Ceramic-to-metal turbine volute attachment for a gas turbine engine
A means of attachment applicable to mating parts which have substantially different coefficients of thermal expansion is disclosed. The means of attachment substantially reduces the friction between the mating surfaces while still keeping the mating parts centered with respect to one another. The approach is based on radial recessed faces wherein the radial faces slide relative to each other. There may be three or more recessed/raised faces on each mating component, which when mated, maintain the alignment between the mating parts while allowing differential growth of the mating parts. This approach also the provides a much larger bearing surface for the attachment than a radial pin/slot approach, for example, and substantially eliminates areas of high stress concentration. It is thus a more robust design for components that undergo many thousands of thermal cycles.
1. A method, comprising:
providing an engine comprising at least one turbo-compressor spool assembly, wherein the at least one turbo-compressor spool assembly comprises a compressor in mechanical communication with a turbine, a ceramic volute directing an inlet gas towards an inlet of a ceramic rotor of the turbine and a ceramic shroud adjacent to the rotor of the turbine, the ceramic shroud directing an outlet gas towards an outlet of the at least one turbo-compressor spool assembly and a metallic housing comprising a metallic base plate having a metallic mating surface to engage a ceramic mating surface of at least one of the ceramic shroud and volute, wherein the metallic and ceramic mating surfaces are perpendicular to an axis of rotation of the rotor, wherein the metallic mating surface has a first coefficient of linear thermal expansion and contraction, wherein the ceramic mating surface has a second coefficient of linear thermal expansion and contraction, wherein the first and second coefficients of thermal expansion and contraction are different by at least a factor of two, wherein the metallic mating surface comprises at least one raised face raised parallel to the axis of rotation of the rotor and at least one recessed face recessed parallel to the axis of rotation of the rotor, and wherein the ceramic mating surface comprises at least one raised face raised parallel to the axis of rotation of the rotor and at least one recessed face recessed parallel to the axis of rotation of the rotor; and
maintaining, during engine operation, the at least one raised face of the metallic mating surface engaged with the at least one recessed face of the ceramic mating surface and the at least one recessed face of the metallic mating surface engaged with the at least one raised face of the ceramic mating surface to inhibit at least one of binding and wear at the engaged metallic and ceramic mating surfaces due to the difference between the first and second coefficients of thermal expansion and contraction between the metallic and ceramic materials in the metallic housing and at least one of the ceramic shroud and volute, respectively.
2. The method of claim 1 , wherein the ceramic volute interfaces with the ceramic shroud and wherein an inlet gas to the turbine is heated by a fuel combustor, wherein the inlet gas has a temperature of from about 850° K to about 1,800° K, and the outlet gas has a temperature less than the inlet gas, the outlet gas temperature ranging from about 1,000° K to about 1,400° K, whereby the shroud is subjected to a temperature differential ranging from about 150° K to about 400° K.
3. The method of claim 2 , wherein the ceramic materials in the rotor and shroud have substantially similar thermal expansion characteristics.
4. The method of claim 3 , wherein the ceramic materials in the shroud and volute each comprise a substantially identical ceramic composition.
5. The method of claim 1 , wherein:
in a cool temperature state, a radial gap exists between an inner edge of the ceramic mating surface and an inner edge of the metallic base plate;
in an intermediate temperature state, the radial gap is smaller than the radial gap in the cool temperature state; and
in a high temperature state, the radial gap is smaller than the radial gap in the cool and intermediate temperature states.
6. The method of claim 1 , wherein the at least one raised face of the metallic mating surface comprises first and second raised faces and the at least one recessed face of the metallic mating surface comprises first and second recessed faces, wherein each of the first and second raised faces is positioned between the first and second recessed faces, and wherein the first and second raised faces are opposite facing and the first and second recessed faces are opposite facing.
7. The method of claim 6 , wherein the at least one raised face of the ceramic surface comprises third and fourth raised faces and the at least one recessed face of the ceramic surface comprises third and fourth recessed faces, wherein each of the third and fourth raised faces is positioned between the third and fourth recessed faces, and wherein the third and fourth raised faces are opposite facing and the third and fourth recessed faces are opposite facing.
8. The method of claim 7 , wherein the first raised face engages the third recessed face, wherein the second raised face engages the fourth recessed face, wherein the first recessed face engages the third raised face, and wherein the second recessed face engages the fourth raised face.
9. The method of claim 1 , wherein the at least one turbo-compressor spool assembly comprises a plurality of turbo-compressor spool assemblies, each turbo-compressor spool assembly comprising a compressor and a turbine attached by a common shaft and a first of the turbo-compressor spool assemblies is in fluid communication with a second of the turbo-compressor spool assemblies, at least one of the common shafts of a selected turbo-compressor spool assembly comprising a metallic compressor rotor and a ceramic turbine rotor connected by a metallic-to-ceramic attachment joint and a first bearing being positioned adjacent to the metallic compressor rotor and a second bearing adjacent to the ceramic turbine rotor and the engine further comprising;
a free power turbine driven by a gas flow output by at least one of the turbo-compressor assemblies; and
a combustor operable to combust a fuel and a gas output by one of the plurality of turbo-compressor spool assemblies.