Patent Publication Number: US-6705569-B1

Title: Axi-symmetric mixed compression inlet with variable geometry centerbody

Description:
This application is a continuation of U.S. patent application Ser. No. 09/397,393 filed on Sep. 16, 1999, now U.S. Pat. No. 6,276,632, which claimed the benefit of U.S. provisional application Ser. No. 60/100,485 filed on Sep. 16, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to aircraft engine inlets, and more particularly, to variable area inlets for supersonic and subsonic aircraft. 
     BACKGROUND OF THE INVENTION 
     A supersonic inlet is a sub-component of an aircraft propulsion system for high speed supersonic aircraft. The supersonic inlet should be designed to efficiently decelerate the approaching high speed airflow to speeds that are compatible with efficient turbojet engine operation and to provide optimum matching of inlet and engine airflow requirements. Entrance airflow speeds to existing airbreathing engines must be subsonic; therefore, it is necessary to decelerate the airflow speed during supersonic flight. Typically, engine entrance Mach numbers for supersonic propulsion systems are 0.3 to 0.4. The inlet must reduce the velocity of the approaching airflow to these subsonic levels while maintaining a minimum of loss in freestream total pressure and while maintaining a near uniform flow profile at the engine entrance. In addition, it is essential that the inlet diffuse the air in a manner to minimize the pressure losses, cowl and additive drag, and flow distortion. 
     Prior art mixed compression inlets designed for supersonic cruise conditions have not been able to achieve high performance, reduced weight and mechanical complexity, as well as supply the large amount of engine airflow required for transonic conditions and takeoff conditions. The inlet must also have a wide range of operability where safety is an important consideration in order to ensure that the inlet will absorb airflow disturbances that can trigger an inlet unstart, which is a potentially dangerous condition which occurs when the normal shock moves out of the inlet duct to a position upstream of the cowl lip, and results in a rapid decrease in flight speed and engine power. Thus prior art inlets have generally traded off one or more important performance parameters at the expense of another. For example, the traditional “translating centerbody” (TCB) axisymmetric inlet has a narrow operability margin and is limited in its transonic airflow capability. Another type of mixed compression inlet known as the “variable diameter axisymmetric centerbody” (VDC) inlet is very mechanically complex and may result in high maintenance or manufacturing costs. A third type of mixed compression inlet referred to as a “two-dimensional” (2D) inlet is heavy and may impose an integration drag penalty when compared to the axisymmetric designs. 
     Thus it is desired to have a new and improved inlet design which provides the high performance, required transonic airflow, while maintaining an acceptable operability margin for external disturbances. 
     SUMMARY OF THE INVENTION 
     The present invention provides an inlet with a new variable geometry scheme that enables a breakthrough in axisymmetric inlet design and offers a large transonic flow capability while maintaining adequate operability margin and high performance at cruise conditions. 
     The invention provides in one aspect an inlet for use in an aircraft comprising an axisymetric centerbody comprising an inner annular wall and a curved exterior surface of varying height along a longitudinal axis of the centerbody. A cowl partially encloses the centerbody and forms a duct therebetween. The centerbody further includes one or more slots, with each slot having an end wall extending radially upward from the inner annular wall of the centerbody and an upper wall extending from the end wall forming an interior cavity within the slot. The centerbody additionally includes one or more segments slidably mounted upon the inner wall of the centerbody and positioned for reception into the interior cavity of an adjacent slot, wherein a longitudinal channel is formed when the segment is slidably positioned within the slot. 
     The invention provides in another aspect an inlet for use in an aircraft comprising a translating axisymetric centerbody having a curved exterior surface of varying height along a longitudinal axis of the centerbody, and a cowl mounted about the centerbody and forming an annular duct therein. The centerbody further includes one or more channels formed on the periphery of the centerbody, with each channel having opposed sidewalls extending longitudinally along the centerbody and a bottom wall connecting the sidewalls. The centerbody further includes one or more slidable segments for insertion into a respective channel, each of the segments having a first portion having a first end hinged to a stationary section of the inlet and a second portion rotatably connected to the first portion and slidably mounted within opposed grooves of the channel sidewall so that when the inlet centerbody translates foreward the segments slide within the grooves exposing the channels. 
     The invention provides in yet another aspect an inlet for use in an aircraft comprising an axisymetric centerbody having a curved exterior surface of varying height along a longitudinal axis of the centerbody and a cowl mounted about the centerbody and forming an annular duct therein. The centerbody further includes one or more channels formed on the periphery of the centerbody, with each channel having opposed sidewalls extending longitudinally along the centerbody and a bottom wall connecting the sidewalls. The centerbody further includes one or more slidable segments for insertion into a respective channel, each of the segments having a first portion having a first end hinged to a stationary section of the inlet, and a second portion rotatably connected to the first portion and slidably mounted within opposed grooves of the channel sidewall so that the channel is exposed when the segments slide within the grooves. 
    
    
     DESCRIPTION OF THE FIGURES 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIGS. 1A and 1B illustrate an isometric cut-away view of the inlet of the present invention with the indexing segments shown retracted in FIG.  1 A and the indexing segments shown closed in FIG. 1B; 
     FIG. 2 is a cross-sectional view of the inlet as shown in FIG. 1; 
     FIG. 3A is a cross-sectional view in the direction A—A of the inlet as shown in FIG. 2, and which shows the indexing segments rotated into the off-design Mach number configuration; 
     FIG. 3B is a cross-sectional view in the direction A—A of the inlet as shown in FIG. 2, and which shows the indexing segments rotated into the on-design Mach number configuration; 
     FIG. 4A is a cross-sectional view in the direction A—A of the inlet as shown in FIG. 2, and which shows one of the typical hydraulic actuator systems for rotating the indexing segments into the off-design Mach number configuration; 
     FIG. 4B is a cross-sectional view in the direction A—A of the inlet as shown in FIG. 2, and which shows one of the typical hydraulic actuator systems in which the indexing segments have been rotated into the on-design Mach number configuration; 
     FIG. 4C is a perspective view of the slide bar and slide components of the hydraulic actuator system of the present invention; 
     FIG. 4D is a perspective view of an indexing segment; 
     FIG. 4E is a cross-sectional view in the direction B—B of FIG. 4B illustrating the segment  70  positioned within a groove of the centerbody inner wall  64 ; 
     FIG. 5 is another embodiment of a drive system for actuation of the segments  70 ; 
     FIG. 6 illustrates engine weight flow versus Mach number for the inlet of the invention; 
     FIGS. 7A and 7B illustrate a perspective view of an alternative embodiment of the inlet system having sliding index segments in the closed position in FIG.  7 A and the open position in FIG. 7B; 
     FIG. 7C is a cross-sectional view of a channel of the inlet system showing the slider segments at varying heights; 
     FIG. 8 illustrates engine weight flow versus Mach number for the inlet of the invention having sliding segments; 
     FIG. 9 is a prior art cross-sectional view of a typical subsonic inlet; 
     FIG. 10 is a subsonic inlet of the present invention shown with two indexing segments; and 
     FIGS. 11A and 11B illustrate cross-sectional views of the subsonic inlet shown in FIG. 10 in which the indexing segments have been rotated into the “unrotated” and “rotated” positions, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As illustrated in FIGS. 1-7, the present invention provides a revolutionary new axi-symmetric inlet and actuation system for a supersonic propulsion system. The present invention provides a unique mixed-compression inlet with very high performance, increased safety by maintaining large operability margins, reduced weight and complexity, and a large transonic airflow capability. As shown in FIG. 1, the mixed-compression inlet system  10  of the present invention comprises an axisymmetric cowl  20  (a section of which has been cutaway for illustration purposes) that partially encloses an axisymmetric centerbody  30 . The annular cowl  20  further includes a lip  22  formed at the leading edge, and inner and outer walls  24 , 26 . The inner wall  24  of the cowl  20  together with the exterior wall  36  of the centerbody  30  form an annular duct  38  of varying cross-sectional area. The cross sectional area of the duct  38  is preferably sized for isentropic compression to the inlet throat. While the invention as described may be utilized with any type of mixed compression inlet, it is preferred for supersonic cruise applications that the aerodynamic design of the inlet  10  employ a moderate amount of internal supersonic compression in the range of about 40-60 percent. Thus it is preferred for supersonic cruise applications that the supersonic compression system of the inlet have a canceled shock at the inlet shoulder with distributed internal compression similar to a 60-40 mixed compression inlet in order to achieve the necessary on-design performance, operability, and required engine airflow at transonic conditions. 
     The centerbody  30  further comprises a cone shaped nose portion  32  and a contoured body section  34  which has been shaped in order to provide a desired area ratio profile for a given application. The centerbody  30  may be stationary, although it is preferred that the centerbody  30  be capable of translating fore arid aft upon demand. FIG. 2 illustrates a hydraulic actuation system  40  that may be used to translate the entire centerbody  30  fore and aft. The centerbody actuation system  40  is preferably mounted within a hollow support tube  42  of the centerbody  30 . The hollow support tube  42  is affixed to the cowl  20  via support struts  44 , and is preferably hollow to allow centerbody bleed to be ducted to the centerbody support struts that provide a passageway for the bleed to exit overboard (not shown). The inlet centerbody  30  is affixed to slidable support struts  38 . A first end  39  of the support struts are affixed to the interior of the inlet centerbody  30 , while a second end  37  has an annular flange which is in sliding engagement with the support tube  42 . Thus when it is desired to translate the entire centerbody  30  foreword relative to the stationary cowl  20 , the actuator  40  is actuated, resulting in linkage arm  43  which is connected to the internal nose portion of the centerbody to be translated forward in desired increments. As the centerbody translates forward, the annular flanges  37  of the support struts  38  slide forward upon the support tube  42  until the linkage arm is fully extended. Thus the centerbody  30  may translate a distance X as referenced in FIG.  2 . It should be readily apparent to those skilled in the art that other actuation systems may be utilized to translate the centerbody  30  fore and aft, and that the invention is not limited to the above description. 
     As shown in FIGS. 1A and 1B, the centerbody  30  further comprises one or more indexing grooves or channels  50  that provide increased airflow area through the inlet duct  38 . These grooves or channels  50  are located on the outer periphery of the centerbody  30  with the longitudinal axis of the channels  50  aligned with the longitudinal axis of the centerbody. FIGS. 1A and 3A illustrate the channels in a fully open position and FIGS. 1B and 3B illustrate the channels  50  in a fully closed position. As shown in the FIGS. and particularly  3 A, three equally spaced channels are shown for illustrative purposes, although one or more channels would work for the invention. Although not shown in the FIGS., fences could be added along the upper edge of the flow channel to prevent airflow migration from the original centerbody surface over into the airflow channels  50 . 
     The centerbody  30  further comprises one or more stationary arcuate slots  60  having an outer or upper curved wall  62  which is flush with the outer surface of the centerbody  36 , and an inner annular wall  64 . Although the floor or inner wall  64  of the opened channel  50  is shown in the FIG. 1A as a planar surface, this surface could be longitudinally contoured (e.g., arc or sine wave) to provide a smoother transitioning from the original centerbody surface  34  than the abrupt turn at the entrance to the channel  50  that is indicated in the figures. Each arcuate slot  60  further includes an end wall  66  joining the outer and inner walls  62 , 64  with an open end  64  opposite the end wall  66 . The arcuate slot  60  has an arcuate shaped interior cavity aligned to receive a mating arcuate segment  70  therein. The arcuate segment  70  includes curved upper and lower walls  72 , 74  joined by end wall  76 . As explained further below, the arcuate segments  70  may be actuated into the “off design” or “open” position as shown in FIG. 3A from the “design” position or closed position as shown in FIG.  3 B. The arcuate segments  70  are affixed to a rotatable ring  80 , which is contained within and mounted to the inner wall  64 . The segments  70  are attached by tabs  78  to the ring  80 , wherein the tabs  78  are positioned within grooves (not shown) of the inner wall  76  such that when the ring  80  rotates, the segments  70  rotate in kind. When the arcuate segments  70  are actuated or rotated towards the open position, the indexing channels are formed by end walls  66  of arcuate slots  60 , inner wall  64  and end walls  76  of arcuate segments  70 . Thus the arcuate segments  70  may be indexed into position as desired in order to control the width of the channel  50  and hence the additional cross sectional area of the duct  38 . Although the shape of the segment  70  and slot  60  have been described above as preferably arcuate, the invention is not limited to this particular shape, as virtually any shape would work for the invention. 
     FIGS. 3A through 4D present actuation systems for use in precisely positioning or articulating the centerbody segments  70  into the slots  60  in order to form the channel  50  for design and off-design flight configurations. The off-design centerbody configuration is shown in FIG. 3A, and the on design centerbody configuration is shown in FIG.  3 B. As shown in the figures, a simple mechanical hydraulic actuator  90  is used to rotate inner ring  80 . The hydraulic cylinder is attached by a bracket  82  to the fixed centerbody hardware inner wall  64  and to the rotating inner ring  80  by tabs  84 . An extension  92  of the actuator  90  causes rotation of the inner ring  80  which in turn causes rotation of the segments  70  which results in the formation of the channels  50  for increased airflow ducting cross-sectional area. In this embodiment, only one simple linear hydraulic actuator is needed to effect rotation of all of the segments  70 . 
     FIGS. 4A through 4E present an alternate embodiment of an actuation system  100  using a multiple cylinder drive system. In FIGS. 4A and 4B, an actuation system  100  is shown for only one indexing segment. This arrangement would be duplicated in the other segments. For this indexing segment actuation system, multiple hydraulic actuators are used to provide rotation of each segment. One of these actuators is a telescoping hydraulic cylinder  102  which has a first end which is attached to a fixed wall bracket  104  which is mounted on the end wall  66  of the slot  60 . The other end of the actuator  102  is attached to a slide  110  at a common pin  112  station with a left end of another actuator  114 . This actuator  114  has a second end which is secured to the interior end wall  76  of the indexing segment  70  via bracket  116 . Therefore, as the actuators retract, they pull bracket  116  and consequently the indexing centerbody segment  70  toward the other fixed bracket  104 . The position of the slide  110  which is slidably mounted on a slide bar  120 , depends on the length of the right actuator  114 . The right actuator  114  could be retracted and then the left actuator, the reverse of this sequence, or any combination of the two. When the two actuators of this system are retracted, the end result provides the configuration as shown in FIG. 4A for the off design condition. The movement of the slide  110  on the slide bar  120  is evident in a comparison of FIGS. 4A and 4B. The two actuators  102  and  114  and the slide bar/slide ( 110  and  120 ) arrangement basically allows linear actuation to be used for circumferential movement of the centerbody segments  70 . This actuation scheme also provides the capability to utilize a larger diameter centerbody support tube  42  than for the system of FIG.  3 . Isometrics of the slide  120  and slide bar  110  are shown in FIG.  4 C. Referring back to FIG. 4B, a retaining system to hold the indexing segments  70  is not shown. However, refer to the cross-section indication B—B in the FIG. The indexing segment  70  and this cross-section (B—B) are shown in FIGS. 4D and E. In FIG. 4D, an isometric of the indexing segment  70  is shown. Located on the interior wall  74  of this segment is one or more rails  130  that makes up part of the B—B cross-section shown in FIG.  4 E. This rail  130  has a flanged end which is retained within a circumferential groove  132  located in the fixed centerbody inner wall  64  to keep the segment  70  located at the same longitudinal location while allowing the segment  70  to slide within the groove  132  of the inner wall  64 . 
     In yet another embodiment of the actuation system as shown in FIG. 5, the above described hydraulic actuators could be replaced by another type of drive system such as a motor (not shown) which drives one or more gears  140  to mesh with similar gear teeth cut into the inner circumference of ring  80 . It is important to note that for all the above described actuation systems, the centerbody  30  may be translated fore and aft in combination with the rotation of the segments  70  into their desired position. 
     The operation of the inlet system can now be described. At takeoff conditions, the centerbody is preferably translated foreward and the centerbody segments  70  are fully rotated into their respective mating slots  60  forming the open channels, which results in an increased throat area of the inlet  10 . This increased throat area is desirable at takeoff conditions and transonic flight speeds where the engine demands a large amount of airflow, as well as all unstarted inlet conditions. The centerbody segments  70  are rotated back into position in order to close off the channels at a flight speed near the starting Mach number for the inlet  10 . The centerbody segments  70  remain closed (no channel) for all inlet started conditions. Once the inlet is started, the inlet centerbody  30  is translated aft for all high speed conditions and may be adjusted to help inlet/engine airflow matching for all started conditions. 
     FIG. 6 shows typical inlet-engine airflow matching curves for the intended operation of the indexing centerbody inlet. The engine airflow schedule is denoted by the solid black line. The dashed arrows represent the inlet airflow supply schedule for the indexing centerbody configuration. Centerbody translation provides the change in airflow from cruise down to the Mach number where the centerbody is indexed to the off-design position. At this Mach number, inlet flow is abruptly increased as the segments are rotated to the open position. Any excess flow supplied by the inlet between the indexing Mach number and transonic is exhausted overboard through the inlet bypass system (denoted by the shaded area on the figure). The Mach number at which the indexing segments are rotated to the open position is determined by the amount of area variation that can be effected by centerbody translation. In general, available area variation from translation increases with increasing amounts of internal area contraction. Thus, the three vertical arrows represent three inlet configurations with increasing amounts of internal compression varying from right to left, as indicated on the figure. While it may be desirable to operate the indexing centerbody segments at positions in between the “open” and “closed” positions and more closely match the engine airflow schedule, at some point the channels  50  will become too narrow to effectively pass the desired flow. It may be desirable to operate the indexing segments  70  at two or more intermediate positions, thus increasing the flow area in a stepwise fashion. 
     An alternate embodiment of the inlet system  10  is presented in FIGS. 7A through 7C. This alternate variable geometry design incorporates sliding centerbody segments which gradually reveal a channel underneath as the centerbody is translated forward. This embodiment results in an improved inlet/engine airflow matching as described in more detail, below. As shown in FIG. 7A and 7B, the centerbody  30  comprises one or more sliding segments  200  which have a long slender rectangular shape although other shapes may work for the invention. It is preferred that the segments have a curved cross-sectional shape to match the curvature of the centerbody surface and a constant width W, a length L and a depth D. The segment  200  comprises a first portion  210  which has an end  212  hinged to the non-translating portion of the centerbody to allow the segment to raise and lower. The first portion  210  is connected to a first end  222  of a second portion  220  by a hinge and pin (not shown). The ends of the pin are mounted within guide grooves  230 . The grooves are shaped or curved to allow the desired trajectory or path of the segments as they are slid aft and downward as the centerbody translates foreward. In addition, the second end  224  has a pinned end which is received within longitudinal grooves  225 . FIG. 7A illustrates the segment  200  in the closed position wherein the first and second portions are flush with the surface  36  of the centerbody  30  such that no portion of the underlying channel  300  is revealed. As the centerbody  30  is translated forward, the end  212  of the first portion  210  of the segment  200  remains stationary (no translation) in position. Hinge pins located in the ends  222 , 224  of the second portion  220  are slid in the guide grooves  230 , 225  resulting in channel  300  being exposed as shown in FIG.  7 B. Channel  300  has a floor  310  (shaded for clarity) of preferably constant width and sidewalls  320  of varying height. The crosssectional shape of the channel is preferably rectangular, although other shapes would work for the invention. FIG. 7C illustrates a cross-sectional view of the channel  300  with the segment  200  shown at varying channel heights. For example at cruise conditions, the segments  200  are positioned flush with the surface of the centerbody  30  in order to close the channels  300  as shown in FIG.  7 A. As the centerbody is translated forward, the segments  200  are slid backward resulting in a decrease in channel height and an increase in exposed channel length. When the centerbody  30  is fully translated forward, the segments  200  rest upon the floor  310  of the channel  300 . In summary, as the indexing segments are moved forward and aft, the depth and length of the channel varies. 
     FIG. 8 shows typical inlet-engine airflow matching schedules for the intended operation of the slider inlet configuration. The engine airflow schedule is denoted by the solid black curve, and the inlet airflow supply schedule is represented by the dashed line. The use of the slider segment  300  allows a continuous smooth variation in inlet airflow, allowing the inlet to match the engine demand curve more closely, thereby eliminating the requirement to bypass large amounts of excess inlet flow at Mach numbers between transonic and cruise. 
     In yet another embodiment of the invention, centerbody indexing segments may be utilized on other types of supersonic inlets or subsonic inlets in order to provide an increase airflow area. In addition, a engine nozzle may be provided with indexing segments in order to open an entire part of an outer surface or wall to the freestream airflow. This design allows a large increase in intake area for an inlet or exit airflow area for an exhaust nozzle as well as redirection of the airflow. 
     An example of an inlet for a subsonic aircraft that would utilize the indexing segments for opening an outer wall described as follows. FIG. 9 presents a cross section of a typical prior art subsonic inlet  400  that includes a centerbody  410  and an outer wall  420  with inner and external surfaces  422  and  424 , respectively. FIG. 10 shows an isometric sketch of the inlet in which indexing segments  430  and  440  have been utilized to open the top portion of the inlet to the incoming airflow. This type of design will reduce foreign object damage by opening the airflow area so that it is increased in the upward direction. This tends to redirect the freestream airflow to a more downward direction and thus reduce the possibility of pulling foreign objects from the runway into the inlet. Even more important for subsonic inlet application is that separation of the airflow from the lower edge of the cowl lip is delayed to very high angles of attack. The resultant extended lower section of the inlet shields engine noise from the ground. A cross-section of the inlet with the segments  430  and  440  in an unrotated position, as well as the rotated position, is shown in FIGS. 11A and 11B, respectively. All surfaces that are exposed to the airflow are rounded to reduce the possibility of separation. 
     The preferred embodiments of the inlet and actuation system have been described in detail, above. However, with the present disclosure in mind it is believed that obvious alterations to the preferred embodiments, to achieve comparable features and advantages, will become apparent to those of ordinary skill in the art. For example, it is readily apparent to a person skilled in the art in this invention could adapt its use on an exhaust nozzle to provide a similar variation in nozzle airflow area.