Abstract:
A control and method for operating a gas turbine engine senses the operation of blades associated with any number of rotors in the gas turbine engine. If the sensors report to the control that the blades are operating at a speed that can potentially cause damage or undue vibration, the control moves that component to a slightly different speed at which it will not have the potential problem. The control may also change other components to ensure that the thrust provided by the gas turbine engine is maintained relatively constant.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application relates to a method and a control that monitors the fatigue level of blades at any number of locations within a gas turbine engine, and changes a spool speed should an undesirable amount of fatigue be predicted at a current state of operation. At the same time, while the spool speed is changed, the control attempts to maintain a relatively constant thrust.  
         [0002]     Gas turbine engines are provided with a number of functional sections, including a fan section, a compressor section, a combustion section, and a turbine section. Air and fuel are combusted in the combustion section. The fan, compressor and turbine sections include rotors that have blades. The products of the combustion move downstream, and pass over a series of turbine rotors, driving the rotors to create power. In turn, the turbine rotors drive the fan and compressor rotors.  
         [0003]     Of course, gas turbine engines operate in a hostile environment. There is a good deal of stress and vibration which tend to be placed onto the blades in the fan, the compressors, and in the turbines. High blade flutter and stress can occur at a very narrow speed range for any one of these components. Flutter and shedding can induce vibration that are of a non-integral order, and can result in high blade stress and potential damage in a very short time. Resonance stress is an integral-order vibration and can also result in high blade stress and potential damage in a relatively short time.  
         [0004]     As is known, gas turbine engines typically have a low speed spool which incorporates a low pressure turbine and a shaft that drives a fan and perhaps a low pressure compressor. A high speed spool includes a high pressure turbine and a shaft driving the high pressure compressor. The speeds that can cause potential damage to the blades in the low spool and the high spool may differ.  
         [0005]     Fan blade health sensors have been developed to record data only. These fan blade health sensors can operate on eddy currents, microwaves, or in some other fashion. However, these sensors have not been incorporated into a control which takes any corrective action should the potential for upcoming stress and damage be identified.  
       SUMMARY OF THE INVENTION  
       [0006]     In a disclosed embodiment of this invention, blade health sensors monitor the potential for high stress and potential damage in blades at various locations within a gas turbine engine. Among the potential locations are the blades in the fan, the blades in an optional low pressure compressor (if included), and the blades in a low pressure turbine. Together, these three components are connected to rotate together on a shaft, with the low pressure turbine driving the fan and low pressure compressor. These combined rotating elements are known as the low spool. Similarly, blade health sensors may monitor the operation of a high pressure turbine blade, and the blades in a high pressure compressor. These components are also connected to rotate together by a common shaft. These combined rotating components are known as the high spool.  
         [0007]     The blade health sensors can be eddy current, microwave, or any other type sensor. The microwave sensors are currently being developed to best withstand higher temperature locations, such as in the turbine section. At least in some embodiments, such sensors may look for blade flutter, or vibrations. Either of these might be an indication that a blade is experiencing, or approaching, a high stress operation moment.  
         [0008]     If potential damage is sensed with regard to the low spool, the speed of the low spool is changed by a controller for the gas turbine engine such that it moves out of the potentially dangerous range. The speed may be changed by adjusting the amount of fuel delivered to the engine, or may be changed in some other fashion such as by adjusting the geometry of a variable vane. In this manner, the speed can be changed, with the vane geometry adjusted to maintain a standard engine thrust. Also, the throat area of a discharge nozzle can be modified to change the speed. The same control occurs in parallel on the high spool.  
         [0009]     As mentioned above, the potential damage range can be a very narrow speed range. Thus, only slight changes in speed may be necessary. The control may simply change the speed in either an increasing or decreasing direction until the blade health sensors provide feedback that the blades are no longer facing potential damage.  
         [0010]     To maintain a relatively constant thrust, the vanes may be changed, and/or the nozzle throat area may be modified. The control algorithms necessary to maintain a particular thrust by varying these components are known. Also, algorithms are known for separately controlling the speed of the low spool and the high spool. It is the application of such changes to the current invention that is inventive.  
         [0011]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic view of a gas turbine engine incorporating the present invention.  
         [0013]      FIG. 2  is a flow chart of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     A gas turbine engine  20  is illustrated in  FIG. 1 . As known, a fan  22  delivers air downstream to a low pressure compressor  24 , and a high pressure compressor  26 . A high pressure turbine  28  is positioned downstream of a combustion section  36 . As known, the fan and compressors deliver compressed air to the combustion section  36 , and the air is mixed with fuel to be combusted. The products of combustion move downstream over the high pressure turbine  28 , and the low pressure turbine  30 . The products of combustion then leave the engine through a nozzle  31 . As known, the high pressure turbine  28  is connected by a shaft  32  to the high pressure compressor  26 , and drives the high pressure compressor  26 . These three components ( 28 ,  32  and  26 ) are known as a “high spool” and tend to rotate at a relatively high speed.  
         [0015]     A low pressure turbine  30  is positioned downstream of the high pressure turbine  28 . It is connected by a shaft  34  to the low pressure compressor  24 , and a fan  22 . These components ( 30 ,  34 ,  24  and  22 ) are known as a “low spool.” 
         [0016]     In the present invention, blade health sensors  42  are associated with the blades in fan  22  and low pressure compressor  24  blades. While the blades are not shown as separate parts, as known, each of the sections  22 ,  24 ,  26 ,  28  and  30  are rotors provided with a plurality of discrete and removable blades. The sensors sense the health of these blades, and are utilized to identify any potential concerns with regard to the vibration and stress applied to the blades at the speed of operation of the blades.  
         [0017]     Similar sensors  44 ,  46  and  48  are associated with the high pressure compressor  26 , high pressure turbine  28 , and low pressure turbine  30 , respectively. All of these sensors report back to an engine control  50 . The engine control  50  senses the feedback provided by the sensors  42 ,  44 ,  46  and  48 , and identifies when any of the sensors report that the blades are operating in a manner that could cause upcoming concern from stress or vibration. A signal  52  is sent from the control  50  when such an occurrence is identified. This signal  52  controls the amount of fuel from a fuel supply  102  delivered to the combustion section  36  to change speed of operation of either the low spool or the high spool. Other methods of changing the gas turbine engine such as changing the throat area of the nozzle  31  by a mechanism  110  with an adjustable throat area  112  may be utilized. Moreover, although shown schematically, the vanes  99  associated with any of the rotor sections  22 ,  24 ,  26 ,  28  and  30  may be varied in their geometry such as through a variable vane geometry mechanism  100 . Mechanisms  100  and  110  are well known in the art, and are shown in an extremely schematic view in this drawing. However, a worker of ordinary skill in the art would recognize what is being disclosed in this application.  
         [0018]     The sensors  42 ,  44 ,  46  and  48  may monitor flutter, or vibration, or some other aspect of the operation of the blades to determine when a potential high stress or high vibration occurrence may be approaching. The sensors may be as known, and the indication of high stress may also be as known in the art. It is the control step of responding to such an identified problem by changing the speed of an associated spool that is inventive here. At the same time, the control attempts to minimize any effect on thrust due to the change in the spool speed. The fuel flow, the variable vane geometry and the size of the nozzle opening can all be controlled to change the speed of either the low spool or the high spool to move it a slight amount either increasing or decreasing, and to move outside of the potential danger range. At the same time, the thrust delivered outwardly of the nozzle  31  can be maintained relatively constant even given the speed change by changing the geometry of the vanes by mechanism  100 , and/or the nozzle with the nozzle adjustment mechanism  110 .  
         [0019]      FIG. 2  is a flow chart showing how the control would operate in this invention. If a potential problem is identified with the low spool, the speed of the low spool is changed. Again, in disclosed embodiments, the control may also maintain a constant thrust. On the other hand, if the speed of the high spool is seen as potentially being a problem, the high spool speed is changed. At the same time, aspects of the control to maintain the speed of the other spool, and to maintain constant thrust might also be occurring. The algorithms necessary to change the speed of one spool without changing the speed of the other, and the algorithms to maintain constant thrust are known in the art. Also, it should be understood that it may be a very narrow speed that provides the potential problem, and thus large changes in speed need not occur. Thus, the change as identified in this method, and in the  FIG. 2  flowchart, may be very small step changes in the speed.  
         [0020]     The present invention thus achieves a simple method and control for ensuring that a gas turbine engine is not operated at a speed range that could prove problematic. Given the relatively short period of time that is required for operation in a problematic speed range to cause damage, the present invention is thus extremely valuable in avoiding such a speed range.  
         [0021]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.