Abstract:
A method of observing an airflow passage within a gas turbine engine includes locating a support in view of an airflow passage and housing an optical fiber within the support.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to a gas turbine engine and, more particularly, to an optical tip-timing probe system therefor. 
         [0002]    Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor section to pressurize an airflow, a combustor section for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. 
         [0003]    Beam Interrupt probes for optical tip-timing typically require two (2) “periscope” probes per channel. Arrangements that involve protrusion of the end of the “periscope” into the flow passage may not be desirable because exposure to the full effects of the hot compressed gases. To minimize the protrusion, the periscope may be designed to “look” obliquely into the flow passage. However, such an arrangement has the disadvantage that the probe&#39;s field of view may be undesirably limited and cannot readily be altered significantly because such alteration requires modification to the engine structure. 
         [0004]    Furthermore, “Periscope” probes may disturb the aerodynamic behavior in the gas-path thereby driving additional (non-production related) vibration in rotating hardware. For this reason the use of “periscope” Beam Interrupt probes in the high pressure compressor (HPC)—particularly the aft stages—has been abandoned, despite the advantages inherent in a Beam Interrupt probes&#39; dual measurement over a traditional spot probe&#39;s single measurement capability. 
       SUMMARY 
       [0005]    A method of observing an airflow passage within a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes locating a support in view of an airflow passage and housing an optical fiber within the support. 
         [0006]    In a further embodiment of the foregoing embodiment, the method further comprising locating the support within static structure. 
         [0007]    In a further embodiment of any of the foregoing embodiments, the method locating the support within a leading edge of an airfoil. 
         [0008]    In a further embodiment of any of the foregoing embodiments, the method further comprising locating the support within a trailing edge of an airfoil. 
         [0009]    In a further embodiment of any of the foregoing embodiments, the method further comprising housing a second optical fiber within a second support in view of the optical fiber. 
         [0010]    In a further embodiment of any of the foregoing embodiments, the method further comprising housing a second optical fiber within a second support opposite the optical fiber to define a beam across the airflow passage. In the alternative or additionally thereto, the foregoing embodiment further comprising angling the beam with respect to an engine axis of rotation. 
         [0011]    A method of observing blades within a gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure includes housing a first optical fiber in a trailing edge of an airfoil and housing a second optical fiber in a leading edge of an airfoil in view of the first optical fiber. 
         [0012]    In a further embodiment of the foregoing embodiment, the method further comprising defining a beam across an airflow passage. In the alternative or additionally thereto, the foregoing embodiment further comprising: angling the beam with respect to an engine axis of rotation. 
         [0013]    An observation system for a gas turbine engine according to another disclosed non-limiting embodiment of the present disclosure includes a support and an optical fiber within said support. 
         [0014]    In a further embodiment of the foregoing embodiment, the support is a hypo tube. 
         [0015]    In a further embodiment of any of the foregoing embodiments, the support is less than approximately 0.04 inches (1 mm) in diameter. 
         [0016]    In a further embodiment of any of the foregoing embodiments, the optical fiber is approximately 0.002-0.008 inches (50-200 microns) in diameter. 
         [0017]    In a further embodiment of any of the foregoing embodiments, the optical fiber is not coupled to an optical lens. 
         [0018]    In a further embodiment of any of the foregoing embodiments, the support is mounted within an airfoil. 
         [0019]    In a further embodiment of any of the foregoing embodiments, the support is mounted within a leading edge of an airfoil. 
         [0020]    In a further embodiment of any of the foregoing embodiments, the support is mounted within a trailing edge of an airfoil. 
         [0021]    In a further embodiment of any of the foregoing embodiments, the support is mounted within a High Pressure Compressor vane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0023]      FIG. 1  is a schematic cross-section of an example gas turbine engine architecture; 
           [0024]      FIG. 2  is a schematic cross-section of another example gas turbine engine architecture; 
           [0025]      FIG. 3  is an expanded view of a High Pressure Compressor section of an example gas turbine engine; 
           [0026]      FIG. 4  is an expanded perspective view of a High Pressure Compressor fixed airfoil according to one disclosed non-limiting embodiment with an optical tip timing probe mounted in a leading edge thereof; 
           [0027]      FIG. 5  is an expanded perspective view of a High Pressure Compressor variable airfoil according to one disclosed non-limiting embodiment with an optical tip timing probe mounted in a trailing edge thereof; 
           [0028]      FIG. 6  is an schematic radial-inward view of a section of the example gas turbine engine with an optical system mounted therein; 
           [0029]      FIG. 7  is an schematic radial-inward view of a section of the example gas turbine engine with a target blade in a first position illustrating a first signal; 
           [0030]      FIG. 8  is an schematic radial-inward view of a section of the example gas turbine engine with a target blade in a second position illustrating a second signal; and 
           [0031]      FIG. 9  is an schematic sectional view of a section of the example gas turbine engine with an optical system mounted therein; 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbo fan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engine architectures  200  might include an augmentor section  202  and exhaust duct section  204  ( FIG. 2 ) among other systems or features. The fan section  22  drives air along a bypass flowpath while the compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a turbofan in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines such as a low bypass augmented turbofan ( FIG. 2 ), turbojets, turboshafts, and three-spool (plus fan) turbofans wherein an intermediate spool includes an intermediate pressure compressor (“IPC”) between a Low Pressure Compressor (“LPC”) and a High Pressure Compressor (“HPC”), and an intermediate pressure turbine (“IPT”) between the high pressure turbine (“HPT”) and the Low pressure Turbine (“LPT”). 
         [0033]    The engine  20  generally includes a low spool  30  and a high spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing structures  38 . The low spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  (“LPC”) and a low pressure turbine  46  (“LPT”). The inner shaft  40  drives the fan  42  directly or through a geared architecture  48  to drive the fan  42  at a lower speed than the low spool  30 . An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system. 
         [0034]    The high spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  (“HPC”) and high pressure turbine  54  (“HPT”). A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
         [0035]    Core airflow is compressed by the LPC  44  then the HPC  52 , mixed with the fuel and burned in the combustor  56 , then expanded over the HPT  54  and the LPT  46 . The turbines  54 ,  46  rotationally drive the respective low spool  30  and high spool  32  in response to the expansion. The main engine shafts  40 ,  50  are supported at a plurality of points by bearing structures  38  within the static structure  36 . It should be understood that various bearing structures  38  at various locations may alternatively or additionally be provided. 
         [0036]    With reference to  FIG. 3 , the HPC  52  generally includes a multiple of stages with alternate stationary vane assemblies  60  and rotational rotor assemblies  62  along an HPC airflow passage  64 . Although the HPC  52  is illustrated in the disclosed non-limiting embodiment, other engine sections will also benefit herefrom. Moreover, although a particular number of HPC stages are illustrated, it should be appreciated that any number of stages will benefit herefrom. 
         [0037]    Each of the vane assemblies  60  are mounted to the engine static structure  36  and include a multiple of airfoils  66  between a radial inner platform  68  and a radial outer platform  70 . In one disclosed non-limiting embodiment, a first sidewall  86  is convex and defines a suction side of airfoil  66 , and a second sidewall  88  is concave and defines a pressure side of airfoil  66  (also shown in  FIG. 4 ). Sidewalls  86 ,  88  are joined at the leading edge  96  and at an axially-spaced trailing edge  98  (also shown in  FIG. 4 ). More specifically, the airfoil trailing edge  98  is spaced chordwise and downstream from the airfoil leading edge  96 . The sidewalls  86  and  88 , respectively, extend longitudinally or radially outward in span from an airfoil root  90  to a stem  92 . It should be appreciated that the airfoils  66  may be variable—shown as the first three (3) stages—or fixed—shown as the last three (3) stages—stator vanes within the HPC  52  that may combine both. In the exemplary embodiment, each airfoil  66  may be manufactured utilizing a metallic alloy such as, but not limited to, titanium or a composite material. 
         [0038]    Each of the rotor assemblies  62  includes a multiple of blades  72  supported by a respective rotor assembly  74 . The radial inner platform  68  and the radial outer platform  70  of the vane assemblies  60  and a platform  76  that extends from each of the multiple of blades  72  generally bounds the HPC airflow passage  64 . 
         [0039]    In order to facilitate observation of the blades  72  to, for example, facilitate operations of a Non-Interference Stress Measurement System (NSMS; illustrated schematically at  84 ), an observation system  94  with optical tip timing probes  100  is located within the HPC airflow passage  64  in an airfoil  66 - 1  forward of the target blades  72 -T and in an airfoil  66 - 2  aft of the target blades  72 . The NSMS determines an actual time of arrival from the optical tip-timing probes  100  that is then referenced to a theoretical time of arrival such that the resultant delta may then be converted to deflection, which then, in turn, is converted to stress/strain measurements. It should be appreciated that other measurements may be determined with the observation system  94  such as temperature measurements. Furthermore, although disclosed in a gas turbine engine environment, the optical tip timing probes  100  may be used for gathering tip-timing data for any type of rotating machinery that experiences vibratory stresses and/or cracking. 
         [0040]    With reference to  FIG. 4 , each of the optical tip timing probes  100  generally includes an optical fiber  102  housed within a support  104  such as a hypo tube. The support  104  may readily brazed directly into the airfoil  66 - 1 ,  66 - 2  ( FIG. 5 ). It should be appreciated that alternative installations will also benefit herefrom as well as alternate or additional positions within other static structure. 
         [0041]    The optical tip timing probes  100  avoid the typical “periscope” of a relatively substantial probe body and lens arrangement required for support and protection within the gas path. The airfoils  66  themselves form the “periscope” which significantly reduces disturbances to the aero environment. That is, only small modification to the airfoils  66  to accommodate the fibers  102  is required rather than having the invasive cylinders of a traditional “periscope” probe. 
         [0042]    The optical fiber  102 , in one disclosed non-limiting embodiment, is typically approximately 0.002-0.008 inches (50-200 microns) in diameter. As the optical tip timing probe  100  is only approximately the diameter of the support  104  the optical tip timing probes  100  may be less than approximately 0.04 inches (1 mm) in diameter compared to a conventional “periscope” probe that is often approximately 0.375 inches (10 mm) as such probes are typically actively cooled. The optical tip timing probes  100  are thereby relatively easily mounted within the trailing edge  98  or the leading edge  96  ( FIG. 3 ) of the respective airfoils  66 - 1 ,  66 - 2 . It should be appreciated that the optical tip timing probes  100  are most typically installed in a fixed airfoil, however, variable airfoils and other structure will also benefit herefrom. 
         [0043]    With reference to  FIG. 6 , one optical tip-timing probes  100  is located within the trailing edge  98  of the airfoil  66 - 1  forward of the target blades  72 -T and another optical tip-timing probe  100  is located within the leading edge  96  of the airfoil  66 - 2  aft of the target blades  72 -T. The optical tip timing probes  100  are thereby directed toward each other such that one optical tip timing probe  100  operates as an emitter and the other optical tip timing probe  100  operates as a receiver. It should be appreciated that the “transmit” and “receive” optical tip timing probes  100  are essentially the same with the distinguishing characteristic being which is attached to a laser and which is attached to a detector. 
         [0044]    The unfocused “transmit” and “receive” optical fibers  102  define respective emission and reception cones  110  that, in the disclosed non-limiting embodiment are of approximately 44 degrees. A theoretical central “beam”  112  is the cylinder of light defined by the apertures of the transmit and receive fibers  102  given that the angle between the normal vectors of the transmit fiber exit plane is less than or equal to the Numerical Aperture (N.A.) of the receive optical fiber  102 . The Numerical Aperture (N.A.) is defined herein as the angle with respect to the normal vector of the exit plane of the fiber at which incidence light will transmit through the fiber  102 . That is, so long as the apertures of the transmit and receive fibers  102  are within the respective transmission and reception cones  110 , the beam  112  will be extant. 
         [0045]    The two optical tip timing probes  100  operate as beam interrupt probes that provide two measurements per channel—one when a blade leading edge  114  of the blade  72 -T breaks the beam ( FIG. 7 ), and a second when a blade trailing edge  116  passes the beam and is restored ( FIG. 8 ). In addition, the two optical tip timing probes  100  may be positioned such that the central “beam”  112  may be angled with respect to the engine axis A so that the intercept upon the blade leading edge  114  of the blade  72  may be located at a different span distance compared to the intercept upon the trailing edge  114  ( FIG. 9 ). 
         [0046]    It should be appreciated that other measurements may be determined with the observation system  94  such as a spot probe single measurement. Furthermore, the integral nature of the optical tip timing probes  100  may lend themselves to a condition monitoring application such as a Health and Usage Monitoring System (HUMS), not just test and development applications. 
         [0047]    It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
         [0048]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
         [0049]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0050]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.