TRANSPIRATION-COOLED ARTICLE HAVING NANOCELLULAR FOAM

Abstract

A transpiration-cooled article includes a body wall that has first and second opposed surfaces. The first surface is adjacent a passage that is configured to receive a pressurized cooling fluid. At least a portion of the body wall includes a nanocellular foam through which the pressurized cooling fluid from the passage can flow to the second surface. The article can be an airfoil that includes an airfoil body that has an internal passage and an outer gas-path surface. At least a portion of the airfoil body includes a nanocellular foam through which cooling fluid from the internal passage can flow to the gas-path surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure claims priority to U.S. Provisional Patent Application No. 62/004,254, filed May 29, 2014.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under contract number N00014-12-C-0434 awarded by the United States Navy. The government has certain rights in the invention.

BACKGROUND

This disclosure relates to cooled structures. Structures that operate in relatively high-temperature environments can be cooled by providing a cooling fluid over the outer surfaces. For example, in a gas turbine engine, airfoils include machined holes for film cooling using relatively cool air from the compressor. Film cooling is effective on the pressure side of an airfoil; yet, it is not possible on the suction side. The suction side has a high degree of boundary layer mixing causing a significant decrease in cooling effectiveness.

SUMMARY

A transpiration-cooled airfoil according to an example of the present disclosure includes an airfoil body that has an internal passage and an outer gas-path surface. At least a portion of the airfoil body includes a nanocellular foam through which cooling fluid from the internal passage can flow to the gas-path surface.

In a further embodiment of any of the foregoing embodiments, the airfoil body includes at least one discrete window of the nanocellular foam surrounded by solid walls.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam has an average pore size of 10 micrometers to 100 nanometers.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam has a porosity of 5-95%.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam has a pore volume of 0.01-0.1 milliliters per gram.

In a further embodiment of any of the foregoing embodiments, the airfoil body includes a leading edge and a trailing edge and a first sidewall and a second sidewall that is spaced apart from the first sidewall. The first sidewall and the second sidewall join the leading edge and the trailing edge and at least partially define the internal passage. The nanocellular foam is located in the first sidewall. The first sidewall is a suction side of the airfoil body.

In a further embodiment of any of the foregoing embodiments, the airfoil body includes a leading edge and a trailing edge and a first sidewall and a second sidewall that is spaced apart from the first sidewall. The first sidewall and the second sidewall join the leading edge and the trailing edge and at least partially define the internal cavity. The airfoil body extends from a platform end wall, and the nanocellular foam is in the platform end wall.

A transpiration-cooled article according to an example of the present disclosure includes a body wall that has first and second opposed surfaces. The first surface is adjacent a passage that is configured to receive a pressurized cooling fluid. At least a portion of the body wall includes a nanocellular foam through which the pressurized cooling fluid from the passage can flow to the second surface.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam is metallic.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam is selected from the group consisting of nickel, tantalum, tungsten, rhenium, niobium, hafnium, platinum, ruthenium, rhodium, palladium, osmium, iridium, copper, iron, molybdenum, yttrium, manganese, aluminum, chromium, cobalt, and combinations thereof.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam is ceramic material.

In a further embodiment of any of the foregoing embodiments, the ceramic material is selected from the group consisting of oxides, nitrides, carbides, borides, silicides, and combinations thereof.

In a further embodiment of any of the foregoing embodiments, the ceramic material is a ternary ceramic.

In a further embodiment of any of the foregoing embodiments, the ceramic material is selected from the group consisting of manganese oxide, zinc oxide, silicon carbide, aluminum oxide, and combinations thereof.

In a further embodiment of any of the foregoing embodiments, the body wall includes at least one discrete window of the nanocellular foam surrounded by solid wall.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam has an average pore size of less than 10 micrometers.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam has a porosity of 5-95%.

In a further embodiment of any of the foregoing embodiments, the nanocellular foam has a pore volume of 0.01-0.1 milliliters per gram.

A transpiration-cooled system according to an example of the present disclosure includes a passage configured to receive a pressurized cooling fluid, and a wall that has first and second opposed surfaces. The first surface is adjacent the passage, and the second surface is a gas-path surface that has a design boundary flow condition. At least a portion of the wall includes a nanocellular foam through which the pressurized cooling fluid from the passage can flow to the second surface. The nanocellular foam has controlled pore characteristics with respect to a design discharge velocity of the pressurized cooling fluid from the nanocellular foam and the design boundary flow condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

FIG. 1 illustrates an example gas turbine engine.

FIG. 2 illustrates a cross-section through a selected portion of a transpiration-cooled article.

FIG. 3 illustrates a micrograph of a representative portion of a nanocellular foam.

FIG. 4 illustrates another example transpiration-cooled article.

FIG. 5 illustrates a cross-section according to the section line shown in FIG. 4.

FIG. 6 illustrates an isolated view of a cross-section through a nanocellular foam window.

FIG. 7 illustrates an isolated view of a cross-section through another example nanocellular foam window.

FIG. 8 illustrates a cross-section through a selected portion of another example transpiration-cooled article.

DETAILED DESCRIPTION

FIG. 1 illustrates an example gas turbine engine 20. The gas turbine engine 20 disclosed herein is a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a bypass flow path B in a bypass duct defined within a nacelle 15, while the compressor section 24 drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it is to be understood that this disclosure is not limited to two-spool turbofans and the teachings herein may be applied to other types of turbine engines, including but not limited to direct-drive engines, three-spool engines, and ground-based power turbines.

The engine 20 includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

The low speed spool 30 includes an inner shaft 40 that interconnects a fan 42, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in the exemplary gas turbine engine 20 is illustrated as a geared architecture 48, to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10). The geared architecture 48 can be an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3, and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The above parameters are only exemplary and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]^0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second.

FIG. 2 illustrates a cross-section through a selected portion of an example transpiration-cooled article 60 (hereafter “article 60”) that can be used in the turbine engine 20. The article 60 can be an airfoil component, a blade outer air seal, a combustor liner, or the like that is exposed to high temperatures. Although the article 60 may be described with respect to use in the environment of the engine 20 or a similar machine, this disclosure is not limited to turbine engines or turbine engine components.

The article 60 includes a body wall 62 that has first and second opposed surfaces 64a and 64b. The first surface 64a is adjacent a passage 66 that is configured to receive a pressurized cooling fluid. For example, the passage 66 is connected with a source of pressurized cooling fluid, such as but not limited to, pressurized air from the compressor section 24.

At least a portion of the body wall 62 includes nanocellular foam 68 through which the pressurized cooling fluid from the passage 66 can flow to the second surface 64b, as represented at 70, to cool the second surface 64b.

The nanocellular foam 68 has controlled pore characteristics with respect to a design discharge velocity of the pressurized cooling fluid 70 and a design boundary flow condition. For example, the second surface 64b of the body wall 62 is a gas-path surface (e.g., in core flow path C). Friction between the moving gas in the gas-path and the second surface 64b creates a boundary layer, generally represented at 72. The gas in the boundary layer 72 moves at a slower velocity than the main flow of gas in the gas-path, represented at G. The controlled pore characteristics of the nanocellular foam 68 are selected such that, at a predefined state of operation having a given pressure of pressurized cooling fluid in the passage 66 and known characteristics that define a design boundary flow condition of the boundary layer 72, there is a design discharge velocity of the pressurized cooling fluid that is leaked or emitted from the nanocellular foam 68. For example, the pore characteristics of the nanocellular foam 68 are selected such that the design discharge velocity is below a velocity threshold that would otherwise jet the pressurized cooling fluid through the boundary layer 72 into the main gas-path flow, where it would be lost and fail to efficiently provide cooling along the second surface 64b of the body wall 62. Rather, the controlled pore characteristics of the nanocellular foam 68 provide a pressure drop between the passage 66 and the second surface 64b such that the design discharge velocity is below the threshold and the pressurized cooling fluid leaks into the boundary layer 72 and across the surface 64b rather than jetting through the boundary layer 72. In this regard, the nanocellular foam 68 can facilitate cooling of the body wall 62.

FIG. 3 shows a micrograph of a representative cross-section of the nanocellular foam 68. As shown, the nanocellular foam 68 includes an interconnected network of ligaments 80 between which interconnected pores 82 extend. The nanocellular foam 68 has an open porosity through which the pressurized cooling fluid can travel from the passage 66 to the second surface 64b. The path provided by the pores 82 is circuitous and narrow such that there is a relatively large pressure drop across the nanocellular foam 68. The pressure drop and circuitous path slow the velocity of the pressurized cooling fluid such that the nanocellular foam 68 emits the cooling fluid at the second surface 64b with a low design discharge velocity.

The nanocellular foam 68 can be formed of a metallic material, polymeric material, a ceramic material, or combinations thereof. The selected composition can depend on article design factors, such as but not limited to, temperature resistance and strength. The metallic material can be selected from nickel, tantalum, tungsten, rhenium, niobium, hafnium, platinum, ruthenium, rhodium, palladium, osmium, iridium, copper, iron, molybdenum, yttrium, manganese, aluminum, chromium, cobalt, and combinations thereof. The ceramic material can be selected from oxides, nitrides, carbides, borides, silicides, and combinations thereof.

In a further example, the ceramic material can be a ternary ceramic (a MAX phase material). A MAX phase material has a formula Mn+1AXn, where n=1-3, M is an early transition metal, A is an A-group element of the Periodic Table, and X includes at least one of carbon and nitrogen. In further examples, the M in the formula can be selected from Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and combinations thereof, and the A in the formula can be selected from Cd, Al, Gd, In, Tl, Si, Ge, Sn, Pb, P, As, S, and combinations thereof. The MAX phase material can be selected from: Ti₂CdC, Sc₂InC, Ti₂AlC, Ti₂GaC, Ti₂InC, Ti₂TlC, V₂AlC, V₂GaC, Cr₂GaC, Ti₂AlN, Ti₂GaN, Ti₂InN, V₂GaN, Cr₂GaN, Ti₂GeC, Ti₂SnC, Ti₂PbC, V₂GeC, Cr₂Alc, Cr₂GeC, V₂PC, V₂AsC, Ti₂SC, Zr₂InC, Zr₂TlC, Nb₂AlC, Nb₂GaC, Nb₂InC, Mo₂GaC, Zr₂InN, Zr₂TlN, Hf₂InC, Hf₂TlC, Ta₂AlC, Ta₂GaC, Ti₂GeC, Ti₂SnC, Ti₂PbC, V₂GeC, Cr₂AlC, Cr₂GeC, Zr₂SnC, Zr₂PbC, Nb₂SnC, Hf₂SnC, Hf₂PbC, Hf₂SnN, V₂PC, V₂AsC, Nb₂PC, Nb₂AsC, Ti₂SC, Zr₂SC, Nb₂SC, Hf₂SC, Ti₃AlC2, V₃AlC₂, Ta₃AlC₂, Ti₃SiC₂, Ti₃GeC₂, Ti₃SnC₂, Ti₄AlN₃, V₄AlC₃, Ti₄GaC₃, Nb₄AlC₃, Ta₄AlC₃, Ti₄SiC₃, Ti4GeC₃, and combinations thereof, but is not limited to these examples.

In further examples, the ceramic material can include at least one of manganese oxide (MnO₂), zinc oxide (ZnO), silicon carbide (SiC), silicon nitride (Si₃N₄) or alumina (Al₂O₃). Examples of polymer materials can include polyamide 66, polyesters, polycarbonates, and polyimede. The disclosed metallic and ceramic materials have relatively high temperature resistance and can, thus, withstand high temperature environments, such as those encountered in the gas turbine engine 20.

In further examples, the controlled pore characteristics of the nanocellular foam 68 can include one or more of a controlled average pore size, controlled hydraulic diameter, percent porosity, surface area and controlled pore volume that are selected with respect to the design discharge velocity of the pressurized cooling fluid from the nanocellular foam 68 and the design boundary flow condition based on the boundary layer 72. For example, the nanocellular foam 68 has an average pore size of 10 micrometers to 100 nanometers, and in further examples less than 1 micrometer. In a further example, the nanocellular foam 68 has a controlled porosity of 5-95%, and in a further example has a porosity of 10-50%. In yet a further example, the nanocellular foam has a controlled pore volume of 0.01-0.1 milliliters per gram.

FIG. 4 illustrates another example transpiration-cooled article, which in this example is a transpiration-cooled airfoil 160 (hereafter “airfoil 160”). FIG. 5 shows a cross-section taken along the section line shown in FIG. 4. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements.

The airfoil 160 includes an airfoil body 160a that has an inner surface 164a and an outer, gas-path surface 164b. The airfoil body includes an internal passage 166 and, similar to the article 60, at least a portion of the airfoil body 160a includes nanocellular foam 168 through which cooling fluid from the internal passage 166 can flow to the gas-path surface 164b. The geometry of the internal passage 166 and the location of the nanocellular foam 168 are not limited to that shown. In further examples, although not limited, the article can be an article as disclosed in U.S. Pat. No. 7,144,220, incorporated in its entirety herein by reference, and the nanocellular foam can be located according to the location of the reticulated regions disclosed therein. The nanocellular foam of the present disclosure can be fabricated using sol-gel processing or nanowire processing, but is not limited to these techniques.

In sol-gel processing, the sol is a mixture of precursor materials in a solvent. The sol can contain dispersed metal-containing compounds, a monomer and a solvent that is a non-aqueous and polar. The sol is then converted to a gel when the precursor materials react. The metal-containing compounds react with the monomer to form metal containing regions bound by polymer ligands. The metal from the salt initiates a reaction to polymerize the polymer precursor and agglomerate metal-intermediates into metal-containing regions bond together by the polymeric ligands. The metal from the salt will later form the metal ligaments of the nanocellular foam 68, 168. The solvent is then removed from the gel using supercritical drying to produce a dry gel of the metal-containing regions bond together by the polymeric ligands. The dry gel is then thermally converted to a metal cellular structure by thermal consolidation or sintering of the metal-containing regions, which also decomposes the polymer ligands. One or more stages of heat treatment can also be conducted in an oxygen-containing environment, such as air, a substantially oxygen-free environment, or a combination thereof to control or alter composition.

Nanowire processing involves forming an arrangement of loose nanowires into the shape of an article using a deposition technique or mold. The nanowires are then bonded into a unitary structure. For example, the nanowires can be sintered together using a suitable technique to form an article. During the thermal sintering, the surfaces of the nanowires that are in contact with each other permanently bond together. The loose nanowires thus serve as the fundamental “building blocks” for fabricating the article.

The airfoil 160 includes an airfoil portion 182 that extends between a leading end 182a and a trailing end 182b and a first sidewall 182c and a second sidewall 182d that is spaced apart from the first sidewall 182c. The sidewalls 182c/182d join the leading end 182a and the trailing end 182b. The internal passage 166 is defined, at least in part, by the first and second sidewalls 182c/182d, which also correspond to the gas-path surface 164b.

In this example, the airfoil portion 182 extends from a platform end wall 184. The platform end wall 184 is on a radially inner end of the airfoil portion 182, relative to the orientation of the airfoil 160 with respect to the longitudinal axis A when the airfoil 160 is mounted in the engine 20. In this example, the airfoil 160 also includes an outer platform end wall 186, although the airfoil 160 is not limited to the design shown, which is a static vane. The airfoil 160 can alternatively have a different design or can be a rotatable blade, such as, but not limited to, a fan blade, a compressor blade, or a turbine blade.

The nanocellular foam 168 can be on the airfoil portion 182, the platform end walls 184/186, or both of these areas. In this example, the nanocellular foam 168 is provided in multiple, discrete windows that are each surrounded by solid walls 188 of the airfoil 160. Although plural windows of equivalent geometry are shown, fewer or additional windows could be used, and the windows may have equivalent or different geometries from each other.

The cooling fluid in the internal passage 166 can only exit from the internal passage 166 through the nanocellular foam 168 windows, as shown at 190 in FIG. 5.

FIG. 6 shows an isolated view of an area through one of the nanocellular foam 168 windows. In this example, the nanocellular foam 168 is flush with the gas-path surface 164b. In an alternate example shown in FIG. 7, the nanocellular foam 168 window is recessed at least from the gas-path surface 164b. The recessing of the nanocellular foam 168 window further facilitates leaking the cooling fluid across the gas-path surface 164b with a desired design discharge velocity below a given threshold, discussed above. As can be appreciated, the above examples of the pore characteristics and composition can also be incorporated into the article 160.

FIG. 8 shows another example transpiration-cooled airfoil 260. In this example, rather than one or more discrete windows of nanocellular foam, a substantial portion of the wall of the airfoil is nanocellular foam 268. For example, at least 50% or more of the area of the wall of the airfoil 260 can be formed of the nanocellular foam 268, to facilitate cooling over a greater surface area.

Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

1. A transpiration-cooled airfoil comprising:

an airfoil body that includes an internal passage and an outer gas-path surface, and

at least a portion of the airfoil body includes a nanocellular foam through which cooling fluid from the internal passage can flow to the gas-path surface.

2. The transpiration-cooled article as recited in claim 1, wherein the airfoil body includes at least one discrete window of the nanocellular foam surrounded by solid walls.

3. The transpiration-cooled article as recited in claim 1, wherein the nanocellular foam has an average pore size of 10 micrometers to 100 nanometers.

4. The transpiration-cooled article as recited in claim 1, wherein the nanocellular foam has a porosity of 5-95%.

5. The transpiration-cooled article as recited in claim 4, wherein the nanocellular foam has a pore volume of 0.01-0.1 milliliters per gram.

6. The transpiration-cooled airfoil as recited in claim 1, wherein the airfoil body includes a leading edge and a trailing edge and a first sidewall and a second sidewall that is spaced apart from the first sidewall, the first sidewall and the second sidewall join the leading edge and the trailing edge and at least partially define the internal passage, and the nanocellular foam is located in the first sidewall, and the first sidewall is a suction side of the airfoil body.

7. The transpiration-cooled airfoil as recited in claim 1, wherein the airfoil body includes a leading edge and a trailing edge and a first sidewall and a second sidewall that is spaced apart from the first sidewall, the first sidewall and the second sidewall join the leading edge and the trailing edge and at least partially define the internal cavity, the airfoil body extending from a platform end wall, and the nanocellular foam is in the platform end wall.

8. A transpiration-cooled article comprising:

a body wall having first and second opposed surfaces, the first surface is adjacent a passage that is configured to receive a pressurized cooling fluid, and

at least a portion of the body wall includes a nanocellular foam through which the pressurized cooling fluid from the passage can flow to the second surface.

9. The transpiration-cooled airfoil as recited in claim 8, wherein the nanocellular foam is metallic.

10. The transpiration-cooled airfoil as recited in claim 9, wherein the nanocellular foam is selected from the group consisting of nickel, tantalum, tungsten, rhenium, niobium, hafnium, platinum, ruthenium, rhodium, palladium, osmium, iridium, copper, iron, molybdenum, yttrium, manganese, aluminum, chromium, cobalt, and combinations thereof.

11. The transpiration-cooled airfoil as recited in claim 8, wherein the nanocellular foam is ceramic material.

12. The transpiration-cooled airfoil as recited in claim 11, wherein the ceramic material is selected from the group consisting of oxides, nitrides, carbides, borides, silicides, and combinations thereof.

13. The transpiration-cooled airfoil as recited in claim 11, wherein the ceramic material is a ternary ceramic.

14. The transpiration-cooled airfoil as recited in claim 11, wherein the ceramic material is selected from the group consisting of manganese oxide, zinc oxide, silicon carbide, aluminum oxide, and combinations thereof.

15. The transpiration-cooled airfoil as recited in claim 8, wherein the body wall includes at least one discrete window of the nanocellular foam surrounded by solid wall.

16. The transpiration-cooled airfoil as recited in claim 8, wherein the nanocellular foam has an average pore size of less than 10 micrometers.

17. The transpiration-cooled airfoil as recited in claim 16, wherein the nanocellular foam has a porosity of 5-95%.

18. The transpiration-cooled airfoil as recited in claim 17, wherein the nanocellular foam has a pore volume of 0.01-0.1 milliliters per gram.

19. A transpiration-cooled system comprising:

a passage configured to receive a pressurized cooling fluid;

a wall having first and second opposed surfaces, the first surface is adjacent the passage, and the second surface is a gas-path surface that has a design boundary flow condition,

at least a portion of the wall includes a nanocellular foam through which the pressurized cooling fluid from the passage can flow to the second surface, and the nanocellular foam has controlled pore characteristics with respect to a design discharge velocity of the pressurized cooling fluid from the nanocellular foam and the design boundary flow condition.