Thin wall cooling system

[0002] This invention relates to cooling of thin wall structures and, more specifically, of thin wall ceramic structures. The cooling structure of the present invention has one or more channels that lie between two opposing surfaces of a thin wall structure.

[0003] Various means of cooling thin wall structures are known in the art. The necessity for such cooling exists for airfoils such as the blades or stator vanes of a gas turbine engine, for combustion structural elements of gas turbine engines, for rocket and jet engine exhaust nozzles, for the skin structure of high performance aircraft, and for other high temperature environment applications. In particular, turbine stators of advanced engines operate at a turbine inlet temperature far exceeding the capability of cooled superalloy material, even when coated with a thermal barrier coating, while at the same time advanced engines need to reduce cooling flow. Cooled ceramics have the potential to yield viable stator and blade designs for these demanding operating conditions.

[0004] An example of a structure for cooling a ceramic airfoil blade for a gas turbine engine is disclosed in U.S. Pat. No. 4,314,794, issued Feb. 9, 1982. In this application, segmented hollow ceramic washers are assembled with provision for airflow into the hollow portion. The cooling airflow then passes through the ceramic wall structure by transpiration facilitated by a porous ceramic wall. The emphasis is on cooling by cool airflow from an interior cavity to the external surface of the blade. Disadvantages to this design include the requirement for construction of the airfoil from a plurality of washers stacked cooperatively, as well as the requirement for use of a structural material that facilitates transpiration cooling. Both of these structural elements introduce unnecessary complexity and cost to the airfoil.

[0005] Another example of a ceramic structure use of through wall cooling flow is found in U.S. Pat. No. 5,030,060, issued Jul. 9, 1991. In this instance, cooling air conduit passages are formed to pass air from an interior chamber metal wall to an exterior ceramic surface wall or layer. The intent is for a cool air film to exist over the ceramic outer layer to prevent hot gas direct impingement on the surface of the ceramic layer. Both this structure and others, which use through wall cooling, are limited in cooling efficiency for reduction of blade surface temperature.

[0006] As can be seen, there is a need for a more efficient means of cooling thin wall structures such as found in gas turbine engines. The present invention incorporates the use of in-wall conduits to channel cooling fluid flow between the two opposing surfaces of, for example, ceramic wall gas turbine engine blades.

[0007] An improved thin wall cooling structure of the present invention comprises one or more channels formed between the two opposing surfaces of a thin wall structure. The channels traverse the thin wall structure generally parallel to the wall surfaces with cooling fluid exit and entry openings at the edge of the wall structure. Depending on the cooling requirements and cooling fluid characteristics, as well as the composition of the thin wall structure, the cooling channels vary in cross section dimension and the path between entry and exit openings. Also, the direction of coolant flow within one channel relative to another may be varied such as same direction flow (i.e., coflow) or opposed (i.e., counterflow).

[0008] These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

[0009] FIG. 1 illustrates a perspective view of a turbine vane with in-wall and through wall cooling channels according to an embodiment of the present invention;

[0010] FIG. 2 illustrates a cross section view of a turbine vane with cooling channels according to an embodiment of the present invention;

[0011] FIG. 3 illustrates a perspective schematic view of a turbine vane with edge walls removed and with generally parallel in-wall channels according to an embodiment of the present invention;

[0012] FIG. 4 illustrates an end cross-section view of a turbine blade with offset in-wall channels and three cavities according to an embodiment of the present invention;

[0013] FIG. 5 illustrates a partial interior cross-sectional view of adjacent channel entry and exit locations according to an embodiment of the present invention.

[0014] The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

[0015] Referring to FIGS. 1 through 3, a thin wall structure 10 such as a gas turbine engine blade or vane having an airfoil shape may include both through wall channels 20 and in-wall channels 30 formed therein and which comprise a thin wall cooling system. The term “thin wall” is intended to mean a wall with thickness on the order of about 10% or less with respect to the longest dimension of the two opposing surfaces forming the thin wall. The through wall channels 20 can allow fluid, such as air introduced into a plurality of vane cavities 12, 13, 14 at a cool temperature relative to the vane 10 exterior surface 15, to exit the vane 10. This can be for purposes of forming a cool air film over the exterior surface 15 to inhibit direct impingement of hot gases thereon. The through wall cooling method is well understood in the art.

[0016] In-wall channels 30, as illustrated, traverse the vane 10 intermediate the opposing surfaces 15, 16 such that the longitudinal axes of the channels 30 extend substantially parallel to the planes of the surfaces 15, 16. For purposes of illustration, the in-wall channels 30 are depicted as tubular, generally parallel conduits with entry openings 21 and exit openings 22 at vane 10 edges 17, 18, respectively. However, other channel structures are possible, such as irregular, turbolated internally finned or tortuous paths from edge 17 to edge 18. Further, the in-wall channels 30 need not all be of the same configuration and need not be equidistant apart as shown in the preferred embodiment. Also, the density of in-wall channels over a given area may be varied to address variances in cooling requirements. Likewise, the cross sectional area of the channels 30 may be varied based on temperature gradients, vane 10 wall composition, desired cooling effect, and like parameters.

[0017] It has been found by experiment that coolant flow through adjacent in-wall channels 30 should preferably be in opposite directions (i.e., counterflow) if it is desired to maintain the temperature relatively uniform at edges 17, 18 as illustrated in FIG. 3 schematic with edge walls removed indicating flow direction. If uniform directional flow is used (i.e., coflow), this can result in excessive vane 10 wall temperatures at the exit opening 22 edge due to the large cooling air heat energy accumulation in relatively low flow volume per hole.

[0018] The vane 10 in FIGS. 3 and 4 is illustrated, for purposes of example, with one and two cross ribs 24, 25. The configuration of cross ribs 24, 25 or additional ribs can be selected to provide support for the overall vane 10 pressure loads, to minimize cross wall pressure difference, to tailor the cooling structure design, and to control distribution of cooling fluid. The vane 10 has through wall channels 20, in-wall channels 30, and trailing edge discharge channel 23 to incorporate the combination of various cooling methods to achieve a particular temperature profile for the vane 10. The in-wall channels are also illustrate with an offset between adjacent channels in FIG. 4 as an alternate embodiment.

[0019] Referring to FIG. 5, a partial interior cross-sectional view of adjacent in-wall channels of a preferred embodiment illustrating entry and exit locations, the in-wall channels 30 have exit openings, 22 located to discharge coolant into the interior of the vane 10. The exit openings 22 may be formed by machining the interior surface 16 with a coolant fluid exit structure such as slots 27 alternating with crossover channels 26.

[0020] The materials for the preferred embodiment vane 10-wall structure are ceramic, including ceramic matrix composites, silicon nitride and silicon carbide. However, the use of in-wall cooling channels 30 applies in general to other materials.

[0021] While the preferred embodiment has been described in the context of cooling a gas turbine engine blade or vane, the invention may be used as a more general heat transfer device between the external environment experienced by the opposing surfaces 15, 16 and the fluid flowing through the in-wall channels 30 where a temperature differential exists between the environment and the fluid. For example, the thin wall structure 10 may be used to transfer heat from an elevated temperature level fluid to a relatively cooler external environment.

[0022] It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.