Passive air seal clearance control

1. A seal for between a rotating component and a stationary component concentrically aligned about an axis of rotation within a gas turbine engine, the seal comprising:

a radially extending elongate sealing member positioned on either the rotating or stationary component of the gas turbine engine and for closing a radial gap between the rotating member and the stationary member; and

a land positioned opposite the sealing member on either the rotating or stationary component of the gas turbine engine such that a clearance height is provided between the sealing member and the land; the land comprising:

a ramp including an axially extending rigid sealing surface wherein a radial distance between the sealing surface and the axis of rotation varies in the axial direction, the surface having:

a radial rise corresponding to a change in the radial gap during operation of the gas turbine engine; and

an axial run corresponding to a change in relative axial position of the sealing member and land during operation of the gas turbine engine;

wherein the sealing member and the land are positioned with respect to each other so that the clearance height is maintained approximately constant during the changes in the radial gap and relative axial position due to thermal expansion and mechanical stress of the engine components arising from operation of the gas turbine engine.

2. The seal of claim 1 wherein the change in the gap during operation of the gas turbine engine is due to radial thermal growth of engine components.

3. The seal of claim 2 wherein the engine components include an engine casing component.

4. The seal of claim 1 wherein the change in relative axial position of the sealing member and land is due to axial thrust loading of an engine component.

5. The seal of claim 4 wherein the engine component comprises a shaft.

6. The seal of claim 5 wherein the shaft is supported by a thrust bearing and a roller bearing such that the sealing member undergoes a predictable expansion from the thrust bearing.

7. The seal of claim 1 wherein the sealing member comprises a labyrinth seal.

8. The seal of claim 1 wherein the sealing member comprises a brush seal.

9. The seal of claim 1 wherein the land comprises an abradable material.

10. The seal of claim 1 wherein the land includes an exponentially shaped surface that is configured to interface with the sealing member.

11. A gas turbine engine seal for maintaining a clearance height between sealing members of a stationary engine component and a rotating engine component, wherein during operation of the gas turbine engine the stationary and rotating engine components undergo a relative axial and radial movement, the sealing members comprising:

a radially extending elongate sealing projection for narrowing a radial gap between the engine components; and

a seal land opposing the sealing projection and comprising an axially extending and radially varying ramp profile having a rise and a run configured to maintain the clearance height between the engine components during the relative movement arising from thermal expansion and mechanical stress of the engine components.

12. The gas turbine engine seal of claim 11 wherein the stationary engine component and the rotating engine component are concentrically disposed about an engine axis.

13. The gas turbine engine seal of claim 12 wherein the relative movement comprises:

an axial displacement between the components; and

a radial displacement between the components.

14. The gas turbine engine seal of claim 11 wherein the rise corresponds to a change in the gap due to the relative radial displacement of the engine components.

15. The gas turbine engine seal of claim 11 wherein the run corresponds to a change in relative axial displacement of the sealing projection and seal land due to the relative movement of the engine components.

16. The gas turbine engine seal of claim 11 wherein the rotating engine component comprises a shaft supported by a thrust bearing and a roller bearing such that the shaft undergoes a predictable expansion from the thrust bearing.

17. A passive clearance control system for a gas turbine engine, the passive clearance control system comprising:

a land radially disposed about a shaft in a gas turbine engine;

a thrust bearing positioned along a length of the shaft such that the shaft undergoes an axial displacement from the bearing due to thermal expansion and mechanical stress of the shaft arising during engine operation; and

a radially extending elongate sealing member secured to a stationary engine component and for interacting with the land to provide a seal having a clearance height between the shaft and the stationary engine component;

wherein the stationary engine component undergoes a radial displacement from the shaft due to thermal expansion of the engine component arising during engine operation; and

wherein the land comprises a radially varying ramp including an axially extending sealing surface wherein a radial distance between the sealing surface and an axis of rotation varies in the axial direction, the surface having a rise and a run for maintaining the clearance height between the land and the sealing member during the radial and axial displacements of the shaft and engine component, the rise corresponding to a change in the radial displacement and the run corresponding to a change in the axial displacement.

18. The passive clearance control system of claim 17 wherein during operation of the gas turbine engine the land translates axially with the shaft to engage the sealing member as the sealing member moves radially relative to the shaft to maintain the clearance height.