Blade of axial flow-type rotary fluid machine

A first bent portion bent toward an intrados and a second bent portion located in the rear of the first bent portion and bent toward an extrados are provided on a camber line on a trailing edge in the rear of 90% of a chord length of a turbine blade having an extremely low aspect ratio for an axial-flow turbine. The inclination of the camber line immediately in the rear of the second bent portion on the side of a blade root is substantially equal to the inclination of the camber line immediately in front of the first bent portion, and the curvature of the second bent portion is decreased from the side of the blade root toward a blade tip. As a result, a higher-pressure portion on the intrados which is a pressure surface of the turbine blade is displaced toward the trailing edge, and thus a secondary flow from the side of the blade tip toward the blade root can be suppressed, whereby a pressure loss particularly in the vicinity of the blade root can be suppressed to the minimum.

RELATED APPLICATION DATA

German priority application No. 10 2005 025 213.3, upon which the present application is based, is hereby incorporated in its entirety herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a three-dimensional shape of a blade used in an axial-flow rotary fluid machine such as an axial-flow turbine and an axial-flow compressor, and particularly to a blade having an extremely small aspect ratio.

2. Description of the Related Art

An airfoil of a turbine blade of an axial-flow turbine described in Japanese Patent Application Laid-open No. 2002-138801 includes an inflection point between an upstream concave portion and a downstream convex portion in the rear of an 80% position on an intrados, so that a shock wave generated from the intrados of a trailing edge is dispersed into two components by the effect of the inflection point to weaken the respective shock wave components, thereby decreasing the energy loss generated due to the interference of these shock wave components with a boundary layer of an extrados of an adjacent turbine blade. In this blade airfoil, a camber line in the vicinity of the trailing edge is curved in an S-shape by the provision of the inflection point on the intrados in the vicinity of the trailing edge.

A turbine blade having a low aspect ratio has a significant tendency (a secondary flow) that the flow of a fluid along a blade surface is deflected from the side of a blade tip toward a blade root, resulting in a problem of an increased pressure loss in the blade. In the above-described conventional blade, however, a three-dimensional shape of the turbine blade, namely, a difference between the airfoil of the blade root and the airfoil of the blade tip is not taken into consideration, so that the pressure loss accompanying the secondary flow cannot be sufficiently decreased.

SUMMARY OF THE INVENTION

The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to decrease the pressure loss in a blade of an axial-flow rotary fluid machine used mainly in a transonic range.

In order to achieve the above-mentioned object, according to a first feature of the invention, there is provided a blade of an axial-flow rotary fluid machine, comprising: an intrados adapted to generate a positive pressure between a leading edge and a trailing edge; and an extrados adapted to generate a negative pressure between the leading edge and the trailing edge, wherein a camber line in the trailing edge includes a first bent portion bent toward the intrados, and a second bent portion located in the rear of said first bent portion and bent toward the extrados, said second bent portion having a curvature decreased from the side of a blade root toward a blade tip.

According to a second feature of the invention, in addition to the first feature, when positions along the camber line are represented in such a manner that the position of the leading edge is represented by a 0% position, and the position of the trailing edge is represented by a 100% position, the position of the first bent portion is in the rear of a 90% position, and the inclination of the camber line immediately in the rear of the second bent portion at least in the blade root is substantially equal to the inclination of the camber line immediately in front of the first bent portion.

According to a third feature of the invention, in addition to the first feature, the blade has one inflection point on the intrados in the vicinity of the trailing edge, and two or more inflection points on the intrados in front of the one inflection point.

With the above arrangement, the front first bent portion bent toward the intrados and the rear second bent portion bent toward the extrados are provided on the camber line on the trailing edge of the blade of the axial-flow rotary fluid machine, and the curvature of the second bent portion is decreased from the side of the blade root toward the blade tip. Therefore, a higher-pressure portion on the intrados which is a pressure surface of the blade is displaced toward the trailing edge, so that a secondary flow from the side of the blade tip toward the blade root can be suppressed, whereby a pressure loss particularly in the vicinity of the blade root can be suppressed to the minimum.

The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

An embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, “X” represents an axial position, “Cax” represents an axial blade chord length, and “rθ” represents a circumferential position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turbine blades according to the present embodiment are disposed in an annular gas passage in an axial-flow turbine to constitute a turbine blade cascade. An airfoil shown inFIG. 1is of a blade root (a portion connected to a hub) at a radial inner end of a turbine stator blade, and an airfoil shown inFIG. 4is of a blade tip at a radial outer end of the turbine stator blade. The airfoil of the turbine blade is changed progressively from the blade root toward the blade tip. As apparent fromFIG. 7B, the three-dimensional shape of the turbine blade has an ultra-low aspect ratio with a span length longer than a chord length.

In the airfoil of the blade root shown inFIG. 1, a broken line shows an airfoil (a baseline) in a comparative example, which is a basis, and a solid line shows an airfoil (optimized) in the embodiment, which is optimized on the basis of the comparative example. The airfoil in the embodiment includes an intrados13(a positive pressure surface) adapted to generate a positive pressure with flowing of a fluid, and an extrados14(a negative pressure surface) adapted to generate a negative pressure with flowing of the fluid, between a leading edge11at a left end and a trailing edge12at a right end.

As apparent from the comparison between the embodiment and the comparative example, the airfoil in the embodiment has a blade thickness in the vicinity of the leading edge11, which is smaller than that of the airfoil in the comparative example, and the airfoil in the embodiment has an S-shaped curved portion in the vicinity of the trailing edge12, which is not present in the comparative example. An intrados13of the airfoil in the comparative example is of a simple concave shape, while five inflection points P1to P5are present in an order from the leading edge11toward the trailing edge12in the intrados13of the airfoil in the embodiment. The curvature at each of the inflection points P1, P3and P5is changed from the concave to the convex in a direction of flowing of a gas, and the curvature at each of the inflection points P2and P4is changed from the convex to the concave in the direction of flowing of the gas.

FIGS. 2 and 3show enlarged shapes of the airfoils in the vicinity of the trailing edge12, in which the airfoil in the embodiment has a remarkable characteristic. A camber line CLb of the airfoil in the comparative example is substantially rectilinear, while a camber line CLo of the airfoil in the embodiment is curved in an S-shape, and hence two bent portions Q1and Q2are present on the camber line CLo in the trailing edge12. The front first bent portion Q1is curved toward the intrados13at its downstream side in the direction of flowing of the fluid, and the rear second bent portion Q2is curved toward the extrados14at its downstream side in the direction of flowing of the fluid. The positions of the first and second bent portions Q1and Q2exist in the rear of 90% of the chord length. In the camber line CLo of the airfoil in the embodiment, the inclination of a section in front of the first bent portion Q1and the inclination of a section in the rear of the second bent portion Q2are substantially parallel to each other by the virtue of the above-described S-shaped curving, whereby the angle of flowing of the fluid from the trailing edge12is adjusted. Between the first and second bent portions Q1and Q2, there is a section having a blade thickness partially smaller than those of sections in front of and in the rear of the bent portions Q1and Q2, respectively.

An airfoil of the blade tip shown inFIGS. 4 to 6is changed progressively from the airfoil of the blade root described with reference toFIGS. 1 to 3. The shape of the intrados13and the shape of the camber line CLo basically take over the feature of the airfoil of the blade root, but are slightly different in the following point: the intrados13of the airfoil of the blade root includes the five inflection points P1to P5(seeFIG. 1), but in the intrados13of the airfoil of the blade tip, the inflection point P1closest to the leading edge11and the inflection point P5closest to the trailing edge12are vanished (seeFIG. 4). The camber line CLo of the airfoil of the blade root is curved in an S-shape including first and second bent portions Q1and Q2(seeFIG. 1), but in the camber line CLo of the airfoil of the blade tip, the second bent portion Q2closer to the trailing edge12is vanished (seeFIG. 5).

However, the vanishing of the two inflection points P1and P5and the second bent portion Q2occurs in the airfoil of the blade tip, and the two inflection points P1and P5and the second bent portion Q2are present without being vanished in a position slightly displaced from the blade tip toward the blade root. As for the second bent portion Q2, its curvature is gradually decreased from a predetermined value at the blade root to zero at the blade tip.

It is known that a secondary flow in a direction from the blade tip toward the blade root is generally present on a surface of a turbine blade (particularly, on the intrados13), and a pressure loss is generated due to the secondary flow to degrade the performance of the turbine blade.FIGS. 7A and 7Bshow flows of a fluid along a surface of a turbine blade, whereinFIG. 7Acorresponds to the comparative example, andFIG. 7Bcorresponds to the embodiment. Secondary flows in a direction from the blade tip toward the blade root are present in both the comparative example and the embodiment. It can be seen in the embodiment that the inclination of flow lines is smaller with respective to a flowing direction of a main flow, and the amount of the secondary flows toward the blade root is decreased. The decrease in the amount of the secondary flows is realized mainly by the first and second bent portions Q1and Q2provided in the vicinity of the trailing edge12of the intrados13.

FIGS. 8 and 9show distributions of isentropic Mach numbers in chord directions on the intrados13(PS) and the extrados14(SS), whereinFIG. 8corresponds to the comparative example, andFIG. 9corresponds to the embodiment. A thick line and a thin line correspond to distributions of speeds on the side of the intrados13and on the side of the extrados14, respectively; a solid line corresponds to the blade root (a 100% position in a span direction; a broken line corresponds to an intermediate portion (a 50% position in the span direction); and a dashed line corresponds to the blade tip (a 90% position in the span direction).

Referring carefully to the distributions of pressures (see the thick lines) on the side of the intrados13in the comparative example and the embodiment, in the embodiment, a section with the higher pressure (a section with the lower Mach number) is displaced significantly toward the trailing edge12as compared with the comparative example, and the Mach number steeply rises in the vicinity of the trailing edge12. The characteristic distribution of pressure in the embodiment is attributable to the presence of the first and second bent portions Q1and Q2in the vicinity of the trailing edge12, and the secondary flow from the blade tip toward the blade root on the intrados13of the turbine blade is suppressed by this distribution of pressure.

FIG. 10shows a distribution of normalized accumulated-entropy in a chord direction from a 0% position (the blade root) to a 50% position (the intermediate portion) in the span direction of the turbine blade, wherein a broken line and a solid line correspond to the comparative example and the embodiment, respectively. As apparent fromFIG. 10, it can be seen that the normalized accumulated-entropy in the embodiment is decreased remarkably in the rear of −1.0 in the X-abscissa in the chord direction more than that in the comparative example. This is considered to be because the secondary flow from the blade tip toward the blade root is suppressed in a region from the chord-wise intermediate portion to the trailing edge12of the intrados13of the turbine blade.

FIG. 11shows a distribution of total pressure loss in the span direction, wherein a broken line and a solid line correspond to the comparative example and the embodiment, respectively. As apparent fromFIG. 11, it can be seen that the total pressure loss in the embodiment is lower than that in the comparative example mainly in a region from the span-wise intermediate portion to the blade root.

Although the embodiment of the present invention has been described in detail, various modifications in design may be made without departing from the subject matter of the invention.

For example, the blade according to the present invention is not limited to the turbine blade in the embodiment, and also applicable to a compressor blade.