Mechanical iris tip clearance control

1. A tip clearance control apparatus comprising:

a mechanical iris having a plurality of mechanical iris leaves, radially inward facing edges of the mechanical iris leaves form an adjustable opening which approximates a circle, wherein the mechanical iris leaves overlap and are stacked in a direction parallel to an axial axis of the mechanical iris, and wherein the mechanical iris leaves are configured to slide over each other in a plane perpendicular to the axial axis which causes a size of the adjustable opening to change;

a ring positioned in the adjustable opening of the mechanical iris, the ring defining an aperture; and

a blade of a gas turbine engine, the blade positioned in the aperture of the ring,

wherein the ring comprises abradable material, and wherein a distance between a tip of the blade and an inner surface of the ring is adjustable based on the size of the adjustable opening of the mechanical iris.

2. The tip clearance control apparatus of claim 1 , wherein the blade and the ring comprise a CMC material.

3. The tip clearance control apparatus of claim 1 , further comprising a sensor configured to detect the distance between the tip of the blade and the inner surface of the ring.

4. The tip clearance control apparatus of claim 1 , wherein the abradable material is bonded to the mechanical iris leaves.

5. The tip clearance control apparatus of claim 1 , wherein the ring comprises a plurality of segments.

6. The tip clearance control apparatus of claim 1 , wherein the abradable material is configured to microly crumple.

7. A system for tip clearance control comprising:

a ring comprising abradable material, the ring encircling a volume in which a blade of a gas turbine engine is configured to rotate; and

a mechanical iris having a plurality of mechanical iris leaves, radially inward facing edges of the mechanical iris leaves form an adjustable opening that encircles the ring, wherein the mechanical iris leaves overlap and are stacked in a direction parallel to an axial axis of the mechanical iris, and wherein the mechanical iris leaves are configured to slide over each other in a plane perpendicular to the axial axis which causes a size of the adjustable opening to change, and wherein a distance between a tip of the blade and an inner surface of the ring is adjustable by the size of the adjustable opening of the mechanical iris.

8. The system for tip clearance control of claim 7 , wherein the blade is a compressor blade of the gas turbine engine.

9. The system for tip clearance control of claim 7 , wherein the blade is a turbine blade of the gas turbine engine.

10. The system for tip clearance control of claim 7 , wherein the mechanical iris further comprises a plurality of iris leaves coupled to a cam plate, and wherein the cam plate is configured to move the plurality of iris leaves in unison.

11. The system for tip clearance control of claim 7 , further comprising an actuator coupled to the mechanical iris, the actuator configured to adjust a size of the adjustable opening of the mechanical iris.

12. The system for tip clearance control of claim 11 , wherein the actuator comprises a motor-driven actuator.

13. The system for tip clearance control of claim 7 , wherein the ring comprises an outer surface that abuts the mechanical iris.

14. A method for controlling tip clearance, the method comprising:

determining a tip clearance, the tip clearance indicative of a distance between a tip of a blade of a gas turbine engine and an inner surface of a ring within which the blade is configured to rotate, the ring positioned in an adjustable opening of a mechanical iris having a plurality of mechanical iris leaves, radially inward facing edges of the mechanical iris leaves form the adjustable opening which approximates a circle, wherein the mechanical iris leaves overlap and are stacked in a direction parallel to an axial axis of the mechanical iris, and wherein the mechanical iris leaves are configured to slide over each other in a plane perpendicular to the axial axis which causes a diameter of the adjustable opening to change; and

adjusting the tip clearance by adjusting the diameter of the adjustable opening of the mechanical iris.

15. The method of claim 14 , further comprising controlling an actuator coupled to the mechanical iris, the actuator causing the diameter of the adjustable opening of the mechanical iris to adjust.

16. The method of claim 15 , wherein the actuator comprises a linear actuator, wherein the linear actuator is driven by a hydraulic mechanism.

17. The method of claim 14 , wherein the tip clearance is within a range from 0.009 inches to 0.011 inches.

18. The method of claim 14 , wherein an outer surface of the ring is bonded to a plurality of the mechanical iris leaves of the mechanical iris.