Abstract:
A mitigating system for reducing flow drag in aircraft engines uses a mitigating device attached to either the nacelle of an engine to mitigate the flow drag of the airflow moving across the nacelle. The mitigating device has an inner sleeve and an outer sleeve, each of which can be adjusted separately to extend any desired length across the inner surface or outer surface of the nacelle. As the sleeves are extended, they cover a greater number of flow drag elements thereby improving the aerodynamic properties of the aircraft engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional patent application No. 62/027,972, filed on Jul. 23, 2014, and entitled “System to Mitigate Laminar Flow Drag.” Such application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to aircraft engines, more specifically to a nacelle, which can include an inlet area, a nose cowl area, and a fan cowl area for turbine engines, and a mitigation device to be fitted over a nacelle or other areas on an aircraft in order to reduce flow drag. 
         [0003]    Flow drag not directly associated with the production of lift is referred to as parasitic drag, which is composed of drag of various aerodynamic components. Important to the current invention is skin friction drag, which is the drag on a body resulting from friction over its contact surfaces. There are mainly two cases where the flow in the boundary layer is entirely laminar or entirely turbulent over the surface. In a usual application the boundary layer is normally laminar near the leading edge of the object undergoing transition to a turbulent layer at some distance back along the surface. 
         [0004]    For an aircraft engine nacelle, it has been calculated that the critical area of concern is the first one-third of the nacelle, or 30 inches back from the leading edge where a laminar boundary layer begins to develop at the leading edge. Downstream from the leading edge the laminar boundary becomes unstable and is unable to suppress disturbances imposed on it by surface roughness or fluctuations in the free stream. Every component or element that has direct contact with airflow, including rivets, joints, seams, and fasteners, has an aerodynamic friction and can product drag. 
         [0005]    Skin gaps or irregular matching seam-surfaces and recesses often cause location transition from laminar to turbulent flow. One area of interest is gaps or joints, such as at the interface between the lipskin and nose cowl and at the interface between the nose cowl the fan cowl. Another area of concern is nacelle lipskins that have been damaged and/or repaired. This is a common occurrence and introduces new drag potential. 
         [0006]    Benefits of laminar flow come in the form of reduced friction drag. Because nacelle friction drag has been approximated to account for 4-5% of the total friction drag of the aircraft, any reduction in nacelle friction drag causes a corresponding reduction in fuel consumption and aircraft operating costs. Thus, it is desirable to maintain laminar flow over as much of the nacelle surface as possible. 
         [0007]    A number of designs exist seeking to reduce drag over a nacelle associated with irregular surfaces and joints or surface gaps. Some, such as is described in U.S. Pat. No. 2,873,931, utilize an air blowing system. Others, such as is described in U.S. Pat. No. 5,368,258, utilize a suction chamber within the nacelle. While certain of such existing designs may well benefit new engine structures, these solutions require the owner of an existing aircraft to remove nacelle parts and replace them with new complex systems, having multiple working components. While the future trend is to integrate the inlet lipskin into the nose cowl and fan cowl sections to avoid connections of separate nacelle sections, greater than 99% of all currently in-service aircraft having nacelles remain with the separate-section construction. Removing an existing nacelle and replacing it with a composite, one-piece nacelle is cost prohibitive. There is a need to provide a drag reduction device that is cost effective for existing aircraft with a design that is scalable and adaptable for multiple areas and the many sizes and shapes of aircraft nacelles and intakes. 
       BRIEF SUMMARY 
       [0008]    The present invention is directed to a system to mitigate flow drag and boundary layer separation over selected areas of the surface of an intake duct or nacelle or other areas of an aircraft by mitigating flow drag caused by interruptions in the surface of an aircraft intake or nacelle, such as, but not limited to, rivets, fasteners, joints, seams, cracks, and irregularities in surface smoothness. In certain embodiments, the invention serves to mitigate flow drag and boundary layer separation over selected areas of the inner surface or throat of an intake duct or nacelle by mitigating flow drag and boundary separations caused by interruptions in the inner surface of an aircraft intake or nacelle, such as, but not limited to, rivets, fasteners, joints, seams, cracks, and irregularities in surface smoothness. In certain embodiments, the invention serves to mitigate flow drag and boundary layer separation over selected areas of the inner surface of an intake duct or nacelle by mitigating flow drag caused by interruptions in the surface of an aircraft intake or nacelle, such as, but not limited to, rivets, fasteners, joints, seams, cracks, and irregularities in surface smoothness. In certain embodiments, the invention can be adapted to the dimensions and curvatures of existing lipskins, to cover only the lipskin when damaged and to improve the aerodynamics of same where applicable, and/or to provide a replacement for the lipskin that may be a part of an extended segment that interfaces with the nose cowl or extends farther aft on the nacelle to interface with the fan cowl or beyond. 
         [0009]    In certain embodiments, the invention serves to mitigate flow drag and boundary layer separation over selected areas of the surfaces of an intake duct or nacelle by mitigating flow drag caused by interruptions in the surfaces of an aircraft intake or nacelle, such as, but not limited to, rivets, fasteners, joints, seams, cracks, and irregularities in surface smoothness. In certain embodiments, the invention has a design based on the dimensions and curvatures of an existing lipskin, such that potential drag from rows of rivets, fasteners, and joins can be mitigated by extending aft of the lipskin edge over the interface between the lipskin and the nose cowl. 
         [0010]    In certain embodiments, the invention serves to mitigate flow drag and boundary layer separation over selected areas of the surface of an intake duct or nacelle by mitigating flow drag caused by interruptions in the surface of an aircraft intake or nacelle, such as, but not limited to, rivets, fasteners, joins, seams, cracks, and irregularities in surface smoothness, where the design of the device is based on the dimensions and curvatures of an existing lipskin. To mitigate potential drag from rows of rivets, fasteners, and joints, and at the lipskin/nose cowl and the nose cowl/fan cowl interfaces the system in certain embodiments is capable of extending aft of the lipskin edge, over the interface between the lipskin and the nose cowl and fan cowl. To mitigate further potential drag in certain embodiments the system includes a means for airflow to be directed over the lipskin/nose cowl/fan cowl interface joints. 
         [0011]    Certain embodiments of the present invention are directed to a system to mitigate flow drag and boundary layer separation that further provides a low coefficient of friction surface and/or a self-cleaning surface and/or an acoustic-absorbing material and/or a means of de-icing and/or anti-icing, such as, but not limited to, a compressor bleed air inlet, an electronic or electric heating system, and/or an anti-icing material or coating. 
         [0012]    Certain embodiments of the present invention are directed to a system to mitigate flow drag and boundary layer separation that further provides a means for and method of attaching a forward material or object, such as but not limited to an engine protection device, to the nacelle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic representation of a side view example of nacelle elements that are known to cause flow drag. 
           [0014]      FIG. 2  is a schematic representation of a side view of one preferred embodiment of the present invention. 
           [0015]      FIG. 3  is a schematic representation of a perspective view of another preferred embodiment of the present invention illustrating the system unconnected to a nacelle&#39;s lipskin. 
           [0016]      FIG. 4  is a schematic representation of a perspective view of another preferred embodiment of the present invention illustrating the system with a first connection to a nacelle&#39;s lipskin. 
           [0017]      FIG. 5  is a schematic representation of a perspective view of another preferred embodiment of the present invention illustrating the system with a first connection to a nacelle&#39;s lipskin. 
           [0018]      FIG. 6  is a schematic representation of a perspective view of another preferred embodiment of the present invention illustrating the system with a first connection to a nacelle&#39;s lipskin. 
           [0019]      FIG. 7  is a schematic representation of a perspective view of one preferred embodiment of the present invention illustrating the system&#39;s inner and outer sleeves. 
           [0020]      FIG. 8  is a schematic representation of a perspective view of one preferred embodiment of the present invention illustrating the system connected to a forward device. 
           [0021]      FIG. 9  is a schematic representation of a front perspective partial cut-away view of one embodiment of the present invention illustrating the outer and inner extended sleeves. 
           [0022]      FIG. 10  is a schematic representation of a front perspective view of one preferred embodiment of the present invention illustrating the system&#39;s inner sleeve. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The present invention is directed to a system capable of mitigating flow drag and boundary layer separation over selected areas of the surface of an intake duct or nacelle.  FIG. 1  shows a schematic representing an example of nacelle  1  segments (within square) that are known to cause flow drag, which includes the lipskin  2 , the leading edge of the lipskin  3 , the nose cowl  6 , and the fan cowl  8 . Rivets  5  are typically used to fasten the lipskin  2  to the nose cowl  6  and to fasten the nose cowl  6  to the fan cowl  8 . Other fasteners are typically used to fasten the nose cowl  6  to the fan cowl  8  on the fan cowl  8  side of the interface of the two sections. A joint  4  is caused by the interface of the lipskin  2  to the nose cowl  6  and the nose cowl  6  to the fan cowl  8 . 
         [0024]    Referring now to  FIG. 2 , a schematic representation shows a side view example of a joint  4  at the intersection of the aft end of the nose cowl  6  and the forward end of the fan cowl  8 , within the nacelle section  1 . The aft end of one preferred embodiment of the mitigating device  10  extends over and covers the section  13  of the surface of the nose cowl  6  up to a point that is just forward of the aft end of the nose cowl  6  and the forward of the fan cowl  8 . The air flow  9 , beginning at the forward end of the nacelle  1 , flows over one preferred embodiment of the mitigating device  10  and leaves the surface of the mitigating device  10  at an angle  11  which causes the air flow  9  to flow over the joint  4  and over the fastener  12  to mitigate drag caused by the fastener  12  and the joint  4 . Airflow  11  continues over the uncovered section  14  of the fan cowl  8 . 
         [0025]    Referring now to  FIG. 3 , a schematic representation shows a perspective view of a preferred embodiment of the mitigating device  10  positioned away (for clarity) from the lipskin  2 , the nose cowl  6 , the fan cowl  8 , and the thrust reverser  18 . The joints  4 ,  4   a,    4   b  are at the interface of each of those sections.  FIG. 4  shows a schematic representation of a perspective view of a preferred embodiment of the mitigating device  10  having the first connection to lipskin  2  to mitigate drag that can be caused by a damaged lipskin  2  or to improve the aerodynamic shape or surface of lipskin  2 . Any such drag will in turn affect the airflow over nose cowl  6 , fan cowl  8 , and thrust reverser  18 . In this embodiment, the mitigating device  10  does not extend over the aft edge of lipskin  2  or over joint  4 . 
         [0026]      FIG. 5  shows a schematic representation of a perspective view of a preferred embodiment of the mitigating device  10  having a first connection to lipskin  2 , extending over the aft edge of lipskin  2 , and continuing over the leading edge of nose cowl  6 . This embodiment mitigates drag that can be caused by rivets (not shown) in the aft edge of the lipskin  2  and rivets in the forward edge of nose cowl  6 . Additionally, this embodiment of the mitigating device  10  covers or mitigates drag that can be caused by the joint  4  between lipskin  2  and nose cowl  6 . The mitigating device  10  is capable of mitigating drag caused by lipskin  2 , nose cowl  6 , and join  4 , promoting the continuation of laminar flow over fan cowl  8  and thrust reverser  18 . The inner sleeve of mitigating device  10  is shown extending into the nacelle over the edge of lipskin  2  to mitigate drag from the inner rivets (not shown) and the inner interface joint  4  at the connection of lipskin  2  and nose cowl  6 . 
         [0027]    Another embodiment of the mitigating system is shown in  FIG. 6 . In this embodiment, the mitigating device  10  has a first connection at lipskin  2 , extends over the aft edge of lipskin  2 , and continues over the leading edge of nose cowl  6 . The mitigating device  10  continues farther to the aft edge of nose cowl  6  just forward of the joint  4  and the fan cowl  8 . In this embodiment the mitigating device  10  mitigates drag that can be caused by rivets (not shown) in the aft edge of lipskin  2 , at the forward edge of nose cowl  6 , and at the aft edge of nose cowl  6 . Additionally, the mitigating device  10  covers or mitigates drag that can be caused by the joint  4  between lipskin  2  and nose cowl  6 . The mitigating device  10  is also capable of mitigating drag caused by joint  4   a  between nose cowl  6  and fan cowl  8  by providing means for air flow to avoid contact with joint  4   a  and fasteners  7 , which extend circumferentially about the surface of the leading edge of fan cowl  8 . The inner sleeve of the mitigating device  10  is shown extending into the nacelle over the edge of lipskin  2  in order to mitigate drag from the inner rivets (not shown) and the inner interface joint  4  at the connection of lipskin  2  and nose cowl  6 . 
         [0028]    An additional embodiment of the mitigating system is shown in  FIG. 7 , which represents a perspective view of a preferred embodiment of the mitigating device  10  with separate outer  19  and inner  20  sleeves. The outer sleeves  19  and inner sleeves  20  are capable of being separately extended to any desired length. The inner sleeve  20  can be extended to cover potential boundary layer separations caused by rivets and seams, such as, but not limited to, the inner-nacelle interface where the lipskin is joined to the nose cowl by rivets within the inner nacelle throat. Additionally, either or both sleeves can contain or be coated or covered with specific materials, such as, but not limited to, acoustic absorbing materials. 
         [0029]    Another embodiment is shown in  FIG. 8 , which shows a schematic representation of a perspective view of a preferred embodiment of the mitigating device  10  with an outside material or device  21  attached mechanically or non-mechanically to the leading edge of the mitigating device  10 , which is attached to nacelle  1 . 
         [0030]    An additional embodiment of the mitigating system is shown in  FIG. 9  with mitigating system  10  with an extended inner sleeve  20 , which reduces drag and boundary layer separation caused by rivets  5   a  and the intersection  4   b  of the lipskin  2  and the nose cowl  6 . The mitigating system  10  may also extend farther into the throat of the nacelle to mitigate flow drag and boundary layer separation from irregular or non-flush inner surface interfaces. The outer sleeve  19  extends over the rearward section of the lipskin  2 , covering the forward-most rivets  5 , and extends over the intersection  4 , with the nose cowl  6  and further extends to cover the outer rivets  5  in the rearward section of nose cowl  6 , and extending to a position forward of the intersection  4   a  of nose cowl  6  and fan cowl  8 . The outer drag reduction system sleeve  19  reduces drag from rivets  5  on the outer surface of lipskin  2  and nose cowl  6  and confers the airflow streamline to transition over seam  4   a  and fasteners  7 , reducing drag from those drag elements. In this and other embodiments, mitigating device  10  may be connected by adhesives or other means. 
         [0031]    An additional embodiment of the mitigating system is shown in  FIG. 10 . This embodiment has an extended inner sleeve  20 , which mitigates flow drag and boundary layer separation from rivets (represented by dotted lines  5 ) and from the interface joint (represented by dotted line  4 ). The mitigating system  10  may also extend farther into the throat of the nacelle to mitigate flow drag and boundary layer separation from irregular or non-flush inner surface interfaces. 
         [0032]    In each of these various embodiments, the mitigating device  10  can extend beyond the aft outside edge of fan cowl  8  and can include portions that are removed or cutout where necessary. The mitigating device  10  is also capable of being interfaced into a nacelle, as a part or as the complete nacelle, such as, but not limited to, in an original equipment system. Still another embodiment of the mitigating device  10  can be used to replace an existing lipskin or can be used as a new lipskin where a current lipskin does not exist, such as, but not limited to, in an original equipment system. This lipskin system can interface with the nose cowl or be extended to interface with the fan cowl, or can be extended further to interface with the thrust reverser section. The mitigating system, in one embodiment, further comprises a thrust reverser section. The mitigating system is also capable of being retrofitted for existing aircraft or may be interfaced into a nacelle, as part or as the complete nacelle. 
         [0033]    The mitigating device is also capable of being a nacelle inlet protective cover that is conformed to the existing lipskin and elongated to provide means to mitigate drag and boundary layer separations arising from the interface of the lipskin and nose cowl and/or the interface of the nose cowl and the fan cowl and/or the interface of the fan cowl and thrust reverser section. The mitigating system in any of the embodiments described herein is capable of being constructed of differing high strength-to-weight materials, such as, but not limited to, metals, metal alloys and/or powders, and composites and/or polymer materials. 
         [0034]    In other embodiments, the mitigating device may be used in applications other than along the lipskin of engine nacelles, such as to cover other areas of aircraft that produce drag, including, for example, bulges along the fuselage or wings for antennas or other equipment, or along leadings edges such as wings, stabilizers, winglets, and canards. The mitigating device may be used as original equipment, as an add-on device to improve laminar flow, or as a means to cover a damaged area on an aircraft. 
         [0035]    Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any systems and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, a limited number of the exemplary systems and materials are described herein. It will be apparent to those skilled in the art that many more modifications are possible without departing from the invent concepts herein. All terms used herein should be interpreted in the broadest possible manner consistent with the context. 
         [0036]    The present invention has been described with reference to certain preferred and alternative embodiments that are intended to be exemplary only and not limited to the full scope of the present invention as set forth in the appended claims.