AU731051B2 - Blade for axial fluid machine - Google Patents

Description

Regulation 3.2

AUST'R'ALIA

Patents Act 1952 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: Actual Inventors: Address for Service: Invention Title: Kabushiki Kaisha Toshiba 72, Horikawa-Cho, Saiwai-Ku, Kawasaki-Shi, Kanagawa-Ken,

JAPAN

SASAKI, Takashi OKUNO, Kenichi KAWASAKI, Sakae DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Blade for Axial Fluid Machine The following statement is a full description of this invention, including the best method of performing it known to us: -1- BACKGROUND OF THE INVENTION The present invention relates to a blade for an axial fluid machine, and more specifically, to blades for an axial fluid machine for lowering a secondary flow loss which is caused when a blade cascade disposed along the axial direction of a rotational shaft passes through a working fluid to thereby improve the efficiency the blade cascade.

In general, although there are various types of prime movers such as an axial type, a radial flow type, a centrifugal type, a volume type and the like in a fluid machine, since a high output can be obtained from the axial type prime mover among them, it has been used to an ultra-large prime mover for an air compressor, a gas turbine, a steam turbine and the like which are used to air crafts and power generation plants.

As shown in FIG. 14, an axial fluid machine, for example, an air compressor is arranged such that it is accommodated in a casing 1, and compressor stages 4 each composed of the combination of a stationary blade 2 and a moving blade 3 are disposed along the axial direction of a rotational shaft 5. An atmosphere 7 sucked from an inlet 6 is compressed by the moving blade 3, high pressure air 2 passing a first compressor stage is then guided to the next compressor stage 4 through the moving blade 3, and the resulting high pressure air 8, which has been compressed to a predetermined pressure, is supplied to a gas turbine, not shown, from an outlet 9.

Further, as shown in FIG. 15, the axial fluid machine, for example, a steam turbine, is arranged such that it is accommodated in a casing 10 and has turbine stages 17 each composed of the combination of a stationary blade 13, which is clamped between a diaphragm outer ring 11 and a diaphragm inner ring 12, and a moving blade 14 planted on the disk 16 of a rotational shaft 15. The turbine stages 17 are disposed along the axial direction of a rotational shaft 15, steam 18 is expanded by the stationary blades 14 and the expanding force thereof is applied to the moving blades 14 so as to rotate them to thereby take out the rotational force thereof. Further, steam leaking at a time when the steam 18 passes through the turbine stages 17 is sealed by the labyrinths 19 planted on the diaphragm inner ring 12.

S"Incidentally, when the high pressure air 8 passes through the stationary blades 2 and the moving blade 3 in the axial air compressor or when the steam 18 passes through the moving blade and the stationary blades 13 in the axial steam turbine, various losses are caused, which result in a reason for lowering a blade cascade (train) 3 efficiency as a blade cascade loss.

The blade cascade loss includes a profile loss caused by the shape of a profile itself, a clearance leakage loss caused by the clearance between a blade tip and a flow passage wall, and an endwall loss caused by the existence of the inner peripheral surface and the outer peripheral wall of a flow passage. Among them, the endwall loss occupies a large weight in the reduction of the blade cascade efficiency.

The wall surface loss is mainly caused by a swirl resulting from a secondary flow generated in the blade cascade and the boundary layer exfoliation of the flow passage wall caused by the swirl. Typical examples of the swirl resulting from the secondary flow and the boundary layer exfoliation are common to the axial air compressor and the axial stem turbine, and it is known that the secondary flow is generated by the behavior of a main stream passing between the blade cascade (although air is a working fluid in the air compressor and stream is the working fluid in the stream turbine, both the working fluids are referred to as the main stream in the following description).

**.The main stream flows along a blade profile on the intermediate portion side of a blade in the lengthwise direction thereof when it passes between the blade cascade, whereas the secondary stream is a stream which flows in a 4 direction which intersects the main stream flowing on the side of an intermediate blade height portion on a blade tip side and a blade root side and is generated by a pressure difference between a blade and an adjacent blade.

When the main stream is made to the secondary stream, it is accompanied by a swirl which is generated as shown in FIG. 16 and the swirl will be grown in a short time. That is, when main streams 20a, 20b accompanied by inlet boundary layers 20a 20b, flow into the flow passages 22a, 22b between blades 21a, 21b, they collide against leading edges 23a, 23b and then generate swirls 24a, 24b.

The swirls 24a, 24b are divided into concave side horseshoe-shaped swirls 24a, 24b, and convex side horseshoe-shaped swirls 24a., 24b 2 When the convex side horseshoe-shaped swirls 24a 2 24b 2 flow along the convex sides 25a, 25b of the blades 21a, 21b which are made to a negative pressure, they flow to trailing edges 26a, 26b while gradually growing by rolling the boundary layers of the flow passages 22a, 22b.

the other hand, when the concave side horseshoe-shaped swirls 24a, 24b, flow toward the convex sides 25b, 25c of the adjacent blade 21b, 21c together with a secondary stream by the pressure difference between the concave sides 27a, 27b of the blades 21a, 21b which are made to a positive pressure and the convex sides 25b, 5 of the adjacent blades 21b, 21c which are made to a negative pressure, they are greatly grown by rolling the boundary layers of the flow passages 22a, 22b, and then the swirls 24a, and 24a 2 will join the convex side horseshoeshaped swirls 24a 2 24b 2 as flow passage swirls 24a 3 24b 3 As described above, it is referred to, as a secondary stream swirl as a whole, that the swirls 24a, 24b, which are generated by the collision of the main streams 20a, 20b against the leading edges 23a, 23b of the blades 21a, 21b, are divided into the concave side horseshoe-shaped swirls 24a 24b, and the convex side horseshoe-shaped swirls 24a 2 24b 2 that the concave side horseshoe-shaped swirls 24a 24b, are greatly grown and made to the flow passage swirls 24a 3 24b 3 and that the convex side horseshoe-shaped swirls 24a 2 24b 2 are greatly grown while they flow along the convex sides 25a, The secondary stream swirl exhibits the flow lines of the main streams 20a, 20b which pass in the vicinity of the wall surfaces of the flow passages 22a, 22b and is a main reason why the blade cascade efficiency of .e the blades 21a, 21b is lowered. Accordingly, it is required to suppress the secondary stream swirl.

For example, Japanese Patent Publication No.

56-19446 discloses a method of suppressing the secondary stream swirl. As shown in FIG. 17, the technology of this publication shows theoretical arrangement in which 6 projecting blade portions 30 are formed to the leading edge 29 of an effective blade portion 28 over distances la from flow passage walls 31 and the lateral cross) sectional shape of each of the projecting blade portions 30 is formed such that a projecting blade portion convex side 32a is caused to coincide with an effective blade portion concave side 32b and a projecting blade portion concave side 33a is bulged more than the effective blade portion convex side 33b as shown in FIG. 18. Further, the intersection point S10 of the projecting blade portion 30 with the flow passage wall 31, the intersection point S20 of the projecting blade portion 30 with the effective blade portion 28 and the projecting point S30 of an intersection point S20 to the flow passage wall 31 shown in FIG. 17 are caused to correspond to the points S10, S20 and S30 shown in FIG. 16, respectively.

*In such technology, the convex side horseshoeshaped swirl of the secondary stream swirl is suppressed to a low level by making the pressure of the effective blade portion convex side 33b higher than that of the projecting blade portion concave side 33a along a blade code c as shown in FIG. 19 in such a manner that the projecting blade portions 30, 30 are formed toward the leading edge 29 of the effective blade portion 28 toward the flow passage walls 31, 31 sides and the code length of the projecting blade portions 30, 30 is increased with the projecting blade portions 30, 30 is increased with 7 P:%op~sba23925-99re.dc.O8/0 11/1 -8respect to the code length of the effective blade portion. That is, a pressing force is applied to the projecting blade portion convex side 33a from the effective blade portion convex side 33b to thereby suppress the growth of the convex side horseshoe-shaped swirl.

As described above, the prior art shown in FIG. 17 has an excellent advantage that the growth of the convex side horseshoe-shaped swirl is suppressed to the low level.

However, since the pressure difference between the effective blade portion concave side 32b and projecting blade portion concave side 32a, and the projecting blade portion convex side 33b is made more higher than a convention pressure difference shown in FIG. 19, the growth of a flow passage swirl from the concave side of a blade to the convex side of the other adjacent blade is more promoted. As a result, the prior art shown in FIG. 17 provides i: a disadvantage that a flow passage swirl which will be greatly grown from the concave side horseshoe-shaped swirl in a short time cannot be suppressed and the blade cascade efficiency cannot be increased.

The reference to any prior art in this specification is not, and should not be taken 15 as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

SUMMARY OF THE INVENTION o *According to the present invention there is provided a blade for an axial fluid 20 machine including an effective blade portion, wherein said effective blade portion is divided into a root blade portion, an intermediate blade portion and a tip blade portion which are formed continuously to and integrally with each other and wherein an axis passing through a center of a cross section of the root blade portion and an axis passing through a center of cross section of the tip blade portion are obliquely formed toward an upstream side with respect to an axis passing through a center of cross section of the intermediate blade portion; wherein said axis passing through the center of cross section of the root blade portion and said axis passing through the center of cross section of the tip blade portion have inclinations in a range of 150 to 450 with respect to said axis passing through the center of cross section of the intermediate blade portion, and wherein a height of said axis RApassing through the center of cross section of the root blade portion and height of said axis ~i~i~passing through the cener of cross secon of the root blade portion and height of sa~id axis P:\opcrrsbl23925-99res.doc-08/01/01 -9passing through the center of cross section of the tip blade portion are set respectively to a range of 1/6 2/6 with respect to an entire blade length of the effective blade portion.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a perspective view schematically showing a first embodiment of a blade for an axial fluid machine according to the present invention; FIG. 2 is a sectional view taken along the line II-II of *•go o *o eoo P:\OPER\GCP\39302.DIV 22/4/99 10 FIG. 1; FIG. 3 is a view explaining the blade for the axial fluid machine according to the present invention in relation to the pressure distribution characteristics of a main stream passing through the blade; FIG. 4 is a view explaining that the inlet angle of the blade for the axial fluid machine according to the S e present invention is within the range of a positive stall margin range so as not to cause a stall; FIG. 5 is a graph showing the blade cascade loss of the blade for the axial fluid machine according to the present invention; FIG. 6 is a view explaining the relationship among the pressure distribution characteristics, the behavior of the main stream passing through the blade and the lateral sectional shape of the blade (section taken along the line VI-VI) when one example of the first embodiment of the blades for the axial fluid machine according to the present invention is shown; FIG. 7 is a perspective view schematically showing a second embodiment of the blade for the axial fluid machine according to the present invention; FIG. 8 is a sectional view taken along the line VIII-VIII of FIG. 7; FIG. 9 is a view explaining the blade of the second embodiment of the blades for the axial fluid machine according to the present invention in relation to the pressure distribution characteristics of a main stream passing through the blade; FIG. 10 is a schematic view showing a first example of the second embodiment of the blade for the axial fluid machine according to the present invention; FIG. 11 is a schematic view showing a second 11 example of the second embodiment of the blades for the axial fluid machine according to the present invention; FIG. 12 is a schematic view showing a third embodiment of the blade for the axial fluid machine according to the present invention; FIG. 13 is a sectional view taken along the line XIII-XIII of FIG. 12; FIG. 14 is a schematic sectional view of a conventional axial air compressor; FIG. 15 is a schematic partial sectional view of a conventional axial stream turbine; FIG. 16 is view explaining the mechanism for generating a swirl and the behavior of the swirl in a conventional blade cascade; FIG. 17 is a schematic view showing the conventional blades for an axial fluid machine: FIG. 18 is a sectional view taken along the line XVIII-XVIII of FIG. 17; and FIG. 19 is a graph showing the pressure distribution of the blade for the axial fluid machine in FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of blades for an axial fluid machine according to the present invention will be described with reference to drawings.

12 FIG. 1 is a perspective view schematically showing a first embodiment in which blades for the axial fluid machine according to the present invention are applicable to an axial air compressor or an axial stream turbine. The profile shown in FIG. 1 is an example of the blades for the axial air compressor.

A blade 34 is formed to a profile in such a manner that it advance toward a main stream F along a stagger line X 2 (a line connecting a blade leading edge to a blade trailing edge) which is displaced at a stagger angle (staggering angle) with respect to a rotational shaft direction line X, and reference blade elements 34d shown by virtual broken lines are stacked from a root portion 34b (blade root) toward a tip 34c (blade tip portion).

*...Further, the blade 34 includes an effective blade portion 34a obtained by stacking the reference blade elements 34d on the stagger line X 2 and changing the angle S S t

S

Sof the stagger line X 2 in a radial direction (blade

S.

lengthwise direction) and projecting blade portions S. S° 35b are formed integrally as portions of the effective blade portion 34a.

The projecting blade portions 35a, 35b are formed by axis reference lines XA, X, which extend from the root portion 34b and the tip portion 34c of the effective blade portion 34a toward the main stream F side and axes YA, YB 13 having arc-shaped curved surfaces which are connected from ends of the axis reference lines XA, XB to the leading edge 34e of the effective blade portion 34a.

Further, the projecting blade portions 35a, are connected by forming the intersection points ZA, Z 8 of the axes YA, Y, with the leading edge 34e of the effective blade portion 34a to a fillet shape (arc having a small curvature).

Further, as shown in FIG. 2, the lateral (cross) sections of the projecting blade portions 35a, 35b which bulge continuously from the leading edge 34e of the effective blade portion 34a integrally therewith and the lateral (cross) section of only the effective blade portion 34a are formed such that they coincide with each other at the portion of the maximum blade thickness W 2 of, for example, the effective blade portion 34a by displacing the

S

camber lines CL, of the projecting blade portions 35a, from the camber line CL 2 of the effective blade portion 34a for making the inlet angle of the main stream F equal to each of the projecting blade portions 35a, 35b and the effective blade portion 34a.

As a result, the lateral sectional shapes of the 5555 5500 projecting blade portions 35a, 35b and the effective blade portion 34a permit the contour line 36b of a concave side 0 4,~ I 36a to coincide with the contour line 37b of a convex side 37a toward a trailing edge 34f.

14 On the other hand, the axes YA, YB of the projecting blade portions 35a, 35b are formed so as to be displaced by the inclinations h, c thereof with respect to the leading edge 34e of the effective blade portion 34a.

Further, the inclined axes YA, YB of the projecting blade portions 35a, 35b are formed so that they have heights L,, L, with respect to the entire blade length L 0 of the effective blade portion 34a, respectively.

The inclinations h, c of the axes YA, YB are set to the range of the following expression.

[Expression 1] 1501 A h,A c 450 The respective ranges of the inclinations h, c of the axes YA, YB are set sufficiently by taking the stall of the main stream F into consideration.

In general, although it is ideal to cause the main stream F to coincide with the blade inlet line F, (tangential lines of the camber lines CL,, CL 2 of a blade .n inlet angle with respect to the coordinate axis X as shown in FIG. 2, actually, it often flows into a blade cascade or train at a flow angle a with respect to the coordinate axis X. In this case, the difference between the blade inlet angle 3 and the flow angle a is called an incidence i (suppressing angle), and it is said as a positive stall Sethat the incidence i causes a stall toward the concave side 36a.

15 Whether the main stream F causes the positive stall or not solely depends on whether the incidence i is large or a small. As a result, the incidence i, more directly, the flow angle a is preliminarily determined by an experiment and when the flow angle a determined by the experiment is within the range of a positive stall margin from the intersect point M of the minimum value w min of blade cascade loss characteristics L to the intersect point N of a blade cascade loss value 2 w min as shown in FIG. 4, the danger of the positive stall can be avoided.

As described above, the inclinations h, c of the axes YA, Y, are set within the range of 15 -450 respectively so that they fall within the range of the positive stall margin shown in FIG. 4 in order to securely avoid the danger that the main stream F stalls. Therefore, if they deviate from the range, there is a possibility of causing a stall.

S• Further, the heights L, of the axes YA, YB are set within the range of the following expression with respect to the entire blade length L 0 of the effective blade portion 34a.

[Expression 2] 1/6 LhL, LC/L05 2/6 The expression is set in relation to the range of 150-450 which is set so that the inclinations h, c of 16 the axes YA, YB fall within the range of the positive stall margin, respectively, to securely avoid the danger of the stall of the main stream F. When they deviate from the range, there is a possibility of causing a stall.

More specifically, when the respective inclinations h, c of the axes YA, YB are set to 15o -45 the respective blade length ratios Lh/La, LC/L of the projecting blade portions 35a, 35b are set within the range of the above expression and the conventional blade cascade loss value, which is obtained in no location of the projecting blade portions 35a, 35b, is compared with a reference, it is confirmed by an experiment that the range 1/6-2/6 of the respective blade length ratios L,/Lo, LC/Lo of the projecting blade portions 35a, 35b are made lower than the conventional comparison reference value 1.0 as shown in FIG. 5 and a favorable result has been obtained.

The first embodiment mentioned above will operate in the following manner.

When the main stream F flows into the blade cascade at a pressure (static pressure) PO, since the flow passage between the blade cascade is limited, its speed is increased and the pressure P 0 is lowered. As a result, as shown by the solid line and the broken line in FIG. 3, the pressure distribution characteristics PA of the main stream F flowing along the blade lengthwise center line X 3 of the effective blade portion 34a and the pressure 17

I.

distribution characteristics PB of the main stream F flowing along the respective blade lengthwise center lines

X

4

X

4 of the projecting blade portions 35a, 35b are such that the pressure of the main stream F is lowered up to a pressure P, at the blade cascade minimum passage portion and then gradually recovered toward the trailing edge 34f.

In this case, since the main stream F first flows to the respective points S, of the projecting blade portions 35b and then flows to the point S 2 of the effective blade portion 34a, a pressure difference is caused between the point S 2 on the line of the leading edge 34e and the points S, 3 S,3, and pressing forces PF are generated by the pressure difference. Since the pressing forces PF act from the blade lengthwise center line X 3 of the effective blade portion 34a toward the root portion 34b and the tip portion 34c, they can suppress the convex side horseshoe-shaped swirls 25a, 25b. The pressure of the main stream F passing through the respective blade lengthwise center lines X 4

X

S of the projecting blade portions 35a, 35b and the blade lengthwise center line X 3 of the effective blade portion 34a is recovered after the pressure of the main stream F reaches the pressure P, and the pressures of the main stream F which has separately passed through the respective center lines again coincide with each other at the points

'S

4 Ss, S 5 on the trailing edge 34f.

Further, as shown in FIG. 2, the blade of the 18 shown embodiment is formed such that the pressure difference between the concave side of one of the blades and the convex side of the other adjacent blade is set lower than the pressure difference [S0lO (S20) S30] of the prior art shown FIG. 17 by causing the maximum blade thickness W 2 of the effective blade portion 34a to coincide with the maximum blade thickness W, of the respective projecting blade portions 35a, 35b, even if a flow passage swirl, which has been grown from the concave side horseshoe-shaped swirl, flows from the concave side of the one blade toward the convex side of the other blade, it can be suppressed to a low level by the pressing forces PF.

As described above, in the present invention, the reference blade elements 34d are piled along the stagger line X 2 and are advanced toward the main stream F side to thereby form the blade 34 including the projecting blade portions 35a, 35b and the effective blade portion 34a, and the pressing forces PF are generated from the center of the effective blade portion 34a toward the root portion 34b and the tip portion 34c. Accordingly, the S" convex side horseshoe-shaped swirl can be suppressed.

Furthermore, in this embodiment, since the pressure difference between the concave side of the one blade and the convex side of the other adjacent blade is lowered than a conventional pressure difference by causing the maximum blade thickness W, of the projecting blade 19 portions 35a, 35b to coincide with the maximum blade thickness W 2 of the effective blade portion 34a, the flow passage swirl from the concave side of the one blade to the convex side of the other adjacent blade can be suppressed to a low level by the pressing forces PF.

Further, since the inclinations h, c of the respective axes YA, Y 8 of the projecting blade portions 35b and the respective heights Lh, L. of the axes YA, Y, thereof are set to the ranges in which the main stream does not stall, even if the flow rate of the main stream F is made relatively small as in the case of partial load operation, the operation can be safely continued.

FIG. 6 is a view explaining one example utilizing the first embodiment of the blades for the axial fluid machine according to the present invention.

Although the example shown in FIG. 6 is applied to an axial steam turbine, it is denoted by the same reference numerals as those used in the first embodiment and the description thereof is omitted because the arrangement of the example is substantially the same as that of the first embodiment except that only a blade thickness is different from that of the first embodiment.

Since this example can also generate pressing forces PF from the blade lengthwise center line X 3 of an effective blade portion 34a toward a root portion 34b and a tip portion 34c, it can suppress a convex side 20 horseshoe-shaped swirl likewise the first embodiment.

Further, since this example causes the maximum blade thickness W 2 of the effective blade portion 34a to coincide with the maximum blade thickness W, of the respective projecting blade portions 35a, 35b, it can suppress a flow passage swirl by the pressing forces PF likewise the first embodiment.

FIG. 7 is a perspective view schematically showing a second embodiment in which the blades for the axial fluid machine according to the present invention is applied to an axial air compressor and an axial steam turbine. Further, it is to be noted that the profile shown in FIG. 7 uses the blade of the axial air compressor as an example. Further, the same components and portions as those of the first embodiment are denoted by the same reference numerals and only different points will be described hereunder.

This example is provided with projecting blade portions, 38a, 38b which are formed continuously to the trailing edge 34f of an effective blade portion 34a S integrally therewith toward the downstream side of a main stream F, in addition to the projecting blade portions according to the first embodiment.

The projecting blade portions 38a, 38b are formed by axis reference lines XA, XB extending from the root portion 34b and the tip portion 34c of the effective blade 21 portion 34a toward the downstream side of the main stream F and axes YA YB, including arc-shaped curved surfaces which are connected from ends of the axis reference lines XA, XB, to the trailing edge 34f of the effective blade portion 34a.

Further, the projecting blade portions 38a, 38b are connected by forming the intersection points ZA ZB of the axes YA,, YB with the trailing edge 34f of the effective blade portion 34a to a fillet shape.

In addition, as shown in FIG. 8, the lateral (cross) sections of the projecting blade portions 38a, 38b which bulge continuously from the trailing edge 34f of the effective blade portion 34a integrally therewith and the lateral (cross) section of only the effective blade portion 34a are formed such that they coincide with each other at the portion of the maximum blade thickness W 2 of, for example, the effective blade portion 34a by displacing the camber lines CLI of the projecting blade portions 35a, from the camber line CL 2 of the effective blade portion 34a for making the inlet angle of the main stream F equal to each of the projecting blade portions 35a, 35b and the effective blade portion 34a. As a result, the camber lines CL, of the projecting blade portions 35a, 35b and the camber line CL 2 of the effective blade portion 34a are displaced as the camberlines CL, and CL 2 advance toward the respective rear edges 34fi, 34f 2 22 On the other hand, the axes YAZ of the projecting blade portions 38a, 38b are formed so as to be displaced by the inclinations ht, ct thereof with respect to the trailing edge 34f of the effective blade portion 34a. Further, the inclined axes Y, Y, of the projecting blade portions 38a, 38b are formed so that they have heights Lht, Let with respect to the entire blade length Lo of the effective blade portion 34a, respectively.

Each of the inclinations ht, ct and the heights Lht, Let is set within the range of the following expression.

[Expression 3] 150° A A t c 1/6 L.t/Lo L t/Lo: 2/6 When each of the inclinations ht, ct and the heights Lht, Let is set within the range of the above expression, the pressure distribution characteristics PA of the main stream F flowing along the blade lengthwise *9 9 9 center line X 3 of the effective blade portion 34a are such that the pressure of the main stream F flowing to the point S21 of the effective blade portion 34a at a pressure P 0 is lowered to a pressure P, when the main stream F reaches a blade cascade minimum passage and thereafter, the pressure thereof is gradually recovered and made to the former pressure P 0 when the main stream F reaches the point S41 of the trailing edge 34f as shown by the broken line in FIG.

23 On the other hand, the pressure distribution characteristics PB of the main streams F flowing along the respective blade lengthwise center lines X 4

X

4 of the projecting blade portions 35a, 35b and 38a, 38b are such that the pressure of the main stream F flowing to the respective points Sll, Sll of the projecting blade portions 35b at the pressure P, is lowered to the pressure P, when the main stream F reaches the blade train minimum passage and thereafter the pressure is recovered and made to the former pressure P 0 when the main streams F reach the respective projecting blade portions 38a, 38b as shown by the solid line in FIG. 9. In this case, pressure differences are caused between the point S21 and the point S31 and between the point S31 and the point S41 and the points S51, S51, respectively and these pressure differences are applied as pressing forces PF, PF from the center of the effective blade portion 34a to the root portion 34b and the tip portion 34c of the front edge 34f and the root portion 34b and the tip portion 34c of the trailing edge 34f, respectively.

As described above, in the described embodiment, the projecting blade portions 35a, 35b, 38a, 38b are formed to the leading edge 34e side and the trailing edge 34f side, respectively continuous to and integral with the effective blade portion 34a, and the double pressing forces 24 PF, PF are generated from the center of the effective blade portion 34a to the root portion 34b and the tip portion 34c, respectively. Accordingly, a convex side horseshoeshaped swirl flowing along the convex side of the blades and a flow passage swirl flowing from the concave side of one of the blades to the convex side of the other adjacent blade can be securely suppressed. Further, although the example explains the axial air compressor as an example, it may be also applied to the blade of a steam turbine.

Further, it is described herein that the projecting blade portions 35a, 35b are formed to the respective root portion 34b and tip portion 34c in the leading edge 34e of the effective blade portion 34a as like in the case where the projecting blade portions 38a, 38b are also formed to the respective root portion 34b and tip portion 34c in the trailing edge 34f. However, the present invention is not limited to the above embodiment, and the projecting blade portions 35a may be formed on the root portion 34b side in the leading edge 34e of the effective blade portion 34a as shown in FIG. 10 or the projecting blade portions 35a, 38a may be formed on the root portion 34b side in the leading edge 34e of the effective blade portion 34a and on the root portion 34b in the trailing edge 34f thereof as shown in FIG. 11. In particular, since the pressing forces PF suppress a centrifugal force generated to the blade 34 being rotated, the embodiment can 25 be effectively applied to the moving blade of the axial air compressor and the axial steam turbine.

FIG. 12 is a schematic view showing a third embodiment of the blades for the axial fluid machine accordingto the present invention, in which components and portions similar to those of the first embodiment are denoted by the same reference numerals.

The third embodiment is arranged such that the effective blade portion 34a of a blade 34 is divided into a root blade portion 39, an intermediate blade portion and a tip blade portion 41, and the respective blade portions 39, 40, 41 are formed continuously to and integrally with each other. The respective reference blade elements 39g of the root blade portion 39 and the intermediate blade portion 40 shown by virtual broken lines are advanced from the leading edge 34e of the S reference blade elements 39g in the intermediate blade portion 40 shown by the virtual broken line toward a main S stream F. In this case, the axis I passing through the center of the lateral (cross) section (inertia main axis) of the root blade portion 39 and the axis K passing through the center of the lateral (cross) section (inertia main axis) of the tip blade portion 41 are formed such that they are displaced by inclinations hi, cl with respect to the axis J passing through the center of the lateral (cross) Ssection (inertia main axis) of the intermediate blade 26 portion 40. Further, the axis I passing through the center of the lateral section of the root blade portion 39 and the axis K passing through the center of the lateral section of the tip blade portion 41 are formed such that they have heights Lh L, with respect to the entire blade length

L

0 of the effective blade portion 34a.

The inclinations hl, cl of the axes I, K passing through the centers of the lateral sections are set within the range of the following expression.

[Expression 4] 150 A ,I A cl 450 The range is set sufficiently taking the stall of the main stream F into consideration likewise the first embodiment and when the range is deviated, there is a possibility of causing a stall.

The heights L,j, of the axes I, K passing through the centers of the lateral sections are set within the range of the following expression with respect to the entire blade length L 0 of the effective blade portion 34a.

[Expression 1/6 L, /LO, L, 2/6 The expression is set in relation to the range of 15°-450 set so that the respective inclinations hi, cl of the axes I, K passing through the centers of the lateral sections are fallen in the range of a positive stall margin in order to securely avoid the danger of a stall of the 27 main stream F.

On the other hand, as shown in FIG. 13, the lateral sections of the root blade portion 39 and the tip blade portion 41, which continuously bulge from the leading edge 34e of the intermediate blade portion 40, and the lateral section of only the intermediate blade portion are formed such that they coincide with each other at the portion of the maximum blade thickness W 21 of, for example, the intermediate blade portion 40 by displacing the camber lines CL, 1 of the root blade portion 39 and the tip blade portion 41 from the camber line CL, of the intermediate blade portion 40 for making the flow angle of the main stream F equal to each of the root blade portion 39, the tip blade portion 41 and the intermediate blade portion As described above, in the third embodiment, since the effective blade portion 34a is divided into the root blade portion 39, the intermediate blade portion and the tip blade portion 41 and since the root blade S portion 39 and the tip blade portion 41 are advanced from the leading edge 34e of the intermediate blade portion toward the main stream F, pressing forces PF can be generated from the intermediate blade portion 40 toward the root portion 34b of the root blade portion 49 and the tip portion 34c of the tip blade portion 41 likewise the first embodiment.

Therefore, in the described embodiment, since the 28 P:\OPER\GCP\39302.DIV 22/4/99 29 pressing forces PF can be generated from the intermediate blade portion 40 toward the root portion 34b of the root blade portion 39 and the tip portion 34c of the tip blade portion 41, respectively, a convex side horseshoe-shaped swirl and a flow passage swirl can be suppressed. In the embodiment, since the pressing forces PF are more generated at the position where a boundary layer is exfoliated by the convex side horseshoe-shaped swirl, the embodiment can be effectively applied to the stationary blade and the moving blade of an axial air compressor.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

S. o o* S e o* S o

Claims (2)

1. A blade for an axial fluid machine including an effective blade portion, wherein said effective blade portion is divided into a root blade portion, an intermediate blade portion and a tip blade portion which are formed continuously to and integrally with each other and wherein an axis passing through a center of a cross section of the root blade portion and an axis passing through a center of cross section of the tip blade portion are obliquely formed toward an upstream side with respect to an axis passing through a center of cross section of the intermediate blade portion; wherein said axis passing through the center of cross section of the root blade i :••portion and said axis passing through the center of cross section of the tip blade portion have inclinations in a range of 150 to 450 with respect to said axis passing through the center of cross section of the intermediate blade portion, and wherein a height of said axis S"passing through the center of cross section of the root blade portion and height of said axis 15 passing through the center of cross section of the tip blade portion are set respectively to a range of 1/6 2/6 with respect to an entire blade length of the effective blade portion. .oo••i A blade for an axial fluid machine according to claim 1, wherein said root blade portion and said tip portion have a maximum blade thickness substantially the same as that 20 of said intermediate blade portion. o.

3. A blade for an axial fluid machine substantially as hereinbefore described with reference to Figures 1 to 13. DATED this 8 t h day of January 2001 KABUSHIKI KAISHA TOSHIBA By its Patent Attorneys DAVIES COLLISON CAVE