Abstract:
An aircraft nacelle air intake includes a duct extending around the circumference of the air intake and elements ( 24 ) for the localized injection of hot air into the duct to make the hot air circulate in the duct along its circumference, characterized in that the injection elements ( 24 ) include a collector tank in a plane secant with the direction of the stream of air flowing through the duct including at least one hole ( 44 ) allowing the air stream flowing in the duct to pass through it and a plurality of injection orifices ( 46 ) which are connected to a hot air supply and arranged around the passage hole or around and/or between the passage holes ( 44 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an air intake of an aircraft nacelle that integrates optimized hot air injection means for frost treatment. 
     2. Description of the Related Art 
     In a known manner, as illustrated in  FIG. 1 , a propulsion system  10  of an aircraft  11 , for example connected under the wing by means of a mast  12 , comprises a nacelle  14  in which a power plant is arranged in an essentially concentric manner. The longitudinal axis of the nacelle is referenced  16 . 
     The nacelle  14  comprises an inside wall that borders a pipe with an air intake  18  at the front that makes it possible to channel the air in the direction of the power plant. 
     This invention relates more particularly to a nacelle that integrates a frost treatment process that uses hot air in contact with the inside wall of the air intake  18 , in particular hot air that is drawn off from the engine  19 . 
     According to an embodiment that is known from the documents FR-2,813,581 and U.S. Pat. No. 6,443,395, illustrated in  FIGS. 2 and 3A  and  3 B, a nacelle  14  comprises, on the inside, a partition that is called a front frame  20  that with the air intake  18  borders a pipe  22  that extends over the entire circumference of the nacelle and that has an essentially D-shaped cross-section in which the hot air circulates. 
     This pipe  22  is supplied with hot air by injection means  24 . 
     The injected hot air makes a 360° passage around the pipe  22  before being discharged. In addition to a centrifugal action, the hot air circulates more on the outer side of the air intake referenced  28  in  FIG. 2 . 
     If the means  24  for injection of hot air are placed at the lowest point of the nacelle, the de-icing capacity is not homogeneous over the circumference. It quickly increases to reach a maximum value and then gradually decreases over the rest of the circumference, with an inconsistency of frost treatment at the lowest level. 
     Because of the centrifugal action and/or the non-homogeneous aspect of the temperature over the circumference, the temperature at the inner side  30  of the air intake cannot be adequate. 
     To remedy this possible inadequacy, it is possible to inject air that is hotter and/or with a higher flow rate. 
     However, this solution is not satisfactory because it is necessary to provide high-temperature-resistant materials for the front frame, the air intake and the optional acoustic treatment coverings. This aspect tends to reduce the selection of usable materials and generally imposes the use of heavy and relatively expensive materials. 
     As illustrated in  FIGS. 3A and 3B , the injection means  24  can come in the form of a tube  32  that is perpendicular to the front frame that has one or more injection openings  34  that are oriented in the direction of circulation of the air that circulates in the pipe  22 . In this case, the injection means generate, in the stream of less hot air that circulates in the pipe  22 , a stream of just injected hot air whose boundary  36 , indicated by dotted lines in  FIGS. 3A and 3B , constitutes the exchange surface between these two air streams. 
     To improve the exchanges, a solution can consist in increasing the exchange surface by increasing the number of injection openings  34 . However, in this case, the injection means are relatively bulky and produce significant pressure drops. In addition, increasing the number of injection openings while preserving an adequate injection rate in the pipe calls for increasing the necessary flow of hot air, which leads to increasing the necessary energy for its production and therefore the consumption of the aircraft. 
     According to another aspect, the greater the difference in temperatures between the injected hot air and the less hot air that circulates in the pipe, the less these two air streams are mixed although the stream of just injected hot air tends to impact the wall of the pipe with a very high temperature. Thus, two streams are obtained, one with a temperature that is significantly higher than the temperature that is necessary for frost treatment, and a second stream whose temperature is inadequate for said treatment. 
     To limit the impact temperature of the stream of just injected hot air, the documents FR-2,813,581 and U.S. Pat. No. 6,443,395 propose placing—behind the injection means  24 —a mixer that comprises a nozzle-type tube that mixes the injected hot air with the less hot air that is already present and that circulates in the pipe  22 . This solution has the advantage of reducing the maximum value of the temperature experienced by the wall of the pipe  22  and because of the mixing makes it possible to obtain a stream of hot air with an adequate temperature for frost treatment, having a flow rate that is significantly higher than that of the stream of just injected very hot air of the prior art without a mixer. 
     However, this mixer is not entirely satisfactory because it constitutes a supplementary part in addition to the injection means that induces a supplementary on-board weight and specific maintenance. However, if the injection means are accessible because of an access flap in the bottom part of the nacelle, the mixer is offset relative to said flap, although it is not easy to inspect it and it is often necessary to remove the air intake in case of malfunction, which calls for a substantial immobilization of the aircraft. 
     SUMMARY OF THE INVENTION 
     Also, the purpose of this invention is to remedy the drawbacks of the prior art by proposing an air intake of an aircraft nacelle that uses hot air for frost treatment, integrating optimized hot air injection means. 
     For this purpose, the invention has as its object an air intake of an aircraft nacelle that comprises a pipe that extends over the circumference of said air intake and means for localized injection of hot air in said pipe providing the circulation of the hot air in the pipe along its circumference, characterized in that the injection means comprise a collector tank in a plane that is secant to the direction of the air flow that circulates in the pipe that comprises at least one hole that makes it possible for the flow of air that circulates in the pipe to pass through it and a number of injection openings that are connected to a supply of hot air and arranged around the passage hole and/or between the passage holes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Other characteristics and advantages will emerge from the following description of the invention, a description that is provided only by way of example, relative to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an aircraft nacelle, 
         FIG. 2  is a cutaway along a longitudinal plane of the front of a nacelle, 
         FIG. 3A  is a side view that illustrates hot air injection means according to an embodiment of the prior art, 
         FIG. 3B  is a side view that illustrates hot air injection means according to another embodiment of the prior art, 
         FIG. 4  is a perspective view that illustrates a part of an air intake that integrates hot air injection means according to the invention, 
         FIG. 5  is a perspective view of the injection means according to the invention, 
         FIG. 6  is a side view of the injection means according to the invention, 
         FIG. 7  is a cutaway along line VII-VII of  FIG. 6  of the hot air injection means according to the invention, 
         FIG. 8  is a cutaway along line VIII-VIII of  FIG. 6  that illustrates an injection opening of the hot air injection means according to the invention, and 
         FIG. 9  shows an aircraft, an aircraft engine and an aircraft nacelle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows an air intake  18  of an aircraft nacelle. The air intake makes it possible to channel an air flow referenced by the arrow  38  to the power plant. 
     The front part of the air intake describes an essentially circular shape that extends in a plane that can be essentially perpendicular to the longitudinal axis, or not perpendicular, with the front part that is located just before 12 o&#39;clock. However, other forms of air intake can be considered. 
     The invention relates more particularly to a nacelle that integrates a frost treatment that consists in using the hot air that is drawn off at the power plant. 
     According to one embodiment, a nacelle comprises a partition that is called a front frame  20  that with the air intake  18  borders a pipe  22  that extends over the entire circumference of the nacelle and that has a D-shaped cross-section. 
     According to one embodiment, this pipe  22  comprises means  24  for localized injection of hot air. 
     In addition, the pipe  22  comprises an exhaust  26  that can be seen in  FIG. 4 . 
     According to the illustrated example, the injection means  24  make it possible to generate a flow in the pipe  22  in the clockwise direction (as illustrated in the figures) or in the counterclockwise direction. 
     These injection means  24  can be arranged at the bottom part of the pipe. 
     The injection means  24  comprise a hot air intake tube  40  that projects relative to the front frame  20  and that is connected by any suitable means to the front frame  20  (for example, a collar), in the extension of an opening that is made in the front frame  20 , with a supply of hot air emptying out at said opening to the rear of the front frame. As a variant, the tube  40  can pass through the front frame  20  and be connected to a hot air supply. 
     The hot air supply is not presented in more detail because it is known to one skilled in the art. The hot air is preferably drawn off at the power plant and directed to the air intake using one or more pipes. 
     According to the invention that is illustrated in more detail in  FIGS. 5 to 8 , the hot air injection means  24  comprise, on the one hand, an annular pipe  42  that is connected to the tube  40 , arranged in a plane that is secant to the direction of the air that circulates in the pipe and that is placed in the pipe  22  in an essentially concentric manner, whereby said annular pipe defines a passage hole  44  for the air that circulates in the pipe, and, on the other hand, several injection openings  46  that are arranged at the periphery of the annular pipe  42  and able to inject hot air in a direction that approximately coincides with that of the air flow that circulates in the pipe  22 . 
     According to an embodiment, the annular pipe  42  is arranged in an essentially radial plane. 
     Radial plane is defined as a plane that contains the longitudinal axis  16  and a radial direction. 
     According to this configuration, just after the injection of hot air, it is noted that the stream of just injected hot air is bordered by a first line  48  whose diameter is greater than or equal to the outside diameter D of the annular pipe  42  and by a second line  50  whose diameter is less than or equal to the inside diameter d of the annular pipe  42 . 
     Thus, this configuration essentially makes it possible to increase the exchange surface between the stream of injected hot air and the stream of air that circulates in the pipe  22  without, however, increasing the space requirement of the injection means in the pipe and therefore pressure drops. 
     In a general manner, the injection means comprise a collector tank in a plane that is secant to the direction of the air flow that circulates in the pipe  22  that comprises a number of holes  44  that make it possible for the flow of air that circulates in the pipe to pass through it and a number of injection openings  46  that are connected to a supply of hot air and arranged around the passage hole or between the passage holes  44 . 
     Thus, the passage holes  44  make it possible not to increase the pressure drops too much and to generate—between the streams of hot air injected through the injection openings  46 —streams of less hot air that circulate already in the pipe, which makes it possible to increase the exchange surface between the just injected hot air and the hot air that already circulates in the pipe. 
     The variant that is presented in  FIGS. 5 to 8  constitutes a simplified variant that comprises a passage hole that makes it possible to optimize the exchange surface and the pressure drops. In addition, this solution makes it possible to optimize the number of openings so as not to increase the consumption of the aircraft. 
     According to another characteristic of the invention, certain injection openings  46  are arranged in such a way as to inject the hot air in convergent directions as illustrated in  FIG. 7 . 
     According to a preferred embodiment, the annular pipe  42  comprises four injection openings  46 , distributed uniformly over the periphery of the annular pipe, at 90°, each provided at the end with an injection pipe  52  with an essentially circular cross-section and with a length on the order of 20 mm. 
     The injection pipes  52  are oriented in such a way that the injected hot air flows are convergent to generate a perturbed and non-laminar flow that promotes the mixing between the injected hot air and the air that is already circulating in the pipe. 
     To optimize the mixing between the injected hot air and the air that already circulates in the pipe, the axes of the injection pipes  52  form an angle α of less than 20°, and preferably on the order of 10 to 15°, with the direction of the air flow that circulates in the pipe. 
     The injection pipes  52  can be oriented in such a way that the injected hot air flows form a flow that has a helical movement around the flow(s) that pass(es) through the passage holes  44 . 
     So as to improve the mixing and to remedy the disruption of flows, each injection pipe  52  has a cross-section that diminishes up to the injection opening for increasing the injection rate of the hot air flow. Thus, the injection pipes  52  have a tapered shape that diminishes up to the injection opening  46  with an angle β of less than 20° and preferably on the order of 5 to 10° as illustrated in  FIG. 8 . 
     To set an order of magnitude, the cross-section of the annular pipe is on the order of 400 mm 2 , the outside diameter of the annular pipe is on the order of 120 mm, and the inside diameter is on the order of 65 mm, with the injection openings  46  having a diameter on the order of 13 mm.