System and method relating to axial positioning turbine casings and blade tip clearance in gas turbine engines

Patent metadata

Field	Value
Publication number	US-9441499-B2
Application number	US-201313955721-A
Country	US
Kind code	B2
Filing date	Jul 31, 2013
Priority date	Jul 31, 2013
Publication date	Sep 13, 2016
Grant date	Sep 13, 2016

Abstract

A system for passively varying an axial position of an inner casing of a gas turbine pursuant to changing pressure in a flowpath during transient engine operation. The system may include: a connection assembly slidably connecting the inner casing to the outer casing for axial movement of the inner casing between a first position and a second position; means for pressurizing the annulus relative to a flowpath pressure; biasing means for axially preloading the inner casing toward the first position; and an inner casing receiving surface configured to receive a pressure in the annulus for axially loading the inner casing in opposition to the axial preload of the biasing means.

First claim

We claim:

1. In a gas turbine engine having a flowpath defined within one of a compressor and a turbine, wherein the flowpath includes a row of circumferentially spaced rotor blades having outer tips that oppose an outboard boundary across a gap clearance defined therebetween, wherein an inner casing defines the outboard boundary, and an outer casing is arranged about the inner casing so to form an annulus therebetween, a system for passively varying an axial position of the inner casing pursuant to changing pressure in the flowpath during transient engine operation, the system comprising:
a connection assembly slidably connecting the inner casing to the outer casing for axial movement of the inner casing between a first position and a second position;
at least one extraction passage for pressurizing the annulus relative to a flowpath pressure, the at least one extraction passage configured to fluidly connect an extraction point on the flowpath to the annulus;
biasing means for axially preloading the inner casing toward the first position; and
an inner casing receiving surface configured to receive a pressure in the annulus for axially loading the inner casing in opposition to the axial preload of the biasing means;
wherein the axial preload comprises a threshold load configured such that: a) during a first mode of engine operation, the axial preload exceeds the axial loading of the inner casing receiving surface so to maintain the inner casing at the first position; and b) during a second mode of engine operation, the axial loading of the inner casing receiving surface exceeds the axial preload such that axial movement to the second position is initiated.

2. The system according to claim 1 , wherein the flowpath is configured to narrow a leakage path upon movement of the inner casing from the first position to the second position.

3. The system according to claim 2 , wherein the flowpath comprises an outboard boundary having an axial tilt; and
wherein the flowpath includes a row of circumferentially spaced stator blades extending from the inner casing.

4. The system according to claim 3 , wherein, relative to the axial tilt, a converging direction in which the flowpath converges and a diverging direction in which the flowpath diverges is defined; and
wherein the axial movement of the inner casing from the first position to the second position is in the diverging direction.

5. In a gas turbine engine having an axial compressor defining a flowpath, and, positioned within that flowpath, a row of circumferentially spaced rotor blades having outer tips that oppose an outboard boundary across a gap clearance defined therebetween, wherein an inner casing includes opposing sides that define the outboard boundary of the flowpath and an inboard boundary of an annulus formed between the inner casing and an outer casing that is arranged concentrically about the inner casing, a method of passively varying an axial position of an inner casing relative to the flowpath based on a pressure differential between axially spaced first and second flowpath regions, the method comprising the steps of:
slidably connecting the inner casing to the outer casing for axial movement between a first axial position and a second axial position;
axially loading the inner casing with a static preload directed toward the first axial position;
dividing the annulus into a first annulus and a second annulus for maintaining a pressure differential therebetween;
pressurizing the first annulus relative to a pressure at the first flowpath region, and pressurizing the second annulus relative to a pressure at the second flowpath region;
configuring the inner casing with opposing receiving surfaces, a first receiving surface disposed in the first annulus and a second receiving surface disposed in the second annulus, wherein the opposing receiving surfaces are configured to axially load the inner casing with a dynamic pressure load directed toward the second axial position, wherein the dynamic pressure load is based upon an amount by which a pressure in the first annulus exceeds a pressure in the second annulus.

6. The method according to claim 5 , wherein the step of pressurizing the first annulus comprises fluidly connecting the first flowpath region to the first annulus via an extraction passage; and
wherein the step of pressurizing the second annulus comprises fluidly connecting the second flowpath region to the second annulus via an extraction passage.

7. The method according to claim 6 , wherein the step of loading the inner casing with the static preload includes mechanically biasing the inner casing with a compression spring.

8. The method according to claim 7 , wherein the compression spring is operably configured for adjusting the static preload;
further comprising the step of adjusting the static preload to a desirable threshold.

9. The method according to claim 8 , wherein the desirable threshold comprises one wherein the static preload: a) exceeds the dynamic pressure load during a first mode of engine operation such that the inner casing comprises the first axial position; and b) is exceeded by the dynamic pressure load during a second mode of engine operation such that axial movement of the inner casing to the second axial position is initiated.

10. The method according to claim 8 , further comprising the step of configuring the boundaries of the flowpath such that axial movement from the first axial position to the second axial position narrows a leakage path; and
wherein the first axial position of the inner casing comprises a downstream position and the second axial position of the inner casing comprises an upstream position.

11. The method according to claim 8 , further comprising the step of configuring mechanical stops that define a range of the axial movement for the inner casing; and
wherein the compression spring comprises a threaded connection that is configured for adjusting the static preload.

12. In a gas turbine engine having a compressor through which a flowpath is defined, the flowpath having a downstream and an upstream direction relative to a flow of working fluid therethrough, wherein an inner casing defines an outboard boundary having an axially tilted profile that conically tapers in the downstream direction, wherein a row of circumferentially spaced rotor blades are positioned in the flowpath, the rotor blades having outer tips that oppose the outboard boundary across a gap clearance defined therebetween, and wherein an outer casing is concentrically arranged about the inner casing so to form an annulus therebetween, a method of passively varying an axial position of the inner casing between an upstream position and a downstream position based upon modes of engine operation, the method comprising the steps of:
slidably connecting the inner casing to the outer casing for axial movement between the downstream position and the upstream position;
forming a high-pressure region and a low pressure region in the annulus by extracting working fluid from axially spaced pressure regions in the flowpath;
configuring the inner casing with opposing receiving surfaces, a first receiving surface disposed in the high-pressure region and a second receiving surface disposed in the low-pressure region of the annulus, for axially loading the inner casing toward the upstream position relative to an amount by which a pressure in the high-pressure region exceeds a pressure in the low-pressure region of the annulus.

13. The method according to claim 12 , further comprising the step of configuring the outboard boundary and an inboard boundary of the flowpath such that leakage p

Assignees

• Gen Electric

Inventors

• Casavant Matthew Stephen
• Johnson David Martin

Classifications

• F05D2250/232

  conical · CPC title

• F01D11/18 Primary

  using stator or rotor components with predetermined thermal response, e.g. selective insulation, thermal inertia, differential expansion · CPC title

• F01D11/16 Primary

  by self-adjusting means (F01D11/12 takes precedence) · CPC title

• F01D25/246

  Fastening of diaphragms or stator-rings · CPC title