Abstract:
A system for diagnosing a rotating airfoil has an image capture device and a light emitting device. A control is programmed to actuate at least one of the image capture device and the light at a particular time to capture an image of a rotating airfoil being monitored, and then compare the captured image to an expected image. A method of diagnosing damage to a rotating airfoil is also disclosed.

Description:
BACKGROUND 
       [0001]    This application relates to a diagnostics system and a method incorporated into a gas turbine engine. 
         [0002]    Gas turbine engines are known and, typically, include a fan delivering air both as bypass air for propulsion and into a compressor. The compressor section includes rotors which rotate to compress air and deliver it into a combustor. The air is mixed with fuel and ignited in the combustor and products of the combustion pass downstream over turbine rotors, driving them to rotate. 
         [0003]    There are any number of challenges to gas turbine engines when utilized in an aircraft. As an example, birds may impact and damage the fan blades. In addition, solid elements, such as rocks, may be ingested by the fan into the engine and can damage the compressor rotors. 
         [0004]    Historically, the fan has rotated at one speed with a compressor rotor. This limited the size of the fan for several reasons. More recently, it has been proposed to incorporate a gear reduction between the fan rotor and the compressor rotor. 
         [0005]    With this change, the diameter of the fan rotor has increased dramatically and the speed of the fan rotor has decreased. This raises challenges with regard to the damage events mentioned above. 
         [0006]    As the fan diameter has increased, the potential for bird strikes also increases. Further, as the fan speed decreases, the likelihood of rocks or other large items passing beyond the fan rotor and impacting the compressor rotor also increases. 
         [0007]    Should any of the damage events mentioned above occur, it would be desirable to quickly identify the damage, such that maintenance or other proactive steps can be initiated. Various types of diagnostic systems have been proposed, but have generally been related to the used of vibration detection. 
         [0008]    Image recognition software is known and has been utilized in any number of applications. As an example, image recognition software has been proposed for use in identifying structural cracks after earthquakes. 
       SUMMARY 
       [0009]    In a featured embodiment, a system for diagnosing a rotating airfoil has an image capture device and a light emitting device. A control is programmed to actuate at least one of the image capture device and the light at a particular time to capture an image of a rotating airfoil being monitored, and then compare the captured image to an expected image. 
         [0010]    In another embodiment according to the previous embodiment, the system is provided with a strobe light as the light. The strobe light is actuated in a timed manner to capture the image of the airfoil. 
         [0011]    In another embodiment according to any of the previous embodiments, the image capture device is a camera provided with a digital shutter timed to capture the image of the airfoil. 
         [0012]    In another embodiment according to any of the previous embodiments, the control also compares an expected time of arrival of a leading edge of the rotating airfoil to the actual time of arrival. 
         [0013]    In another embodiment according to any of the previous embodiments, the control identifies cracks on the rotating airfoil utilizing the captured image. 
         [0014]    In another embodiment according to any of the previous embodiments, the size of an expected crack is compared to prior captured image over time to identify a growth of a crack. 
         [0015]    In another embodiment according to any of the previous embodiments, the image capture device and the light are mounted on an aircraft and capture the images during flight operation. 
         [0016]    In another embodiment according to any of the previous embodiments, the rotating airfoil is part of a gas turbine engine. 
         [0017]    In another embodiment according to any of the previous embodiments, the system is utilized with at least one of a rotating fan blade, a first stage of a low pressure compressor and a first stage of a high pressure compressor. 
         [0018]    In another embodiment according to any of the previous embodiments, the system is associated with each of the fan blades and the low and high pressure compressor first stage rotors. 
         [0019]    In another embodiment according to any of the previous embodiments, a gear reduction is placed between the fan rotor and the low pressure compressor rotor. 
         [0020]    In another embodiment according to any of the previous embodiments, the captured image is of a leading edge of the rotating airfoil. 
         [0021]    In another embodiment according to any of the previous embodiments, an air curtain is passed along the image capture device to clean the image capture device. 
         [0022]    In another embodiment according to any of the previous embodiments, protective glass is positioned between the image capture device and the rotating blade. 
         [0023]    In another embodiment according to any of the previous embodiments, the rotating airfoil is a propeller in a turboprop engine. 
         [0024]    In another embodiment according to any of the previous embodiments, the rotating airfoil is a propeller on a helicopter. 
         [0025]    In another embodiment according to any of the previous embodiments, the rotating airfoil is part of a lift fan. 
         [0026]    In another featured embodiment, a method of diagnosing damage to a rotating airfoil includes the steps of illuminating a rotating blade at a controlled time and capturing a digital image of the illuminated leading edge, and comparing the captured image of the rotating blade to an expected image, and utilizing image recognition software to identify defects in the rotating blade. 
         [0027]    In another embodiment according to the previous embodiment, the system is provided with a strobe light as the light. The strobe light is actuated in a timed manner to capture the leading edges. 
         [0028]    In another embodiment according to any of the previous embodiments, the image capture device is a camera provided with a digital shutter timed to capture the rotating blade at an expected time. 
         [0029]    In another embodiment according to any of the previous embodiments, the image capture device and the light are mounted within an aircraft and capture images during flight operation. 
         [0030]    In another embodiment according to any of the previous embodiments, the rotating airfoil is part of a gas turbine engine. 
         [0031]    In another embodiment according to any of the previous embodiments, the rotating blade is at least one of a rotating fan blade, a first stage of a low pressure compressor and a first stage of a high pressure compressor. 
         [0032]    In another embodiment according to any of the previous embodiments, the rotating blade includes each of the rotating fan blade, the first stage of a low pressure compressor, and the first stage of a high pressure compressor. 
         [0033]    In another embodiment according to any of the previous embodiments, the captured image of the rotating blade is of a leading edge of the rotating blade. 
         [0034]    In another embodiment according to any of the previous embodiments, the rotating airfoil is a propeller in a turboprop engine. 
         [0035]    In another embodiment according to any of the previous embodiments, the rotating airfoil is a propeller on a helicopter. 
         [0036]    In another embodiment according to any of the previous embodiments, the rotating airfoil is part of a lift fan. 
         [0037]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  schematically shows a gas turbine engine. 
           [0039]      FIG. 2  schematically shows details of a portion of a gas turbine engine. 
           [0040]      FIG. 3A  shows damage to a fan blade. 
           [0041]      FIG. 3B  shows another view of the damaged blades. 
           [0042]      FIG. 4A  shows a diagnostic system for identifying damage. 
           [0043]      FIG. 4B  shows optional features. 
           [0044]      FIG. 5  shows another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]      FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
         [0046]    The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
         [0047]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
         [0048]    The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of gear system  48 . 
         [0049]    The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
         [0050]    A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram° R)/(518.7° R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
         [0051]      FIG. 2  shows an example engine  100  which may be generally constructed as engine  10 . An outer nacelle  101  surrounds a large fan blade  102 . Downstream, a low pressure compressor first stage  104  and a high pressure compressor first stage  106  are spaced further inwardly. 
         [0052]    A camera system  108  may communicate with a computer control  110  for analyzing the health of the fan  102 , as described below. 
         [0053]    An optic fiber  112  may be positioned to transmit images of the health of the compressor first stage  104  to a camera system  114  and communicates with a computer control  115 . Similarly, an optic fiber  116  may monitor the health of the first stage high pressure rotor  106 . The optical fiber  116  is shown communicating with a camera system  118  for capturing images and communicating with the computer control  119 . In this embodiment, the optical fibers  112  and  116  allow the camera systems  114 / 118  and controls  115 / 119  to be positioned within a core housing  103  and, thus, better protected. In practice, the controls  110 / 115 / 119  may be combined as a single control. The image capture and analysis described below occurs during flight and other operation of the engine. 
         [0054]      FIG. 3A  shows one type of damage that can occur to a fan  102 . As shown, there are a plurality of blades spaced circumferentially. A first blade  125  is shown to be undamaged and to have a predictable and smooth curve on a leading edge  124 . The leading edge  126  of adjacent blades  131  are shown to have a damaged portion  128 . This may be caused by a bird strike or a strike by some other item. As shown, the damaged area  128  includes a bend such that the leading edge  126  is no longer smooth.  FIG. 3B  more dramatically shows the bend schematically. 
         [0055]      FIG. 4A  shows a system  191  which will monitor the blade leading edges  124  and  126 . It should be understood that a similar system would be utilized with the first stage rotors  104  and  106 . As shown, the camera  108  system actually includes a camera  108 B for capturing an image and a light  108 A. The light  108 A may be a strobe timed to flash each revolution or even uniformly synced to each blade&#39;s passing to capture the image of the leading edge  126 / 125  of each of the plurality of rotating fan blades  124 / 131 . Alternatively, a digital shutter on the camera  108 B may be so timed. The control  110  is programmed to provide images of the blade periodically, such that the leading edge of each of the blades is monitored during operation of the engine. 
         [0056]    A visual display  190 , such as a computer display, is shown including an image  192  of an expected leading edge  126  and an image  194  of the actual leading edge having the damaged area  196 . The damaged area  196  shows clearly as a “glint” to image recognition software programmed into the computer control  110 . Computer control  110  can be programmed to identify damage, such as the bird strike damage  128 . Alternatively, digital data about the glint , such as angle of small segments of the glint along the leading edge can be programmed and changes noted for either a safe shutdown of the engine or a maintenance message can be sent requesting on-wing blending of the defect if it is digitally determined to be small. 
         [0057]    Further, the software may be programmed to identify the actual time of arrival of any of the leading edges compared to an expected time of arrival. This would also be indicative of large-scale potential damage such as a crack in the root attachment or even the disk lugs. Further, the software may be programmed to identify cracks in most areas of the airfoil. Over time, such software can identify an increase in the size of the cracks and an increase in the departure of the arrival time from the expected arrival time. All of this information can be utilized to schedule maintenance or even shut down of the engine depending on the severity of the damage. 
         [0058]    The glint will typically have a role and there may be other readily profiled areas with a baseline geometry stored in the system and possibly some adjustments to the baseline geometry to adjust for engine acceleration, deceleration, altitude and power. Staying with the glint for example, it has a certain time of arrival relative to a reference feature that is freezing the blade in one position. A maintenance flag is set if the line of the glint, along one small section of the blade deviates from the line of the glint elsewhere. In another example, the system may call for an in-flight shutdown if large sections of the glint were distorted relative to other parts of the blade or if the entire glint arrived late, indicating that the entire blade was coming loose due to some major attachment area distress. 
         [0059]      FIG. 4B  shows an alternative camera system  208 . The cameras  208 B have a curved forward face  210 . Protective glass  212  may be positioned to protect the camera  208 B. Further, as a second alternative, an air curtain  214  may be created to clean the glass  212  or the forward face  210  of the camera should glass  212  not be utilized. 
         [0060]      FIG. 5  shows alternative embodiments  600 . In alternative embodiments  600 , the system for diagnosing a rotating airfoil  606  is associated with something other than internal rotors within a gas turbine engine. As an example, the system  602  could be a helicopter, a turboprop engine, or even an F-135 lift fan. In such systems, the rotating airfoil  604  could be the propeller, and any propeller location on a helicopter, or could be the F-135 lift fan. A vertical flight segment has a chance of bird strike, or other system failure, and thus the application of the system  606  to such locations provides valuable benefits. 
         [0061]    Image recognition software is known and commercially available. An appropriate program can be tailored to achieve the goals of this disclosure utilizing only the commercially available software. 
         [0062]    Although an 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 disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.