A turbine stage for a turbomachine, the stage comprising a rotor wheel mounted inside a sectorized ring carried by an outer casing, and a sectorized nozzle fastened to the casing downstream from the wheel, each ring sector having a downstream end that is held bearing radially outwards against a cylindrical rail of the casing by means of the nozzle, the casing rail including an annular row of through radial notches reducing the areas for heat exchange by conduction both between the casing and the ring sectors and between the casing and the nozzle.
1. A turbine stage for a turbomachine, comprising a rotor wheel mounted inside a sectorized ring carried by an outer casing, and a sectorized nozzle fastened to the casing downstream from the wheel, each ring sector having a downstream end that is held bearing radially outwards against a cylindrical rail of the casing by means of the nozzle, wherein the casing rail includes an annular row of through radial notches reducing the areas for heat exchange by conduction both between the casing and the ring sectors and between the casing and the nozzle.
2. A turbine stage according to claim 1 , wherein the number of notches of the casing is equal to the number of nozzle sectors.
3. A turbine stage according to claim 1 , wherein each notch has a circumferential extent that is less than the circumferential extent of a nozzle sector, and is in axial alignment with said sector.
4. A turbine stage according to claim 3 , wherein each notch has a circumferential extent of the order of 10° to 20°, approximately.
5. A turbine stage according to claim 3 , wherein each notch is generally U-shaped.
6. A turbine stage according to claim 1 , wherein the casing rail extends downstream, and the notches are formed in its downstream end portion.
7. A turbine stage according to claim 1 , wherein the nozzle has an upstream annular rim for attaching to the casing rail, said rim bearing radially inwards against an outer cylindrical surface of the casing rail, and the axial dimension of the bearing zone between the rim and the casing being less than the depth or the axial dimension of the notches.
8. A turbine stage according to claim 1 , wherein the end walls of the notches are outwardly inclined from upstream to downstream.
9. An outer casing for a turbine stage according to claim 1 , the casing including cylindrical rails for attaching nozzles, and wherein at least one of said rails includes an annular row of through radial notches.
10. A turbomachine such as an airplane turboprop or turbojet, wherein the turbomachine includes at least one turbine stage according to claim 1 .
11. A turbine stage according to claim 1 , wherein the number of notches of the casing lies in the range 16 to 20.