DE102014226689A1 - Rotor blade of an axial flow machine - Google Patents

Abstract

The invention relates to a rotor blade (1) of an axial flow machine, which has a front edge (11), a trailing edge (12), a pressure side (13) and a suction side (14). It is envisaged that the front edge (11) of the airfoil (1) in the axial direction is S-shaped viewed from the front.

Description

The invention relates to a rotor blade of an axial flow machine.

To limit the crack growth in a material, it is always desirable to introduce internal compressive stresses into the material. This also applies to the blades of the rotor of an axial flow machine, in which cracks can occur, for example, due to foreign objects which impinge on the blade surface.

In order to improve the robustness of an airfoil against such foreign bodies, it is known to compress residual stresses by external measures such. B. Shot peening or deep rolling. In shot peening, for example, small balls, sand particles or the like are applied to the surface of the workpiece at high speed, plastically deforming the surface and thereby generating residual compressive stresses. The disadvantage is also the surface roughness increases.

It is an object of the present invention to provide a rotor blade of an axial flow machine which readily provides robustness against foreign body generated damage.

This object is achieved by a rotor blade with the features of claim 1. Embodiments of the invention are specified in the subclaims.

Thereafter, the solution according to the invention provides that the front edge of the airfoil is viewed in the axial direction viewed from the front S-shaped. It has surprisingly been found by experiments that by means of such a shaping of the airfoil compressive residual stresses can be introduced into the airfoil. These compressive stresses are not provided by external measures as in the prior art, but automatically induced during operation of the blade. Thus, the blade is in operation, d. H. when rotating about an axis of rotation, due to the centrifugal forces acting on the blade. This raising of the blade during rotation results in the blade geometry according to the invention for generating the desired residual compressive stresses.

The solution according to the invention is thus based on the idea of introducing compressive residual stresses into the airfoil by means of a specific shaping of the rotor airfoil.

The desired residual compressive stresses are introduced in the solution according to the invention, in particular in the region of the front edge, adjacent to the leading edge and / or in the region of the pressure side in the rotor blade, which is to be regarded as advantageous, since in the case of foreign bodies, the blade leading edge and the pressure side in particular Dimensions are at risk of being damaged by the foreign body.

At the same time it should be noted that the inventive shape of the leading edge of the airfoil and the compressive residual stresses provided thereby do not preclude it, in addition by external measures such. B. Shot blasting to a greater extent to introduce residual compressive stresses in the blade.

According to one embodiment of the invention, it is provided that the front edge of the airfoil in the axial direction viewed from the front is S-shaped, that it is convexly curved in a radially upper region to the pressure side and concavely curved in a radially lower region to the pressure side. Alternatively, the conditions may be reversed, for which case the leading edge is concavely curved in a radially upper region to the pressure side and convexly curved in a radially lower region to the pressure side. In the alternative embodiment, the "S" is thus mirror-inverted. Again, this is to be understood by the term "S-shaped".

In the transition region between the convexly curved area and the concave area of the front side is necessarily a turning point, in which the leading edge changes its curvature behavior. According to one embodiment of the invention, it is provided that the turning point is located in a blade blade height, which is below 50% of the height of the airfoil, in particular in a range between 30% and 50% of the height of the airfoil. The turning point is in other words in the lower half of the leading edge of the airfoil.

The terms "bottom" and "top" refer to the axis of rotation about which the rotor blade rotates during operation of the rotor, or a comparable reference axis.

According to one embodiment of the invention, the leading edge of the airfoil is considered embedded in a cylindrical coordinate system containing the coordinates x, r and θ, where x indicates the axial direction, r the radial direction and θ the circumferential direction. The angle θ in this case runs on the front edge as a function of the radius S-shaped.

The axial direction corresponds to the axis of rotation about which the rotor blade blade rotates during operation of the axial flow machine in which the rotor blade is arranged. The axial direction is equal to or substantially equal to the direction in which gas is flowed around the rotor blade. The radial direction indicates the distance to the x-axis and extends radially outward from the x-axis. The angle θ indicates an angle in the circumferential direction against an excellent direction. This corresponds to the usual definition of a cylindrical coordinate system.

The value of the coordinate r indicates its height in the region of the blade, so that each point on the front edge of the blade has a different radius r.

It should be noted that the x-axis does not necessarily coincide with the axis of rotation of the rotor airfoil. For example, it may alternatively be provided that the x-axis is placed in the area of the blade root, so that the values for r coincide with the actual height of the blades, or that the x-axis is placed in the middle of the flow channel, in which the Rotate blades.

According to one embodiment of the invention, it is provided that a local extreme value of the angle θ to the suction side is present in the range between 15% and 40% of the height of the airfoil. A further embodiment provides that a local extreme value of the angle θ to the pressure side is present in the range between 50% and 90% of the height of the airfoil to the pressure side. A local extreme value is a maximum or a minimum. If the angle is defined as positive in the clockwise direction, with the viewing direction in the axial direction from the front to the front edge of the blade, for example, a local maximum of the angle θ to the suction side is in the range between 15% and 40% of the height of the airfoil and / or is there a local minimum of the angle θ to the pressure side in the range between 50% and 90% of the height of the airfoil.

The form-related introduction of internal compressive stresses in a rotor blade is additionally influenced by a further parameter according to a further embodiment of the invention. Here again a cylindrical coordinate system with the coordinates x, r and θ is considered. The other parameter is the angle θ, but now based not on the blade leading edge, but on the center of gravity of profile sections of the airfoil. In an advantageous embodiment of the invention, this angle continuously increases or decreases with increasing radius. It is assumed, for example, that the angle is defined as positive in the clockwise direction, the viewing direction extending in the axial direction from the front to the front edge of the blade.

For this embodiment, it is pointed out that the airfoil can be divided into profile sections, each profile section indicating a profile at a defined radial height r. Through a plurality of profile sections, each having a defined radial distance Δr, the profile can be defined in its entirety in its three-dimensional form.

It has been found that, when considering the center of gravity of individual profile sections of the airfoil, it increases the generation of residual compressive stresses in the airfoil when the angle θ increases or decreases continuously with increasing radius with respect to the respective profile center of gravity. It is therefore considered in each case the centroid of the individual profiles. Illustratively, this feature means that the rotation of the blade increases or decreases continuously in the radial direction about the axis of rotation.

In particular, it can be provided that the profile of the angle θ with respect to the centroid of the profile sections of the airfoil has no inflection points with increasing radius and assumes a maximum in the upper region of the airfoil.

According to a further embodiment of the invention, an S-shape is formed not only at the leading edge of the airfoil, but also at its trailing edge, so that the trailing edge of the airfoil viewed in the axial direction from the rear (opposite to the x-direction) also formed S-shaped is. This makes it possible to additionally introduce residual compressive stresses in the airfoil when it rises and revolves by the centrifugal force during rotation of the blade.

It is provided in one embodiment that the trailing edge of the airfoil in the axial direction viewed from behind is S-shaped, that it convexly curved in a radially upper region to the pressure side and a radially lower portion is curved concave to the pressure side, or vice versa ,

A rotor having a plurality of rotor blades according to the invention is designed in an advantageous embodiment of the invention in an integrated design. An integrated design comprises in particular a BLISK design (BLISK = "blade integrated disc"), ie a design in which the individual rotor blades are integral with the disc on which they are arranged, are formed. Another integrated design is the BLING construction (bling = "bladed ring"), ie a construction method for the manufacture of integrally bladed rings. Since with integrated construction individual damaged blades can not be replaced, the repair of a rotor manufactured in an integrated design is complicated and expensive. Therefore, the present invention, which limits cracks and the like in their growth, is of particular importance in integrated design rotors.

The invention also relates to a compressor with a rotor having rotor blades according to the invention. The compressor is, for example, a low-pressure compressor, a medium-pressure compressor or a high-pressure compressor of a jet engine. In principle, however, it may be any compressor, or a fan stage of a jet engine.

The invention will be explained in more detail with reference to the figures of the drawing with reference to several embodiments. Show it:

1 a front view in the axial direction of an embodiment of a rotor airfoil;

2 a top view of the rotor blade of the 1 with additional representation of the axial direction x, the radial direction r and the circumferential direction θ;

3 a rear view opposite to the axial direction of the rotor blade of the 1 ;

4 a perspective view obliquely from the front of a rotor blade according to a second embodiment;

5 a side view of the rotor blade of the 4 ;

6 a perspective view obliquely from behind the rotor blade of the 4 ;

7 a first embodiment of the course of the angle θ at the leading edge of a rotor blade as a function of the radius;

8th a second embodiment of the course of the angle θ at the leading edge of a rotor blade as a function of the radius;

9 a first embodiment of the angle θ with respect to the center of gravity of profile sections of a rotor blade as a function of the radius;

10 a second embodiment of the angle θ with respect to the center of gravity of profile sections of a rotor blade as a function of the radius;

11 a front view of the rotor blade of the 1 and a rotor blade of the prior art;

12 a rear view of the blades of the 11 ;

13A a representation of the on the pressure side of a rotor blade according to the 1 occurring compressive and tensile stresses;

13B a representation of the suction side of a rotor blade according to the 1 occurring compressive and tensile stresses;

14A a representation of the on the pressure side of a rotor blade according to the prior art of 11 and 12 occurring compressive and tensile stresses; and

14B a representation of the suction side of a rotor blade according to the prior art of 11 and 12 occurring compressive and tensile stresses.

The 1 shows a front view in the axial direction of a rotor blade 1 which forms part of a rotor of an axial flow machine, for example a rotor of a compressor of an aircraft engine.

The blade 1 has a leading edge 11 , a trailing edge 12 , a printed page 13 and a suction side 14 on. The leading edge 11 includes an upper area 15 and a lower area 16 , Furthermore, imaginary profile sections 20 of the airfoil 1 shown.

As well as the 2 can be taken, any point on the surface of the blade 1 in a cylindrical coordinate system having the coordinates x, r and θ. Where x is the axial direction, r is the radial direction (out of the plane of the drawing), and θ is the angle in the circumferential direction. For example, the coordinate origin may be defined such that the x-axis is identical to the axis of rotation of the airfoil 1 is selected. Starting from this x-axis, the radial direction points radially outward. The value of r indicates the height of the blade 1 at.

The individual in the 1 illustrated profile sections 20 thus differ by the amount Δr in height from each other. The angle θ is measured with respect to a reference direction and is for example, defined so that an increasing angle in the clockwise direction is defined as positive.

The scoop of the 1 is characterized by the fact that the leading edge 11 of the blade in the axial direction viewed from the front is S-shaped. So forms the leading edge 11 of the airfoil 1 from top to bottom, consider a curve that is in its radially upper region 15 to the print side 13 is convex and convex in its radially lower area 16 to the print side 13 is concavely arched. The to the pressure side 13 convex arched area 15 and the pressure side 13 concave arched area 16 together form an S-shape of the leading edge 11 , Between these two areas 15 . 16 the leading edge 11 is necessarily a turning point of the curvature. This one in the 1 not shown, but in relation to the 7 and 8th explained inflection point is for example in a range between 30 and 50% of the height of the airfoil 1 ,

The 3 shows the scoop of the 1 in a view from the rear, leaving the blade trailing edge 12 facing the viewer. It is again next to the trailing edge 12 the front edge 11 , the print side 13 and the suction side 14 as well as an upper area 17 and a lower area 18 the trailing edge 12 to recognize.

In the illustrated embodiment, but not necessarily, the trailing edge is also 12 of the airfoil 1 viewed in the axial direction from the rear S-shaped. This is how the trailing edge points 12 of the airfoil 1 a curved course such that they are in the radially upper region 17 to the print side 13 convexly curved and in the radially lower area 18 to the print side 14 is concavely arched. The course at the trailing edge 12 can according to the course at the front edge 11 respectively.

Due to the S-shaped design of the front edge 11 of the airfoil 1 will compress residual stresses in the airfoil 1 introduced when the blade 1 due to the centrifugal forces during rotation of the blade erects and turns up. This effect is enhanced, though the trailing edge 12 S-shaped.

The 4 to 6 show three-dimensional representations of another embodiment of a rotor blade with a leading edge 11 , which is viewed in the axial direction from the front S-shaped, wherein the 4 a view diagonally from the front, the 5 a side view and the 6 a view at an angle from behind. In particular, the side view of 5 can be seen that both the leading edge 11 as well as the trailing edge 12 may have a sweep, ie the leading edge 11 and the trailing edge 12 are not exactly perpendicular to the flow direction, which runs in the axial direction x. At the front edge 11 the sign of the sweep angle changes. This is viewed in the radial direction over approximately the first lower two-thirds of the blade height negative and then positive. At the trailing edge, the sign of the sweep angle is consistently positive.

The 7 shows the S-shaped configuration of the leading edge of a blade in the cylindrical coordinate system, wherein the angle θ is shown as a function of the radius. Corresponding to the S-shaped course of the leading edge, the angle θ at the leading edge also has an S-shape. The leading edge forms a local maximum 31 to the suction side 14 out, with this maximum 31 in the range between 15% and 40% of the height of the airfoil. Further, the leading edge forms a local minimum 32 to the print side 13 out, with this local maximum 32 in the range between 50% and 90% of the height of the airfoil. Between the two extremes 31 . 32 is a turning point 33 in the curvature of the leading edge 11 in front.

The 8th shows a second embodiment of an S-shaped profile of the leading edge 11 a rotor blade. Also in this embodiment are a local maximum 31 to the suction side 14 out and a local minimum 32 to the pressure side and a turning point 33 shown. The course is different in so far as in the 7 , as the S-shaped curve is less pronounced.

In both embodiments, that applies in the range of the lower extreme value 31 the front edge 11 to the print side 13 Concave arched (or to the suction side 14 convex) and near the upper extreme value 32 to the print side 13 convexly curved (or to the suction side 14 concave).

The 9 shows the course of the angle θ as a function of the height of the airfoil with respect to another parameter, to which experiments have shown that in a course corresponding to the 9 Residual compressive stresses are generated in the blade. The parameter considered is the angle θ, but this time not related to the leading edge or the trailing edge of the airfoil 1 , but based on the focus of profile sections of the airfoil 1 ,

It is thus in the 9 the course of the angle θ relative to the centroid of the individual, for example in the 1 and 3 illustrated profile sections 20 shown. Every such profile cut 20 has a centroid 25 on that in the 3 is exemplified for the lowest profile section. The course of the angle θ to the centroid of these profile sections provides a measure of the rotation of the blade 1 to the rotation axis.

It should be noted that in the 9 unlike in the 7 and 8th the relative height of the bucket is given in percent instead of as in the 7 and 8th the distance to the axis of rotation.

The angle θ increases continuously with increasing radius. The largest value of the angle θ results at the upper end of the blade (at a relative height of 100%). The angle θ is in the 9 as well as in the 7 and 8th defined, ie the angle is defined as positive in a clockwise direction. If one defined the angle in a counterclockwise direction as positive, the angle would decrease steadily with increasing height. It is important that the course of the angle θ increases or decreases continuously with increasing radius.

The 10 shows the course of the angle θ as a function of the relative height of the blade for a further embodiment. Also in this further embodiment, the angle θ increases continuously with increasing radius. In this embodiment, an approximately constant angle θ is approximately in the range between a relative height of 40% and 60%.

As already mentioned, as a result of the design of the blade leaf in such a way that the profile of the angle θ increases or decreases continuously with increasing radius relative to the center of gravity of the profile sections, compressive residual stresses are introduced to a greater extent into the rotor blade airfoil.

The increased introduction of compressive residual stresses by the solution according to the invention has been checked and verified by means of measurements. The 11 schematically shows on the one hand a blade according to the invention 1 with an S-shaped front edge 11 and a blade formed according to the prior art 100 with a leading edge 101 that is not S-shaped. The two shovels 1 . 100 are drawn together to make the differences in the course more clear. The 12 shows the two blades 1 . 100 in a view from behind, according to the representation of the 3 , The shovel 1 has a leading edge 11 and a trailing edge 12 and the shovel 100 of the prior art a leading edge 101 and a trailing edge 102 on.

The 13A shows the residual stresses on the pressure side 13 a blade according to the invention 1 with S-shaped front edge 11 , The residual stresses occurring are coded by different shades or by different narrow hatching. A dark shading or close hatching indicates the existence of compressive stresses and a light shading or wide shading the existence of tensile stresses. It can be seen that high residual compressive stresses at the leading edge 11 as well as in the upper area of the pressure side 13 , in particular in a range above 50% of the blade height occur. These areas are particularly endangered in terms of occurring cracks due to collision with foreign bodies, so that high residual compressive stresses in these areas are advantageous.

The 13B shows the suction side 14 the scoop of the 13A , On the suction side mainly tensile stresses occur, but immediately adjacent to the leading edge 11 also compressive stresses are present.

The 14A . 14B in contrast show the stress distribution on an airfoil 100 of the prior art, wherein the 14A the stress distribution on the pressure side 103 and the 14B the stress distribution on the suction side 104 represents. At the blade 100 The state of the art is the conditions on the two blade sides 103 . 104 essentially inversely compared to the situation with the blade according to the invention 1 in the 13A . 13B , So are the scoop 100 of the prior art on the printing side 103 mainly tensile stresses and on the suction side 104 formed predominantly compressive stresses.

The solution according to the invention thus causes compared to a blade 100 According to the prior art, the tensile stresses are displaced to the suction side, while the desired compressive stresses reinforced at the leading edge and on the pressure side of the rotor airfoil 1 be generated. The solution according to the invention thus causes the introduction of compressive residual stresses in the blade 1 in areas which are particularly at risk of being damaged by collision with foreign bodies in the gas stream, so that an increased robustness of the airfoil 1 provided. The solution according to the invention works without external measures and causes the generation of residual compressive stresses solely by the shaping of the airfoil.

The invention is not limited in its embodiment to the embodiments shown above, which are to be understood only as examples. For example, the course of the S-beat at the leading edge can be done in a different manner than shown in the figures.

It should also be understood that the features of each of the described embodiments of the invention may be combined in various combinations. Where ranges are defined, they include all values within those ranges as well as all subranges that fall within an area.

Claims (13)

Rotor blade ( 1 ) of an axial flow machine having a leading edge ( 11 ), a trailing edge ( 12 ), a printed page ( 13 ) and a suction side ( 14 ), characterized in that the leading edge ( 11 ) of the airfoil ( 1 ) is viewed in the axial direction from the front S-shaped. Rotor blade according to claim 1, characterized in that the leading edge ( 11 ) of the blade in the axial direction viewed from the front is S-shaped in such a way that it is in a radially upper region ( 15 ) to the print side ( 13 ) convexly curved and a radially lower portion ( 16 ) to the print side ( 13 ) is concave or vice versa. Rotor blade according to claim 1, characterized in that a turning point ( 33 ) between the pressure side ( 13 ) convex curved area ( 15 ) and the pressure side ( 13 ) concave arched area ( 16 ) of the leading edge ( 11 ) is arranged at a blade blade height which is less than 50% of the height of the airfoil ( 1 ), in particular in a range between 30% and 50% of the height of the airfoil ( 1 ) lies. Rotor blade according to one of the preceding claims, characterized in that in a cylindrical coordinate system with the coordinates x, r, and θ, where x is the axial direction, r the radial direction and θ the angle in the circumferential direction, the angle θ at the Leading edge ( 11 ) is S-shaped depending on the radius. Rotor blade according to claim 4, characterized in that a local extreme value ( 31 ) of the angle θ to the suction side ( 14 ) in the range between 15% and 40% of the height of the airfoil ( 1 ) lies. Rotor blade according to claim 4 or 5, characterized in that a local extreme value ( 32 ) of the angle θ to the pressure side ( 13 ) in the range between 50% and 90% of the height of the airfoil ( 1 ) lies. Rotor blade according to one of the preceding claims, characterized in that in a cylindrical coordinate system with the coordinates x, r, and θ, where x is the axial direction, r the radial direction and θ indicate the angle in the circumferential direction in the clockwise direction, the course of Angle θ relative to the center of gravity ( 25 ) of profile sections ( 20 ) of the airfoil ( 1 ) increases or decreases continuously with increasing radius. Rotor blade according to one of the preceding claims, characterized in that the trailing edge ( 12 ) of the airfoil ( 1 ) viewed in the axial direction from the rear is also formed S-shaped. Rotor blade according to claim 8, characterized in that the trailing edge ( 12 ) of the airfoil ( 11 ) viewed in the axial direction from the rear is S-shaped in such a way that it is in a radially upper region ( 17 ) to the print side ( 13 ) convexly curved and a radially lower portion ( 18 ) to the print side ( 13 ) is concave or vice versa. Rotor of a compressor stage with a plurality of rotor blades ( 1 ) according to one of claims 1 to 9. Rotor according to claim 10, wherein the rotor is designed in integrated construction, in particular in BLISK design or in BLING design. A compressor with a rotor according to claim 10. A compressor according to claim 12, wherein the compressor is a fan, a low pressure compressor, a medium pressure compressor or a high pressure compressor of a jet engine.

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