Abstract:
Change in swirl of gas turbine exhaust gases at off-design conditions is a key driver of exhaust diffuser inefficiency that adversely impact the gas turbine performance. Conventional ways to control swirl such as blowing, suction, and vortex generation are undesirable since they require parasitic power, are complex to design, and dilute the exhaust gas energy. To address such short comings, shape memory devices are incorporated into struts of an exhaust diffuser of a gas turbine. The shape memory devices change shape in accordance with heat, which can be applied through memory device heaters. By controlling the memory device heaters, the heat applied to the shape memory devices can be controlled. The shapes of the struts can be altered through altering the shapes of the memory device in consideration of load conditions to increase the efficiency.

Description:
[0001]    One or more aspects of the present invention relate to method, apparatus and system for controlling swirl of exhaust in a gas turbine. In particular, one or more aspects relate to improving gas turbine part load performance. 
       BACKGROUND OF THE INVENTION 
       [0002]    A typical gas turbine system includes a compressor, one or more combustors, and a turbine at the rear. The compressor compresses ambient air. The compressed air exits the compressor and flows to the combustors where it mixes with fuel and ignites to generate combustion gases having high temperature and pressure. The high energy gas exits the combustors and flow to the gas turbine where they expand to produce work. An exhaust diffuser downstream of the turbine converts the kinetic energy of the exhaust gas flow exiting the turbine into potential energy in the form of increased static pressure. The exhaust diffuser typically includes struts that support the bearing. 
         [0003]    Change in swirl of gas turbine exhaust gases at off-design/part load conditions is a key driver of exhaust diffuser inefficiency that adversely impacts gas turbine performance. Conventional ways to control the swirl include blowing, suction, vortex generation, and so on. Unfortunately, these methods are complex to design, operate, require higher parasitic power and dilute the exhaust energy which can negate any efficiency gains. 
         [0004]    It would be desirable to control the swirl, tunable at part loads, with reduced auxiliary power and maintaining the exhaust energy grade. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    An aspect of the present invention relates to a strut of an exhaust diffuser of a gas turbine. The strut can comprise a foil part, one or more shape memory devices attached to the foil part, and one or more memory device heaters. Each shape memory device can be structured to change its shape in accordance with a temperature of that shape memory device. Each memory device heater can be structured to apply heat to at least one shape memory device in accordance with an externally provided shape actuating signal. 
         [0006]    Another aspect of the present invention relates to an exhaust diffuser of a gas turbine. The exhaust diffuser can comprise a shroud, a wall surrounding the shroud, and a plurality of struts extending from the shroud to the wall so as to define a plurality of exhaust flow passages. Each flow passage can be bounded by the shroud, the wall and adjacent struts. At least one strut can comprise a foil part, one or more shape memory devices attached to the foil part, and one or more memory device heaters. Each shape memory device can be structured to change its shape in accordance with a temperature of that shape memory device. Each memory device heater can be structured to apply heat to at least one shape memory device in accordance with an externally provided shape actuating signal. 
         [0007]    Another aspect of the present invention relates to a gas turbine system. The gas turbine system can comprise a compressor structured to compress oxidant and provide compressed oxidant, a combustor structured to combust a mixture of fuel and the compressed oxidant from the compressor and provide high energy gas, a gas turbine structured convert energy of the high energy gas from the combustor into useful work, and a controller structured to control an operation of the gas turbine system. The gas turbine can include an exhaust diffuser. The exhaust diffuser itself can comprise a shroud, a wall surrounding the shroud, and a plurality of struts extending from the shroud to the wall so as to define a plurality of exhaust flow passages. Each flow passage can be bounded by the shroud, the wall and adjacent struts. At least one strut can comprise a foil part, one or more shape memory devices attached to the foil part, and one or more memory device heaters. Each shape memory device can be structured to change its shape in accordance with a temperature of that shape memory device. Each memory device heater can be structured to apply heat to at least one shape memory device in accordance with a shape actuating signal provided from the controller. The controller can be structured to receive one or more sensor signals from one or more of a compressor sensor, a combustor sensor, a turbine sensor, an ambient sensor and a load sensor. Based on these sensor signals, the controller can provide the shape actuating signals to the to the memory device heaters. 
         [0008]    Another aspect of the present invention relates to a method for controlling exhaust gases exiting through an exhaust diffuser of a gas turbine of a gas turbine system such as the gas turbine system described above. The method can comprise a step of receiving, at the controller of the gas turbine system, one or more sensor signals from one or more of a compressor sensor, a combustor sensor, a turbine sensor, an ambient sensor and a load sensor. The method can also comprises providing from the controller one or more shape actuating signals based on the sensor signals. 
         [0009]    The invention will now be described in greater detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    These and other features of the present invention will be better understood through the following detailed description of example embodiments in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1  illustrates a front view of an example exhaust diffuser embodiment of a gas turbine according to the present invention; 
           [0012]      FIGS. 2 and 3  illustrate top and side views of an example strut embodiment of the present invention; 
           [0013]      FIGS. 4 and 5  illustrate example changes in the exhaust flow passage as due to changes in shape memory devices; 
           [0014]      FIG. 6  illustrates an architecture of an example gas turbine system embodiment according to the present invention; and 
           [0015]      FIG. 7  illustrates a flow chart of an example method to control exhaust gases according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Novel method, system, and apparatus for controlling swirl of exhaust gas in a gas turbine are described. In one aspect, the described method, system, and apparatus utilize memory materials to control the flow area of the exhaust gas, the swirl angle of the exhaust gas, or both based on the load on the gas turbine. 
         [0017]      FIG. 1  illustrates a front view of an example exhaust diffuser embodiment of a gas turbine according to the present invention. As seen the example exhaust diffuser  100  can include a shroud  110  and a wall  120  that surrounds the shroud  110 . The exhaust diffuser  100  may be double walled. In this instance, the exhaust diffuser  100  may also comprise an outer wall  130  that surrounds the wall  120 , which may also be referred to as the inner wall  120 . The exhaust diffuser  100  can include a plurality of struts  140 . Each strut  140  can extend from the shroud  110  to the wall  120 . A plurality of exhaust flow passages  145  can be defined. Each flow passage  145  can be bounded by the shroud  110 , the wall  120  and adjacent struts  140 . 
         [0018]      FIG. 2  illustrates a top view and  FIG. 3  illustrates a side view of an example strut  140 . As seen in these figures, the strut  140  can include a support part  210  and a foil part  220  that surrounds the support part  210 . A strut cavity  235  can be formed in between the support part  210  and the foil part  220 . In one aspect, the strut cavity  235  can be used to carry cooling fluid so as to keep the temperature of the strut  140  within a predetermined range. 
         [0019]    The strut  140  can also include one or more shape memory devices  230  attached to the foil part  220 . Preferably all, but at least one shape memory devices  230  can be structured to change its shape in accordance with a temperature of that shape memory device  230 . The shape memory device  230  may be a memory metal such as a nickel-titanium alloy. Memory metals are also referred to as shape memory alloy (SMA), shape memory metal (SMM), smart metal, memory alloy, smart alloy, and so on. There are known uses for smart materials. Semmere et al. (U.S. Pat. No. 7,462,976 B2) and Care et al. (U.S. Pat. No. 6,485,255 B1), both incorporated by reference herein in their entirety, disclose examples of such known uses. When heat is applied to the memory metal, its shape can change. 
         [0020]    Shape characteristics—e.g., first shape at first temperature, second shape at second temperature, and so on—of the memory metal, or more generally, of the shape memory device  230  may be designed into the device  230 . When there are multiple shape memory devices  230 , they all need not be exactly alike. That is, at least two shape memory devices  230  can differ in their shape characteristics. 
         [0021]    As seen in  FIG. 2 , the strut  140  can include one or more memory device heaters  240 . Each memory device heater  240  can be provided with a shape actuating signals from an external source, such as from a controller which is described in further detail below. Based on the provided shape actuating signal, each memory device heater  240  can apply heat to at least one shape memory device  230  so as to affect the shape of that shape memory device  230 . The amount of heat applied can vary in accordance with the shape actuating signal provided to that memory device heater  240 . One example of the memory device heater  240  is an electrically powered heater, such as a resistor or a coil. 
         [0022]    In one aspect, a memory device heater  240  can be attached to a shape memory device  230 . This provides a direct way to apply heat to the attached shape memory device  230 . In another aspect, a memory device heater  240  can be attached to the foil part  220  and in close proximity to a shape memory device  230  such that the heat from the memory device heater  240  is applied to that shape memory device  230 . That is, the memory device heater  240  and the shape memory device  230  can be considered to be in thermal connection with each other. In yet another aspect, the memory device heater  240  may be a microwave device structured to apply microwave energy to a shape memory device  230 . 
         [0023]    When there are multiple memory device heaters  240 , they all need not be exactly alike. For example, one memory device heater  240  can be a resistor and another may be a coil. As another example, one may be capable of applying relatively high heat as opposed to another. Also, the strut  140  may be structured such that a common shape actuating signal is provided to all memory device heaters  240  of the strut  140 . Alternatively, the strut  140  may be structured such that at least one memory device heater  240  receives its corresponding shape actuating signal independent of the shape actuating signal received by another memory device heater  240 . 
         [0024]    There can be any number of shape memory devices  230  and any number of memory device heaters  240 , and the two need not necessarily be equal. In one aspect, one memory device heater  240  can be structured to apply heat to multiple shape memory devices  230 . In another aspect, one shape memory device  230  may be heated by multiple memory device heaters  240 . 
         [0025]    When the numbers of the shape memory devices  230  and of the memory device heaters  240  are equal, there can be one-to-one correspondence. That is, the strut  140  can be structured such that each memory device heater  240  applies heat to only one shape memory device  230 . Alternatively, even when the numbers are equal, a group of memory device heaters  240 , the group comprising more than one memory device heater  240 , may commonly apply heat to a group of shape memory devices  230 , again the group comprising more than one shape memory devices  230 . 
         [0026]    Use of memory device heaters  240  is one way to apply heat to the shape memory devices  230 . In another way, the cooling fluid flowing within the strut cavity  235  can also be used. That is, one or more shape memory devices  230  can be thermally connected with the cooling fluid via the foil part  220 . By controlling the temperature of the cooling fluid, heat applied to the shape memory devices  230  can be controlled. The cooling fluid and the memory device heaters  240  can be used exclusive of each other or can be used in combination. 
         [0027]      FIGS. 4 and 5  illustrate example changes in the exhaust flow passage  145  as due to changes in shape memory devices  230 . Under normal operating conditions, shape actuating signals may be provided to the memory device heaters  240  (not shown in these figures) so as to control the shapes of the shape memory devices  230  to maximize the area of the exhaust flow passage  145  as illustrated in  FIG. 4 . Often, the foil part  220  is aerodynamically contoured. Thus, the shape memory devices  230  may be structured substantially conform to the contour of the outer strut  220  when maximum exhaust flow area is desired. Of course, this is not a strict requirement. 
         [0028]    Under part load conditions, the rate of the exhaust flow is reduced. Thus, it is also desirable to correspondingly reduce the area of the exhaust flow passage  145  as illustrated in  FIG. 5 . This can be accomplished by providing the appropriate shape actuating signal or signals to the one or more memory device heaters  240 . 
         [0029]    Note that the shapes of the shape memory devices  230  need not be the same under all operating conditions. As indicated above, one shape memory device  230  can differ in its shape characteristics from another shape memory device  230 . But even if two shape memory devices  230  have identical shape characteristics, the applied heat can be different for the two devices. For example, the strut  140  can be structured such that the shape actuating signal received by at least one memory device heater  240  is independent of the actuating signal received by at least one other memory device heater  240 . 
         [0030]    The shape memory devices  230  can be controlled so as to affect not only the area of the exhaust flow passage  145 , but also affect the swirl angle of the exhaust gas flow. More generally, by providing appropriate shape actuating signal or signals to the one or more memory device heaters  240 , one or both of the area of the exhaust flow passage  145  and the swirl angle of the exhaust gas flowing through the exhaust flow passage  145  can be controlled. 
         [0031]    Recall that in addition to the adjacent struts  140 , each exhaust flow passage  145  can also be bounded by the shroud  110  and the wall  120 . Thus, while not particularly illustrated in the figures, one or more shape memory devices  230  can be attached to the shroud  110  or to the wall  120  along with one or more memory device heaters  240  structured to apply heat to the shroud  110  or the wall  120  attached shaped memory devices  230  in accordance with the received shape actuating signals. Through providing appropriate shape actuating signals to these memory device heaters  240 , the area of the exhaust flow passage  145  and/or the swirl angle of the exhaust gas flowing through the exhaust flow passage  145  can also be controlled. 
         [0032]      FIG. 6  illustrates an architecture of an example gas turbine system  600 . As seen, the system  600  may include a compressor  610 , a combustor  620  fluidly connected to the compressor  610 , and a gas turbine  630  fluidly connected to the combustor  620 . The compressor  610  can be structured to compress oxidant, e.g., air, and provide the compressed oxidant to the combustor  620 . The combustor  620  can be structured to combust a mixture of fuel and the compressed oxidant and provide high energy gas to the gas turbine  630 , which can in turn be structured convert energy of the high energy gas from into useful work to drive a load  660 . In  FIG. 6 , the load  660  is a generator, and the useful work is in the form of mechanical energy used to drive the generator to generate electricity. While not shown, the useful work can come in a form of a thrust which can be used to propel an airplane. 
         [0033]    The system  600  can include any one or more of a compressor sensor  615 , a combustor sensor  625 , a turbine sensor  635  and a load sensor  665 , each structured to monitor its respective system component. For example, the compressor sensor may detect or otherwise determine any one or more of an intake oxidant temperature, oxygen content of the compressed oxidant, pressure of the compressed oxidant, compressor discharge temperature, etc. The combustor sensor  625  may detect or otherwise determine any one or more of a combustion temperature and acoustical dynamics. The turbine sensor  635  may detect or otherwise determine any one or more of an exhaust temperature and pressure, flow rate of the energized gas through various stages (e.g., high pressure, intermediate pressure, low pressure), etc. The load sensor  665  may detect or otherwise determine the load on the gas turbine  630 . The system  600  can also include one or more ambient sensors  640  that are not necessarily specific to any of the system component. For example, an ambient sensor  640  may detect or determine an ambient temperature. 
         [0034]    The system  600  can also include a controller  650  structured to control an operation of the gas turbine system  600 . As seen, the controller  650  can receive as inputs the sensor signals from any one or more of the sensors  615 ,  625 ,  635 ,  640 ,  665 . The controller  650  can also receive operation inputs such as instructions for start up, partial load operation, full load operation, shut down, and so on. Based on the inputs, the controller  650  can output control signals to any one or more of the system components  610 ,  620 ,  630 . 
         [0035]    In  FIG. 6 , the sensor signals from the sensors  615 ,  625 ,  635 ,  640 ,  665  to the controller  650  and the control signals from the controller  650  to the system components  610 ,  620 ,  630 . To minimize clutter, the connections of the sensor and control signals between the controller  650  and the system units  610 ,  620 ,  630  are not explicitly shown. 
         [0036]    Among the control signals, the controller  650  can provide one or more shape actuating signals to the external diffuser  100  located towards the exhaust end of the gas turbine  630 . In particular, the controller  650  can provide the shape actuating signals to the one or more memory device heaters  240 . These shape actuating signals can be based on the load signal indicative of the load on the gas turbine  630 . The load signal can be provided by the load sensor  660 . The shape actuating signals can also be based on an ambient temperature signal from one of the ambient sensors  640  that detects or determines an ambient temperature. Just for explanatory purposes and not as a limitation, a range of ambient temperature may range between −20° F. and 120° F. Generally, a drop in ambient temperature results in a reduction of the exhaust temperature. 
         [0037]    Other sensor signals that may be taken into account by the controller  650  in providing the shape actuating signals include temperature of the compressor discharge (e.g., from the compressor sensor  615 ) and the gas turbine exhaust temperature (e.g., from the turbine sensor  635 ). Of course, these are not exhaustive. It suffices to indicate that many of the sensor inputs that are taken into account to actuate swirl control may also serve as inputs taken into account to provide shape actuating signals. 
         [0038]    Recall from above discussion that between any two memory device heaters  240 , they need not receive the same shape actuating signal even under identical circumstances. For example, assume that at least one strut  140  comprises multiple memory device heaters  240  including first and second memory device heaters  240  respectively structured to apply heat to first and second shape memory devices  230 . The controller  650  can provide a first shape actuating signal to the first shape memory device  230  and independently provide a second shape actuating signal to the second shape memory device  230 . 
         [0039]    As another example, assume that the exhaust diffuser  100  includes multiple struts  140  including first and second struts  140 . The controller  650  can provide a first shape actuating signal to one or more memory device heaters  240  of the first strut  140  and independently provide a second shape actuating signal to one or more memory device heaters  240  of the second strut  140 . The first and second actuating signals in regards the first and second struts  140  discussed in this paragraph are not necessarily the same as the first and second actuating signals in regards the first and second memory device heaters  240  discussed in the previous paragraph. 
         [0040]    Flexibility to provide independent shape actuating signals to a particular strut  140  can allow the controller  650  to finely control the shapes of the shape memory units  230  of that particular strut  140 . Flexibility to provide independent shape actuating signals among the struts  140  can allow the controller  650  to finely control the shapes of the shape memory units  230  across the plurality of struts  140 . Of course, both flexibility within and among the struts are possible. 
         [0041]    In another aspect, the control signals can include signals to control one or both of a temperature and a flow rate of the cooling fluid flowing within the strut cavity  235  of one or more struts  140 . The shape change actuating signals and the cooling fluid control signals can be exclusive of each other or in conjunction with each other. 
         [0042]      FIG. 7  illustrates a flow chart of an example method to control exhaust gases exiting through an exhaust diffuser of a gas turbine of a gas turbine system. For purposes of explanation, the gas turbine system  600  of  FIG. 6  is assumed. The method  700  in  FIG. 7  can be performed by the controller  650 . 
         [0043]    In step  710 , the controller  650  can receive sensor signals from any one or more of the sensors  615 ,  625 ,  635 ,  640  and  665 . A load signal indicative of the load on the gas turbine  630 , e.g., from the load sensor  665 , may be included among the received sensor signals. In step  720 , the controller  650  may also receive one or more operation inputs. Based at least on the received load signal, the controller  650  in step  730  may provide one or more shape actuating signals to one or more memory device heaters  240 . Alternative to or in conjunction with step  730 , the controller  650  can provide one or more cooling fluid control signals to the gas turbine  630  based on the sensor and/or operation input signals. 
         [0044]    In step  710 , the received sensor signals may also include ambient temperature signal from the ambient sensor  640 . Then in step  730 , the ambient temperature signal may also be taken into account when the controller  650  provides the shape actuating signals. In step  730 , shaping signals can be independently provided to multiple memory device heaters  240  within any particular strut, independently provided to multiple struts  140 , or both. 
         [0045]    Several advantages can be realized by one or more aspects of the disclosed subject matter. A non-exhaustive list of advantages include:
       Improved efficiency;   Improved part-load operation; and   Reduced auxiliary power to control exhaust swirl.       
 
         [0049]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.