US20100322774A1

US20100322774A1 - Airfoil Having an Improved Trailing Edge

Info

Publication number: US20100322774A1
Application number: US12/486,274
Authority: US
Inventors: Jay A. Morrison
Original assignee: Siemens Energy Inc
Current assignee: Siemens Energy Inc
Priority date: 2009-06-17
Filing date: 2009-06-17
Publication date: 2010-12-23

Abstract

An airfoil (101) is provided which includes a suction side and a pressure side joined along a trailing edge (106), wherein a trailing edge portion of the airfoil is configured to take a wavelike form along a radial direction of the airfoil, thereby improving the radial bending strength of the airfoil and reducing the magnitude of fluid flow wakes (128′) formed in a working fluid flowing over the airfoil.

Description

FIELD OF THE INVENTION

This invention relates generally to airfoils. More specifically, this invention relates to a modified external surface of an airfoil, to enhance a resistance to bending of the airfoil and to reduce instances of downstream wakes generated by the airfoil while being used in an aerodynamic system.

BACKGROUND OF THE INVENTION

The design of the trailing edge of an airfoil is preferably dictated by aerodynamic considerations. For improved aerodynamic performance, it is commonly preferred to provide a thin trailing edge in an airfoil used in an aerodynamic system, such as a gas turbine, for example. However, the thinness of the trailing edge may result in physical weakness, and such structural limitations often limit the trailing edge design and necessitate the use of a design that is less than optimal from an aerodynamic perspective.
FIG. 1 illustrates a known arrangement for an airfoil 10 which may be oriented in a radial direction 23 (perpendicular to the plane of FIG. 1) in a gas turbine engine (not shown). A cord line 12 extends in an axial direction through the airfoil 10, from a leading edge 14 to a trailing edge 16 of the airfoil 10. Based on an angle of attack 18 between the incident fluid flow and the cord line 12, high pressure working fluid is configured to travel over a pressure side 20 of the airfoil 10, while lower pressure fluid is configured to travel over a suction side 22 of the airfoil 10, thereby generating a lifting force or stress on the airfoil 10, including on the trailing edge 16. As illustrated in FIG. 1, the conventional airfoil 10 features a trailing edge 16 having a noticeable thickness 21 (somewhat exaggerated in the figure for illustration purposes) such that the high pressure fluid from the pressure side 20 and low pressure fluid from the suction side 22 merge over this noticeable thickness 21 and generate planar wakes 28 incident from the trailing edge 16 The wakes 28 move with the working fluid to impact a subsequent airfoil (not illustrated) of the gas turbine engine. The intensity and/or instance of these planar wakes 28 may reduce the aerodynamic performance of the engine and/or result in undesirable mechanical effects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the drawings that show:

FIG. 1 is a cross-section view of a prior art gas turbine engine airfoil;

FIG. 2 is a partial top view of an embodiment of an improved airfoil;

FIG. 3 is a cross-sectional view of the improved airfoil taken along the line 3-3 in FIG. 2;

FIG. 4 is an end view of the improved airfoil taken along the line 4-4 in FIG. 2;

FIG. 5 is a cross-sectional view of the improved airfoil taken along the line 5-5 in FIG. 2;

FIG. 6 is a cross-sectional view of the improved airfoil taken along the line 6-6 in FIG. 2;

FIG. 7 is an end view of an alternate embodiment of the improved airfoil; and

FIG. 8 is a cross-section view of the improved airfoil illustrated in FIG. 2 used within a gas turbine engine showing a downstream airfoil.

DETAILED DESCRIPTION OF THE INVENTION

In order to address the shortcomings of the conventional airfoil addressed above, the present inventor has developed an improved airfoil including a modified trailing edge, where the thickness of the trailing edge is minimized such that the aerodynamic performance of the airfoil is maximized, while the trailing edge retains a capability of resisting axial stress imposed during a typical operation of the airfoil within a gas turbine engine. Additionally, the modified trailing edge of the improved airfoil reduces the intensity of planar wakes incident from the trailing edge during use of the airfoil in a working fluid flow steam. Hence, the aerodynamic performance/efficiency of a gas turbine incorporating the improved airfoil is improved. Although some embodiments of the present invention discuss an airfoil used within a gas turbine engine, the present invention is not limited to airfoils used within gas turbines, and may be applied to any airfoil used in any aerodynamic application during which stress/force is imposed on the airfoil in a direction perpendicular to the radial orientation of the airfoil and/or in any aerodynamic application during which planar wakes are created as the high pressure fluid and low pressure fluid merge at the trailing edge of the airfoil.
FIG. 2 illustrates an exemplary embodiment of a system 100 including an airfoil 101, such as a stationary airfoil (vane) used within a gas turbine engine. The airfoil 101 has a longitudinal axis oriented in a radial direction 110 and includes a leading edge 107 and a trailing edge 106 which are separated by a cord length 116. A trailing edge portion 108 of the airfoil 101 extends from the trailing edge 106 toward the leading edge 107 by a distance 124 which is a subset of the cord length 116.
FIG. 3 (taken along line 3-3 of FIG. 2) illustrates that a suction side 102 and a pressure side 104 of the airfoil 101 are joined along the leading edge 107 and trailing edge 106. FIG. 3 also illustrates that the trailing edge portion 108 of the airfoil 101 thickness varies from a thickness 118 at the trailing edge 106 to a greater thickness 126 at a predetermined distance 124 from the trailing edge 106. As discussed in the following description, the trailing edge portion 108 takes a wavelike form along the radial direction 110 of the airfoil 101.
FIG. 4 (taken along line 4-4 of FIG. 2), FIG. 5 (taken along line 5-5 of FIG. 2) and FIG. 6 (taken along line 6-6 of FIG. 2) illustrates the wavelike form of the trailing edge portion 108 at respective distances from the trailing edge 106 along the cord length 116. As discussed below, an amplitude 112,113 of the wavelike form and the thickness 118,119,126 of the trailing edge portion 108 varies based on the respective distance from the trailing edge 106 along a cord length 116 of the airfoil 101.
FIG. 4 illustrates the wavelike form of the trailing edge portion 108 at the trailing edge 106 may take a sine wave form, for example. However, the wavelike form may take any known wave form, such as the illustrated sine-wavelike form configuration or a non-sine wavelike form, for example. The amplitude 112 (centerline peak to peak distance) of the wavelike form at the trailing edge 106 may be in a range of 0.2-2 times the thickness 118 of the trailing edge 106 in some embodiment, although is not necessarily so limited. In an exemplary embodiment, the amplitude 112 of the wavelike form at the trailing edge 106 is approximately equal (i.e. within normal manufacturing tolerances for the material of construction of the airfoil) to the thickness 118 of the trailing edge 106. Although FIG. 4 illustrates only a portion of the trailing edge 106 extending in the radial direction 110, the entire trailing edge 106 extending in the radial direction 110 may have the wavelike form. However, the entire trailing edge 106 need not take the wavelike form. Additionally, as illustrated in FIG. 4, a wavelength 120 (peak to peak) of the wavelike form along the trailing edge 106 may be in a range of 2-4 times the thickness 118 of the trailing edge 106. However, the wavelength 120 of the wavelike form at the trailing edge 106 need not be within any particular multiple range of the thickness 118 of the trailing edge 106 and may vary along the radial direction 110.
FIG. 5 illustrates a cross-sectional view at a distance 114 from the trailing edge 106 along the cord length 116. The amplitude 113 of the wavelike form of the trailing edge portion 108 at the distance 114 is less than the amplitude 112 of the wavelike form of the trailing edge portion 108 at the trailing edge 106 (FIG. 4). The amplitude 113 may be equal to or greater than the amplitude 112, however, for the embodiments currently envisioned for gas turbine applications, the amplitude of the wavelike form will gradually reduce to zero along a distance 124 defining the trailing edge portion 108. Additionally, the thickness 119 of the trailing edge portion 108 at the distance 114 from the trailing edge 106 along the cord length 116 is greater than the thickness 118 of the trailing edge 106. In an exemplary embodiment, the trailing edge portion 108 may be designed such that the amplitude of the wavelike form at a respective distance from the trailing edge 106 along the cord length 116 is inversely proportional to the thickness of the trailing edge portion 108 at the respective distance and/or to the respective distance itself.
FIG. 6 illustrates a cross-sectional view at an outermost boundary of the trailing edge portion 108 from the trailing edge 106, at the predetermined distance 124 from the trailing edge 106 along the cord length 116. As illustrated in FIGS. 4-6, the amplitude 112, 113 of the wavelike form along the trailing edge portion 108 decays from a maximum amplitude 112 at the trailing edge 106 to the amplitude 113 at the distance 114 from the trailing edge 106 along the cord length 116, and to zero at the predetermined distance 124 long the cord length 116. Although FIGS. 4-6 illustrate discrete amplitudes of the wavelike form along the trailing edge portion 108 at respective distances from the trailing edge 106, the amplitude actually continuously varies as the distance from the trailing edge 106 along the cord length 116 increases. Additionally, as illustrated in FIG. 6, the thickness 126 of the airfoil 101 at the predetermined distance 124 from the trailing edge 106 may be in a range of 2-3 times the thickness 118 of the trailing edge 106, although it is not necessarily so limited.
FIG. 7 illustrates an alternate embodiment of the present invention, in which the wavelike form of the trailing edge portion may take a non-sinusoidal waveform, such as an imperfect (tapered) square wave, in which the waveform oscillates between alternating flat levels 132, 134, having different relative elevations joined by respective sloped sections 136 joining the two levels. The amplitude 138 (perpendicular distance between the two levels 132,134) of the wavelike form at the trailing edge 130 may be in a range of 0.2-2 times the thickness 140 of the trailing edge 130 in some embodiments, although is not necessarily so limited. In an exemplary embodiment, the amplitude 138 of the wavelike form at the trailing edge 130 is approximately equal to the thickness 140 of the trailing edge 130. Although FIG. 7 illustrates only a portion of the trailing edge 130 extending in the radial direction, the entire trailing edge 130 extending in the radial direction may have the wavelike form, or the entire trailing edge 130 need not take the wavelike form. Additionally, a duty cycle, or ratio of the length 142 of the first level 132 to the length 144 of the second level 134, may be different in various embodiments to achieve optimal aerodynamic performance of the trailing edge 130.
FIG. 8 illustrates a system 100′ including a gas turbine 103′ which has a stationary airfoil 101′ (vane) and a rotating airfoil 105′ (blade) positioned downstream from the stationary airfoil 101′. The stationary airfoil 101′ has properties similar to the stationary airfoil 101 discussed above in the embodiments of FIGS. 2-6, including the trailing edge portion 108′ and other elements similar to the elements of the stationary airfoil 101 discussed above and numbered with prime notation. Although FIG. 8 illustrates a gas turbine 103′ with one stationary airfoil 101′ and one rotating airfoil 105′, one skilled in the art will realize that these airfoils are only a portion of respective rows of airfoils and that multiple such vane/blade rows may be used in the gas turbine engine 103′.
The wavelike form of the trailing edge portion 108′ provides several performance advantages during operation of the gas turbine 103′. Since the wavelike form of the trailing edge portion 108′ necessarily displaces material of the trailing edge portion 108′ away from the radial axis (see FIGS. 4-5), the moment of inertia of the trailing edge portion 108′ about the a radial axis 110 increases as compared to a conventional non-wavy trailing edge portion. Differences in pressure across a typical airfoil result in lateral bending forces on the trailing edge 106′, which are more effectively resisted by the wavelike form of the trailing edge portion 108′. As previously discussed, the trailing edge 106′ resistance to these lateral bending forces may be a limiting factor in minimizing the thickness of the trailing edge 106′, and thus a limiting factor to enhancing aerodynamic efficiency. Thus, the wavelike form of the trailing edge portion 108′ permits the thickness 118′ of the trailing edge 106′ to be minimized beyond that of a conventional trailing edge utilizing the same materials, and thereby achieves improved aerodynamic advantages. Such aerodynamic advantages include the ability of the trailing edge 106′ of the stationary airfoil 101′ to adequately mix the pressurized air from the suction side 102′ and the pressure side 104′, and to control the direction of air flow incident from the trailing edge 106′ to the rotating airfoil 105′. The stationary airfoil 101′ reduces instances and intensity of planar wakes 128′ incident from the stationary airfoil 101′ on the rotating airfoil 105′ of the gas turbine 103′ when compared to a thicker trailing edge of equivalent strength in a prior art non-wavy trailing edge. Such advantages are useful for airfoils of any material of construction, but are particularly useful for airfoils or airfoil trailing edge portions made of ceramic or ceramic matrix composite (CMC) materials where traditionally thicker trailing edge designs have been required than with traditional metal airfoil embodiments.
An additional performance advantage of the wavelike form of the trailing edge portion 108′ is an increased radial compliance of the trailing edge 106′ to thermal growth during the operation of the airfoil 101′. A ceramic or CMC airfoil is routinely subjected to rapid thermal transients, and because the trailing edge is thinner, it responds faster to these transients than the remainder of the airfoil. The growth of the trailing edge is constrained by the bulkier part of the airfoil, thus concentrating stresses in the trailing edge portion of the airfoil. The increased radial compliance of the trailing edge 106′ when compared to a prior art trailing edge provides some compliance in the radial direction and alleviates such thermal stresses in the trailing edge portion 108′.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims

1. An airfoil comprising:

a suction side and a pressure side joined along a trailing edge;

wherein a trailing edge portion of the airfoil is configured to take a wavelike form along a radial direction of the airfoil.

2. The airfoil of claim 1, wherein an amplitude of said wavelike form varies from a maximum value at the trailing edge to zero at a predetermined distance along a cord length of the airfoil.

3. The airfoil of claim 2, wherein an amplitude of said wavelike form at said trailing edge is in a range of 0.2-2 times a thickness of the trailing edge.

4. The airfoil of claim 3, wherein said amplitude of said wavelike form at said trailing edge is approximately equal to the thickness of the trailing edge.

5. The airfoil of claim 2, wherein a thickness the airfoil at said predetermined distance is in a range of 2-3 times a thickness of the trailing edge.

6. The airfoil of claim 1, wherein a wavelength of said wavelike form along said trailing edge is in a range of 2-4 times a thickness of the trailing edge.

7. The airfoil of claim 1, wherein the wavelike form comprises a sine wave form.

8. The airfoil of claim 1, wherein the wavelike form comprises a tapered square wave form comprising alternating flat levels having different relative elevations joined by respective sloped sections joining the two levels.

9. A system comprising:

a stationary airfoil;

a rotating airfoil positioned downstream from the stationary airfoil in a fluid flow stream;

wherein a trailing edge portion of the stationary airfoil is configured to take a wavelike form along a radial direction of the stationary airfoil effective to enhance a mixture of pressurized fluid from respective suction and pressure sides of the stationary airfoil downstream of the trailing edge and to reduce instances of planar wakes incident from said stationary airfoil onto said rotating airfoil.

10. The system of claim 9, wherein an amplitude of said wavelike form varies from a maximum at the trailing edge to zero at a predetermined distance along a cord length of the airfoil.

11. The system of claim 10, wherein a thickness the stationary airfoil at said predetermined distance is in a range of 2-3 times a thickness of the trailing edge.

12. The system of claim 9, wherein said trailing edge portion of the stationary airfoil comprises a ceramic matrix composite material.

13. The system of claim 9, wherein the wavelike form comprises a sine wave form.

14. The system of claim 9, wherein the wavelike form comprises a tapered square wave form comprising alternating flat levels having different relative elevations joined by respective sloped sections joining the two levels.

15. A system comprising a row of stationary airfoils upstream of a row of rotating airfoils in a working fluid flow stream, said respective stationary airfoils each comprising a suction side and a pressure side joined along a trailing edge, wherein the improvement comprises a trailing edge portion of each stationary airfoil comprising a wavelike form.

16. The system of claim 15, wherein an amplitude of said respective wavelike forms varies from a maximum at the trailing edge to zero along a chord length of the respective stationary airfoil, and a thickness of the respective stationary airfoil at said predetermined distance is in a range of 2-3 times a thickness of the trailing edge.

17. The system of claim 15, wherein said trailing edge portion of each stationary airfoil comprises a ceramic matrix composite material.

18. The system of claim 15, wherein the wavelike form comprises a sine wave form.

19. The system of claim 15, wherein the wavelike form comprises a tapered square wave form comprising alternating flat levels having different relative elevations joined by respective sloped sections joining the two levels.