Abstract:
Variable elements of a turbine engine such as variable inlet guide vanes, variable bleed valves and variable stator vanes can be adjusted to provide a desired level of power and/or efficiency for the turbine engine across a range of operating conditions. The variable element settings typically determined through experimentation when the engine is new. Unfortunately, over the life cycle of the turbine engine, as wear occurs, the original variable element settings may no longer provide a desired level of power and efficiency. To correct this problem, offsets to the original variable element settings are calculated based on observable operational conditions which provide a measure of the wear that has occurred. The offsets are applied to the original variable element settings to generate corrected variable element settings. These corrected variable element settings are then used to configure the turbine engine. The corrected variable element settings allow the turbine engine to continue to operate at a desired level of power and/or efficiency over the life of the turbine engine, despite any deterioration which may have occurred due to normal life cycle wear.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Some turbine engines have variable geometry, or elements which can be adjusted to ensure that the turbine engine provides desirable power and/or efficiency over a range of operating conditions and for a range of engine quality or deterioration levels. For instance, a turbine engine could include an adjustable inlet guide vane section. The inlet guide vanes can be adjusted to control the flow of air entering the low pressure compressor. 
         [0002]    A turbine engine could also include variable bleed valves/doors, which are typically located at the exit of the low pressure compressor. The bleed valves/doors could be controlled by a single or multiple actuators. Further, the bleed valves could be provided on both the low pressure compressor and the high pressure compressor. The amount of air which is allowed to bleed off through each of the individual bleed valves can be adjusted to ensure that the engine provides a desirable level of power and/or efficiency and compressor stability margins. 
         [0003]    In addition, a high pressure compressor could include variable stator vanes. The angle of the variable stator vanes can be adjusted to ensure that the turbine engine provides a desirable level of power and/or efficiency and compressor stability margins. 
         [0004]    A controller can be used to send signals to the variable stator vane assembly in the high pressure compressor, to the variable bleed valves/doors, and to the variable inlet guide vanes to instruct these variable elements to assume a particular setting. Thus, a controller can be used to adjust the settings of each of these elements to ensure that the turbine engine provides a desirable level of power and/or efficiency and compressor stability margins for any given operational condition and turbine engine quality. 
         [0005]    The desirable settings for these variable elements of the turbine engine are typically determined by experimentation when the turbine engine is new. The result of the experimentation is a set of “schedules,” which list the settings to be used for each of the variable elements based upon a sensed operational condition within the turbine engine. For instance, the setting for the inlet guide vanes could be determined using a schedule which lists settings for various different high pressure compressor exit temperatures. The variable bleed valve setting and the variable stator vane settings could be based upon the rotational speed of the turbine engine. To determine the desired settings for each of the variable elements of the turbine engine, one would first sense the relevant operational condition of the engine, and then consult the experimentally determined schedules to find the proper setting. This setting would then be applied to the variable element of the turbine engine through the controller. 
         [0006]    The schedules listing the settings for each of the variable elements of the turbine engine are typically determined when the engine is new. However, during the life of the turbine engine, wear occurs. As a result of that wear, the settings provided in the experimentally determined schedules may no longer provide a desirable level of power and/or efficiency for the turbine engine. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    In one aspect, the invention may be embodied in a method of determining at least one variable element setting for a turbine engine that includes the steps of obtaining an original variable element setting based on a sensed operational condition of the turbine engine from a setting schedule, determining at least one setting correction factor that is based on a sensed operational condition of the turbine engine, and calculating a corrected variable element setting based on the obtained original variable element setting and the at least one correction factor. 
         [0008]    In another aspect, the invention may be embodied in a method of determining a variable element setting for a turbine engine that includes the steps of obtaining an original variable element setting from a schedule of settings that are experimentally determined when the turbine engine is new, wherein the original settings in the schedule are indexed to at least one operational condition of the turbine engine, determining at least one variable element setting correction factor that is based on a sensed operational condition of the turbine engine, wherein the sensed operational condition provides an indication of the degree of wear which the turbine engine has experienced during its lifecycle, and calculating a corrected variable element setting based on the obtained original variable element setting and the determined at least one variable element correction factor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a diagram of the major elements of a turbine engine that includes variable elements; 
           [0010]      FIG. 2  is a diagram setting forth inlet guide vane settings based on the high pressure compressor exit pressure; 
           [0011]      FIG. 3  is a diagram setting forth variable bleed valve settings based on a corrected high pressure compressor rotational speed and the engine inlet temperature; 
           [0012]      FIG. 4  is a diagram setting forth variable stator vane settings based on the corrected high pressure compressor rotational speed; 
           [0013]      FIG. 5  illustrates how various observable operational conditions of a turbine engine change over the lifetime of the turbine engine; 
           [0014]      FIG. 6  illustrates the values of a variable used to calculate an offset, the value of the variable being determined based upon a turbine exit temperature; 
           [0015]      FIG. 7  illustrates the values of a variable used to calculate an offset, the value of the variable being determined based upon a compressor exit temperature; 
           [0016]      FIG. 8  illustrates the values of a variable used to calculate an offset, the value of the variable being determined based upon a compressor exit pressure; and 
           [0017]      FIG. 9  illustrates steps of a method of calculating a corrected or adjusted inlet guide vane setting for a turbine engine. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    The basic elements of a turbine engine with variable geometry are illustrated in  FIG. 1 . As shown therein, the turbine includes a low pressure compressor  100 , a high pressure compressor  200 , a high pressure turbine  300  and a low pressure turbine  400 . 
         [0019]    The turbine engine illustrated in  FIG. 1  includes an adjustable inlet guide vane section  110 . The inlet guide vanes  110  can be adjusted to control the flow of air entering the low pressure compressor  100 . 
         [0020]    The turbine engine also includes variable bleed valves/doors  120 , which are typically locates near the exit of the low pressure compressor  100 . The blood valves/doors  120  could be controlled by a single or multiple actuators. In the illustrated embodiment, three variable bleed valves/doors  120  are provided. However, only one or any number of bleed valves could be provided. Further, the bleed valves could be provided on both the low pressure compressor  100  and the high pressure compressor  200 . The amount of air which is allowed to bleed off through each of the individual bleed values can be adjusted to ensure that the engine provides a desired level of power and/or efficiency. 
         [0021]    In addition, the high pressure compressor  200  includes variable stator vanes  210 . The angle of the variable stator vanes can be adjusted to ensure that the turbine engine provides maximum power and/or efficiency. 
         [0022]    In the embodiment illustrated in  FIG. 1 , a controller  500  sends signals to the variable stator vane assembly  210  in the high pressure compressor  200 , to the variable bleed valves/doors  120 , and to the variable inlet guide vanes  110  to instruct these variable elements to assume a particular setting. Thus, the controller  500  can be used to adjust the settings of each of these elements to ensure that the turbine engine provides maximum power and/or efficiency for any given operational condition and turbine engine quality. 
         [0023]    The disclosed technology for controlling the variable geometry elements of a turbine engine applies to singe spool or multi-spool turbine engines. For purposes of describing the technology, a two spool turbine engine will be used as an example. It should be understood that the technology is equally applicable to single spool turbines engines. 
         [0024]    As noted above, the original settings for variable elements of a turbine engine are typically determined through experimentation on a new engine. The settings determine how to configure the variable elements, given the current engine operational conditions, to obtain a desired level of power and/or efficiency. However, because of the wear which occurs over the lifecycle of the turbine engine, the original settings for the variable elements may not provide the desired level of power and/or efficiency once the turbine engine has experienced appreciable wear. 
         [0025]    The methods and principles described below are intended to allow an operator to adjust the original variable element settings to account for the wear that has occurred. The basic idea is to sense one or more operational conditions of the turbine engine to obtain an indication of the degree of wear which has occurred. Based upon the sensed operational conditions, one then calculates a variable element offset which is applied to the original settings. The offset is used to correct the original variable element settings to create corrected or adjusted variable element settings. And these corrected or adjusted variable element settings are then used to configure the turbine engine for a desired level of power and/or efficiency. 
         [0026]      FIGS. 2 ,  3  and  4  provide three examples of variable element setting schedules which could be established through experimentation when a turbine engine is new. 
         [0027]      FIG. 2  illustrates the settings for the inlet guide vanes of a turbine engine. The settings are based upon the high pressure compressor exit pressure, and the engine inlet temperature. Note, there are different lines for the settings depending on the engine inlet temperature. To determine a setting, one would first determine the engine inlet temperature. One would then sense the high pressure compressor exit pressure, and that value would then be used to determine the inlet guide vane setting using the appropriate temperature line. If the actual sensed temperature is between two of the temperature lines, one could interpolate a value by looking at the area between the two closest temperature lines. As explained, this setting would provide a desired level of power and/or efficiency when the engine is new. 
         [0028]      FIG. 3  illustrates the settings for variable bleed valves of a turbine engine. To determine the desired variable bleed valve setting, one would first sense the engine inlet temperature. This temperature would correspond to one of the four lines illustrated in  FIG. 3 . One would also determine the corrected high pressure compressor rotational speed. Using the corrected high pressure compressor rotational speed, and the appropriate temperature line, one then determines the variable bleed valve setting to provide a desired power and/or efficiency for the turbine engine when the turbine engine is new. If the actual sensed temperature is between two of the temperature lines, one could interpolate a value by looking at the area between the two closest temperature lines. 
         [0029]      FIG. 4  is a diagram which indicates the variable stator vane settings based upon the corrected high pressure compressor rotational speed. 
         [0030]    The schedules setting forth the settings for the variable bleed valves and the variable stator vanes both rely, at least in part, on the corrected high pressure compressor rotational speed. The actual high pressure compressor rotational speed, which is also called the “core speed,” is corrected to account for the ambient temperature at which the turbine engine is operating, or the high pressure compressor inlet temperature. For instance, one formula for determining the corrected high pressure compressor speed is provided as follows: 
         [0000]    
       
         
           
             
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                   518.67 
                 
               
             
           
         
       
     
         [0031]    The high pressure compressor inlet temperature in the formula set forth above is to be entered in the formula in degrees Rankin. The corrected core speed given by the formula is a normalized speed which accounts for variations in the day-to-day ambient temperature of the environment surrounding the turbine engine. 
         [0032]      FIG. 5  illustrates three key operational conditions of a turbine engine that change over the lifecycle of the turbine engine, as wear accumulates. As shown in  FIG. 5 , one would expect the turbine exit temperature to gradually increase over the lifecycle of the engine. Likewise, one would expect the high pressure compressor exit temperature to gradually decline over the lifecycle of the engine. One would also expect the high pressure compressor exit pressure to gradually decline over the lifecycle of the turbine engine. By sensing the actual values for one or more of these parameters, one can determine the degree of wear which has accumulated. 
         [0033]    Of course, the three parameters illustrated in  FIG. 5  are not the only parameters that can provide an indication of wear. Other values such as the turbine exit pressure, and the exit temperature and exit pressure of the low pressure compressor, as well as other parameters could also be used to determine or approximate the degree of wear which has occurred. The important point is that one senses the actual operational conditions of the turbine engine to determine a state of deterioration of the turbine engine. 
         [0034]    Because different parameters can provide different indications of the wear that has occurred, in some instances it may be advantageous to use multiple observable parameters together to calculate an offset that will be applied to the original variable element settings. For instance, one could sense the actual turbine exit temperature, the high pressure compressor exit temperature, and the high pressure compressor exit pressure, and then use all three of these sensed values together to calculate the offset. 
         [0035]    One method of calculating an offset to be applied to the original settings for the inlet guide vanes of a turbine engine will now be described. However, it should be understood that the following method is only one possible way of determining an offset to be applied to the original variable inlet guide vane settings. A variety of other methods can also be used to calculate such an offset. 
         [0036]    In this example method, one senses the turbine exit temperature, and the temperature is used to determine the value of a first variable. One also determines the high pressure compressor exit temperature, and this temperature is used to determine the value of a second variable. One also senses the high pressure compressor exit pressure, and this pressure is used to determine the value of a third variable. The first, second and third variable values are then combined in some fashion to calculate an offset. And this offset is then applied to the original variable inlet guide vane settings. 
         [0037]      FIG. 6  is a diagram illustrating how the turbine exit temperature can be used to determine the value of a first variable X. One would sense the actual exit temperature of the turbine, and then consult the schedule illustrated in  FIG. 6  to determine the value of the variable X. 
         [0038]      FIG. 7  illustrates a schedule used to determine the value of a second variable Y, which is based upon the actual high pressure compressor exit temperature. One would sense the actual high pressure compressor exit temperature, and then consult the schedule illustrated in  FIG. 6B  to determine the value of variable Y. 
         [0039]      FIG. 8  is a schedule which is used to determine the value of a third variable Z, which is based upon the high pressure compressor exit pressure. One would measure the actual high pressure compressor exit pressure, and then consult the schedule illustrated in  FIG. 8  to determine the value of variable Z. 
         [0040]    One could then combine the three variables X, Y and Z to determine an offset value. For instance, one could simply add the three variables X+Y+Z to determine the value of an offset which is then applied to the original settings for the inlet guide vanes. Of course, the values of X, Y and Z could be mathematically combined in some other fashion to determine the offset. For instance, multipliers could be applied to one or more of the variable values before they are added. Or, alternatively, two or more of the variable values could be multiplied together. Any sort of mathematical combination that is appropriate to obtain a useful and accurate offset could be used. 
         [0041]    In some instances, the amount of wear experienced by the turbine engine could be approximated by checking the actual value of an observable condition of the engine, such as the turbine exhaust temperature or pressure. In other instances, the amount of wear could be approximated by determining the amount or percentage that the observable value has changed since the turbine was first put in service. So, for instance, one could note the turbine exhaust temperature when the engine is first put in service, then check the turbine exhaust temperature later, after wear has occurred, and calculate a percentage change in the value. And that percentage of change could be used to obtain the value of a variable that is ultimately used to calculate an offset. 
         [0042]    Another factor that may play into determining the correct value of a variable used to calculate an offset is the ambient temperature and pressure. For instance, one might detect an observable operating condition of a turbine engine, and then use a chart or schedule to determine the value of a variable. And that variable value might also be corrected for the current temperature and/or atmospheric pressure. The corrected variable value would then be used to calculate the offset. 
         [0043]    The values provided in the schedules illustrated in  FIGS. 6-8  could also be obtained through experimentation which is conducted throughout the lifecycle of a typical turbine engine. In this instance, the value of each of the individual variables would have a basis in actual real world testing. 
         [0044]    In addition, a fourth variable value could be used to provide protection against a stall. For instance, a stall protection variable A could be determined based upon the values of one or more of the variables X, Y and Z. Alternatively, the value of the stall protection variable A could be determined based on an observable operational condition of the turbine. In other instances, the value of the stall protection variable A could be based on the number of hours that the turbine engine has been operating since its last major servicing. The fourth variable value A could then be mathematically combined with the first three variable values X, Y and Z to determine the actual offset to be used to correct the original inlet guide vane settings. 
         [0045]    In addition, in each of the alternative methods described above, all three of the variable values X, Y and Z are combined in some fashion to determine the final offset value. In alternate embodiments, only one or only two of the three variable values could be combined to determine the actual offset. In addition, more than three variable values could be used to determine the offset. For instance, another variable value could be based upon another observable operational condition of the turbine engine, and that fourth variable value could be mathematically combined with one or more of the first three variable values described above to determine the actual offset value. The important point is that the various different variable values are each based upon an observable condition of the turbine engine which provides some indication of the deterioration of the turbine engine. Those variable values are then combined in some mathematical fashion to arrive at the offset value. 
         [0046]      FIG. 9  illustrates steps of a method of calculating a corrected inlet guide vane setting. As illustrated in  FIG. 9 , the method would start in step S 700 . The method would then proceed to step S 702  where the original inlet guide vane position would be determined from the original schedule, based upon the high pressure compressor exit pressure. The method would then proceed to step S 704  where the value of variable X would be determined based upon the turbine exit temperature. The method would then proceed to step S 706  where the value of variable Y would be obtained based upon the high pressure compressor exit temperature. The method would then proceed to step S 708  where the variable value Z would be determined based upon the high pressure compressor exit pressure. Finally, in step S 710 , a corrected inlet guide vane setting would be determined based upon the values obtained in steps S 702 , S 704 , S 706  and S 708 . For instance, the values of the variable X, Y and Z would be mathematically combined in some fashion to determine an offset value. This offset value would then be applied to the original inlet guide vane setting obtained in step S 702  to calculate a corrected or adjusted inlet guide vane setting. 
         [0047]    In each of the methods described above, the actual sensed operating conditions of a turbine engine are used to correct the original inlet guide vane setting to account for deterioration of the turbine engine. The same types of methods could be applied to calculate a corrected variable bleed valve setting or a corrected variable stator vane position. Here again, one would start with the original setting from schedules illustrated in  FIGS. 3 and 4 , one would determine an offset to be applied to that original setting based on the state of deterioration of the turbine engine (as reflected in one or more sensed operating conditions), and one would then determine a corrected setting based upon the original setting and the offset. 
         [0048]    The actual variable values used to determine an offset could change from one type of variable element of the turbine engine to another. For instance, an offset for the variable bleed valve setting could be based upon a first set of observable operational conditions, whereas an offset for the variable stator vane setting could be based upon a second set of observable operational conditions. Moreover, during the lifecycle of a turbine engine, different variable values might be used to create an offset for one of the original settings. For instance, during the first half of the normal lifecycle of a turbine engine, a first set of variable values could be used to determine an offset to be applied to the original inlet guide vane setting. However, during the second half of the normal lifecycle of the turbine engine, a second different set of variables could be used to calculate the offset for the original inlet guide vane setting. Likewise, the mathematical operations used to combine two or more variable values could also change over the lifecycle of the turbine engine. 
         [0049]    In the examples provided above, the inlet guide vane settings, variable bleed valve settings and variable stator vane settings are adjusted. However, to the extent the turbine engine includes other elements which are also capable of variable settings, those variable elements could also be adjusted based upon the state of deterioration of the turbine engine as indicated by observable operational conditions of the turbine engine. 
         [0050]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.