Active clearance control for gas turbine engine

• US 5,012,420 A
• Filed: 03/31/1988
• Issued: 04/30/1991
• Est. Priority Date: 03/31/1988
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Walker, Roger C., Joyce, David L., Kastrup, David A., Reese, Scott P.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US07/175,894
• Time in Patent Office: 1,125 Days
• Field of Search: 364/431.02, 364/550, 60/39.29, 60/39.75, 415/1, 415/115, 415/116, 415/118, 415/134, 415/138, 415/175, 415/178
• US Class Current: 701/100
• CPC Class Codes: F01D 11/24 by selectively cooling-heating stator or rotor components
• CPC Class Codes: G01B 13/12 for measuring distance or clearance between spaced objects or spaced apertures G01B13/18 takes precedence
• CPC Class Codes: G01B 21/16 for measuring distance of clearance between spaced objects
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature

Abstract

The invention concerns an active clearance control for controlling clearance between a turbine and a casing in a gas turbine aircraft engine.

The invention calculates the instantaneous clearance between a turbine casing and a turbine rotor, based on temperature. Two temperatures are involved. First, a steady state temperature (SSTemp) is computed for the rotor and the casing. SSTemp is a predicted, future temperature, which will be attained when the engine reaches steady state operation. Each SSTemp is computed based on presently occurring engine operating conditions, such as selected temperatures, pressures, and rotational speeds.

Changes which occur in the SSTemp'"'"'s indicate the second temperatures, which are the instantaneous temperatures of the casing and rotor. These changes in SSTemp are caused by changes in the present operating conditions, which occur during engine acceleration and deceleration. The instantaneous temperatures indicate the diameters of the casing and the rotor, and thus the instantaneous clearance between them.

In another form of the invention, the computed instantaneous clearance is used to control air which is bled from the fan and ducted onto the casing, in order to attain a desired clearance.

Claims

1. A clearance control for a gas turbine engine, comprising:

(a) means for calculating steady-state turbine rotor and casing diameters, based on measurements of selected engine operating characteristics;

(b) means for computing a desired clearance between the rotor and casing based on engine speed; and

(c) means for adjusting the temperature of the casing in order to drive the casing toward the desired clearance.

2. A clearance control for a gas turbine engine, comprising:

(a) means for calculating steady-state turbine rotor and casing temperatures, based on measurements of selected engine operating characteristics;

(b) means for calculating turbine rotor and casing diameters, based on the respective temperatures of (a);

(c) means for computing a desired clearance between the rotor and casing based on engine speed; and

(d) means for adjusting temperature of the casing in order to attain the desired clearance.

3. A clearance control for a gas turbine engine, comprising:

(a) means for calculating steady-state turbine rotor and casing temperatures, based on measurements of selected engine operating characteristics;

(b) means for inferring actual turbine rotor and casing temperatures, based on the behavior of the temperatures of (a);

(c) means for calculating turbine rotor and casing diameters, based on the respective actual temperatures of (b);

(d) means for computing a desired clearance between the rotor and casing based on engine speed; and

(e) means for adjusting temperature of the shroud in order to attain the desired clearance.

4. A clearance control for a gas turbine engine, comprising:

(a) means for calculating first, steady-state, turbine rotor and casing temperatures, based on measurements of selected engine operating characteristics;

(b) means for modifying the first temperatures, based on the respective behaviors of the first temperatures;

(c) means for calculating turbine rotor and casing diameters, based on the modified temperatures of (b);

(d) means for computing a desired clearance between the rotor and casing based on engine speed; and

(e) means for adjusting temperature of the casing in order to attain the desired clearance.

5. A clearance control for a gas turbine engine, comprising:

(a) means for calculating a steady-state turbine rotor temperature and a steady-state casing temperature, based on measurements of selected engine operating characteristics;

(b) means for estimating actual turbine rotor and casing temperatures, based on the behavior of the respective temperatures of; and

(c) means for adjusting temperature of the casing based on the estimated rotor and casing temperatures.

6. A clearance control for a gas turbine engine, comprising:

(a) means for calculating a desired clearance value between turbine rotor and turbine casing;

(b) means for calculating the temperature of the turbine rotor web and the temperature of the turbine rotor bore (designated SSTW and SSTB, respectively) which would eventually exist at steady-state operation, based on

(i) core speed,

(ii) compressor discharge temperature, and

(iii) compressor discharge pressure;

(c) means for inferring the present temperatures of the web and bore, based on the time-behavior of SSTW and SSTB;

(d) means for inferring displacement of the turbine rotor from its cold position, based on

(i) the present temperatures of the web and the bore,

(ii) the present temperature of turbine blades, and

(iii) centrifugal growth of the web and bore;

(e) means for calculating the temperature (SSTC), which would exist at steady-state operation, of the turbine casing;

(f) means for inferring the present temperature of the turbine casing, based on the time-behavior of SSTC;

(g) means for calculating displacement of the casing from its cold position, based on the present temperature of (f) and pressure within the casing;

(h) means for calculating a demanded casing displacement, based on

(i) the desired clearance,

(ii) the displacement of the turbine rotor, and

(iii) a correction factor for cold clearance;

(i) means for ascertaining deviations of the actual displacement of the casing from the demanded displacement of the casing; and

(j) means for reducing the deviation of the actual casing displacement from the demanded displacement by adjusting casing temperature.

7. In a clearance control, for controlling clearance between a casing and turbine blades in a gas turbine engine, which controls a valve which applies air to a turbine casing in order to shrink the casing, the improvement comprising:

(a) means for detecting a throttle burst and producing a signal in response; and

(b) means for reducing air flow through the valve in response to the signal.

8. In a clearance control in a gas turbine engine, in which air is ducted to a turbine casing in order to control the size of the casing by changing temperature of the casing, the improvement comprising

(a) prediction means for predicting steady-state displacements of turbine rotor and turbine casing from their respective cold positions, based on airflow conditions and speed of the engine;

(b) estimation means for estimating actual, transient, displacements of the rotor and casing based on the behavior of the predicted steady-state displacements; and

(c) means for adjusting temperature of the casing based on the predicted transients of the rotor and casing displacements.

9. A control according to claim 8 in which the estimation means comprises first means for incrementally adjusting the estimated displacements in response to changes in the predicted steady-state displacements.

10. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) calculating diameter changes in the rotor based on rotor centrifugal growth and rotor thermal growth; and

(b) adjusting temperature of a casing which surrounds the rotor, based on the calculated diameter changes, in order to maintain a predetermined clearance between the rotor and the casing.

11. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) estimating temperature of a turbine rotor based on length of time the engine has been shut down; and

(b) adjusting temperature of a casing which surrounds the rotor, based on the estimated temperature.

12. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) estimating present temperature of a first engine component based on the behavior of a temperature which would exist in the component at steady state under present operating conditions; and

(b) adjusting temperature of a second component, based on the estimated temperature, in order to control distance between the first and second components.

13. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) computing changes in diameter of a turbine rotor based on temperature change in two rotor regions; and

(b) adjusting temperature of a casing surrounding the rotor in order to control clearance between the casing and rotor.

14. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) calculating changes in size of a turbine casing, based on pressure and temperature of air within the casing; and

(b) adjusting temperature of the casing in order to control size of the casing.

15. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) computing size changes of supports for a turbine casing based on temperature;

(b) deriving a diameter of the casing, based on the size changes and other inputs; and

(c) adjusting temperature of the casing in order to control the size of the casing.

16. In a digital active clearance control for a gas turbine engine, which includes a cooling airflow which cools a turbine casing, the improvement comprising the steps of:

(a) computing size changes of the casing based on

(i) amount of cooling airflow,

(ii) amount of core flow,

(iii) temperature of the cooling airflow, and

(iv) temperature of the core flow; and

(b) adjusting temperature of the casing in order to attain a predetermined casing size.

17. In a digital active clearance control for a gas turbine engine, which includes an airflow which cools a turbine casing, the improvement comprising the step of:

(a) computing size changes of the casing based on

(i) flow rates of one or more airflows near the casing, and

(ii) temperatures of the airflows; and

(b) adjusting temperature of the casing in order to attain a predetermined casing size.

18. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) calculating dimensional changes of a first component based on temperature and a thermal expansion coefficient of the component;

(b) modifying the coefficient based on temperature; and

(c) adjusting temperature of a second component, based on the dimensional changes, in order to attain a desired clearance between the first and second components.

19. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, and in which an airflow is ducted to a turbine casing in a duct having a valve, the improvement comprising the steps of:

(a) calculating maximum flow expected in the duct when the valve is fully open, based on a pressure drop along the duct and the speed of sound of air in the duct;

(b) calculating actual flow in the duct based on the maximum flow of (a) and valve position; and

(c) adjusting valve position in order to attain a predetermined flow rate.

20. In a digital active clearance control for a gas turbofan engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) cooling a turbine casing using a fan bleed; and

(b) terminating cooling if a predetermined type of malfunction occurs to thereby cause the casing to expand.

21. In a digital active clearance control for a turbine rotor and casing in a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) providing a signal indicative of dimensional changes of a turbine rotor which occur almost simultaneously with rotor acceleration; and

(b) when the signal indicates that the dimensional changes exceed a limit, allowing the turbine casing to expand.

22. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) calculating a first, estimated steady-state temperature of a component of the engine based on engine operating conditions;

(b) when changes in the estimated steady-state temperature occur, causing a variable to incrementally approach the first temperature; and

(c) modulating the airflow which is used to adjust temperature of the component, based on said variable.

23. In a digital active clearance control for a gas turbine engine which contains a turbine rotor which includes a disc and blades, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising the steps of:

(a) computing displacement of the rotor from its cold size, based on

(i) thermal displacement of the disc;

(ii) centrifugal displacement of the disc; and

(iii) thermal displacement of the blades; and

(b) adjusting temperature of a casing which surrounds the rotor, based on the computed displacement.

24. The improvement according to claim 23 in which the thermal displacement of the blades is computed based on the temperatures of cooling air flowing through the blades and gases flowing between the blades.

25. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for providing a first signal indicative of temperature of a turbine rotor based on selected engine operating parameters;

(b) means for providing a second signal indicative of the temperature of the rotor when the engine is not running;

(c) means for selecting the first signal for computation of rotor size when the engine is running and for selecting the second signal for computation of rotor size when the engine is not running; and

(d) adjusting temperature of a casing which surrounds the rotor, based on the computed rotor size.

26. The improvement according to claim 25 and further comprising means for computing rotor size based on the temperature signal selected.

27. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for predicting the steady state temperature which a turbine disc will attain at steady state, based on selected present operating conditions;

(b) means for estimating the actual temperature of the disc based on the time-behavior of the steady state temperature, and including

(i) lag means which causes the estimated actual temperature to lag the steady state temperature; and

(c) means for adjusting the temperature of a casing which surrounds the disc, based on the estimated actual temperature of the disc.

28. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for providing at least one time constant from which temperature behavior of an engine component can be inferred;

(b) means for modifying the time constant in response to changes in engine operating parameters, which parameters include engine speed, and the pressure and temperature of air which is in contact with the component; and

(c) adjusting airflow which affects clearance between the component and a second component, based on the inferred temperature behavior.

29. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) a heat transfer model from which temperature of an engine component can be estimated based on

(i) one or more time constants and

(ii) changes in a first group of engine operating parameters which include engine speed and compressor discharge temperature;

(b) means for adjusting the time constants based on changes in a second group of engine operating parameters which include engine speed and the temperature and pressure of air in contact with the component; and

(c) adjusting airflow which affects clearance between the component and a second component, based on said estimated temperature.

30. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for computing the steady state temperature which will be eventually attained by an engine component, based on selected engine operating parameters which are presently occurring;

(b) means for estimating present temperature of the component, which includes a lag system for causing a variable to pursue and lag the steady state temperature; and

(c) means for adjusting airflow which affects the clearance between the component and a second component, based on the estimated present temperature.

31. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) a heat transfer model which computes temperature and size which will be attained at steady state for each of two parts of a turbine disc;

(b) means for estimating present temperature of the two parts, based on changes in the temperatures of; and

(c) means for adjusting size of a casing which surrounds the disc, based on one or more of the estimated present temperatures.

32. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for estimating present temperature of a turbine casing;

(b) means for computing size of the casing based on the present temperature, thermal expansion coefficient of the casing, and a pressure within the casing;

(c) means for comparing the computed size with a desired size; and

(d) if the computed size differs from the desired size, adjusting the size of the casing by altering the casing temperature.

33. Apparatus according to claim 32 and further comprising means for modifying the thermal expansion coefficient based on the temperature of the casing.

34. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for estimating temperature of a turbine casing based on temperatures of airflows located near the casing;

(b) means for computing casing size based on casing temperature; and

(c) means for adjusting the size of the casing by altering the temperature of the casing.

35. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) a heat transfer model from which temperature of a turbine casing can be estimated based on

(i) one or more time constants and

(ii) changes in a first group of engine operating parameters which include engine speed and compressor discharge temperature;

(b) means for adjusting the time constants based on changes in airflow through the engine; and

(c) means for adjusting temperature of the casing, in order to attain a desired temperature, which is computed based on engine operating parameters.

36. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for providing data regarding temperature of a turbine casing;

(b) means for computing casing displacement from a cold position of the casing, based on the temperature and a thermal expansion coefficient of the casing; and

(c) means for adjusting temperature of the casing in order to attain a predetermined casing size.

37. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for computing a steady state temperature (SSTemp) for an engine component;

(b) means for estimating the present temperature of the component based on changes occurring in the SSTemp; and

(c) means for adjusting airflow which affects the clearance between the component and a second component, based on the estimated present temperature.

38. In a digital active clearance control for a gas turbine engine, in which a digital computer controls airflow to a turbine casing, in order to control the size of the casing by adjusting the temperature of the casing, the improvement comprising:

(a) means for computing, based on selected engine operating conditions, a steady state temperature (SSTemp) which will be attained by an engine component;

(b) means for estimating the present temperature of the component based on changes occurring in the operating conditions; and

(c) means for adjusting airflow which affects the clearance between the component and a second component, based on the estimated present temperature.