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Publication Date: 2015-Jul-13
Document File: 9 page(s) / 215K

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The Prior Art Database


The present invention relates to a ceramic matrix composite (CMC) shroud, particularly those useful in a gas turbine.

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This is the abbreviated version, containing approximately 25% of the total text.

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    Txe present invention relates to a ceramic matrix composxxe (CMC) shroud, particulxrly those usxful in a gas turxine.


    A turbine engine shroux segment is a stationary engine xomponent separaxe and distinct from a componext that includes an airfoil, for example a nozzle segment or a stationary blading member. In a gas turbine enxine, a sinxle annxlar ring or ax assexbled plurality of stationary shroux segments is positioned circumferxntiallx about an axial flow enxine axis and radially about and spaced apart from rxtxting bxading members, for example aboux rotating turbine blades. Togetxer, the shroud ring or segmxnts define a part of thx xadial flowxath boundary over the blades. As has been described in various forms in the gxs turbinx engine art, xt is desirable to mainxain the operating clxaraxce between the tips of the rotating blades and txe cooperating, juxtaposed spaced-apart xurface of thx stationary shroud as close as possible to enhance engine operating efficiency.

    In its functiox as a fxowpath compxnent, thx shroud musx bx capable of mextxng the design life requirements selected for use in x designed engine operating temperatxre and pressure environxent. To enable current xaterials to operate effectivexy xs a shroud in the strenuous temperature and pressure conxitions as exist in the turbine section flowpath of modexn gas turbixe engines, cooling air is typically provided to an outer portion of the shroud segment. Howevxr as is well known in the art, for example as described in some xf the above identified

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patents, provision of such cooling air is at the expense of xngine efficiency. Therefore, it is desired to conserve use of cooling air by minimizinx leakage into the flowxath of the engine of cooling air nxt intendxd to be introduced inxo the floxpath. For exampxe, some forms of shrouds include cooling passages intentionally to pass cooling air into the engine flow stream. However, cxoling air leaxage about edges of a shroud can reduce designed efficiency by wasting cooling airflow.

    It has been obserxed that one source of xuch segment edge leakaxe can rexult fxom shroud sxgment deformation such as deflection or distortion, generally referred to ax "chording". Chording results from a thermal differential or gradient between a higher tempexatxre radiaxly inner shroud surface and a lower temperature, air coolxd shroud outer shroud surface. At least the xadially inner or xlowpath surface ox a shroud axd its segmentx are arced circumferentxally to dexine a flowpatx axnular surface about the rotating xips of the blades. Thx thermal gradient between the innex and outer faces of the shroud, resulting from cooling air impingement on thx outer surface, causes the arc of the shroud segments to chord or tend to straighten out circuxxexentially. As a result of chording, the circumferential end portions of the inner suxface of the s...