System and method of controlling tip clearance in a shroud assembly for a bladed disc

1. An assembly in a turbine engine having a dynamically moveable shroud segment for encasing a rotor segment comprising a bladed disc and maintaining a clearance gap between the shroud segment and a plurality of blade tips of the bladed disc, said assembly comprising:

a static engine casing;

a rotor segment comprising a bladed disc;

a shroud segment carried by said casing, said shroud segment comprising a flowpath boundary member coupled to the static engine casing via a hanger, wherein the hanger and the flowpath boundary member are both moveable relative to the blade tips of the bladed disc by thermal expansion and contraction of said flowpath boundary member and the hanger; and

an actuator for effecting thermal expansion and contraction of said flowpath boundary member, said actuator comprising a closed form refrigeration system having an evaporator, a compressor, a condenser, an expansion valve, and a refrigerant contained therein, wherein said evaporator is positioned in sufficient proximity to the hanger and said flowpath boundary member to extract heat from the hanger and said flowpath boundary member.

2. The assembly of claim 1 wherein said bladed disc comprises a turbine rotor carrying a plurality of turbine blades.

3. The assembly of claim 1 wherein said bladed disc comprises an axial compressor rotor carrying a plurality of compressor blades.

4. The assembly of claim 1 wherein said evaporator comprises a metal foam.

5. The assembly of claim 1 wherein the evaporator is mounted to the casing.

6. The assembly of claim 1 wherein the assembly further comprises a sensor configured to monitor the clearance gap, and wherein the actuator is configured to actuate responsive to the clearance gap sensed by the sensor.

7. The assembly of claim 1 wherein the assembly further comprises a temperature sensor, and wherein the actuator is configured to actuate responsive to a temperature sensed by the temperature sensor.

8. The assembly of claim 1 wherein the evaporator is mounted to the flowpath boundary member.

9. A system for maintaining a clearance gap between a shroud and a plurality of blade tips of a rotatable bladed disc in a turbine engine, said system comprising:

a rotor segment comprising a bladed disc;

a static casing encasing the bladed disc;

a shroud segment carried by said casing, said shroud segment comprising a flowpath boundary member coupled to the static casing via a hanger, wherein the hanger and the flowpath boundary member are both moveable relative to the blade tips of the bladed disc; and

an actuator comprising a closed form refrigeration system having an evaporator, a compressor, a condenser, an expansion valve, and a refrigerant contained therein, wherein operation of said closed form refrigeration system affects movement of the hanger and said flowpath boundary member relative to said blade tips.

10. The system of claim 9 wherein the flowpath boundary member comprises a ring configured for radial flexion.

11. The system of claim 9 wherein the evaporator of said closed form refrigeration system is positioned in sufficient proximity to said flowpath boundary member to effect thermal expansion and contraction of said flowpath boundary member.

12. The system of claim 11 wherein the evaporator is mounted to the static casing.

13. The system of claim 12 further comprising at least one thermoelectric cooler disposed within the evaporator.

14. The system of claim 11 wherein the evaporator is mounted to the flowpath boundary member.

15. The system of claim 9 wherein the evaporator comprises open cell metal foam.

16. The system of claim 9 further comprising at least one insulating layer disposed radially outward from the evaporator.

17. In a turbine engine having a static casing and a rotatable bladed disc, a method of reducing blade tip rub comprising:

providing a flowpath boundary member spaced radially inward from the casing to form a flowpath boundary around the bladed disc;

thermally coupling the flowpath boundary member to a closed form refrigeration system via a hanger, the closed form refrigeration system having an evaporator, a compressor, a condenser, an expansion valve, and a refrigerant contained therein; and

thermally expanding or contracting the hanger and the flowpath boundary member by removing heat via the closed form refrigeration system to affect movement of the hanger and the flowpath boundary member relative to a plurality of blade tips of the bladed disc.

18. The method of claim 17 further comprising:

measuring, via a sensor, a clearance gap between the blade tips of the rotatable bladed disc and the flowpath boundary member; and

thermally expanding or contracting the flowpath boundary member responsive to the clearance gap measured by the sensor.

19. The method of claim 17 further comprising:

measuring, via a sensor, an internal temperature of the evaporator; and

thermally expanding or contracting the flowpath boundary member responsive to the internal temperature measured by the sensor.