STRUCTURE AND METHOD FOR IMPROVING FILM COOLING USING SHALLOW TRENCH WITH HOLES ORIENTED ALONG LENGTH OF TRENCH
A turbine airfoil includes a plurality of shallow trenches. Each trench includes a plurality of film holes disposed within and located along the lengthwise direction of the trench and angled through an airfoil substrate in the lengthwise direction of the trench.
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The invention relates generally to film-cooled parts and more particularly to a method of film cooling common locations on virtually all cooled turbine airfoils.
Gas turbines and other high-temperature equipment use film cooling extensively for effective protection of the hot gas path components, such as turbine blades. Film cooling refers to a technique for cooling a part in which cool air is discharged through a plurality of small holes in the external walls of the part to provide a relatively thin, cool layer or barrier along the external surface of the part and prevent or reduce direct contact with hot gasses.
Common locations employed to cool turbine airfoils include, among others, the airfoil leading edge showerhead film and film holes on forward endwall regions. One common cooling technique utilizes rows of axially round holes inside a shallow trench in which the axis of each hole is oriented substantially transverse to the lengthwise direction of the trench. The use of a shallow trench increases spreading of the film cooling, making the film cooling less susceptible to freestream turbulence effects, and also tolerant to effects due to deposits on the surface.
These known turbine airfoil film cooling techniques using shallow trenches improve film cooling effectiveness over prior film cooling techniques that employ film holes in the absence of shallow trenches. It would be advantageous to provide a next generation of turbine airfoil film cooling that improves film cooling effectiveness beyond that achievable using known turbine airfoil film cooling techniques that employ shallow trenches.
BRIEF DESCRIPTIONBriefly, in accordance with one embodiment, a turbine airfoil is configured with at least one shallow trench, each trench comprising a plurality of film holes disposed therein and located along the lengthwise direction of the corresponding trench and angled through a corresponding airfoil substrate substantially in the lengthwise direction of the corresponding trench.
According to another embodiment, a method of film cooling a turbine airfoil comprises:
configuring a turbine airfoil with at least one shallow trench having a lengthwise direction in a desired location; and
providing a plurality of film cooling holes within each trench, each film cooling hole having a central axis oriented substantially in the lengthwise direction of the corresponding trench such that film jets emanating from the plurality of film cooling holes issue into the corresponding trench substantially parallel to the lengthwise direction of the corresponding trench.
According to yet another embodiment, a film-cooled aerodynamic component comprises at least one shallow trench having a length and a width, each trench comprising a plurality of film holes disposed therein along the lengthwise direction of the trench, each film hole angled through the aerodynamic component substantially in the lengthwise direction of the corresponding trench.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
While the above-identified drawing figures set forth alternative embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.
DETAILED DESCRIPTIONHot gases may flow in any direction relative to the lengthwise direction 46 of shallow trench 14, but the majority of applications will have hot gases flowing substantially transverse to the lengthwise direction 46 of shallow trench 14. Coolant passes out through film-cooling holes 42 in a direction substantially parallel to the lengthwise direction 46, filling the trench 14 prior to exiting the trench, and cooling airfoil part 40. Because the central axis 44 of each film-cooling hole 42 is substantially parallel with the shallow trench 14 side walls 16, substantially all of the coolant exiting the film-cooling holes 42 is allowed to fill in the length of the trench 14 and avoid immediate mixing with the hot gases, thereby also exiting the trench 14 as a more continuous cooling layer in the lengthwise direction 46 of airfoil part 10 to maximize optimization of airfoil part 40 cooling.
According to one embodiment, the centerline 44 of the film cooling holes 42 is oriented between about 15 degrees and about 50 degrees relative to the bottom surface 80 of the trench 14 illustrated in
In some embodiments, the depth of the shallow trench 14 is less than the average throat diameter of the film cooling holes 42. In other embodiments, the depth of the shallow trench 14 is less than about 50% of the average throat diameter of the film cooling holes 42. These relative dimensions are in marked contrast to deep slots often used in the prior art.
As shown in
In summary explanation, a structure and method is described herein for improving film cooling for a variety of turbine airfoil locations, including without limitation, the showerhead film and the film holes on the forward endwall regions of a turbine airfoil. Rows of film holes, or with holes oriented axially along the trench width inside shallow trenches, are replaced by holes having corresponding central axis oriented substantially in the lengthwise direction of the corresponding trenches. The use of the shallow trench increases spreading of the film cooling, making the film cooling less susceptible to freestream turbulence effects, and also more tolerant to effects due to deposits on the surface of the turbine airfoil. It shall be understood that the embodiments described herein are in no way restricted to use of round holes and that many other hole shapes may be employed to provide the advantages in accordance with the principles described herein.
The orientation of film holes, generally rows of film holes, angled through the substrate but along the direction of the trench rather than transverse to the direction of the trench (i.e., oriented along the trench width) cause the film jets to issue into the trench without hitting the side walls or other obstructions. The coolant flow more easily fills the trench before issuing onto the external component aerodynamic surface as a nearly uniform layer of film cooling. This structure is particularly beneficial for rows of film holes that are otherwise constrained by manufacturing to be oriented in fixed directions, such as showerhead film rows that are radial, and also forward endwall film rows that are circumferential (azimuthal). Film cooling hole orientation along the length of the trench also benefits film rows with greater spacing between the individual holes, since the trench acts as a buffer region for coolant spreading before the coolant interacts with the hot mainstream gases.
The shallow trench(s) can be formed in the protective coatings of the component according to one embodiment. The shallow trench(s) can be partially in the substrate according to another embodiment. These embodiments improve film cooling effectiveness for common airfoil locations that are constrained in geometry and manufacturing. Such regions would not otherwise be able to employ axially oriented film holes or even shaped film hole exits. Particular embodiments were found to improve regional airfoil film cooling by about 25% over that achievable with known structures. The embodiments described herein provide an advantage in ability to reduce total cooling flow for the turbine and increase efficiency offered commercially.
It shall be understood that bond layers, also known as bondcoats, as well as the TBC topcoats can be comprised of multiple layers or compositions. The embodiments described herein are not to be limited to a simple bondcoat and topcoat each of one composition only. Exemplary products today use at least a two-layer bondcoat system. Furthermore, the shallow trench might be formed only in the topcoat, or into the bondcoat, or even into the substrate, since it depends on the relative thicknesses used.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims
1. A turbine airfoil comprising at least one shallow trench, each trench comprising a plurality of film holes disposed therein as a single row and located along the lengthwise direction of the corresponding trench and angled through a corresponding airfoil substrate substantially in the lengthwise direction of the corresponding trench.
2. The turbine airfoil according to claim 1, wherein the shallow trench is disposed within a showerhead region of the turbine airfoil.
3. The turbine airfoil according to claim 1, wherein an angle between a central axis of each hole and the bottom surface of its corresponding trench is between about 15 degrees and about 50 degrees.
4. The turbine airfoil according to claim 1, wherein an angle between a central axis of each hole and the bottom surface of its corresponding trench is between about 20 degrees and about 35 degrees.
5. The turbine airfoil according to claim 1, wherein the shallow trench is disposed on a forward endwall region of the turbine airfoil.
6. The turbine airfoil according to claim 1, wherein the depth of the shallow trench is less than the average throat diameter of the corresponding film cooling holes.
7. The turbine airfoil according to claim 1, wherein each trench comprises a width substantially equal to the maximum exit width of a corresponding film hole measured in the direction as that which defines the trench width.
8. The turbine airfoil according to claim 1, wherein each trench comprises a width between about 1.0 and about 1.5 times the maximum exit footprint width of a corresponding film hole.
9. The turbine airfoil according to claim 1, wherein each trench is substantially rectangular and comprises side walls having an angle between about 70 degrees and about 90 degrees with respect to the bottom surface of the trench.
10. The turbine airfoil according to claim 1, wherein each trench is substantially rectangular comprising at least one rounded or chamfered top corner and at least one filleted internal corner.
11. A method of film cooling a turbine airfoil, the method comprising:
- configuring a turbine airfoil with at least one shallow trench having a lengthwise direction in a desired location; and
- providing a plurality of film cooling holes within each trench disposed therein as a single row, each film cooling hole having a central axis oriented substantially in the lengthwise direction of the corresponding trench such that film jets emanating from the plurality of film cooling holes issue into the corresponding trench substantially parallel to the lengthwise direction of the corresponding trench.
12. The method according to claim 11, wherein at least one shallow trench is disposed within a showerhead region of the turbine airfoil.
13. The method according to claim 11, wherein at least one shallow trench is disposed on a forward endwall region of the turbine airfoil.
14. The method according to claim 11, wherein configuring a turbine airfoil with at least one shallow trench comprises configuring the depth of each shallow trench to be less than the average throat diameter of the corresponding film cooling holes.
15. A film-cooled aerodynamic component comprising at least one shallow trench having a length and a width, each trench comprising a plurality of film holes disposed therein as a single row along the lengthwise direction of the trench, each film hole angled through the aerodynamic component substantially in the lengthwise direction of the corresponding trench.
16. The film-cooled aerodynamic component according to claim 15, further comprising:
- an aerodynamic component substrate;
- a bond layer bonded to a surface of the aerodynamic component substrate; and
- an overlying thermal barrier coating attached to the opposite side of the bond layer, wherein the shallow trench penetrates the bond layer and the overlying thermal barrier coating, and further wherein each film hole penetrates the aerodynamic component substrate.
17. The film-cooled aerodynamic component according to claim 15, wherein the shallow trench further partially penetrates the substrate.
18. The film-cooled aerodynamic component according to claim 15, wherein at least one shallow trench is disposed within a showerhead region of a turbine airfoil.
19. The film-cooled aerodynamic component according to claim 15, wherein at least one shallow trench is disposed on a forward endwall region of a turbine airfoil.
20. The film-cooled aerodynamic component according to claim 15, wherein an angle between a central axis of each hole and the bottom surface of its corresponding trench is between about 15 degrees and about 50 degrees.
21. The film-cooled aerodynamic component according to claim 15, wherein an angle between a central axis of each hole and the bottom surface of its corresponding trench is between about 20 degrees and about 35 degrees.
22. The film-cooled aerodynamic component according to claim 15, wherein the depth of each shallow trench is less than the average throat diameter of the corresponding film cooling holes.
23. The film-cooled aerodynamic component according to claim 15, wherein each trench comprises a width substantially equal to the maximum exit width of a corresponding film hole measured in the direction as that which defines the trench width.
24. The film-cooled aerodynamic component according to claim 15, wherein each trench comprises a width between about 1.0 and about 1.5 times the maximum exit footprint width of a corresponding film hole.
25. The film-cooled aerodynamic component according to claim 15, wherein each trench is substantially rectangular and comprises side walls having an angle between about 70 degrees and about 90 degrees with respect to the bottom surface of the trench.
26. The turbine airfoil according to claim 15, wherein each trench is substantially rectangular comprising at least one rounded or chamfered top corner and at least one filleted internal corner.
Type: Application
Filed: Oct 23, 2009
Publication Date: Apr 28, 2011
Applicant: GENERAL ELECTRIC COMPANY (SCHENECTADY, NY)
Inventor: Ronald Scott Bunker (Niskayuna, NY)
Application Number: 12/604,460
International Classification: F01D 25/12 (20060101); F01D 5/18 (20060101);