Abstract:
A method and apparatus for assessing damage to machine components is provided. The method includes calculating an expected parameter value based on a first parameter value indicator, calculating an estimate of an actual parameter value based on a second parameter value indicator, the second parameter value indicator being different than the first parameter value indicator, determining if the calculated expected parameter value is different than the calculated estimate of the actual parameter value by a predefined limit, and generating a damage flag based on a result of the comparison. The apparatus includes a computing device including a processor and a memory communicatively coupled to the processor, the processor programmed to execute a software product code segment that includes a detection boundary module, an estimator, and a comparator wherein the computing device is programmed to assess damage within an engine.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0001] The U.S. Government may have certain rights in this invention pursuant to contract number N68936-99-C-0117. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates generally to gas turbine engines and, more particularly, to methods and apparatus for assessing damage to engines.  
           [0003]    Gas turbines are used in different environments, such as, for providing propulsion as aircraft engines and/or for generating power in both landbased power systems and/or sea-borne power systems. During normal operation gas turbine engines may experiences large changes in ambient temperature, pressure, and power output level, and although such changes occur during normal operation, such change may result in undesirable changes in engine dynamics.  
           [0004]    To facilitate maintaining engine efficiency, at least some known turbine engines include a controller that continuously monitors the engine to ensure that mechanical, aerodynamic, thermal, and flow limitations of the turbo machinery are maintained. However, despite continuous monitoring of the turbine engine, undesirable engine performance may occur without detection by the controller. For example, an erroneous actuator position feedback, or an obstruction in the afterburner duct may cause the variable exhaust nozzle (VEN) of a gas turbine engine to exhibit anomalous behavior that may not be detectable until a physical inspection of the VEN is performed. However, continued operation with the anomalous behavior may adversely effect engine operating performance.  
           [0005]    Variable area exhaust nozzles (VEN) on gas turbine engines typically are manipulated to regulate a pressure ratio in the engine. Physically, the pressure drop across the nozzle changes in response to changes in the effective nozzle area, which may affect, for example, a fan operating line, and a core engine pressure ratio. Known VEN control logic can detect position sensor failure or actuator failure, however, more subtle damage scenarios, such as a hole resulting from ballistics damage, would be compensated for by manipulating the VEN position, but the damage is undetected by the control logic unless the needed compensation exceeds the physical limits of the VEN.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0006]    In one aspect, a method of assessing damage to machine components is provided. The method includes calculating an expected parameter value based on a first parameter value indicator, calculating an estimate of an actual parameter value based on a second parameter value indicator, the second parameter value indicator being different than the first parameter value indicator, determining if the calculated expected parameter value is different than the calculated estimate of the actual parameter value by a predefined limit, and generating a damage flag based on a result of the comparison.  
           [0007]    In another aspect, apparatus for detecting damage in a gas turbine engine is provided. The apparatus includes a computing device including a processor and a memory communicatively coupled to the processor, the processor is programmed to execute a software product code segment including a detection boundary module, an estimator,, and a comparator wherein the computing device is programmed to assess damage within an engine.  
           [0008]    In yet another aspect, a gas turbine assembly is provided. The assembly includes a variable area exhaust nozzle including an inlet side, and an outlet side, and a computing device that includes a processor and a memory communicatively coupled to the processor wherein the processor is programmed to execute a software product code segment that includes a detection boundary module, an estimator, and a comparator, and wherein the computing device is programmed to assess damage within the gas turbine assembly.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic illustration of a gas turbine engine;  
         [0010]    [0010]FIG. 2 is an exemplary block diagram of a variable area exhaust nozzle damage detector that may be used with the gas turbine engine shown in FIG. 1;  
         [0011]    [0011]FIG. 3 is a graph illustrating exemplary traces of an engine test;  
         [0012]    [0012]FIG. 4 is a graph illustrating exemplary traces of a computer simulation test of a hole in developed in the afterburner duct of the engine;  
         [0013]    [0013]FIG. 5 is a graph illustrating exemplary traces of results of the damage detector for engine test data;  
         [0014]    [0014]FIG. 6 is a graph illustrating exemplary traces of results of the damage detector as applied to simulation data; and  
         [0015]    [0015]FIG. 7 is a process flow diagram for a damage assessment process of the damage detector shown in FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    [0016]FIG. 1 is a schematic illustration of a gas turbine engine  10  including a fan assembly  12 , a high pressure compressor  14 , and a combustor  16 . In one embodiment, engine  10  is a F414 military aircraft engine available from General Electric Company, Cincinnati, Ohio. Engine  10  also includes a high pressure turbine  18  and a low pressure turbine  20 . Fan assembly  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 .  
         [0017]    In operation, air flows through fan assembly  12  and compressed air is supplied from fan assembly  12  to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow from combustor  16  drives rotating turbines  18  and  20  and exits gas turbine engine  10  through an exhaust system  28 . Exhaust system  28  includes a variable area exhaust nozzle (VEN)  30 .  
         [0018]    [0018]FIG. 2 is an exemplary block diagram of a variable area exhaust nozzle damage detector  200  that may be used with gas turbine engine  10  shown in FIG. 1. Damage detector  200  may be embodied in a processor coupled to engine  10  and configured to perform the below described processes. As used herein, the term processor is not limited to just those integrated circuits referred to in the art as processors, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits. In the exemplary embodiment, damage detector  200  is embodied in a Full Authority Digital Electronic Control (FADEC) available from General Electric Company, Cincinnati, Ohio. Damage detector  200  is used to identify potential damage cases including holes, or other damage that causes an increase in the physical area downstream of the turbines and/or blockages, or erroneous position feedback signals, or other damage that causes a decreased physical area downstream of the turbines. Damage detector  200  includes a detection boundary module  202  that is communicatively coupled to a parameter value indicator  204 . In the exemplary embodiment, gas turbine engine  10  includes VEN  28  and parameter value indicator  204  is a nozzle actuator position feedback  204 . In an alternative embodiment, parameter value indicators  204  may include engine process parameters used to infer a nozzle actuator position feedback.  
         [0019]    An effective area estimator  206  utilizes engine cycle data to determine a nozzle area implied by engine process parameters that are affected by the actual nozzle area. A comparator  208  receives signals from detection boundary module  202  and estimator  206 , and compares the received signals relative to each other and to a predetermined limit. If the comparison result exceeds a pre-defined limit value, a damage flag  210  is generated. In the exemplary embodiment, a maximum expected value of effective nozzle area is computed based on parameter value indicator  204 . Additionally, other operating condition information may be used to infer a desired parameter value indicator. More specifically, the maximum expected value represents the detection boundary. An estimate of the actual effective nozzle area is then calculated in estimator  206  using engine cycle data  212 , including, for example, rotor speed, gas pressure or temperatures, engine power, altitude, Mach number, and fuel flow. The maximum expected value of the effective nozzle area and estimate of the actual effective nozzle area are compared at comparator  208 , and an estimated effective area greater than the detection boundary results in a damage flag  210 .  
         [0020]    Effective area estimator  206  generates an estimated value of effective nozzle area as a function of engine cycle data  212 . In the exemplary embodiment, the function is a simple linear function of the inputs. In an alternative embodiment, the function is a neural network. In another alternative embodiment, the function is a nonlinear function of the inputs. Additionally, estimator  206  may be trained using real or simulated engine data, of both damaged and undamaged engines  10 . In yet another alternative embodiment, the function may be a physics-based model of an effective nozzle area that uses upstream parameters as inputs.  
         [0021]    Similar logic, using a minimum expected value of effective nozzle area for the detection boundary, may be used to detect VEN or afterburner duct blockages or erroneous position feedback signals. During such conditions, the effective nozzle area is smaller than what would be expected based on the actuator position feedback value  204 . Such logic may be used in conjunction with the “maximum area” logic described above, and such use is consistent with the intent and operation of both types of logic.  
         [0022]    [0022]FIG. 3 is a graph  300  illustrating exemplary traces of an engine test wherein damage detector  200  is implemented in software for a military aircraft engine, available from General Electric Company, Cincinnati, Ohio. The test includes engine cycle data and engine test data. During the engine test, a pre-existing hole in the side of the afterburner duct section was exposed which resulted in increasing the effective area downstream of turbines  18  and  20 . A first hole was exposed at partial power early in the test, prior to an elapsed time of forty (t=40) seconds. Accordingly, data shown in graph  300  represents a condition wherein the afterburner duct includes simulated pre-existing VEN damage. An additional hole was exposed from engine  10 , near the rear of the afterburner section after engine  10  was brought to maximum dry power (IRP) and after approximately forty-seven (t=47) seconds had elapsed. Fan speed trace  302  illustrates a response of fan speed (QN 2 ) to a sudden increase in effective nozzle area due to exposure of the second hole. LP turbine exit temperature (QT 5 ) trace  304  illustrates the response of LP turbine exit temperature to the initial increase in fan speed  302 . LP turbine exit pressure (QP 56 ), as shown in trace  306 , initially decreases in response to the increased exhaust area. Trace  308  illustrates a response of the exhaust nozzle actuator position feedback (QA8X). As the FADEC detects, and then compensates for the increased effective exhaust nozzle area, the control system commands the exhaust nozzle to close down. As the exhaust nozzle closes, it can be seen that fan speed, as shown in trace  302 , LP turbine exit temperature, as shown in trace  304 , and LP turbine exit pressure, shown in trace  306 , return to values near their pre-event values. Notably, in the exemplary case, the simulated damage was not sufficient to exceed the limits of the capability of exhaust nozzle  28  to correct for the damage, and as such may have gone undetected until physical inspection was performed.  
         [0023]    [0023]FIG. 4 is a graph  400  illustrating exemplary traces of a computer simulation test of a hole developed in the afterburner duct of engine  10 . FIG. 4 illustrates the simulation results of injecting the equivalent of a 20 in 2  hole in the afterburner duct or nozzle area. The operating conditions are similar to those of the engine test shown in FIG. 3. The damage is injected at the five second mark (t=5), and the corresponding increase in fan speed illustrated in trace  402 , and decrease in LP turbine exit temperature, illustrated in trace  404  and LP turbine exit pressure, illustrated in trace  406  are compensated for by a reduction in exhaust nozzle actual area, illustrated in trace  408 , commanded by the FADEC.  
         [0024]    [0024]FIG. 5 is a graph  500  illustrating exemplary results of damage detector  200  for the engine test data. Graph  500  includes a throttle position (PLA) trace  502 , an effective exhaust nozzle area (AE8) estimate trace  504 , and an AE8 Margin trace  506 . Trace  504  illustrates a detection boundary trace  508 , which is a computed estimate of effective nozzle area based on A8 actuator position feedback. In the exemplary embodiment, detection boundary trace  508  includes additional margin built in. An estimated AE 8  trace  510  is an estimate of effective nozzle area based on engine cycle data  212 . At the beginning of the test (t=40) , estimated AE8 trace  510  is greater than detection boundary trace  508  due to the exposure of first hole. However, at approximately the forty-seven second time mark (t=47), the second hole is exposed. Estimated AE8 trace  510  responds by increasing initially due to additional exhaust area provided by the hole. As the FADEC begins to compensate, AE8 estimate trace  510  and detection boundary trace  508  decrease. When the second hole is exposed, the difference between estimated AE8 trace  510  and detection boundary trace  508  changes by approximately 30 in 2  as illustrated by graph  506 . AE8 Margin trace  506  illustrates the difference between AE8 Estimate trace  510  and detection boundary trace  508 . In the exemplary embodiment, a signal represented by AE8 margin graph is used to set damage flag  210 . In the case of a nozzle or afterburner duct blockage, AE8 estimate graph  506  would illustrate a trace acting in an opposite direction and the difference between estimated AE8 trace  510  and detection boundary trace  508  would increase in a positive reference direction.  
         [0025]    [0025]FIG. 6 is a graph  600  of results of damage detector  200  applied to simulation data. Graph  600  illustrates a damage trace  602  that would result from a 20 in 2  hole and a damage trace  604  that would result from a 40 in 2  hole. Each of traces  602  and  604  include a Detection Boundary trace  606  and  608 , an Estimated AE8 trace  610  and  612 , and an AE8 trace  614  and  616 . The simulation results show similar behavior as the engine test data shown in FIG. 5, except that the simulated pre-existing damage is not present, therefore Estimated AE8 trace  606 ,  608  is approximately equal to AE8 trace  614 ,  616 . After an elapsed time of approximately five seconds during the simulation, damage to the engine corresponding to a 20 in 2  hole and a 40 in 2  hole is simulated as shown in traces  602  and  604  respectively. In each simulation, Estimated AE8 trace  610 ,  612  and AE8 trace  614 ,  616  increase sharply because the simulated damage presents a larger nozzle area permitting more flow through engine  10 . The FADEC compensates for the increased flow through the engine by closing exhaust nozzle  28 , reducing the nozzle area and restricting flow through engine  10 .  
         [0026]    [0026]FIG. 7 is a process flow diagram for a damage assessment process  700  of the damage detector shown in FIG. 2. Process  700  calculates  702  an expected parameter value based on a first parameter value indicator  204 , which is responsive to a damage symptom. In the exemplary embodiment, first parameter value indicator  204  is a position feedback signal for a gas turbine engine exhaust nozzle actuator. In an alternative embodiment, first parameter value indicator  204  may be any monitored parameter or parameter that may be inferred from other monitored parameters. The engine exhaust nozzle actuator position feedback signal may be selected because in one known damage scenario, such as, a hole in a wall of the engine afterburner duct, the engine FADEC compensates for the hole by causing the exhaust nozzle to close down. The position feedback signal indicates a repositioning of the nozzle in response to damage to the engine. An estimate of an actual parameter value is calculated  704  based on a second parameter value indicator. In the exemplary embodiment, the second parameter value indicated is a plurality of sensors monitoring machine parameters that may be combined to infer an estimate of the actual parameter value. In an alternative embodiment, the second parameter value indicated may be a redundant sensor monitoring the same parameter as the first parameter value indicator. The results of the calculated expected parameter value is compared  706  to the calculated estimate of the actual parameter value based on a predefined limit. If the results of the comparison exceed the limit, a damage flag is generated  708 . Damage flag  708  may indicate a hole or otherwise excess flow condition, or may indicate a blockage of the afterburner duct or a faulty actuator position feedback. Damage flag  708  may be used to initiate automatic corrective action, signal a visual and/or sonic warning, write an entry to a fault log, or may be used in concert with other flags to diagnose and/or report engine problems to a supervisory control system and/or human operator.  
         [0027]    The above-described damage detector system is cost-effective and highly reliable. Each system includes a detection boundary module that is communicatively coupled to a parameter value indicator, an effective area estimator to determine a nozzle area, and a comparator that receives signals from the detection boundary module and the estimator and compares the received signals relative to each other and to a predetermined limit. If a result of the comparison exceeds a limit value, a damage flag is generated. Accordingly, the damage detector system facilitates operation and maintenance of machines, and in particular gas turbine engines, in a cost-effective and reliable manner.  
         [0028]    Exemplary embodiments of damage detector system components are described above in detail. The components are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each damage detector system component can also be used in combination with other damage detector system components.  
         [0029]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.