Power plants – Reaction motor – Liquid oxidizer
Reexamination Certificate
1998-10-15
2001-03-13
Thorpe, Timothy S. (Department: 3746)
Power plants
Reaction motor
Liquid oxidizer
C060S039300
Reexamination Certificate
active
06199371
ABSTRACT:
TECHNICAL FIELD
This invention relates to gas turbine engines in general, and in particular to the structure of thermal protection liners within gas turbine engines.
BACKGROUND ART
Liners are often employed in gas turbine engines to enclose high temperature, core gas paths. An augmentor which forms an additional combustion chamber for afterburning the gas turbine exhaust, may use a cylindrical liner to define a flow path for the core gas flow from the turbine to the exhaust nozzle. The liners within the augmentor duct protect the duct from excessive temperatures associated with the turbine exhaust.
Liners typically include an outer wall, an inner wall and a means for spacing the two walls a distance apart. A duct defined by such spaced walls is used as a cooling air passage. Cooling air is supplied between the liner walls for convection cooling of the liner. Cooling air also flows inwardly through perforations in the outer wall of the liner to provide impingement cooling of the inner surface of the inner wall of the liner. Perforations in the inner wall of the liner provide a path for the cooling air to exit into the core gas flow.
It is known to provide liners with stiffening structure (“stiffeners”) extending between the two walls to maintain spacing the two walls a distance apart. Fasteners attach the stiffeners and the walls together and collectively the stiffeners and the fasteners form a rigid cylindrical structure. Stiffeners protect the liners from buckling or collapsing under differential pressure loads between the outer and inner walls. For example, a significant pressure difference exists across the liner during stall conditions. During a stall condition, a higher pressure exists surrounding the outer wall of the liner relative to the pressure on the inner liner wall. This creates a tendency for the liner to collapse or buckle under the external loading. The sizing of the perforations in the inner and outer liner walls do not allow for enough air flow to form the outer to the inner liner wall to diffuse the pressure loading across the liner walls.
Further, high core gas temperatures can also limit the useful life of the augmentor liner. The inner wall of the liner may operate on the order of 500 degrees Fahrenheit hotter, than the surrounding outer wall of the liner. Cooling schemes such as described hereinabove and thermal barrier coatings are typically used to provide cooling to decrease the rate of thermal damage to the liner walls but do not solve the problem caused by the differential thermal growth of the liner walls.
The stiffeners in the liners of the prior art design provide a very stiff structure that results in low cycle fatigue problems for the liner. In addition, due to differential thermal growth and movement between the outer wall and the inner wall of the liner, the liner experiences undesirable stress. There is a high probability that the stress will result in cracks in the coating disposed on the inner wall of the liner. The stress and cracks compromise the durability of the liner.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide a thermally compliant liner.
A further object of the present invention is to provide a liner with adequate stiffness.
According to the present invention, a liner for a gas turbine engine includes a stiffener having a flexible or pliant medial portion to accommodate differential rates of thermal growth between the outer and inner walls of the liner and radially extending sections to prevent buckling of the double wall liner due to pressure differentials between the inner or outer walls.
The length of the flexible medial portion of the stiffener is determined by the need for the required stiffness provided primarily by the radially extending sections of the stiffener. The number of stiffeners is determined based on pressure loading requirements for particular engine designs and the length of the liner.
The liner of the present invention is durable, having a required stiffness to alleviate any cycle fatigue problems. The liner of the present invention accommodates the different rates of thermal growth of the outer wall and inner wall.
A still further advantage of the present invention is that the thermal barrier coating remains more readily adhered to the surface of the liner walls as compared to the liner walls of the prior art. The inner wall sections are less apt to significantly warp due to thermal loads because they may expand more readily than the prior art liner walls. Reducing the warpage helps minimize stress between the coating and the inner wall of the liner. Overstress frequently results in coating separation from the inner wall.
The foregoing and other objects, features and advantages of the present invention will become more apparent in the following detailed description of the Best Mode for Carrying Out The Invention and from the accompanying drawings, which illustrate an embodiment of the invention.
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Brewer Keith S.
Chaplin Gary F.
Olsen David R.
Krasinski Monica
Thorpe Timothy S.
Torrente David J.
United Technologies Corporation
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