations (1) to (3),

an expression β2h,spl−β2h,full≥5° is satisfied where β2h,fulland β2h,splare respectively blade angles on hub side edges of each long blade and each short blade at the outlet portion.

The fluid flowing along a blade surface from the hub side toward the tip side leaks across the tip side edge, then the tip leakage flow is generated. Thus, the load of the short blades even on the hub side is reduced, which can further suppress the tip leakage flow. According to the above configuration (4), the difference between the blade angle on the tip side edge of each short blade at the outlet portion and the blade angle on the tip side edge of each long blade at the outlet portion is 5° or more. Since the load of each short blade on the hub side is reduced, the tip leakage flow can be further suppressed.

(5) In some embodiments, in the above configuration (4),

an expression βs,spl,m=mLE−βs,full,m=mLE≥5° is satisfied, where βs,full,m=mLEand βs,spl,m=mLEare respectively blade angles on the tip side edges of each long blades and each short blade at a position of a leading edge of the short blade when the impeller wheel is viewed from a meridian plane direction.

When a load is applied to the leading edge of each short blade, in a vicinity of the leading edge, a high pressure region having a high pressure is formed on a pressure surface side and a low pressure region having a low pressure is formed on a suction surface side. When the leak flow reaches the leading edge of each short blade, the tip leakage flow goes around the leading edge so as to avoid the high pressure region. Thus, the leakage is repeated. However, according to the above configuration (5), the difference between the blade angle on the tip side edge of each short blade and the blade angle of the on the tip side edge of each long blade at the leading edge of the short blade when the impeller wheel is viewed from the meridian plane direction, is 5° or more. Since the load on the leading edge of each short blade is reduced, it is difficult to form the high pressure region. As a result, the tip leakage flow which goes around the leading edge of each short blade is reduced. Since the tip leakage flow which reaches the leading edge of each short blade flows toward the downstream of the flow passage by the fluid flowing through the flow passage. Thus, the multiple tip leakage flow is suppressed so as to improve efficiency of the centrifugal compressor.

(6) In some embodiments, in the above configuration (4),

an expression βh,full,m=mLE>βh,spl,m=mLEis satisfied, where βh,full,m=mLEand βh,spl,m=mLEare respectively blade angles on the hub side edges of each long blade and each short blade at a position of a leading edge of the short blade when the impeller wheel is viewed from a meridian plane direction.

A secondary flow toward the suction surface of each short blade is generated in a boundary layer in the vicinity of the hub. The secondary flow reaches the suction surface and flows toward the tip side edge along the suction surface of each short blade, which increases the tip leakage flow. However, according to the above configuration (6), the blade angle on the hub side edge of each short blade is smaller than the blade angle on the hub side of each long blade at the position of the leading edge of the short blade when the impeller wheel is viewed from the meridian plane direction. Since a deviation between the blade angle on hub side edge at the leading edge of each short blade becomes small, the secondary flow flowing on the suction surface is reduced, which can suppress the tip leakage flow. As a result, it is possible to further improve efficiency of the centrifugal compressor.

(7) In some embodiments, in the above configuration (5),

the leading edge of each short blade includes a first portion and a second portion positioned radially outward from the first portion, and

an expression θ1>θ2is satisfied, where θ1is an acute angle between a direction in which the first portion extends and a rotational axis of the impeller wheel when viewed from a meridian plane, and θ2is an acute angle between a direction in which the second portion extends and the rotational axis of the impeller wheel when viewed from the meridian plane.

When the load on the leading edge of each short blade is reduced (in the above configuration (5)), the work amount of the short blades is decreased. However, according to the above configuration (7), since the leading edge of each short blade in the vicinity of the tip side edge is inclined toward the inlet portion side compared with the other parts, this portion becomes a region in which no work is performed, then the high pressure region is hard to be formed. On the other hand, since the work in the other portion is performs, it is possible to suppress the multiple tip leakage flow while suppressing the decrease in the work amount.

(8) A centrifugal compressor according to at least one embodiment of the present invention comprises the impeller wheel according to any one of the above (1) to (7).

According to the above configuration (8), the multiple tip leakage flow is suppressed, which can further improve efficiency of the centrifugal compressor.

According to the at least one embodiment of the present disclosure, the blade angle on the tip side edge of each short blade at the outlet portion is larger than the blade angle on the tip side edge of each long blade at the outlet portion, which can reduce the load of the short blade in comparison with the load of the long blade. As a result, although the tip leakage flow leaking across the tip side edge of each long blade may not be reduced, the tip leakage flow leaking across the tip side edge of each short blade is reduced. Since the tip leakage flow which does not cross the tip side edge of each short blade flows toward the downstream of the flow passage by the fluid flowing through the flow passage. Thus, the multiple tip leakage flow is suppressed so as to improve efficiency of the centrifugal compressor.

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 unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the following embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention unless particularly specified.

As shown inFIG. 1, an impeller wheel1according to Embodiment 1 includes a hub2, a plurality of full blades5, which is long blades, disposed on a circumferential surface of the hub2and extending from an inlet portion3to an outlet portion4of fluid, and a plurality of splitter blades7, which is short blades, each disposed on the circumferential surface of the hub2and extending from a downstream side of leading edges5aof the full blades5to the outlet portion4in a flow passage6formed between adjacent long blades5,5. In Embodiment 1, the impeller wheel1will be described as being provided in a centrifugal compressor of a turbocharger.

As shown inFIG. 2, the full blades5each have a leading edge5awhich is an edge on a side of the inlet portion3, a trailing edge5bwhich is an edge on a side of the outlet portion4, a hub side edge5cwhich is an edge on a side connecting with the hub2, and a tip side edge5dwhich is a side facing the hub side edge5c.The splitter blades7each have a leading edge7awhich is an edge on a side of the inlet portion3, a trailing edge7bwhich is an edge on a side of the outlet portion4, a hub side edge7cwhich is an edge on a side connecting with the hub2, and a tip side edge7dwhich is a side facing the hub side edge7c.The tip side edges5d,7deach face an inner wall surface of a casing not shown and each form a gap (hereinafter, referred to as “clearance”) with the inner wall surface of the casing.

FIG. 3is a diagram for developing the respective tip side edges5d,7dof the full blades5and the splitter blades7on a plane along a rotation axis line L of the impeller wheel1(seeFIG. 2) from the inlet portion3to the outlet portion4. An angle β formed between the rotation axis line L and each of the full blades5and splitter blades7is defined as a blade angle. The blade angle β takes a value of 0 to 90° at an arbitrary position in a meridian plane length direction of the full blades5and the splitter blades7and at an arbitrary position in a blade height direction (inFIG. 2, a direction from the hub side edges5c,7cto the tip side edges5d,7d).

InFIG. 3, a ratio m of a length from the leading edge5aof the full blades5in the meridian plane length direction to a meridian plane length of the full blades5is taken as the axis in the meridian plane length direction. Based on the definition m, the position of the leading edge5abecomes m=0, and the position of the trailing edges5b,7bbecome m=1. Further, when the values of m are the same, the positions when viewed from the meridian plane direction are the same.

In the following description, the position of the leading edge7aof the splitter blades7is represented by m=mLE.

FIG. 4shows a distribution of the blade angles of the hub side edges5c,7cand the tip side edges5d,7dof the full blades5and the splitter blades7from the leading edges5a,7ato the tailing edges5b,7b.A blade angle βh,splof the hub side edge7cof each splitter blade7has the same distribution of a blade angle βh,fullof the hub side edge5cof each full blade5in a range of mLE≤m≤1.

A blade angle βs,fullof the tip side edge5dof each full blade5decreases as m increases, and becomes the same as βh,fullwhen m=1. That is, an expression β2s,full=β2h,fullis satisfied where β2s,fulland β2h,fullare respectively the blade angles β on the tip side edge5dand the hub side edge5cwhen m=1.

A blade angle βs,splon the tip side edge7dof each splitter blade7becomes the same as βh,fullwhen m=mLE. That is, an expression βs,full,m=mLE=βh,full,m=mLEis satisfied where βs,full,m=mLEand βh,full,m=mLEare respectively the blade angles on the tip side edges5d,7dwhen m=mLE. On the other hand, an expression β2s,full<β2s,splis satisfied where β2s,splis the blade angle on the tip side edge7dat the outlet portion4, that is, m=1.

The larger the blade angles at the outlet portion4, the smaller the total load, which is a total work amount, of the blades. According to the above configuration of Embodiment 1, since the blade angle β2s,splon the tip side edge7dof each splitter blade7at the outlet portion4is larger than the blade angle β2s,fullon the tip side edge5dof each full blade5at the outlet portion4(β2s,full<β2s,spl), the load of the splitter blade7can be reduced in comparison with the load of the full blade5. Accordingly, as shown inFIG. 5, even if the tip leakage flow10leaking the clearance so as to across the tip side edge5dof each full blade5is not reduced, the tip leakage flow11leaking the clearance so as to across the tip side edge7dof each splitter blade7. Thus, the tip leakage flow11flows toward the downstream of the flow passage6by the fluid12flowing the downstream of the flow passage6, which suppresses the multiple tip leakage flow by that amount. As a result, it is possible to improve efficiency of the centrifugal compressor.

The effect of improving efficiency of the centrifugal compressor when β2s,full<β2s,splis confirmed by numerical calculation. The results are shown inFIG. 6.FIG. 6shows the relationship between the difference Δβ2s(=β2s,spl−β2s,full) between the blade angle β2s,splon the tip edge side7dof each splitter blade7and the blade angle β2s,fullon the tip edge side5dof each full blade5at the outlet portion4, and the efficiency of the centrifugal compressor. In case of ββ2s=0, the blade angle β2s,splon the tip side edge7dof each splitter blade7is the same as the blade angle β2s,fullon the tip side edge5dof each full blade5at the outlet portion4. In this case, under the condition of β2s,full<β2s,spl, the efficiency of the centrifugal compressor is improved in the range of Δβ2s≤17° as compared with the case of Δβ2s=0°. In order to reliably improve the efficiency of the centrifugal compressor as compared with the case of Δβ2s=0°, the range of Δβ2s≥5° is preferable. The range of 5°≤Δβ2s≤13 is more preferable.

Next, the impeller wheel according to Embodiment 2 will be described. The impeller wheel according to Embodiment 2 is different from Embodiment 1 in that the distribution of the blade angles along the meridian plane length of the tip side edge7dof each splitter blade7is modified. In Embodiment 2, the same constituent elements as those in Embodiment 1 are associated with the same reference numerals and not described again in detail.

As shown inFIG. 7, the blade angle βs,splon the tip side edge7dof each splitter blade7is larger than the blade angle βs,fullon the tip side edge5dof each full blade5in the range of mLE≤m≤1, that is, over the entire length of the splitter blade7(βs,full<βs,spl). The other configuration is the same as that of Embodiment 1.

In Embodiment 2, an expression βs,full<βs,splis satisfied over the entire length of each splitter blade7, thus the multiple tip leakage flow is securely suppressed in the whole area of the splitter blades7. Accordingly, it is possible to further improve efficiency of the centrifugal compressor in comparison with Embodiment 1.

Next, the impeller wheel according to Embodiment 3 will be described. The impeller wheel according to Embodiment 3 is different from each of Embodiments 1 and 2 in that the distribution of the blade angles along the meridian plane length of the tip side edge7cof each splitter blade7is modified. In the following description, Embodiment 3 will be described in an aspect in which the distribution of the blades along the meridian plane length of the hub side edge7cof each splitter blade7is modified with respect to the configuration of Embodiment 2. However, Embodiment 3 can be described in an aspect in that the distribution of the blade angles along the meridian plane length of the hub side edge7cof each splitter blade7is modified with respect to the configuration of Embodiment 1. In Embodiment 3, the same constituent elements as those in Embodiments 1 and 2 are associated with the same reference numerals and not described again in detail.

As shown inFIG. 8, an expression β2h,spl−β2h,full≥5° is satisfied at the outlet portion4, that is, m=1. The other configuration is the same as that of Embodiment 2.

The tip leakage flow is generated by the fluid flowing along the blade surface from the hub side toward the tip side and leaking from the clearance over the tip side edges5d,7d(seeFIG. 2). Thus, the load of the splitter blades7even on the hub side is reduced, which can further suppress the tip leakage flow. In Embodiment 3, the difference between the blade angle β2h,splon the tip side edge7dof each splitter blade7at the outlet portion4and the blade angle β2h,fullon the tip side edge5dof each full blade5at the outlet portion4is 5° or more. Since the load of the splitter blades7even on the hub side can be reduced, the tip leakage flow can be further suppressed in comparison with Embodiment 2.

Next, the impeller wheel according to Embodiment 4 will be described. The impeller wheel according to Embodiment 4 is different from Embodiment 3 in that the distribution of the blade angles along the meridian plane length of the tip side edge7dof each splitter blade7is modified. In Embodiment 4, the same constituent elements as those in Embodiments 1 to 3 are associated with the same reference numerals and not described again in detail.

As shown inFIG. 9, the blade angle βs,splon the tip side edge7dof each splitter blade7is larger than the blade angle βs,fullon the tip side edge5dof each full blade5in the range of mLE≤m≤1, that is, over the entire length of the splitter blade7(βs,full<βs,spl). Further, an expression βs,spl,m=mLE−βs,full,m=mLE≥5° is satisfied where βs,full,m=mLEand βs,spl,m=mLEare respectively the blade angles on the tip side edge5dof the full blade5and on the tip side edge7dof the splitter blade7at m=mLE. The other configuration is the same as that of Embodiment 3.

As shown inFIG. 10, when a load is applied to the leading edge7aof each splitter blade7, in a vicinity of the leading edge7a,a high pressure region20having a high pressure is formed on a side of a pressure surface7eand a low pressure region21having a low pressure is formed on a side of a suction surface7f.When the leak flow10reaches the leading edge7a,the tip leakage flow10goes around the leading edge7aso as to avoid the high pressure region20. Thus, the leakage is repeated. However, in Embodiment 4, the expression βs,spl,m=mLE−βs,full,m=mLE≥5° is satisfied where m=mLE. Since the load of the leading edge7ais reduced, it is difficult to form the high pressure region20. As a result, the tip leakage flow10which goes around the leading edge7ais reduced. The tip leakage flow13leaking from the clearance across the tip side edge7dof each splitter blade7is weakened and flows toward downstream of the flow passage6by the fluid12flowing the flow passage6. Then the multiple tip leakage flow is suppressed, which improves efficiency of the centrifugal compressor.

Next, the impeller wheel according to Embodiment 5 will be described. The impeller wheel according to Embodiment 5 is different from Embodiment 3 in that the distribution of the blade angles along the meridian plane length of the tip side edge7cof each splitter blade7is modified. In Embodiment 5, the same constituent elements as those in Embodiments 1 to 3 are associated with the same reference numerals and not described again in detail.

As shown inFIG. 11, an expression βh,full,m-mLE>βh,spl,m-mLEis satisfied where βh,full,m=mLEis the blade angle on the hub side edge5cof each full blade5and βh,spl,m=mLEis the blade angle on the hub side edge7cof each splitter blade7when m=mLE. The other configuration is the same as that of Embodiment 3.

In shown inFIG. 12, a secondary flow30toward the suction surface7fof each splitter blade7is generated in a boundary layer in the vicinity of the hub2. The secondary flow30reaches the suction surface7fand flows toward the tip side edge7d(in the direction of Arrow P) along the suction surface7f,which increases the tip leakage flow. However, in Embodiment 5, the expression βh,full,m=mLE>βh,spl,m=mLEis satisfied where m=mLE. Since a deviation between the blade angle on the hub side edge7cat the leading edge7aof each splitter blade7and a direction of the secondary flow30becomes small, the secondary flow30flowing on the suction surface7fis reduced, which can suppress the tip leakage flow. As a result, it is possible to further improve efficiency of the centrifugal compressor.

Next, the impeller wheel according to Embodiment 6 will be described. The impeller wheel according to Embodiment 6 is different from Embodiment 4 in that the shape of the leading edge7aof each splitter blade7is modified. In Embodiment 6, the same constituent elements as those in Embodiments 1 to 4 are associated with the same reference numerals and not described again in detail.

As shown inFIG. 13, the leading edge7aof each splitter blade7includes a first portion41and a second portion42positioned radially outward from the first portion41. an expression θ1>θ2is satisfied, where θ1is an acute angle between a direction D1in which the first portion41extends and a rotational axis L of the impeller wheel1when viewed from the meridian plane, and θ2is an acute angle between a direction D2in which the second portion42extends and the rotational axis L of the impeller wheel1when viewed from the meridian plane. The other configuration is the same as that of Embodiment 4.

If the load of the leading edge7aof each splitter blade7is reduced as in Embodiment 4, the work amount of the splitter blades7is decreased. However, according to Embodiment 6, since the leading edge7aof each splitter blade7in the vicinity of the tip side edge7dis inclined toward the inlet portion3side compared with the other parts, this portion becomes a region in which no work is performed, then the high pressure region (see the high pressure region20inFIG. 10) on the pressure surface7eof the splitter blade7is hard to be formed. On the other hand, since the work in the other portion is performs, it is possible to suppress the multiple tip leakage flow while suppressing the decrease in the work amount.