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A turbine flowpath apparatus is provided for a gas turbine engine having a centerline axis. The apparatus includes: an annular flowpath member of low-ductility material, the flowpath member having a flowpath surface and an opposed back surface, and having a cross-sectional shape comprising a general

A turbine flowpath apparatus is provided for a gas turbine engine having a centerline axis. The apparatus includes: an annular flowpath member of low-ductility material, the flowpath member having a flowpath surface and an opposed back surface, and having a cross-sectional shape comprising a generally cylindrical forward section and an aft section that extends aft and radially outward at a non-perpendicular, non-parallel angle to the centerline axis; an annular stationary structure surrounding the flowpath member; and an annular centering spring disposed between the stationary structure and the flowpath member, the centering spring urging the flowpath member towards a centered position within the stationary structure.

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1. A turbine flowpath apparatus for a gas turbine engine having a centerline axis, the apparatus comprising: an annular flowpath member comprising low-ductility material, the flowpath member having a primary flowpath surface and an opposed back surface, and having a cross-sectional shape including t

1. A turbine flowpath apparatus for a gas turbine engine having a centerline axis, the apparatus comprising: an annular flowpath member comprising low-ductility material, the flowpath member having a primary flowpath surface and an opposed back surface, and having a cross-sectional shape including the flowpath surface comprising a generally cylindrical forward section and an aft section, wherein substantially all of the aft section extends aft and radially outward at a non-perpendicular, non-parallel angle to the centerline axis;an annular stationary structure surrounding the flowpath member;an annular centering spring disposed between the stationary structure and the flowpath member, the centering spring urging the flowpath member towards a centered position within the stationary structure, wherein the centering spring has a generally frustoconical shape with a radially-outwardly-extending, L-shaped flange at one axial end;wherein radial pins are fixed to the centering spring and extend into corresponding slots formed in the back surface of the flowpath member, so as to prevent relative lateral movement and relative rotation of the flowpath member and the centering spring; anda rotor comprising a rotatable disk that carries an array of airfoil-shaped turbine blades, wherein the forward section of the flowpath member surrounds the turbine blades and defines a portion of a flowpath through the turbine blades. 2. The apparatus of claim 1 wherein the flowpath member comprises a ceramic matrix composite material. 3. The apparatus of claim 1 wherein the centering spring includes an annular array of resilient spring fingers separated by generally axially-aligned slots. 4. The apparatus of claim 1 further including axial pins fixed to the stationary structure and extending into corresponding slots formed in a flange of the flowpath member, so as to prevent relative lateral movement and relative rotation of the flowpath member and the stationary structure. 5. A turbine flowpath apparatus for a gas turbine engine having a centerline axis, the apparatus comprising: an annular shroud support;an annular shroud hanger engaged with the shroud support;an annular flowpath member comprising low-ductility material, the flowpath member having a primary flowpath surface and an opposed back surface, and having a cross-sectional shape including the flowpath surface comprising a generally cylindrical forward section and an aft section, wherein substantially all of the aft section extends aft and radially outward at a non-perpendicular, non-parallel angle to the centerline axis, where a forward end of the flowpath member abuts the hanger;an annular turbine case surrounding the flowpath member and the shroud support;an annular centering spring disposed between the turbine case and the flowpath member, the centering spring urging the flowpath member towards a centered position within the turbine case, wherein the centering spring includes an annular array of resilient spring fingers separated by generally axially-aligned slots;wherein radial pins are fixed to the centering spring and extend into corresponding slots formed in the back surface of the flowpath member, so as to prevent relative lateral movement and relative rotation of the flowpath member and the centering spring; anda rotor comprising a rotatable disk that carries an array of airfoil-shaped turbine blades, wherein the forward section of the flowpath member surrounds the turbine blades and defines a portion of a flowpath through the turbine blades. 6. The apparatus of claim 5 wherein the flowpath member comprises a ceramic matrix composite material. 7. The apparatus of claim 5 wherein the centering spring has a generally frustoconical shape with a radially-outwardly-extending, L-shaped flange at one axial end. 8. The apparatus of claim 5 wherein the flowpath member includes an aft flange which extend radially outward from an aft end thereof, the aft flange abutting an axially down-stream turbine nozzle. 9. The apparatus of claim 8 further including axial pins fixed to the turbine case and extending into corresponding slots formed in the aft flange of the flowpath member, so as to prevent relative lateral movement and relative rotation of the flowpath member and the turbine case. 10. A turbine flowpath apparatus for a gas turbine engine having a centerline axis, the apparatus comprising: an annular shroud support;an annular shroud hanger engaged with the shroud support;an annular flowpath member comprising low-ductility material, the flowpath member having a primary flowpath surface and an opposed back surface, and having a cross-sectional shape including the flowpath surface comprising a generally cylindrical forward section and an aft section, wherein substantially all of the aft section extends aft and radially outward at a non-perpendicular, non-parallel angle to the centerline axis, where a forward end of the flowpath member abuts the hanger;an annular turbine case surrounding the flowpath member and the shroud support;an annular centering spring disposed between the turbine case and the flowpath member, the centering spring urging the flowpath member towards a centered position within the turbine case, wherein the centering spring includes spring tabs which abut the annular retainer, such that the centering spring urges the retainer axially against the shroud support;a rotor comprising a rotatable disk that carries an array of airfoil-shaped turbine blades, wherein the forward section of the flowpath member surrounds the turbine blades and defines a portion of a flowpath through the turbine blades;a retaining ring engaging a groove in the shroud support and axially abutting the hanger; anda resilient, annular retainer having a C-shaped cross-section clamping the shroud support and the retaining ring together.