Abstract:
A method of operating a gas turbine engine for testing, comprising: providing an aircraft on a tarmac, the aircraft having a gas turbine engine with an inlet; selecting a power setting for the engine that is capable of producing a vortex between the inlet and the tarmac; and inhibiting formation of the vortex. A suppressor for preventing a vortex between an inlet of a gas turbine engine on an aircraft and a tarmac. The suppressor comprises: a base facing the tarmac; and an inclined surface extending in a direction from the tarmac towards the inlet at an angle to the base. The suppressor prevents formation of the vortex.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to an apparatus and a method for preventing an inlet vortex. Specifically, this invention relates to an apparatus and method for preventing the formation of a vortex at an inlet of a gas turbine engine while the engine operates on an aircraft located on a tarmac.  
           [0002]    Technicians have several options when performing tests with in-service engines. For example, the technician can perform the engine testing on a test stand. Or the technician can perform the engine testing while the engine operates on the aircraft static on the ground. Each testing method has benefits and drawbacks.  
           [0003]    Testing an engine in a test stand generally allows for the greatest amount of data acquisition. The test stand can measure the thrust of the engine and includes all of the instrumentation necessary to collect and to interpret engine conditions during operation. The test stand also provides a uniform standard for ensuring that each engine meets all of the flight acceptance requirements established by the certifying authority.  
           [0004]    The drawback, however, of a test cell is that the engine must be removed from the aircraft. Removing the engine from the aircraft adds cost and time to the testing procedure.  
           [0005]    Testing an engine while the aircraft operates statically on the ground is faster and does not include the expense of engine removal. Such testing does have drawbacks. The main drawback of typical engine installations is the limited power settings available during the test. The technician can only operate typical engine installations at low power settings.  
           [0006]    At elevated power settings, operating the engine while the aircraft remains static on the ground can produce vortices between the tarmac and the engine inlet. The vortices can damage the engine by inducing a compressor surge, by creating unstable operating conditions, or by picking up debris.  
           [0007]    The present invention increases the range of power settings allowed by the testing of the engine while the aircraft remains static on the ground. Preferably, the present invention expands the range of power settings such that the engine can operate at any power setting while the aircraft remains static on the ground. In other words, the present invention even allows the engine to operate at full power while the aircraft remains static on the ground.  
         SUMMARY OF INVENTION  
         [0008]    It is an object of the present invention to provide an apparatus and method for assisting the testing of a gas turbine engine.  
           [0009]    It is a further object of the present invention to provide an apparatus and method for preventing the formation of a ground plane induced inlet vortex during engine testing.  
           [0010]    It is a further object of the present invention to expand the range of power settings allowed by the testing of an engine while the aircraft remains static on the ground.  
           [0011]    It is a further object of the present invention to allow an engine to operate at any power setting while the aircraft remains static on the ground.  
           [0012]    It is a further object of the present invention to allow full power operation of an engine while the aircraft remains static on the ground.  
           [0013]    It is a further object of the present invention to prevent compressor surge due to formation of a ground vortex during engine testing while the aircraft remains static on the ground.  
           [0014]    It is a further object of the present invention to provide stable operating conditions during engine testing while the aircraft remains static on the ground.  
           [0015]    It is a further object of the present invention to allow the testing of an engine at elevated power settings without the need to remove the engine from the aircraft.  
           [0016]    It is a further object of the present invention to provide an engine test at a reduced cost.  
           [0017]    It is a further object of the present invention to provide a more rapid engine test.  
           [0018]    These and other objects of the present invention are achieved in one aspect by a method of operating a gas turbine engine for testing. The method includes the steps of: providing an aircraft on a tarmac, the aircraft having a gas turbine engine with an inlet; selecting a power setting for the engine that is capable of producing a vortex between the inlet and the tarmac; and inhibiting formation of the vortex.  
           [0019]    These and other objects of the present invention are achieved in another aspect by a method of preventing vortex formation. The method includes the steps of: providing an aircraft on a tarmac, the aircraft having a gas turbine engine with an inlet; operating the engine; determining whether the operating step is likely to produce a vortex between the inlet and the tarmac; and placing an object between the tarmac and the inlet should the determining step indicate a likelihood of the vortex.  
           [0020]    These and other objects of the present invention are achieved in another aspect by a method of operating a gas turbine engine mounted on an aircraft located on a tarmac at an elevated engine pressure ratio (EPR) greater than a threshold EPR. The method comprises the steps of: placing an object between the tarmac and the engine; and operating the engine at the elevated EPR. Without the object, operating the engine at the threshold EPR would not create an inlet vortex, but operating the engine at the elevated EPR would create the inlet vortex.  
           [0021]    These and other objects of the present invention are achieved in another aspect by a method of performing a test. The test includes a step of operating a gas turbine engine at an engine pressure ratio that typically requires removing the engine from an aircraft located on a tarmac and placing the engine on a test stand. The improvement comprises positioning a movable object between the engine and the tarmac to allow the engine to remain on the aircraft for the test.  
           [0022]    These and other objects of the present invention are achieved in another aspect by a suppressor for preventing a vortex between an inlet of a gas turbine engine on an aircraft and a tarmac. The suppressor comprises: a base facing said tarmac; and an inclined surface extending in a direction from said tarmac towards said inlet at an angle to said base. The suppressor prevents formation of said vortex. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0023]    Other uses and advantages of the present invention will become apparent to those skilled in the art upon reference to the specification and the drawings, in which:  
         [0024]    [0024]FIG. 1 is a partial front elevational view of an aircraft having a gas turbine engine and located on a tarmac;  
         [0025]    [0025]FIG. 2 a  is a cross-sectional view of the aircraft in FIG. 1 taken along line II-II during engine operation at a low power setting, with dashed lines showing various air flow paths entering the engine inlet;  
         [0026]    [0026]FIG. 2 b  is the aircraft of FIG. 2 a  during engine operation at an elevated power setting, where flow separation from the tarmac has created a ground vortex;  
         [0027]    [0027]FIG. 3 is front view of one alternative embodiment of a ramp of the present invention beneath the aircraft of FIG. 1;  
         [0028]    [0028]FIG. 4 is a cross-sectional view of the aircraft and the ramp of the present invention during engine operation at an elevated power setting, with dashed lines showing various air flow paths entering the engine inlet;  
         [0029]    [0029]FIG. 5 is a side elevational view of the ramp in FIG. 3;  
         [0030]    [0030]FIG. 6 is a rear elevational view of the ramp in FIG. 3;  
         [0031]    [0031]FIG. 7 is a chart of the preferred sizes for the ramp in FIG. 3; and  
         [0032]    [0032]FIG. 8 is a perspective view of another alternative embodiment of a ramp of the present invention that allows easy transportation and positioning of the ramp under the test engine.  
     
    
     DETAILED DESCRIPTION  
       [0033]    [0033]FIG. 1 displays an aircraft  11  on a tarmac T. The aircraft  11  has one or more powerplants  13 . Each powerplant  13  comprises a gas turbine engine  15  surrounded by a nacelle  17 . The engine  15  could be a high bypass turbofan.  
         [0034]    The centerline of the powerplant  13  resides at a height h above the tarmac T. The powerplant  13  could mount to the aircraft  11  in any known fashion. For example, the powerplant  13  could extend from a strut  19  below a wing  21 . The nacelle  17  includes an inlet  23  that allows air to enter the engine  15 . The inlet  23  has an internal throat diameter D.  
         [0035]    [0035]FIG. 2 a  displays the powerplant  13  operating at a low power setting. The engine  15  draws in air (shown as dashed lines) from locations surrounding the inlet  23 . Since the aircraft  11  remains static on the tarmac T, the engine  15  draws in air from both upstream and downstream of the inlet  23 .  
         [0036]    Engine Pressure Ratio (EPR) is a common performance parameter when discussing power settings. EPR is the ratio of the total turbine discharge pressure to the total pressure of the air entering the compressor. Although specific to each powerplant, a high bypass turbofan engine could operate at EPR values of between approximately 1.01 (idle) and 1.65 (takeoff thrust).As the power setting of the engine  15  increases, the engine  15  draws in greater amounts of air. Above a threshold power setting, a vortex V (FIG. 2 b ) can form between the inlet  23  of the static aircraft  11  and a point A on the tarmac T. Engines  15  located closer to the tarmac T are more prone to vortex formation than engines  15  located further from the tarmac. For example, engines  15  with a h/D value of less than approximately 2.5 tend to produce such vortices V. Engines  15  with a h/D value of greater than approximately 2.5 tend to operate without forming vortices V.  
         [0037]    [0037]FIG. 2 b  displays the engine  115  operating at an elevated power setting. At the elevated power setting, the engine  15  produces the vortex V. The vortex V can damage the engine  15  by inducing a compressor surge, by creating unstable engine operating conditions or by picking up debris.  
         [0038]    Conventionally, technicians avoided formation of the vortex V by testing the engine  15  only at power settings up to the threshold EPR. Testing the engine  15  an elevated EPR above the threshold EPR conventionally occurred in a test cell (not shown). In other words, conventional techniques required the technicians to remove the engine  15  from the aircraft  11  in order to perform an engine test at elevated EPRs.  
         [0039]    Since each engine/aircraft combination has different characteristics ( e.g. centerline height h above tarmac, inlet diameter D, nacelle shape, etc.), different threshold power settings may exist for each engine/aircraft combination. For example, a high bypass turbofan engine could have a threshold EPR of approximately of 1.25.  
         [0040]    The present invention allows technicians to test the engine  15  on the aircraft  11  at elevated EPRs above the threshold EPR. For example, the present invention could allow testing of the engine  15  at an elevated EPR of at least 1.5. In fact, the present invention could even allow testing of the engine  15  at full power. As discussed earlier, a full power setting for a typical high bypass turbofan engine  15  is approximately 1.65 EPR.  
         [0041]    The present invention allows testing at these elevated EPRs by inhibiting formation of the vortex V. FIGS.  3 - 6  display one embodiment of the present invention.  
         [0042]    The present invention comprises a ramp  101  placed between the inlet  13  and the tarmac T. The ramp  101  includes a frame  103 . The frame  103  could have any suitable construction, such as interconnected horizontal members  105 , vertical members  107  and angled members  109 . The frame  103  could be assembled in any suitable manner, such as by welding the metallic members  105 ,  107 ,  109  together.  
         [0043]    The ramp  101  includes an inclined surface  111 . The inclined surface  111  preferably extends at an angle α from the tarmac T. Preferably, the angle α is approximately 45° . However, the angle α could have any range of values that still prevent formation of the vortex V during engine operations at elevated EPRs.  
         [0044]    As seen in FIG. 4, technicians place the ramp  101  on the tarmac T adjacent the nacelle  17 . In such a location, the ramp  101  inhibits formation of the vortex V. The ramp  101  inhibits formation of the vortex V by facilitating the turning of the airflow near the tarmac T towards the engine  115 . In other words, the ramp  101  prevents the separation of the flow from the tarmac T and prevents the formation of a stagnation point.  
         [0045]    The ramp  101  has an apex  113 . Preferably, the apex  113  resides at a height w above the tarmac T. The apex  113  could have any suitable height w that inhibits formation of the vortex V. FIG. 7 displays the preferred heights for the ramp  101 .  
         [0046]    The preferred heights for the ramp  101  depend on engine geometry (namely centerline height h above the tarmac T and inlet diameter D). The figure includes an upper line U and a lower line L. The lines U, L divide the chart into three areas. The preferred height w for the ramp  101  resides in a first area A between the lines U, L. For example, FIG. 7 shows that the preferred height w for the ramp  101  used with an engine  15  having an h/D value of 1.5 can range between approximately 0.25D and 0.5D.  
         [0047]    As discussed above, engines  15  with an h/D value of greater than 2.5 tend to operate without forming vortices V. The dashed line in FIG. 7 that extends from 2.5 h/D signifies where the use of the ramp  101  is no longer necessary.  
         [0048]    The dashed line in FIG. 7 that extends from 0.5 h/D represents the lower physical limit of h/D values. An engine with a round inlet cannot have an h/D value below 0.5. At h/D values below 0.5, the engine  15  would be in contact with the tarmac T.  
         [0049]    The other two areas of the chart reside above the upper line U and below the lower line L, respectively. Sizing a ramp  111  within these areas (ie. outside of the first area A) is not preferred since the ramp  101  may be too large or too small for the engine  15 .  
         [0050]    The chart also shows that the technicians can use a given ramp  101  on several engine/aircraft arrangements. For example, FIG. 7 shows that technicians could use a ramp  101  with a height w of 0.25D on any engine/aircraft with an h/D value of between 1 and 1.5. This increases the versatility of the present invention.  
         [0051]    The ramp  101  also has a length. Preferably, the length of the ramp  101  is at least 2.5 times greater than the inlet diameter D. The length could be longer in order to increase the versatility of the ramp  101 . A longer ramp  101  can allow the technicians to use the ramp on engines (not shown) with larger or smaller inlet diameters D than the engine  15 .  
         [0052]    The present invention preferably positions the apex  113  of the ramp  101  directly beneath the inlet  23 . However, the technician could locate the apex  113  of the ramp  101  at a position fore or aft of the inlet  23  that still prevents formation of the vortex V during engine operations at elevated EPRs. For example, the technician could position the apex  113  of the ramp  101  between approximately 1.0 w fore of the inlet and 1.0 w aft of the inlet  23 .  
         [0053]    The ramp  101  is preferably a movable structure. To assist such movement, the ramp  101  could include openings  115  at the base to receive tines (not shown) of a fork lift (not shown).  
         [0054]    Other methods of moving the present invention are possible. FIG. 8 displays an alternative embodiment of the present invention showing several of these possibilities. Like ramp  101 , this embodiment comprises a ramp  201  having a frame  203 . Arms  205 ,  207  extend from the frame  203 . The arms  205 ,  207  help move the ramp  201 .  
         [0055]    For example, the technician could place a floor jack (not shown) under the arm  205  and attach a wheel assembly  209  to the ramp  201  using conventional techniques. Likewise, the technician could attach a tow ring  211  or a stabilizing jack  213  to the other arm  207 . With the tow ring  211  and wheel assembly  209 , the technicians can use an aircraft tow tractor (not shown) to move the ramp  201 . With the stabilizing jack  213  and the wheel assembly  209 , the technicians can move the ramp  201  manually.  
         [0056]    Although not shown in the figures, another alternative embodiment of the present invention is possible. For example, the ramp  301  could be formed (e.g. injection molded) with an internal chamber that receives ballast material such as water. Technicians could manually maneuver the ramp without the ballast. Once in place, the technicians add ballast to the chamber through a suitable inlet. To move the ramp, the technicians would first need to drain the ballast through a suitable outlet.  
         [0057]    Although described with particular reference to wing-mounted powerplants  13 , the present invention could used with powerplants  13  located elsewhere on the aircraft  11 . For example, the technicians could use the present invention on powerplants  13  mounted to the bottom of the fuselage of the aircraft  11 .  
         [0058]    The present invention has been described in connection with the preferred embodiments of the various figures. It is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.