Structure and method for improving film cooling using shallow trench with holes oriented along length of trench   

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.

Briefly, 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:

FIG. 1 is a perspective view illustrating a plurality of film-cooling holes inside a shallow trench known in the art;

FIG. 2 illustrates the angular relationship between the shallow trench walls and the central axis of a film-cooling hole depicted in FIG. 1 depicting in further detail;

FIG. 3 is a perspective view illustrating film-cooling flow due to lateral flow blockage for the film-cooling holes shown in FIG. 1;

FIG. 4 is a perspective view illustrating a plurality of film-cooling holes inside a shallow trench in which each hole includes a central axis oriented in the lengthwise direction of the trench according to one embodiment;

FIG. 5 illustrates a plurality of film-cooling holes inside corresponding shall trenches applied to a showerhead film cooled region of a turbine airfoil according to one embodiment;

FIG. 6 is an end view of the film-cooling holes depicted in FIG. 4; and

FIG. 7 is a view transverse to the lengthwise direction of the shallow trench depicted in FIGS. 4 and 6 showing another view of the central axis of a film-cooling hole oriented in the lengthwise direction of the trench.

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 DESCRIPTION

FIG. 1 is a perspective view of an airfoil part 10 illustrating a plurality of film-cooling holes 12 inside a shallow trench 14 known in the art. Part 10 is cooled by a fluid coolant passing through an interior of the part 10. The fluid coolant may be compressor extraction air or another fluid having known thermodynamic properties such as nitrogen. Some of the coolant passes through film-cooling holes 12 to an exterior of part 10. Part 10 may have several such shallow trenches, though only one is shown here for purposes of illustration.

FIG. 2 illustrates an end view of the trench 14 depicted in FIG. 1 showing the angular relationship between the shallow trench 14 side walls 16 and the central axis 18 of each film-cooling hole 12. Hot gases 30 shown in FIG. 3 flow in a direction transverse to the lengthwise direction of channel 14. Coolant passes out through film-cooling holes 12 in a direction substantially parallel to the flow of the hot gases 30, spreads within the trench 14 prior to coming out of the trench, and cooling airfoil part 10. Because the central axis 18 of each film-cooling hole 12 forms an angular relationship with the shallow trench 14 side walls 16, some of the coolant exiting the film-cooling holes 12 are blocked or otherwise restricted to prevent the maximum amount of coolant 32 from mixing with the hot gases 30 to impede optimization of airfoil part cooling. FIG. 3 is a perspective view illustrating film-cooling flow 32 due to lateral flow blockage for the film-cooling holes 12 shown in FIG. 1.

FIG. 4 is a perspective view illustrating a plurality of film-cooling holes 42 inside a shallow trench 14 located on an airfoil part 40 in which each hole 42 includes a central axis 44 oriented in the lengthwise direction 46 of the trench 14 according to one embodiment. Part 40 is cooled by a fluid coolant passing through an interior of the part 40. The fluid coolant may be compressor extraction air or another fluid having known thermodynamic properties such as nitrogen. Some of the coolant passes through film-cooling holes 12 to an exterior of part 40. Part 40 may have several such shallow trenches, though only one is shown here for purposes of illustration.

Hot 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.

FIG. 5 illustrates a plurality of film-cooling holes 42 inside corresponding shallow trenches 14 applied to a showerhead film cooled region 50 of a turbine airfoil part according to one embodiment. Each film-cooling hole 42 has a central axis oriented substantially in the lengthwise direction 46 of the corresponding shallow trench 14 and substantially parallel to the side walls 16 of the corresponding shallow trench 14.

FIG. 6 is an end view of the film-cooling holes 42 inside the shallow trench 14 located on the airfoil part 40. A substrate 60 represents the wall of an airfoil part which requires cooling on one or more surfaces, e.g., the wall of airfoil part 40 in FIG. 4. The substrate 60 includes hot surface 62 and cooler surface 64. Combustion gases enumerated 30 in FIG. 3 are conventionally channeled over the airfoil part 40, i.e., over coated surface 73. Coolant air 32 flows upwardly from the cooler surface through film cooling holes 42. The holes have an average throat diameter 76. Substrate 60 is partially coated with a bond layer 70 and an overlying thermal bather coating (TBC) 72. In this embodiment, shallow trench 14 is formed within the bond layer 70 and TBC 72, and has a desired depth. Usually (but not always), the side-walls 16 of the shallow trench 14 are substantially perpendicular to surface 62 of the substrate 60. (Thus, the side-walls 16 are usually substantially perpendicular to the bottom surface 80 of trench 14).

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 FIG. 7. According to another embodiment, the centerline of the film cooling holes 42 is oriented between about 20 degrees and about 35 degrees relative to the bottom surface 80 of the trench 14. The width of the trench 14 is substantially equal to the maximum exit width of the film cooling hole 42 according to one aspect of the invention. If a film cooling hole is perfectly aligned in the lengthwise direction of its corresponding trench, then the width is equal to the film cooling hole diameter for a round hole. If the film cooling hole 42 is aligned somewhat off angle, such as up to 20 degrees, then the width would be greater. It shall be understood that the trench width can be greater than the film hole exit and still work well to achieve the desired cooling results according to the principles described herein, whether the film hole is perfectly aligned or not. One embodiment employs a trench width from about 1.0 to about 1.5 times the maximum exit footprint width of its corresponding film cooling holes 42. It shall also be understood that a trench 14 need not have perfect square-edged features. Any one or more of the top corners of the trench 14 can be somewhat rounded or chamfered, and any one or more of the internal corners of the trench 14 can have small fillets.

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 FIG. 6, trench 14 serves as a “spillway” trench for coolant 32 exiting cooling holes 42. Side-walls 16 direct the flow of the coolant 32. As a result, the coolant spreads into the trench prior to exiting the trench along hot surface 73 (i.e., surface 62 as-coated). The coolant thus stays in close contact with the hot surface, rather than separating from it quickly, as the increased coolant spreading over the hot surface is now less susceptible to freestream turbulence effects, and also is more tolerant to effects due to deposits on the surface. This in turn results in greater cooling effectiveness for the airfoil part 40 as stated herein before.

FIG. 7 is a view transverse to the lengthwise direction 46 of the shallow trench 14 depicted in FIGS. 4 and 6 showing another view of the central axis 44 of a film-cooling hole 42 oriented in the lengthwise direction 46 of the trench 14.

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.