Abstract:
A gas turbine engine is provided with a nacelle having a hollow inner space. The inner space is utilized as a plenum for directing air from an inlet to an outlet at the upstream end of the nacelle to allow control of an effective lip width of the nacelle under certain flight conditions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention generally relates to a gas turbine engine, and more particularly to a nacelle inlet for a turbofan gas turbine engine. 
         [0002]    In an aircraft gas turbine engine, such as a turbofan engine, a fan delivers air to a compressor. The pressurized air is mixed with fuel in a combustor for generating hot combustion gases. The hot combustion gases flow downstream through a turbine stage, which extracts energy from the gas. The turbine powers the fan and compressor. 
         [0003]    Combustion gases are discharged from the turbofan engine through a core exhaust nozzle and fan air is discharged through an annular fan exhaust nozzle defined at least partially by a nacelle surrounding the core engine. A majority of propulsion thrust is provided by the pressurized fan air which is discharged through the fan exhaust nozzle, while the remaining thrust is provided from the combustion gases discharged through the core exhaust nozzle. 
         [0004]    It is known in the field of aircraft gas turbine engines that the performance on the turbofan engine varies during diverse flight conditions experienced by the aircraft. An inlet lip section located at the foremost end of the turbofan nacelle is typically designed to enable operation of the turbofan engine and prevent the separation of airflow from the inlet lip section of the nacelle during diverse flight conditions. For example, the inlet lip section requires a “thick” inlet lip section design to support operation of the turbofan during specific flight conditions, such as cross-wind conditions, take-off and the like. Disadvantageously, the “thick” inlet lip section may reduce the efficiency of the turbofan engine during other conditions, such as cruise conditions of the aircraft. 
         [0005]    Accordingly, it is desirable to optimize the performance of a turbofan gas turbine engine during diverse flight requirements to provide a nacelle having a reduced thickness, reduced weight and reduced drag. 
       SUMMARY OF THE INVENTION 
       [0006]    It has previously been proposed to selectively direct bleed air to locations adjacent the front of the nacelle to simulate a “thick” lip. At conditions when the thick lip is not necessary (e.g., cruise conditions), the bleed air is stopped. A continuous conduit captures air at a downstream end of the nacelle and delivers it to the upstream end. 
         [0007]    In a disclosed embodiment, the interior of the nacelle is utilized as a plenum for bleed air being delivered to an outlet near the upstream end of the nacelle. An inlet pipe captures air from a bypass air flow, and directs that air into the interior of the nacelle. The air is directed into the plenum, and then into an inlet passage leading to the outlet at an upstream end of the nacelle. The bleed air could also be derived from any engine stages (fan, compressor, turbine, and or customer bleed ports) and may be mixed together to control the air temperature in plenum. In one embodiment, the outlet is at an outer surface of the nacelle. In an alternative embodiment, the outlet is in an interior surface. The inlet pipe is spaced from the outlet by the plenum. 
         [0008]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  schematically shows a turbofan gas turbine engine. 
           [0010]      FIG. 2  is a cross-sectional view through a first embodiment of this invention. 
           [0011]      FIG. 3  is a view of a portion of the second embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    A gas turbine engine  10 , such as a turbofan gas turbine engine, circumferentially disposed about an engine centerline, or axial centerline axis  12  is shown in  FIG. 1 . The engine  10  includes a fan  14 , compressors  15  and  16 , a combustion section  18  and turbine rotors  23  and  25 . As is well known in the art, air compressed in the compressors  15  and  16  is mixed with fuel and burned in the combustion section  18 , and expanded at turbine rotors  23  and  25 . The air compressed in the compressor and the fuel mixture expanded in the turbine can both be referred to as a hot gas stream flow. The turbine rotors  23  and  25  include blades  20  and static airfoils or vanes  19 . This structure is shown somewhat schematically in  FIG. 1 . 
         [0013]    As shown in  FIG. 1 , a nacelle  100  surrounds the bypass air flow from the fan. A cowl  97  surrounds the interior components, and defines a bypass passage with the nacelle  100 . 
         [0014]    The nacelle  100  is shown in  FIG. 2  to be generally hollow. Of course, there are components such as a fan control belt  99  within the nacelle. However, there is open communication in the nacelle between a downstream end  101  and an upstream end  99 . In the  FIG. 2  embodiment, an aft closure  112  closes off this space to define plenum  120 . Fan cowl doors  110  are shown sealed to enclose the plenum  120 . Doors  110  may be opened for various purposes. An inlet pipe  114  has an intake  116  and a diffuser outlet  118 . Air from the bypass flow flows into the intake  116 , and out a diffuser outlet  118  into the plenum  120 . As shown in  FIG. 2 , an intake  102  for a pipe  103  directs air in the plenum to an outlet  104  at the outer periphery of the nacelle  100  at upstream end  99 . This bleed air provides an effective boundary layer control to simulate a “thick lip” for various flight conditions. The direction of air could be in the illustrated direction, the opposite direction or at any different angle to the free stream air. To achieve selective control of the flow through this section, a valve such as valve  115  may be positioned on the pipe  103 . A control  200  for achieving this selective control of the bleed air is shown schematically. A worker in the art would know when the thicker lip is desirable. 
         [0015]    Prior proposed systems for creating this bleed air have included a conduit or pipe communicating the air from the downstream end to the upstream end. By utilizing the plenum  120  to communicate the air from the inlet pipe  114  to the pipe  103 , the present invention eliminates a good deal of required piping and other plumbing structure. 
         [0016]    As shown in  FIG. 3 , in an alternative embodiment, the pipe  105  incorporates an intake  106 , and an outlet  108  that directs the air to an inner periphery of the nacelle  100 . This will energize the boundary layer to reduce or eliminate flow separation 
         [0017]    While a single inlet pipe  114 , pipe  103  and outlet  104  are illustrated, in fact, there would likely be several circumferentially spaced ones of these elements. 
         [0018]    While a single inlet pipe  104  or  105 , pipe  103  or  105  and outlet  104  or  108  are illustrated, in fact, there would likely be several circumferentially spaced ones of these elements (discreet or continuous). 
         [0019]    While several embodiments of this invention have been disclosed, a worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.