Abstract:
Total air temperature (TAT) measurement systems, apparatus, and methods for measuring TAT within an airflow are disclosed. A TAT within an airflow may be measured by (1) positioning a probe within an airflow, the probe including an airfoil and a wedge defining a single channel, the single channel including a temperature sensor; (2) receiving a portion of the airflow through the single channel; and (3) determining TAT for the received portion of the airflow using measurements from the temperature sensor.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention relates generally to temperature measurement. More specifically, it relates to total air temperature (TAT) sensors and methods for measuring TAT within an airflow. 
       BACKGROUND OF THE INVENTION 
       [0002]    Jet powered aircraft require accurate measurement of air temperature for input to an air data computer and other airborne systems to optimize engine performance. Total air temperature (TAT) sensors are used to measure temperature at various stages of an engine to determine flight parameters, including static temperature, true airspeed computation, fuel consumption, and turbine engine control. Conventional TAT sensors include a temperature sensor located within a probe that can be immersed within an airflow. The temperature sensor is used to compute the TAT of the engine at various stages. The accuracy of conventional TAT sensors, however, may be compromised at higher speeds (e.g., speeds above Mach 0.6). 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is embodied in a TAT measurement system, apparatus, and method for measuring TAT within an airflow. A probe for measuring temperature within an airflow may include a flange configured for attachment to an aircraft, a support coupled to the flange, and a temperature measurement apparatus coupled to the support to receive the airflow. The temperature measurement apparatus may include an airfoil having a leading edge and first and second surfaces extending away from the leading edge. The leading edge of the airfoil may be positioned to receive the airflow. The temperature measurement apparatus may also include a wedge having a first surface and a second surface opposite the first surface, the first surface of the wedge facing the second surface of the airfoil, defining a channel between the airfoil and the wedge, and a temperature sensor positioned within the channel between the airfoil and the wedge. 
         [0004]    Methods of measuring total air temperature (TAT) within an airflow may include the steps of (1) positioning a probe within an airflow, the probe including an airfoil and a wedge defining a single channel, the single channel including a temperature sensor; (2) receiving a portion of the airflow through the single channel; and (3) determining TAT for the received portion of the airflow using measurements from the temperature sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The invention is best understood from the following detailed description when read in connection with the accompanying drawings, with like elements having the same reference numerals. When a plurality of similar elements are present, a single reference numeral may be assigned to the plurality of similar elements with a small letter designation referring to specific elements. When referring to the elements collectively or to a non-specific one or more of the elements, the small letter designation may be dropped. The letter “n” may represent a non-specific number of elements. Also, lines without arrows connecting components may represent a bi-directional exchange between these components. According to common practice, the various features of the drawings are not drawn to scale. On the contrary, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
           [0006]      FIG. 1  is a 2-dimensional cross sectional view of an aircraft engine with multiple TAT sensors in accordance with aspects of the present invention; 
           [0007]      FIG. 2  is a perspective view of a total air temperature (TAT) sensor in accordance with aspects of the present invention; 
           [0008]      FIG. 3  is a cross sectional view of the TAT sensor of  FIG. 2  illustrating a single airfoil, wedge, channel, and temperature sensor; 
           [0009]      FIG. 4  is a perspective view of the airfoil and wedge of the temperature measurement apparatus of  FIG. 3 ; 
           [0010]      FIG. 5  is a another cross sectional view of the airfoil, wedge, channel, and temperature sensor of  FIG. 3  depicting chord angle and airflow in accordance with aspects of the present invention. 
           [0011]      FIG. 6  is a flow chart depicting steps for measuring total air temperature (TAT) within an airflow in accordance with aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  is a 2-dimensional view of an aircraft engine  100 . In the embodiment illustrated in  FIG. 1 , the aircraft engine  100  includes a fan  120 , a high-pressure compressor  117  and low-pressure compressor  118  (collectively referred to as “compressor  108 ”), a high-pressure turbine  116  and low-pressure turbine  115  (collectively referred to as “turbine  107 ”), and a combustion chamber  104 . For the purposes of this application, the generic terms “compressor  108 ” and “turbine  107 ” will be used in place of specific terms high-pressure compressor  117 , low-pressure compressor  118 , high-pressure turbine  116 , and/or low-pressure turbine  115 . Airflow  101  enters the compressor  108  by travelling through air intake  109 . The compressor  108  squeezes air that enters it into progressively smaller areas, resulting in an increase in air pressure. The increased air pressure results in an increase in the energy potential of the air. In the combustion chamber  104  this air is mixed with fuel and then ignited. This provides a high temperature, high energy airflow. The turbine  107  rotates about a high-pressure shaft  113  and low-pressure shaft  114  (collectively referred to as “shaft  103 ”) to extract energy from the airflow  101  and converts it into useful work. The high-energy airflow out of the combustion chamber  104  enters the turbine  107 , causing the turbine&#39;s blades to rotate. A nozzle  105  is the exhaust duct of the aircraft engine  100 . The energy depleted airflow that passes through the turbine  107 , in addition to the colder air that bypasses the engine core, produces a force when exiting the nozzle  105  that acts to propel the aircraft engine  100 . 
         [0013]    A centerline  106  extends along the low-pressure shaft  114  of the aircraft engine  100 . The engine cowling  111  is designed to straighten incoming airflow  101  such that it is parallel to the centerline  106 . In use, however, the direction of the straightened airflow varies depending on airspeed and the direction of the incoming airflow  101 . Airflow that flows parallel to the centerline  106  is referred to herein as standard airflow  110 . Airflow  101  that does not travel parallel to the centerline  106  is referred to herein as nonstandard airflow. 
         [0014]    Aircraft engine  100  may use one or more sensors to measure temperature at one or more stages of the engine. In  FIG. 1 , two probes  200  for measuring TAT in accordance with embodiments of the present invention are mounted within the aircraft engine  100 . The placement of the probes  200  in  FIG. 1  is exemplary. Those of ordinary skill in the art will understand from the description herein that a single probe or multiple probes may be placed in various locations of the aircraft engine  100 . TAT sensors are typically used to determine flight parameters, including static temperature, true airspeed computation, fuel consumption, and turbine engine control. 
         [0015]      FIG. 2  is a perspective view of a probe  200  for measuring temperature within the airflow. The illustrated probe  200  includes a flange  201 , a support  204  coupled to the flange  201 , and a temperature measurement apparatus  206  ( FIGS. 3-5 ) coupled to the support  204 . The flange  201 , support  204 , and temperature measurement apparatus  206  may be cast as a single piece of metal (such as stainless steel or aluminum) or may be formed separately and assembled. 
         [0016]    The support  204  extends from a first surface of the flange  201 . Electrical connectors  205  extend from a second surface of the flange that is opposite the first surface. The electrical connectors  205  provide an interface between the monitoring equipment within an aircraft (not shown) and the sensor(s) within the probe, which will be described in further detail below. The monitoring circuits include electronics or electrical circuits of the type known to one of skill in the art for use with conventional TAT sensors for measuring TAT. The flange  201  connects the TAT sensor  200  to the aircraft engine  100  such that the probe  204  is located within the airflow  101  and the electrical connectors  205  are located beneath the skin of the aircraft engine  100 . The probe  204  includes an inlet  202  through which airflow  101  enters the probe  204 . Airflow  101  that enters the inlet  202  of the probe  204  may exit an outlet  203  of the probe  204 . 
         [0017]      FIG. 3  is a 2-dimensional view of a cross section of the probe  200  ( FIG. 2 ) illustrating aspects of the temperature measurement apparatus  206 . Temperature measurement apparatus  206  includes an airfoil  303 , a wedge  307 , and a temperature sensor  306  positioned between the airfoil  303  and wedge  307 . A leading edge of the airfoil  303  protects the temperature measurement apparatus  206  from impact by, for example, hail, ice, sand, and birdstrikes. The airfoil  303  protects the components of the temperature measurement apparatus  206  from high speed impact with any of the aforementioned materials. 
         [0018]    In the illustrated embodiment, a single channel  310  separates the airfoil  303  and the wedge  307  and provides a pathway for airflow to reach the temperature sensor  306 . The airfoil  303  has a leading edge  301  and a trailing edge  305 . A first surface  302  and a second surface  311  each have convex shapes adjacent to the leading edge  301  of the airfoil  303 . The first surface  302  and the second surface  311  extend away from the leading edge  301  of the airfoil  303  and towards the trailing edge  305  of the airfoil  303 . An optional gap  304  may be located on the first surface of the airfoil  303  following its convex shape. In the illustrated embodiment, the optional gap  304  may be triangular in shape. The first surface  302  and second surface  302  may each have a straight portion following their respective convex shapes. 
         [0019]    A wedge  307  is located opposite the second surface of the airfoil  303 . The wedge  307  has a first surface  309  and second surface  308  opposite the first surface  309 . The single channel  310  is located between the second surface  311  of the airfoil  303  and first surface  309  of the wedge  307 . The channel  310  contains an inlet  202 , where airflow enters, and an outlet  203 , where airflow  101  may exit. 
         [0020]    The temperature sensor  306  is located within the single channel  310  of the temperature measurement apparatus  206 . More specifically, the temperature sensor  306  is positioned between the straight portion of the second surface  311  of the airfoil  303  and the first surface  309  of the wedge  307 . In one embodiment, the temperature sensor is a resistance temperature detector (RTD) used to measure temperature by correlating the resistance of the RTD element with temperature. The RTD may be a length of fine coiled wire wrapped around a core (e.g., ceramic or glass) or thin film variety in which the resistance is a conductive pattern on a small ceramic chip. Airflow  101  enters the channel&#39;s inlet  202 , and immerses the temperature sensor  306 . The airflow  101  then exits the channel&#39;s outlet  203 . The cross section of the probe  204  is designed to slow the airflow&#39;s  101  velocity at the temperature sensor  306  in order to measure the TAT. 
         [0021]    Conventional temperature measurement apparatuses include two airfoils and two channels. In such temperature measurement apparatuses, a leading channel is used to siphon air to the rear of the probe, with the second channel encompassing the temperature sensor. In such designs, at high speeds (e.g., above Mach 0.6) airflow may reverse itself within the first channel, leading to degradation of the probe&#39;s accuracy. By using a single airfoil and channel, the present invention provides unexpected favorable outcomes with respect to recovery error (i.e., the error in measuring TAT due to an incomplete conversion of air speed to temperature). 
         [0022]      FIG. 4  is a perspective view of the airfoil  303  and wedge  307  of the temperature measurement apparatus  206  of  FIG. 3 . As illustrated in  FIG. 4 , the wedge  307  is opposite the second surface  311  of the airfoil  303 . The perspective view of the temperature measurement apparatus  206  provides another view of the leading edge  301 , trailing edge  305 , first surface  302  and second surface  311  of airfoil  303 . A different view of first surface  309  and second surface  308  of wedge  307  can also be seen, as well as a different perspective of the single channel  310  that is formed between the second surface  311 . of the airfoil and the first surface  309  of the wedge. Although the temperature sensor  306  is not illustrated in  FIG. 4 , the temperature sensor  306  would be located within the channel  310  of a fully formed probe. 
         [0023]      FIG. 5  depicts an embodiment of the temperature measurement apparatus  206  overlaid upon the centerline  106  of an aircraft engine  100  ( FIG. 1 ). A straight line that intersects the airfoil&#39;s leading edge  301  and the airfoil&#39;s trailing edge  305  is defined herein as the chordline  502 . The temperature measurement apparatus  206  is directed with the probe  200  ( FIG. 2 ) such that the chordline  502  has a specific angular relationship with respect to the centerline  106  when the probe  200  is installed. The intersection of the centerline  106  and the chordline  502  creates an angle  501 . In an embodiment of the present invention, the chordline  502  of the airfoil  303  forms an angle between about 12 degrees and about 18 degrees. Preferably the angle may be between about 14 degrees and about 16 degrees, and more preferably is about 15 degrees. In an exemplary embodiment of the present invention, recovery error associated with probe to probe variation and airflow angle variation is reduced over conventional probe designs by such angular relationships, which reduces recovery error—resulting in higher engine thrust. 
         [0024]      FIG. 6  is a block diagram of the process for measuring temperature within an airflow  101 . In block  602 , a probe  204  is positioned within an airflow  101 . As discussed above, the probe includes temperature measurement apparatus  206 , which encompasses an airfoil  303 , a wedge  307 , and a single channel  310  that is situated between the second surface  311  of the airfoil  303  and the first surface  309  of the wedge  307 . Within the single channel  310  of the temperature measurement apparatus  206  is a temperature sensor  306 , which is used to compute TAT. 
         [0025]    In block  604 , a portion of the airflow  101  is received through the single channel  310  of the temperature measurement apparatus  206 . The airflow  101  entering the channel  310  immerses the temperature sensor  306 . 
         [0026]    In block  606 , TAT is determined for the portion of the airflow  101  that is received through the single channel  301 . The temperature sensor  306  uses measurements from the airflow  101  that immerses the temperature sensor  306  to determine TAT. TAT is the maximum temperature which can be attained by 100% conversion of the kinetic energy of the flight. Suitable algorithms for determining TAT will be understood by one of skill in the art from the description herein. 
         [0027]    As used herein, the terms convex, concave, straight, and parallel mean at least substantially convex, concave, straight, or parallel, respectively. Thus, for example, a straight portion referred to herein would encompass straight or substantially straight portions (e.g., portions with a slight curvature). 
         [0028]    Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.