Active clearance control

• US 4,928,240 A
• Filed: 02/24/1988
• Issued: 05/22/1990
• Est. Priority Date: 02/24/1988
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Clark, Aidan W., Davison, Samuel H., Kast, Kevin H.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Ham, Seung
• Application Number:
  US07/160,052
• Time in Patent Office: 818 Days
• Field of Search: 60/39.29, 60/39.75, 415/178, 415/115, 415/116, 415/175, 415/176, 364/431.03, 364/431.01, 364/431.02, 73/660
• US Class Current: 701/100
• CPC Class Codes: F01D 11/24 by selectively cooling-heating stator or rotor components

Abstract

The invention relates to a control system which controls the diameter of a turbine shroud which surrounds a turbine in a gas turbine aircraft engine. The invention seeks to minimize the clearance between the turbine rotor and the shroud. Air is bled from the compressor in the engine and ducted to the shroud in order to heat or cool the shroud in order to, respectively, either expand or shrink the shroud to a proper diameter. The air temperature which is required is computed based on compressor speed and other engine parameters, but not upon directly measured rotor temperature, despite the fact that rotor temperature has a significant influence upon rotor diameter, and thus upon shroud diameter needed. Air at two different temperatures is bled from two different compressor stages in the engine and mixed together in a ratio which is determined according to flight conditions, in order to provide air of the required temperature for the shroud, and then ducted to the shroud in order to modify shroud size. Further, during accelerations and decelerations of the engine, a different air temperature is provided, as compared with that provided during steady state operation. In the event that the system just described should fail, back-up systems control shroud diameter. There exist two back-up systems, one for use during steady state, and the other for use during accelerations and decelerations.

Claims

1. In a method of controlling the clearance between turbine blades and a shroud in a gas turbine engine, the improvement comprising the step of

(a) computing a demanded temperature for the shroud, based on a historical record of turbine speed behavior.

6. The method according to claim 1 and further comprising the following step:

(c) adjusting shroud temperature in response to the demanded shroud temperature.

2. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) ascertaining turbine rotor temperature;

(b) computing a demanded shroud temperature in response to the rotor temperature; and

(c) adjusting actual shroud temperature in response to the demanded shroud temperature.

3. A method according to claim 2 in which turbine rotor temperature is ascertained from rotor speed.

7. The method according to claim 2 and further comprising the following steps:

(d) computing a back-up shroud temperature; and

(e) adjusting shroud temperature in response to the back-up shroud temperature when demanded shroud temperature is inaccurate.

4. In a method of controlling clearance between turbine blades and a shroud in a turbine in a gas turbine engine, the improvement comprising:

(a) deriving a demanded temperature for the shroud from a turbine rotor temperature.

9. The method according to claim 4 and further comprising the following step:

(c) adjusting shroud temperature in response to the demanded shroud temperature.

5. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) inferring rotor temperature from rotor speed;

(b) computing demanded shroud temperature in response to inferred rotor temperature; and

(c) adjusting actual shroud temperature in response to the demanded shroud temperature.

10. The method according to claim 5 and further comprising the following steps:

(c) computing a back-up shroud temperature; and

(d) adjusting shroud temperature in response to the back-up shroud temperature when demanded shroud temperature is inaccurate.

8. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) calculating the deviation of rotor temperature from a steady-state temperature;

(b) computing demanded shroud temperature in response to the deviation; and

(c) adjusting actual shroud temperature in response to the demanded shroud temperature.

11. In a method of controlling tip clearance in a turbine in a gas turbine engine, the improvement comprising:

(a) deriving a demanded temperature for the shroud for back-up use during transients; and

(b) deriving a demanded temperature for the shroud for back-up use during steady state.

12. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) deriving turbine rotor temperature from turbine rotor speed;

(b) deriving a demanded shroud temperature from the turbine rotor temperature;

(c) computing a back-up demanded shroud temperature based on derived rotor temperature and rotor speed; and

(d) adjusting actual shroud temperature in response to the demanded shroud temperature during normal operation.

13. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) deriving turbine rotor temperature from turbine rotor speed;

(b) deriving a first demanded shroud temperature from the turbine rotor temperature;

(c) computing a back-up demanded shroud temperature by interpolating between second and third demanded shroud temperatures; and

(d) adjusting the actual shroud temperature in response to the first demanded shroud temperature during normal operation.

14. A method according to claim 13 in which the second and third demanded shroud temperatures

(d) each correspond to a different rotor temperature, and the interpolation is based on the derived shroud temperature of (b).

15. In a method of controlling clearance between turbine blades and a shroud in a gas turbine engine, the improvement comprising the following steps:

(a) deriving turbine rotor temperature from turbine rotor speed; and

(b) computing a back-up demanded shroud temperature by interpolating between

(i) a first demanded shroud temperature corresponding to a first rotor temperature and

(ii) a second demanded shroud temperature corresponding to a second rotor temperature, and making the interpolation based on derived rotor temperature.

16. In a method of controlling clearance between turbine blades and a shroud in a gas turbine engine, the improvement comprising the following steps:

(a) deriving turbine rotor temperature from turbine rotor speed; and

(b) computing a back-up demanded shroud temperature by interpolating between a first demanded shroud temperature and a second demanded shroud temperature based on derived rotor temperature.

17. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) deriving turbine rotor temperature from turbine rotor speed;

(b) computing a demanded shroud temperature from the turbine rotor temperature; and

(c) computing a back-up demanded shroud temperature using the following steps;

(i) ascertaining the deviating of measured rotor temperature from a stabilized temperature;

(ii) ascertaining demanded shroud temperature for the stabilized temperature; and

(iii) modifying the demanded shroud temperature of (b) based on the deviation.

18. A method of controlling tip clearance in a turbine in a gas turbine engine, comprising the following steps:

(a) deriving turbine rotor temperature from turbine rotor speed;

(b) computing a demanded shroud temperature from the turbine rotor temperature; and

(c) computing a first, back-up, demanded shroud temperature using the following steps;

(i) ascertaining whether the engine is undergoing a transient and producing a transient signal in response;

(ii) in response to the transient signal, ascertaining demanded shroud temperatures for different rotor temperatures; and

(iii) deriving the first, back-up, demanded shroud temperature by interpolating between demanded shroud temperatures of (c)(ii).

19. A method of backing up an active clearance control for a turbine shroud in a gas turbine engine, comprising the following steps:

(a) computing a back-up shroud temperature needed for a turbine rotor operating at a reference temperature; and

(b) modifying the shroud temperature based on an inferred deviation of actual rotor temperature from the reference temperature.

20. A method of computing turbine rotor temperature for use in a control system in a gas turbine engine, comprising the following steps:

(a) measuring turbine rotational speed;

(b) maintaining a schedule of data pairs, each pair containing

(i) a turbine temperature and

(ii) a rotational speed;

(c) storing an intermediate signal (HPRTEMP) indicative of the turbine temperature paired with present rotational speed;

(d) when turbine speed changes, causing HPRTEMP to indicate the magnitude and direction of the change; and

(e) after a turbine speed change, causing HPRTEMP to return, at a controlled rate, to a value indicating steady-state operation.

21. A method of controlling shroud clearance in a gas turbine engine, comprising the following steps:

(a) computing the deviation of actual rotor temperature from steady-state rotor temperature;

(b) computing the deviation of shroud temperature from a steady-state shroud temperature;

(c) using the deviation of paragraph (a), computing a demanded shroud temperature; and

(d) adjusting the actual shroud temperature based on the demanded shroud temperature.

22. A method according to claim 21 in which the computing of a demanded shroud temperature comprises the step of interpolating between

(i) a demanded shroud temperature for a cold rotor and

(ii) a demanded shroud temperature for a rotor at steady-state temperature, based on the deviation of paragraph (a).

23. In a method of controlling clearance between a turbine rotor and a shroud in a gas turbine engine, the improvement comprising the step of:

(a) computing the deviation in shroud temperature from a steady-state value which corresponds to a measured deviation of rotor temperature from a steady-state value.

24. In an active clearance control for controlling clearance between a shroud and turbine blades in a gas turbine engine, the improvement comprising:

(a) a system for computing a back-up demanded shroud temperature.

25. In a system which controls clearance between turbine blades and a shroud in a gas turbine engine, the improvement comprising:

(a) a back-up system which computes demanded shroud temperature based on deviation of inferred turbine rotor temperature from a reference.

26. In an active clearance control for a turbine in a gas turbine engine, the improvement comprising:

(a) means for inferring rotor temperature from rotor speed and

(b) means for computing a demanded shroud temperature in response to the rotor temperature.

27. In an active clearance control for a turbine in a gas turbine engine, the improvement comprising:

(a) means for detecting a deviation of rotor temperature from a steady state value; and

(b) means for computing a demanded shroud temperature based on the deviation.

28. In an active clearance control for a gas turbine, the improvement comprising:

(a) means for detecting a change in rotor speed, and

(b) means for computing a demanded shroud temperature in response.

29. A control according to claim 28 and further comprising:

(c) means for modifying shroud temperature in response to demanded shroud temperature.

30. In an active clearance control for a gas turbine engine, the improvement comprising:

(a) a data base of steady-state rotor temperatures, each associated with a rotor speed;

(b) means for inferring deviation of rotor temperature from steady state temperature; and

(c) means for computing a demanded shroud temperature in response to the deviation of paragraph (b).

31. A back up system for use with an active clearance control for a turbine shroud in a gas turbine engine, comprising:

(a) a schedule which indicates shroud temperature needed under reference operating conditions;

(b) means for inferring the shroud temperature needed under non-reference conditions by extrapolating from the schedule based on deviation of the non-reference operating conditions from the reference operating condition; and

(c) means for adjusting actual shroud temperature in response to the needed shroud temperature which was inferred in paragraph (b).

32. A back-up system for use with an active clearance control for a turbine shroud in a gas turbine engine, comprising:

(a) a schedule which indicates shroud temperatures needed for respective turbine speeds under steady-state operating conditions; and

(b) means for modifying one of the scheduled shroud temperatures based on deviation of an operating condition from the steady-state conditions.

33. A control for controlling the clearance between a turbine rotor and a shroud in a gas turbine engine, comprising:

(a) temperature calculation means for providing a signal (HPRTEMP) indicative of rotor temperatures;

(b) shroud demand means for providing a signal (TCDMD) indicative of a demanded shroud temperature in response to HPRTEMP;

(c) means for bleeding air at a first, low, temperature from a compressor stage of the engine;

(d) means for bleeding air at a second temperature, higher than the first, from a different compressor stage of the engine;

(e) duct means for delivering bleed air to the shroud; and

(f) valve means for controlling the relative amounts of low temperature and high temperature air applied to the shroud.

34. A control according to claim 33 in which the temperature calculation means derives HPRTEMP from measured rotor speed.

35. A control according to claim 33 in which the temperature calculation means further comprises a model of engine performance which infers HPRTEMP from a group of measured variables, the group including rotor speed.

36. A control according to claim 33 in which the shroud demand means derives TCDMD by interpolating between

(i) a shroud temperature for a cold rotor and

(ii) a shroud temperature for a rotor at a stabilized temperature.

37. A control according to claim 33 in which the shroud demand means comprises means for interpolating between

(i) a schedule of corrected shroud temperatures for a cold rotor at different speeds;

and

(ii) a schedule of corrected shroud temperatures for a rotor at a stabilized temperature, the corrected temperatures being corrected based on temperature in a selected compressor stage.

38. An apparatus according to claim 33 and further comprising:

(b) detection means for ascertaining whether the first demanded shroud temperature is correct.

39. In a primary system for controlling tip clearance of a turbine, the improvement comprising:

(a) a back-up system for use when the primary system is not operating properly, comprising;

(i) transient detection means for ascertaining whether the turbine is accelerating, decelerating, or operating at steady state;

(ii) means for computing a first demanded shroud temperature if the turbine is not at steady state; and

(iii) means for computing a second demanded shroud temperature if the turbine is at steady state.

40. An apparatus according to claim 39 and further comprising:

(a) means for modifying the first and second demanded shroud temperatures during takeoff.

41. An apparatus according to claim 39 in which the back-up system further comprises:

(b) means for modifying the first demanded shroud temperature based on transient severity.

42. An apparatus according to claim 39 in which the transient back-up system further comprises:

(b) means for modifying the first demanded shroud temperature based on transient duration.

43. An apparatus according to claim 39 in which the transient detection means comprises means for ascertaining the severity of a transient.

44. In a clearance control for a turbine in a gas turbine engine, the improvement comprising a pair of back-up systems, including:

(a) a first back-up system comprising

(i) detection means for detecting the occurrence of a transient and providing a transient signal in response;

(ii) means for deriving the shroud temperature needed during a transient based on both the transient signal and measured rotor temperature; and

(b) a second back-up system comprising

(i) means for deriving the shroud temperature needed during steady state based on measured rotor temperature.

45. A control for controlling the clearance between a turbine rotor and a shroud in a gas turbine engine, comprising:

(a) temperature calculation means for providing a signal (HPRTEMP) indicative of rotor temperatures;

(b) shroud demand means for providing a signal (TCDMD) indicative of a demanded shroud temperature in response to HPRTEMP;

(c) means for bleeding air at a first, low, temperature from a compressor stage of the engine;

(d) means for bleeding air at a second temperature higher than the first, from a different compressor stage of the engine;

(e) duct means for delivering bleed air to the shroud; and

(f) valve means for controlling the relative amounts of low temperature and high temperature air applied to the shroud, and comprising;

(i) a first inlet chamber for receiving low temperature air;

(ii) a second inlet chamber for receiving higher temperature air;

(iii) an outlet chamber;

(iv) a first aperture connecting the first inlet chamber with the outlet;

(v) a second aperture connecting the second inlet chamber with the outlet;

(vi) poppet means for selectively

(A) blocking both apertures;

(B) blocking the first aperture completely, while blocking the second aperture to a first predetermined degree;

(C) blocking the first aperture completely, while blocking the second aperture to a second, greater, predetermined degree;

(D) partially blocking both apertures to respective predetermined degrees;

(E) blocking the second aperture completely, while restricting the first aperture in a predetermined amount; and

(F) partially blocking both apertures in amounts computed in response to TCDMD.

46. A control for controlling the clearance between a turbine rotor and a shroud in a gas turbine engine, comprising:

(a) temperature calculation means for providing a signal (HPRTEMP) indicative of rotor temperature;

(b) shroud demand means for providing a signal (TCDMD) indicative of a demanded shroud temperature in response to HPRTEMP;

(c) means for bleeding air at a first, low, temperature from a compressor stage of the engine;

(d) means for bleeding air at a second temperature, higher than the first, from a different compressor stage of the engine;

(e) duct means for delivering bleed air to the shroud;

(f) valve means for controlling the relative amounts of low temperature and high temperature air applied to the shroud; and

(g) a proportional-integral-derivative controller for controlling the valve means.

47. A control for controlling the clearance between a turbine rotor and a shroud in a gas turbine engine, comprising:

(a) temperature calculation means for providing a signal (HPRTEMP) indicative of rotor temperatures;

(b) shroud demand means for providing a signal (TCDMD) indicative of a demanded shroud temperature in response to HPRTEMP;

(c) means for bleeding air at a first, low, temperature from a compressor stage of the engine;

(d) means for bleeding air at a second temperature, higher than the first, from a different compressor stage of the engine;

(e) duct means for delivering bleed air to the shroud;

(f) valve means for controlling the relative amounts of low temperature and high temperature air applied to the shroud; and

(g) a control system for controlling the valve, in which the gain varies approximately as follows;

(i) for frequencies below a first frequency, the gain decreases with increasing frequency;

(ii) for frequencies between the first frequency and a second frequency, the gain remains substantially constant; and

(iii) for frequencies above the second frequency, the gain increase with increasing frequency.