Abstract:
Integrated engine exhaust systems and techniques for operating integrated engine exhaust systems are disclosed. In one embodiment, a propulsion system includes an engine installation configured to be mounted on a wing assembly of an aircraft. The engine installation includes an engine, and an exhaust system operatively coupled to the engine. The exhaust system includes at least one nozzle to exhaust an exhaust flow from the engine. The nozzle includes a variable portion configured to vary an exit aperture of the nozzle from a first shape to a second shape to change a flowfield shape of at least a portion of the nozzle flowfield proximate the wing assembly, thereby reducing at least one of drag and thermal loading on the wing assembly. In a further embodiment, the exhaust system includes an inner nozzle that exhausts a core exhaust flow, and an outer nozzle that exhausts a secondary exhaust flow, the outer nozzle having the variable portion configured to vary the exit aperture of the outer nozzle.

Description:
This patent application is a divisional application of co-pending, commonly-owned U.S. patent application Ser. No. 11/379,971 entitled “Integrated Engine Exhaust Systems and Methods for Drag and Thermal Stress Reduction” filed Apr. 24, 2006, which application is incorporated herein by reference. 

   TECHNICAL FIELD 
   The present disclosure relates to aircraft propulsion systems, and more specifically, to integrated engine exhaust systems and methods for providing reduced drag and/or thermal stress reduction for an aircraft. 
   BACKGROUND 
   Many types of aircraft, including transport aircraft, are equipped with wing-mounted turbofan engines. In this configuration, the exhaust flow from the wing-mounted engines may impinge upon the wing surfaces. Some conventional aircraft may utilize the exhaust flow to augment wing lift during low-speed operations, enabling short field take off and landing capabilities for such aircraft. 
   Although desirable results have been achieved using existing wing-mounted turbofan engines, there is room for improvement. For example, reduced drag will enable aircraft operation from even shorter airfields. In addition, due to the impingement of the high temperature exhaust on the flap and wing surfaces of some aircraft configurations, these surfaces must be designed to withstand extreme thermal loads. Titanium flaps may be required rather than aluminum flaps to withstand the harsh thermal environment. Generally, these design considerations add weight to the aircraft and increase manufacturing costs. Novel systems that mitigate the weight and cost penalties associated with wing-mounted engines would therefore have utility. 
   SUMMARY 
   Integrated engine exhaust systems and techniques of operating integrated engine exhaust systems are disclosed. In some embodiments, methods for providing lower drag and thermal stress of an aircraft may advantageously reduce take off and landing distances, reduce aircraft weight, reduce fuel consumption, reduce production and maintenance costs, and reduce noise levels. 
   In one embodiment, a propulsion system for an aircraft includes an engine installation configured to be mounted on a wing assembly of the aircraft. The engine installation includes an engine, and an exhaust system operatively coupled to the engine. The exhaust system includes at least one nozzle configured to exhaust an exhaust flow from the engine. The nozzle includes a variable portion configured to vary an exit aperture of the nozzle from a first shape to a second shape to change the flowfield shape of at least a portion of the exhaust flowfield proximate the wing assembly to reduce at least one of drag and thermal loading on the wing assembly. In a further embodiment, the exhaust system includes an inner nozzle that exhausts a core exhaust flow, and an outer nozzle that exhausts a secondary exhaust flow, the outer nozzle having the variable portion configured to vary the exit aperture of the outer nozzle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The detailed description is described with reference to the accompanying Figures. The same reference numbers in different Figures indicate similar or identical items. 
       FIG. 1  is a partial isometric view of an aircraft in accordance with an illustrative embodiment of the disclosure. 
       FIG. 2  is an enlarged isometric view of an exhaust system of the aircraft of  FIG. 1  operating in a conventional mode of operation. 
       FIG. 3  is an enlarged isometric view of an exhaust system of the aircraft of  FIG. 1  operating in a representative non-conventional mode of operation in accordance with an illustrative embodiment of the disclosure. 
       FIG. 4  is an isometric view of the exhaust system operating in the conventional mode of operation as shown in  FIG. 2  including a cutaway view of an exhaust flowfield. 
       FIG. 5  is an isometric view of the exhaust system operating in the non-conventional mode of operation as shown in  FIG. 3  including a cutaway view of the exhaust flowfield. 
       FIG. 6  is an isometric view of the exhaust flowfield of  FIG. 4  and an impingement pattern on a wing assembly for the exhaust system operating in the conventional mode of operation. 
       FIG. 7  is an isometric view of the exhaust flowfield of  FIG. 5  and an impingement pattern on the wing assembly for the exhaust system operating in the representative non-conventional mode of operation. 
       FIG. 8  shows the effect of engine exhaust on span load distribution in accordance with an illustrative embodiment of the disclosure. 
       FIG. 9  is a lower elevational view of a wing temperature distribution of the exhaust system operating in the conventional mode of operation as shown in  FIG. 2 . 
       FIG. 10  is a lower elevational view of a wing temperature distribution of the exhaust system operating in the non-conventional mode of operation as shown in  FIG. 3 . 
       FIGS. 11 and 12  are isometric views of aircraft exhaust systems in accordance with alternate embodiments of the disclosure. 
   

   DETAILED DESCRIPTION 
   Techniques for operating integrated engine exhaust systems may advantageously lower drag and thermal stress on an aircraft. Many specific details of certain embodiments are set forth in the following description and in  FIGS. 1-12  to provide a thorough understanding of such embodiments. The present disclosure, however, may have additional embodiments, or may be practiced without one or more of the details described below. Although the methods described herein are illustrated using an aircraft in exemplary embodiments, it should be appreciated that the techniques described herein may be applied to a variety of vehicles such as automobiles, maritime vessels, helicopters, spacecraft, trains, etc. 
   Techniques of operating integrated engine exhaust systems may advantageously reduce aerodynamic drag, weight, and production and maintenance costs of aircraft having coupled propulsion and high-lift (or powered-lift) systems. In general, embodiments of the integrated engine exhaust system described herein utilizes a variable shape fan exhaust nozzle to control exhaust flow field shape during operation. The resulting exhaust flowfield (including one or both of an outer flowfield and an inner flowfield) affects the wing spanload, resulting in less induced drag and reduced thermal stresses on the wing assembly. 
     FIG. 1  is a partial isometric view of an aircraft  100  in accordance with an illustrative embodiment of the disclosure. The aircraft  100  includes a fuselage  102  and a wing assembly  104  that includes a main wing portion  106 . A slat portion  108  extends along a leading edge of the main wing portion  106 , and a flap portion  110  extends along a trailing edge of the main wing portion  106 . 
   The aircraft  100  further includes an engine installation  120  coupled to the wing assembly  104  by a pylori  112 . The engine installation  120  includes an engine nacelle  122 , and an exhaust system  124  situated at a downstream (or aft) end portion of the engine installation  120 . Any suitable turbofan engines may be employed, including, for example, those engines manufactured by General Electric of Fairfield, Conn., Pratt &amp; Whitney of East Hartford, Conn., and Rolls-Royce of London, U.K. 
     FIG. 2  is an enlarged isometric view of the exhaust system  124  of  FIG. 1 . The exhaust system  124  includes an inner nozzle  126  configured to exhaust a core exhaust flow from a combustor portion of the engine installation  120 , and an outer nozzle  128  disposed about the inner nozzle  126  and located proximate a trailing edge portion of the engine nacelle  122 . As illustrated in  FIG. 2 , the inner nozzle  126  may be elongated in comparison with the outer nozzle  128 . The outer nozzle  128  is configured to exhaust a relatively-cooler fan flow passing through the engine installation  120 . This type of nozzle is referred to as a separate flow nozzle. 
   In an alternative embodiment of the exhaust system  124 , the outer nozzle  128  may be an outer fan nozzle and the inner nozzle  126  may be a short core nozzle buried inside of the outer fan nozzle. This type of alternative nozzle is referred to as a mixed flow nozzle. 
   With continued reference to  FIG. 1 , the outer nozzle  128  may adjusted controllably to provide changes in the shape of its exit aperture. For example, as shown in  FIG. 2 , in a conventional mode of operation  130 , the outer nozzle  128  has a circular-shaped exit aperture. In cooperation with the outer surface of the inner nozzle  126 , the outer nozzle  128  forms an annular-shaped nozzle exit  132  for exhausting the fan flow in the conventional mode of operation  130 . 
   In some embodiments, the shape of the exit aperture of the outer nozzle  128  may be adjusted to a non-circular shape.  FIG. 3  shows the exhaust system  120  in a non-conventional mode of operation  134 . In this embodiment, the exit aperture of the outer nozzle  128  includes a flattened upper portion  136 , while the remainder of the exit aperture is modified such that the exit area is the same as the exit area of the conventional nozzle. Keeping the area of the exit aperture of the non-conventional nozzle the same as that of the conventional engine ensures similar engine thrust levels and maintain engine cycle compatibility. Thus, the inner and outer nozzles  126 ,  128  cooperatively form a non-annular nozzle exit  138  for exhausting the fan flow in the non-conventional mode of operation  134 . In one particular embodiment, for example, in the non-conventional mode of operation  134 , a separation distance between the inner nozzle  126  and the flattened upper portion  136  of the outer nozzle  128  is reduced to one-half (50%) of the corresponding separation distance between the inner and outer nozzles  126 ,  128  in the conventional mode of operation  130 . 
   The outer nozzle  128  may employ a variety of mechanisms to achieve the desired variation in shape of the exit aperture. For example, in one embodiment, the outer nozzle  128  includes a plurality of flaps which collectively form the exit aperture. The flaps may be controllably adjusted by a set of actuators that enable the exit aperture of the outer nozzle  128  to be adjusted to a non-circular shape. The plurality of flaps may be controllably actuated by any known means, including hydraulic, electric, or shape-memory-alloy (SMA) actuation. More specifically, the plurality of flaps and associated actuation systems of the outer nozzle  128  may include, for example, any of those systems and methods generally disclosed in U.S. Pat. No. 7,004,047 B2 issued to Rey et al., U.S. Pat. No. 5,893,518 issued to Bruchez et al., U.S. Pat. No. 5,245,823 issued to Barcza, U.S. Pat. No. 4,994,660 issued to Hauer, U.S. Pat. No. 4,245,787 issued to Freid, U.S. Pat. No. 4,000,610 issued to Nash et al., and in published U.S. patent application Ser. No. 11/014,232 by Webster, and U.S. patent application Ser. No. 11/049,920 by Rey et al. 
     FIG. 4  is an isometric view of the exhaust system  124  operating in the conventional mode of operation  130  ( FIG. 2 ), including a cutaway view of an exhaust flowfield  400 . In the conventional mode of operation  130 , the exit aperture of the outer nozzle  128  is circular, and the exhaust flowfield  400  is generally axisymmetric. An annularly-shaped fan flow  402  emanates from the outer nozzle  128  and is disposed about a central, approximately axisymmetric core flow  404  that emanates from the inner nozzle  126 . 
   For comparison,  FIG. 5  is an isometric view of the exhaust system  124  operating in the non-conventional mode of operation  134  ( FIG. 3 ), including a cutaway view of an exhaust flowfield  500 . In the non-conventional mode of operation  134 , the exit aperture of the outer nozzle  128  is non-circular and includes the flattened upper portion  136 . Consequently, the exhaust flowfield  500  is non-axisymmetric with a non-annular fan flow  502  emanating from the outer nozzle  128  and disposed about an approximately axisymmetric core flow  504  emanating from the inner nozzle  126 . As shown in  FIG. 5 , an upper portion  506  of the non-conventional exhaust flowfield  500  is varied in shape and less concentrated than a comparable upper portion  406  of the axisymmetric, conventional exhaust flowfield  400  shown in  FIG. 4 . 
     FIG. 6  is an isometric view of the exhaust flowfield (shown by Mach number)  400  of  FIG. 4 , and a pressure distribution  600  on the wing assembly  104 , for the exhaust system  124  operating in the conventional mode of operation  130  ( FIG. 2 ). Similarly,  FIG. 7  is an isometric view of the exhaust flowfield (shown by Mach number)  500  ( FIG. 5 ) and pressure distribution  700  for the exhaust system  124  operating in the non-conventional mode of operation  134  ( FIG. 3 ). Comparison of the pressure distributions  600 ,  700  shown in  FIGS. 6 and 7  shows that in the non-conventional mode of operation  134 , the exhaust flowfield  500  results in a more uniform pressure distribution on the flap portion  110  of the wing assembly  104  in comparison with the conventional exhaust flowfield  400 . More specifically, in this embodiment, the pressure distribution  600  for the conventional mode of operation  130  ( FIG. 6 ) is marked by a relatively concentrated pressure pattern having a central, relatively-higher peak pressure value (shown as a central dark region). On the other hand, the pressure distribution  700  for the non-conventional mode of operation  134  exhibits a relatively less-concentrated pressure pattern with a relatively-lower peak pressure value (shown as a central, relatively-lighter region). Consequently, there is a smoother spanload distribution and a reduction in induced drag on the wing assembly  104  in the non-conventional mode of operation  134 . 
     FIG. 8  shows the effect of variation of the shape of the engine exhaust on span load distribution in accordance with an illustrative embodiment of the disclosure. More specifically,  FIG. 8  shows a graph  1200  of sectional lift versus spanwise position along the wing. A first lift distribution  1202  shows predicted drag data (in terms of the Oswald efficiency factor “e”) for the exhaust system  124  operating in the conventional mode of operation  130  ( FIG. 2 ), and a second load distribution  1204  shows predicted drag data for the exhaust system  124  operating in the non-conventional mode of operation  134  ( FIG. 3 ). As shown in  FIG. 8 , the non-conventional mode of operation  134  provides a more favorable load distribution than the conventional mode of operation  130  due to its relatively less-concentrated pressure pattern with a relatively-lower peak pressure value. For a twin engine aircraft, the predicted aerodynamic efficiency due to the variable fan exhaust increases by about 10% relative to the conventional axisymmetric configuration. This efficiency is proportionately related to the induced component of the drag. Thus, a significant reduction in total drag may be realized since the induced drag is the largest component of airplane drag, including during high lift conditions. Proportionately larger gains in aerodynamic efficiency may be realized from a four-engine aircraft. Reduced total drag translates to reduced required engine power, and hence, it leads to shorter take off distance. 
     FIGS. 9 and 10  show wing temperature distributions  800 ,  900  for the exhaust system  124  operating in conventional and non-conventional modes of operation  130 ,  134 , respectively. Comparison of the wing temperature distributions  800 ,  900  shown in  FIGS. 9 and 10  shows that in the non-conventional mode of operation  134 , the exhaust flowfield  500  results in lower temperatures on the flap portion  110  of the wing in comparison with the conventional exhaust flowfield  400 . More specifically, in this embodiment, the temperature distribution  800  for the conventional mode of operation  130  ( FIG. 9 ) exhibits a relatively concentrated temperature pattern having a central, relatively-higher peak temperature value (shown as a central dark region). On the other hand, the temperature distribution  900  for the non-conventional mode of operation  134  exhibits a relatively less-concentrated temperature pattern with a relatively-lower peak temperature value (shown as a central, relatively-lighter region). Consequently, there is less thermal load on the wing assembly  104  in the non-conventional mode of operation  134 . 
   Embodiments of the disclosure may provide significant advantages over the prior art. By exploiting the interaction of the non-circular fan exhaust with the surrounding flow passing over the engine nacelle and with the engine core exhaust, embodiments of the disclosure alter the turbulent mixing of the exhaust flow such that the nozzle flowfield interaction with the wing and flap surfaces results in smoother pressure increment and reduced temperature in comparison with the conventional flowfield impingement. Thus, embodiments of the disclosure may be used to tune wingspan load distributions, reduce induced drag, enhance jet mixing, and accelerate temperature decay. 
   The economical and operational impacts of the drag reduction afforded by the disclosure may be substantial, and may allow the use of smaller engines or shorter runways. Reduced engine size may, in turn, lead to reduced aircraft weight, reduced fuel consumption, reduced maintenance costs and reduced noise levels. Similarly, the reduction in structural temperature limits may allow the use of aluminum flaps rather than titanium flaps, which leads to reduced production costs and reduced aircraft weight. 
   It will be appreciated that a variety of alternate embodiments may be conceived. In the following discussion of alternate embodiments, components which remain unchanged from the previously described embodiments are designated with like reference numerals. For the sake of brevity, only substantial structural and operational differences from the previously-discussed embodiments will be described. 
     FIG. 11  shows an isometric view of an aircraft exhaust system  1024  in accordance with an alternate embodiment of the disclosure. In this embodiment, in a non-conventional operating mode  1034 , an outer nozzle  1028  of the exhaust system  1024  includes both a flattened upper portion  1036  and a flattened lower portion  1038 . The resulting exit aperture of the outer nozzle  1028  is a non-circular shape disposed about the axisymmetric inner nozzle  126 . Consequently, the resulting non-conventional exhaust flowfield (not shown) is varied in shape proximate to the wing assembly, and less concentrated (e.g. having relatively-lower peak pressure and temperature values at the surfaces of the wing assembly  104 ) than the comparable upper portion  406  of the axisymmetric, conventional exhaust flowfield  400  shown in  FIG. 4 . 
   Similarly,  FIG. 12  shows an isometric view of an aircraft exhaust system  1124  in accordance with another alternate embodiment of the disclosure. In a non-conventional operating mode  1134 , an outer nozzle  1128  of the exhaust system  1124  is controllably positioned into an approximately elliptical shape with a vertical minor axis. Again, the resulting non-conventional exhaust flowfield (not shown) is varied in shape and less concentrated (e.g. having relatively-lower peak pressure and temperature values at the surfaces of the wing assembly  104 ) than the comparable upper portion  406  of the axisymmetric, conventional exhaust flowfield  400  shown in  FIG. 4 . Thus, the advantages of reduced drag and reduced thermal loads, as described more fully above, may be achieved using a variety of alternate exhaust system embodiments. 
   CONCLUSION 
   While embodiments of the disclosure have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the disclosure. Accordingly, the scope of the disclosure is not limited by the disclosure of these embodiments. Instead, the disclosure should be determined entirely by reference to the claims that follow.