Abstract:
A clearance probe includes a sensor component with a sensor face. A housing is arranged about the sensor component and includes multiple gas passage exit holes that are arranged about the sensor face and are operable to create a gas curtain circumferentially surrounding the sensor face. This gas curtain displaces a portion of the particles in the area between the probe and the blade tip, thereby improving the accuracy of the clearance measurement.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to rotor tip clearance probes, and more specifically to an improved housing arrangement for the same. 
         [0002]    Rotating machines, such as gas turbine engines, require optimized rotor tip clearances to be maintained within the rotating machine for proper operation of the rotating machine. In order to ensure that the proper blade tip clearance is achieved, it is common to include a tip clearance probe in the rotating machine to measure the clearance between the rotor blade tip and an interior surface of the outer air seals of the rotating machine. 
         [0003]    Various types of tip clearance probes are utilized in the art to determine the tip clearances. However, due to the unknown composition of a gas flowing through the clearance region (the gap between the probe and rotor tip), the tip clearance probes can be inaccurate. In particular, the number and amount of particles such as dust, water vapor, or products of combustion between the probe and the blade tip at any given time is variable and unknown. 
       SUMMARY 
       [0004]    A clearance probe according to an exemplary embodiment of this disclosure, among other possible things includes a sensor component having a sensor face, a housing arranged about the sensor component, a plurality of gas passages within the housing, a probe face including the sensor face, the sensor face is circumscribed by a housing face, and the housing face comprises a plurality of gas passage exit holes arranged about the sensor face and operable to create an air curtain circumferentially surrounding the sensor face. 
         [0005]    In a further embodiment of the foregoing clearance probe, a ceramic fitting is between the housing and the sensor component. 
         [0006]    In a further embodiment of the foregoing clearance probe, a gas cooling system is operable to cool the housing of the clearance probe. 
         [0007]    In a further embodiment of the foregoing clearance probe, the gas cooling system comprises a cooling gas inlet connected to the plurality of gas passages such that each of the gas passages is operable to cool the clearance probe. 
         [0008]    In a further embodiment of the foregoing clearance probe, the gas cooling system includes a cooling gas at least partially comprising GN2. 
         [0009]    In a further embodiment of the foregoing clearance probe, the housing further comprises a gas inlet connected to the plurality of gas passages via a manifold. 
         [0010]    In a further embodiment of the foregoing clearance probe, an upper ceramic is contacting the sensor component and a housing cap. 
         [0011]    In a further embodiment of the foregoing clearance probe, the sensor component is a capacitive sensor component. 
         [0012]    In a further embodiment of the foregoing clearance probe, the sensor component is a sensor type selected from a microwave sensor component, an eddy current sensor component, or a laser blade tip clearance sensor. 
         [0013]    In a further embodiment of the foregoing clearance probe, each of the gas passage exit holes is arranged approximately equal distance from each adjacent gas exit hole, thereby creating an evenly distributed gas curtain. 
         [0014]    A clearance probe according to an exemplary embodiment of this disclosure, among other possible things includes a method for detecting a rotor clearance circumscribing a sensor face of a tip clearance probe with a gas curtain such that particulate passing through a sensed region is minimized. 
         [0015]    In a further embodiment of the foregoing method, an additional step of passing a gas through the clearance probe housing, and ejecting the gas from a plurality of gas exit holes on a sensor face of the tip clearance probe, thereby creating the gas curtain is performed. 
         [0016]    In a further embodiment of the foregoing method, the step of passing a gas through the tip clearance probe housing comprises passing a cooling gas through the housing, thereby cooling the tip clearance probe. 
         [0017]    In a further embodiment of the foregoing method, passing the cooling gas through the tip clearance probe housing comprises passing nitrogen gas through the tip clearance probe housing. 
         [0018]    A turbine engine according to an exemplary embodiment of this disclosure, among other possible things includes a gas path including a plurality of rotors and stators, a clearance probe configured to detect a clearance between at least one of the rotors and an outer diameter wall of the gas path, the clearance probe comprises, a sensor component having a sensor face, a housing arranged about the sensor component, a plurality of gas passages within the housing, a probe face including the sensor face, wherein the sensor face is circumscribed by a housing face, and wherein the housing face comprises a plurality of gas passage exit holes arranged about the sensor face and operable to create a gas curtain circumferentially surrounding the sensor face. 
         [0019]    In a further embodiment of the foregoing turbine engine, the clearance probe further comprises a ceramic fitting between the housing and the sensor component 
         [0020]    In a further embodiment of the foregoing turbine engine, the clearance probe, further comprises a gas cooling system operable to cool the housing of the clearance probe. 
         [0021]    In a further embodiment of the foregoing turbine engine, the gas cooling system comprises a cooling gas inlet connected to the plurality of gas passages such that each of the gas passages is operable to cool the clearance probe. 
         [0022]    In a further embodiment of the foregoing turbine engine, the housing further comprises a gas inlet connected to the plurality of gas passages via a manifold. 
         [0023]    In a further embodiment of the foregoing turbine engine, the sensor component is a capacitive sensor component. 
         [0024]    In a further embodiment of the foregoing turbine engine, each of the gas passage exit holes is arranged approximately equal distance from each adjacent gas exit hole, thereby creating an evenly distributed gas curtain. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0025]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0026]      FIG. 1  schematically illustrates a turbine engine gas path including a tip clearance probe. 
           [0027]      FIG. 2  schematically illustrates an isometric view of a tip clearance probe. 
           [0028]      FIG. 3  schematically illustrates a cross-sectional view of the tip clearance probe of  FIG. 2 . 
           [0029]      FIG. 4  schematically illustrates an operational side view of the tip clearance probe of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  schematically illustrates a portion of a gas path  10  that passes through a turbine engine. Included in the gas path  10  are multiple rotors  30  and stators  50 . The rotors  30  are airfoil shaped blades that are forced to rotate due to expanding gases passing through the gas path  10 . Each of the rotors  30  has a rotor tip  32 . In order to validate the gas turbine engine design, the gap between the rotor blade tip  32  and the outer air seal must be accurately measured. In order to measure the tip clearance, a clearance probe  20  is included in the outer air seal  60  and measures the tip clearance (distance between the rotor tip  32  and the outer air seal  60 ) of a corresponding rotor  30 .  FIG. 1  is not drawn to scale, and certain elements, such as the clearance probe  20 , are exaggerated for illustrative effect. 
         [0031]    Due to the inherent nature of turbine engines, the gas  40  passing through the gas path  10  can vary in composition and can carry an indeterminate amount of particles such as dust, water vapor, or other products of combustion. The presence of particulate in the gas  40  in the flow-path  10  can undesirably affect the readings of a tip clearance probe. 
         [0032]      FIG. 2  schematically illustrates a tip clearance probe  100  capable of providing accurate tip clearance measurements despite the presence of unknown particulates in the gas  40  passing through the gas path  10  (illustrated in  FIG. 1 ). The tip clearance probe  100  includes a housing  110  containing a sensor component  120 . A ceramic insulator  130  positions the sensor component  120  within the housing  110  and holds the sensor component  120  in place. An electrical lead  140  extends out of the housing  110  and connects the tip clearance probe  100  to a signal conditioner (not pictured). 
         [0033]    The tip clearance probe  100  also includes a sensor face  160  that is positioned facing a corresponding rotor tip when the tip clearance probe  100  is in an installed position. A gas/cooling inlet tube  150  is connected to the tip clearance probe  100  via a housing manifold inlet opening  114 . The sensor face  160  also includes multiple gas exit holes  112  that expel gas inserted into the housing manifold (illustrated in  FIG. 3 ) via the gas/cooling inlet tube  150 . The gas is expelled toward the corresponding rotor tip  32 . 
         [0034]    In the illustrated example of  FIG. 2 , the gas/cooling inlet tube  150  facilitates an insertion of a cooling gas, such as nitrogen (GN2), into the housing manifold. As the cooling gas passes through the housing  110 , the cooling gas cools the housing  110 , ensuring that the tip clearance probe  100  stays within standard clearance probe temperature parameters and does not overheat. In alternate examples the cooling system for the tip clearance probe  100  can be a separate system and the gas/cooling inlet tube  150  can insert any gas capable of generating an air curtain effect (described below with regards to  FIG. 4 ). 
         [0035]      FIG. 3  illustrates a cross-sectional view of a tip clearance probe  200 , such as the tip clearance probe  100  illustrated in  FIG. 2 . As with the example of  FIG. 2 , the tip clearance probe  200  includes a housing  210  containing a sensor component  220 . The sensor component  220  is maintained in position within the housing via a lower ceramic insulator  230  and an upper ceramic insulator  280 . An electric lead  240  extends out of the top of the tip clearance probe  200 . The electric lead  240  is connected to the sensor component  220  via a sensor wire  242  and transmits sensor data to a signal conditioner (not pictured). The sensor wire  242  is maintained in contact with the sensor component  220  via a strap  290 . 
         [0036]    Each of the ceramic insulators  230 ,  280 , the sensor component  220 , the strap  290  and the electric lead  240  are held in place by a cap  270  that exerts a downward pressure on the internal components of the clearance probe  200 . The cap  270  is maintained in place by any known technique such as welding or press fitting to the housing. 
         [0037]    Inside the housing  210  is a housing manifold  262  that receives a gas from a gas/cooling inlet tube  250  via a housing manifold input opening  214 . The gas is distributed from the housing manifold  262  to each of multiple gas exit holes  212  on the sensor face  224  via gas passages  260  that connect the housing manifold  262  to the gas exit holes  212 . The gas exit holes  212  are located on a sensor face  224  of the tip clearance probe  200  and surround a sensor component face  222  thereby generating an air curtain effect surrounding the sensed region and displacing problematic gas-path elements. 
         [0038]    The sensor components  120 ,  122  described above with regards to  FIGS. 2 and 3  are capacitance based proximity sensors. However, alternate types of sensors such as laser blade tip clearance sensors and microwave tip clearance sensors can also be beneficially used in the described arrangement. 
         [0039]      FIG. 4  illustrates a side view of a tip clearance probe  300  in operation. During operation of the turbine engine, the capacitance based tip clearance probe  300  sensor component detects the tip clearance based on the dielectric strength of the gap between the sensor face  320  and the rotor tip  382  using an electric field  322 . As described above, the gas flow  380  passing through the gap can carry with it particles that affect the dielectric strength of the gap or otherwise skew the measurements of the sensor component  320 . In order to prevent the particulate from passing through the gap, and thereby skewing the dielectric strength of the gap, gas exit holes  392  expel gas toward a rotor tip  384  passing below the tip clearance probe  300 . The expelled gas creates an obstruction  390  in the gas path  380  that prevents the gas and particulate from passing through the sensed region (the gap). This obstruction  390  is alternately referred to as an “air curtain”. The air curtain blocks a significant portion of the particles in the gas flow from passing through the electric field  322 . 
         [0040]    The gas used to generate the obstruction  390  is initially injected into the clearance probe  300  housing manifold through a gas/cooling injection tube  350  and a housing manifold inlet opening  314 . The gas fills the manifold and is forced through the gas passages (illustrated in  FIG. 3 ) with enough force to create the air curtain effect blocking particulates. Thus, the air curtain minimizes the amount of particulate passing through the gap and increases the reliability and accuracy of the tip clearance probe  300 . 
         [0041]    In some example arrangements, the gas used to create the air curtain is also used to cool the probe housing  310 . In such an arrangement, the cooling gas can originate from a pressurized cooling gas storage device. In other example arrangements, the tip clearance probe  300  has an independent cooling system or is not directly cooled, and the pressurized gas can come from alternate sources such as a turbine engine compressor bleed. 
         [0042]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.