Patent Application
20190218972
This invention relates generally to gas turbine engines and in particular to flowpath structures such as cooling ducts within a gas turbine engine.
A typical gas turbine engine includes a turbomachinery core having a high-pressure compressor, a combustor, and a high-pressure turbine in serial flow relationship. The core is operable in a known manner to generate a primary gas flow. In practical applications the core is typically combined with other elements such as power turbines, fans, augmentors, etc. to create a useful engine for a specific application, such as turning a propeller, powering an aircraft in flight, or driving a mechanical load.
Generally, within the gas turbine engine several housings used to enclose heat sensitive items, such as ignition exciters and/or other electronics, are positioned in the “under-cowl” area of the gas turbine engine. The temperature in the under-cowl area may reach several hundred degrees Fahrenheit. For example, at the upstream end of the gas turbine engine near the fan, the temperature might be approximately 149° C. (300° F.). Downstream near the combustor and/or turbines, the temperature might be approximately 260° C. to 371° C. (500° F. to 700° F.). These are steady-state operating temperatures. The under-cowl temperatures can be even higher during hot soak conditions after the engine has been shut down, because the source of cooling air has been removed.
As a result, cooling ducts or “blast tubes” have been used to cool the interior of these housings using air from a relatively cool source. For example, fan discharge air for a turbofan engine typically does not exceed 121° C. (250° F.) and may be used for the purpose of cooling. The air may be bled off from the fan by appropriate means such as a scoop or opening, and then channeled through the cooling ducts.
The cooling ducts must have adequate structural strength to support their own weight and any gas pressure loads during operation. The cooling ducts must also have sufficient temperature capability so they do not fail during operation when exposed to relatively high temperatures. Further, the cooling ducts must have sufficient insulating properties so that excessive heat gain from the exterior environment does not enter into the cooling duct, which would heat the air inside and reduce its effectiveness or make it useless for cooling purposes.
One known prior art combination uses a metal duct e.g. stainless steel or nickel, insulated with conventional lagging (insulation) such as a blanket of ceramic fibers which is in turn surrounded by a sheet steel foil barrier. One known brand is sold under the trade name MIN-K. Unfortunately, this combination results in a heavy cooling duct. Another known prior art combination utilizes nonmetallic composite materials such as carbon fibers in an epoxy matrix (inherently temperature resistant). While lighter than the metal duct, it is very expensive to produce.
At least one of the above-noted problems is addressed by a cooling apparatus formed of a low-temperature capable structural polymeric material surrounded by a thermal barrier material.
According to one aspect of the technology described herein, a cooling apparatus for a gas turbine engine includes a wall structure defining an air flowpath, the wall structure comprising a thermoplastic material; and a thermal barrier layer surrounding the wall structure.
According to another aspect of the technology described herein, a gas turbine engine includes a turbo machinery core surrounded by a casing; a cowling surrounding the casing such that an under-cowl area is defined between the casing and the cowling; and a cooling apparatus disposed in the under-cowl area. The cooling apparatus including a wall structure defining an air flowpath, the wall structure comprising a thermoplastic material; and a thermal barrier layer surrounding the wall structure.
According to another aspect of the technology described herein, a cooling assembly for a gas turbine engine includes an inner tube comprising a thermoplastic material; a housing connected in fluid communication with the inner tube and comprising a thermoplastic material; and a thermal barrier layer surrounding the inner tube and housing
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
It is noted that, as used herein, the terms “axial” and “longitudinal” both refer to a direction parallel to the centerline axis 11, while “radial” refers to a direction perpendicular to the axial direction, and “tangential” or “circumferential” refers to a direction mutually perpendicular to the axial and radial directions. As used herein, the terms “forward” or “front” refer to a location relatively upstream in an air flow passing through or around a component, and the terms “aft” or “rear” refer to a location relatively downstream in an air flow passing through or around a component. The direction of this flow is shown by the arrow “F” in
A core cowl 41 surrounds the casing 12, thereby defining an under-cowl area 42. As shown, the cooling duct 40 is positioned in the under-cowl area 42 and is connected between opening 44 and housing 46 to provide cooling air to the housing 46. The housing 46 contains heat sensitive components and/or electronics. For example, the housing 46 may contain an ignition exciter (not shown) used to power an igniter 48 for the gas turbine engine's 10 combustor 20. As illustrated, the cooling duct 40 is in the form of a tubular duct having a circular cross-section; however, it should be appreciated that other suitable cross-sectional shapes may be used. Individually and collectively, the cooling duct 40 and the housing 46 are example of “cooling apparatus” as that term is used herein.
The opening 44 allows cooling air to be bled off from the fan 14. It should be appreciated that other air diverting structures such as a scoop may be used in combination with the opening 44 to divert the cooling air into the cooling duct 40. Once the cooling air is directed into the cooling duct 40, the air is directed into an interior of the housing 46 to maintain a suitable temperature therein. For example, in some applications, it may be desirable to maintain a temperature of about 120° C. (250° F.).
Referring to
The thermal barrier 52 protects inner tube 50 from temperatures exceeding the temperature capability of the polymeric material from which the inner tube 50 is constructed. One suitable material is a silicone-based material. Silicones, also known as polysiloxanes, are polymers that include any inert, synthetic compound made up of repeating units of siloxane, which is a chain of alternating silicon atoms and oxygen atoms, frequently combined with carbon and/or hydrogen.
The thermal barrier 52 may be a homogeneous, unreinforced material. The thermal barrier 52 may be applied to the inner tube 50 by wrapping sheets of the thermal barrier 52 around the inner tube 50 and then adhering the thermal barrier to the inner tube 50 using an adhesive such as a room temperature vulcanizing (“RTV”) silicone material. The thermal barrier 52 may also be sprayed on in a wet state. Optionally, as shown in
The polymeric material allows the inner tube 50 to be formed into any suitable flow path and/or shape. As illustrated in
As an example, the inner tube 50 may have a diameter of approximately 7.62 cm to 10.16 cm (3 to 4 inches). The thermal barrier 52 may be very thin. For example, for the same 8 cm to 10 cm (3 to 4 inch) diameter tube, the wall thickness of the thermal barrier 52 might be in the range of about 10 mils (0.01 inches) to about 150 mils (0.150 inches).
As discussed above, the cooling duct 40 may be connected to housing 46 to supply cooling air to the housing 46. Typically, in the prior art, housings like housing 46 are constructed of metal and then an insulating material is attached thereto. As shown in
Once the inner housing 70 is constructed, the thermal barrier 52 may be applied to the inner housing 70 to insulate the inner housing 70 from excess temperatures above the temperature capability of the polymeric material. It should be appreciated that the cooling duct 40 and housing 46 may be assembled prior to installation in the under-cowl area 42. It should also be appreciated that the inner tube 50 may be connected to the inner housing 70 prior to applying the thermal barrier 52. Once the inner tube 50 and inner housing 70 have been connected into an assembly, the thermal barrier 52 may be applied to the entire assembly at one time.
The foregoing has described a thermally protected thermoplastic duct and assembly for a gas turbine engine. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
