Abstract:
The active system for the wide area suppression of a ground vortex generated by the engine of an aircraft includes an actuator assembly in fluid communication with a fluid source; and, at least one nozzle assembly, including at least one movable nozzle. The movable nozzle is in fluid communication with the actuator assembly for receiving fluid from the actuator assembly. The actuator assembly controls the motion of the movable nozzle, wherein fluid is injected over a desired region relative to an inlet of the engine to disrupt the flow structure of a ground vortex, thus mitigating ground vortex ingestion. This ensures the operational health of the engine during airplane maneuvering on the ground.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to gas turbine engines (turbo-prop or turbo-jet) used for aircraft propulsion and is particularly directed to an active control method and apparatus for the alleviation of the ground vortex ingested by the engine.  
           [0003]    2. Description of the Related Art  
           [0004]    Aircraft with engines mounted relatively close to the ground develop vortex activity during high-power, low speed and/or static ground operation. The ground vortex can generate high velocities near the ground, capable of dislodging foreign objects from the surface. This debris can become entrained in the airflow drawn into the engine inlet. The abrasion resulting from dust and dirt ingestion cause engine performance deterioration and reduced service life. Moreover, if the ingested debris includes large objects, engine failure with catastrophic consequences may result. The vortex can also create severe enough distortion to the core flow of the engine to result in engine surge.  
           [0005]    The problems stemming from ground vortex ingestion are especially acute for large, heavy transport airplanes. Vortex ingestion greatly hinders the ability of these aircraft to land in austere fields and to perform essential ground maneuvers on unimproved terrain. Consequently, this can pose a severe limitation on their global reach.  
           [0006]    In addition, some of the new commercial airplane concepts developed in recent years have a higher propensity for engine vortex formation due to unique propulsion-airframe configurations.  
           [0007]    As will be disclosed below, the present invention provides the means to annihilate the ground vortex. Consequently, it prevents damage and/or premature engine removal caused by foreign object ingestion or engine surge.  
           [0008]    The ground vortex phenomenon is schematically described in FIG. 1 (Prior Art). At low speeds the suction generated by the engine  1  results in the formation of a stagnation point  2  on the ground (like a vacuum cleaner effect). Usually, the ambient flow contains significant amounts of vorticity  3  (turbulence) due to gusts, ground turbulence, wake flow of neighboring aircraft components (i.e., wing, fuselage) and mixing of engine reverser plumes (when thrust-reversers are deployed). The mechanism of ground vortex formation is the amplification of the seed vorticity in the ambient flow due to the stretching of the contracting streamlines  4  approaching the engine inlet. This interaction results in a concentrated vortex  5  originating at the ground plane  6  and terminating inside the engine. Flow visualization indicates that the flowfield is unsteady, and the movement of the point of origination of the vortex on the ground is sporadic. Consequently, the vortex filament fluctuates over a significant portion of the lower inlet sector. The rotational flowfield induced by the ground vortex is the cause for kicked up dust and dirt, and it is a major source of engine compressor erosion. In addition, the tornado-like flow is capable of dislodging sizable foreign objects off the ground, causing Foreign Object Damage (FOD) to the engine. Another major concern is the inlet distortion created by the ground vortex, which may result in engine surge. As can be further seen in this figure, as the head wind velocity increases the streamlines become less stretched until there is little interaction between the engine inlet and the ground plane.  
           [0009]    There have been several attempts to solve the engine problems stemming from ground vortex ingestion. In some of these approaches compressor bleed air is being used as a source for jets of air directed down and forward of the engine. The device described in U.S. Pat. No. 2,915,262, issued to H. J. Klein, uses a blow away jet that impinges on the ground, fans out forward of the engine and prevents the formation of the ground vortex. Other devices that utilize aft blowing jets underneath the engine cowl have been described in U.S. Pat. No. 3,599,429, issued to Bigelis et al. and U.S. Pat. No. 4,070,827, issued to Vanfleet et al. These jets produce entrainment underneath the engine, thus blocking the airflow from moving forward in the space between the bottom of the nacelle and the ground. These devices are used on commercially operated transports having wing mounted engines hung close to the ground which are generally operated over relatively clean surfaces.  
           [0010]    A protective screen concept for alleviating engine FOD is described in U.S. Pat. No. 3,298,637, issued to Shao-Tang Lee. It requires the modification of the engine at the intake to include an encircling enlarged hollow conduit containing a series of holes around its circumference. Pressurized air is discharged through the holes to create an air screen to restrain or block dust that would tend to be thrown up by the engine at high power setting. This protective screen arrangement is a continuous flow system that creates a curtain of air to prevent the stagnation point from forming, requiring a large amount of bleed air and consequently draining the engine power. The creation of the air curtain will also cause a large amount of debris to become airborne, potentially causing more FOD problems. The configuration also requires a series of channels and doors to duct and direct the airflow, increasing the complexity and cost of the system.  
           [0011]    A more recent attempt to solve the ground vortex is disclosed in U.S. Pat. No. 5,915,651, issued to Asaki et al. This device is operational in conjunction with the thrust reverser of a turbofan engine. During thrust reverser deployment the flow from a fan air bypass duct is being redirected downward and aft in order to create an air curtain for preventing inlet suction from underneath the engine. However, it has been demonstrated that in order for this device to obviate vortex activity, excessive amounts of airflow are needed, thus compromising the engine performance. Additionally, the high velocity air impinging on the ground blows dust and heavier objects up off the ground. This defeats the purpose of eliminating engine FOD, and also impairs crew&#39;s visibility.  
           [0012]    Another system to prevent ground inlet vortices is shown in U.S. Pat. No. 6,129,309, issued to Smith, et al. This system uses pulsating high pressure air to alternatively eject a control flow from two stationary nozzles mounted underneath the engine nacelle. The injection nozzles are directed towards the vortex stagnation point. The amount of air required to affect the inlet vortex is well within the bleed limits of the engine. However, tests have shown that steady blowing can have the same level of vortex alleviation as pulsing the jets. Additional testing would be required to determine if the pulsing jets would be more effective during crosswind conditions. This system also has the same potential problem as the previous mentioned system—impingement on the ground may create FOD. However, the amount of flow is lower and relative distance from the ground is much higher which may limit the amount of FOD generated.  
           [0013]    None of the prior techniques has proven to be entirely satisfactory in an operational sense. Many airplanes operate in a manner and environment where the engines are exposed to continuous operation at high power, at low speeds and statically, over ramp surfaces which are not clean. In particular, some airplanes use thrust reverse powerback for parking and ground maneuvering. Thrust reverser operation is a condition that is even more susceptible to ground vortex formation. One of the salient features of flows with increased propensity to ground vortex activity is the unsteady characteristic of the air motion. There are numerous factors contributing to the apparent randomness of the flow in a realistic and an uncontrolled environment. These include gusts with varying strengths and direction (time-variation of ambient flow), ensuing structural response of aircraft components (i.e., the flexing of the entire wing/engine assembly) and the unsteady turbulent mixing of the thrust reverser plumes.  
           [0014]    The existing techniques target specific flow situations and they do not provide effective solutions for real life applications. Specifically, they constitute ‘point design’ solutions since they provide localized treatment of a ground vortex without consideration to the inherent problem of sporadic vortex motion. It is therefore highly desirable to develop a robust technique that addresses the underlying problem associated with vortex ingestion.  
         SUMMARY  
         [0015]    The present invention is an active system for the wide area suppression of a ground vortex generated by the engine of an aircraft. In a broad aspect it includes an actuator assembly in fluid communication with a fluid source; and, at least one nozzle assembly, including at least one movable nozzle. The movable nozzle is in fluid communication with the actuator assembly for receiving fluid from the actuator assembly. The actuator assembly controls the motion of the movable nozzle, wherein fluid is injected over a desired region relative to an inlet of the engine to disrupt the flow structure of a ground vortex, thus mitigating ground vortex ingestion. This ensures the operational health of the engine during airplane maneuvering on the ground. The fluid source is preferably the compressor of an engine of an aircraft.  
           [0016]    Inlet vortices have plagued propeller and jet powered aircraft since their inception. Many solutions have been put forward with limited success in real life situations. Typically they have failed due to the complexity of the invention or by their limited capability to eliminate the inlet vortex. The present invention has addressed these shortfalls by: (a) considering the fundamental problem of unsteady characteristics of realistic inlet vortex flows, (b) keeping the invention simple by minimizing the number of moving parts, and (c) eliminating FOD due to the active system itself by preventing ground impingement of the control jet.  
           [0017]    Other objects, advantages, and novel features will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 (Prior Art) is a schematic illustration of the conditions for the formation of a ground vortex as a function of head wind velocity.  
         [0019]    [0019]FIG. 2 is a schematic view of an aircraft engine that includes an embodiment of the active system for the wide area suppression of a ground vortex, of the present invention.  
         [0020]    [0020]FIG. 3 is a perspective view of the active system of the present invention mounted on the underside of an engine cowl.  
         [0021]    [0021]FIGS. 4 a - 4   h  illustrate examples of the variety of scanning patterns that may be provided by the present invention.  
         [0022]    [0022]FIGS. 5 a  and  5   b  illustrate the effect of the ground vortex suppression on engine reingestion. FIG. 5 a  shows the streaklines before activation. FIG. 5 b  shows the streaklines after activation.  
         [0023]    [0023]FIG. 6 illustrates the active jet provided by the present invention.  
         [0024]    [0024]FIGS. 7 a - 7   d  show the time evolution of the flow pattern around an engine equipped with active flow control according to an embodiment of the present invention. FIG. 7 a  shows the flow before jet activation. FIGS. 7 b ,  7   c  and  7   d  present the flow structure at 0.38, 0.76 and 1.14 seconds from the instant of jet application, respectively.  
         [0025]    [0025]FIGS. 8 a - 8   d  provide an assessment of ground impingement of the active flow control of the present invention. FIGS. 8 a  and  8   b  show front views of the flow pattern before and after jet application, respectively. FIGS. 8 c  and  8   d  show side views of the flowfield before and after jet activation, respectively. 
     
    
       [0026]    The same parts or elements throughout the drawings are designated by the same reference characters.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring again now to the drawings and the characters of reference marked thereon, FIG. 2 illustrates a preferred embodiment of the active system of the present invention, designated generally as  10 , contained within an aircraft engine, designated generally as  12 . The active system  10  includes an actuator assembly, designated generally as  14  and a nozzle assembly, designated generally as  16 .  
         [0028]    The actuator assembly  14  includes a shut-off valve  17  connected to the compressor  18  of the engine  12 . In this particular embodiment a conduit  20  supplies the high pressure bleed air from the compressor  18  to a system actuator  22 . A typical pressure range in which this system operates is between about 30 and 60 psig. The system actuator  22  includes a control system for controlling the shut-off valve  17  and a movable nozzle  24  of the nozzle assembly  16  to provide movement of the nozzle  24  through a desired path. The system actuator  22  may be, for example, pneumatically, electrically or hydraulically driven. The actuation system may be, for example, a cam system and linkages that are driven from any of these power sources. The nozzle  24  may be, for example, a simple convergent nozzle, or a convergent/divergent nozzle if higher velocities are required. The cross section of the nozzle can be circular or other suitable shape. The shape of the cross section of the nozzle can vary along nozzle length (for example, it can vary from a circular section to an elliptical section at the nozzle exit). The nozzle and distribution ducting downstream of the actuation system should be designed to minimize pressure losses, using techniques well known to those skilled in the art.  
         [0029]    The movable nozzle  24  is deployable from within the cowl  26  of the engine  12 . (Phantom lines indicate the stowed position.) It may be deployed by a variety of different methods that would be understood by those skilled in the art. For example, it may be deployed by utilization of a cowl  26  with a sliding door  28 . The door  28  may be pneumatically actuated when the shut-off valve is opened. A portion of the air may be directed to a piston (not shown) which compression drives a linkage to open the door  28 . When pressure is removed from the piston a spring (also not shown) closes the door  28 .  
         [0030]    Referring now to FIG. 3, the active system  10  is shown in operation on an airplane  30 . System  10  is shown deployed from the cowl  26 . In this embodiment the nozzle is shown deployed from the bottom of the cowl  26 . The nozzle, however, may be placed at other circumferential locations on the cowl. After deployment, the nozzle of the system  10  moves through a prescribed path to inject flow over a large region in front of the engine inlet. The slew motion of the ejecting fluid disrupts the global flow field in front of the engine and prevents the formation of vortices. A vortex filament  32  is illustrated in this figure. An active jet flow  34  from the system  10  is also illustrated. The controlled motion of the nozzle is predetermined in order to achieve best volume coverage and maximum vortex suppression.  
         [0031]    Examples of scanning patterns are shown in FIGS. 4 a - 4   h , in the form of jet footprints  36 ,  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 , respectively, from the ground plane  6  upon imaginary vertical planes upstream of the engine  52  and perpendicular to its axis. These patterns have been obtained by using select combinations of sinusoidal, longitudinal and latitudinal motions (i.e., sets of amplitude, frequency and phase of the two angular motions). Other designs of nozzle motions and nozzle layouts can also be utilized, for example, configurations with multiple nozzles.  
         [0032]    A Computational Fluid Dynamics procedure has been applied for the simulation of ground vortex ingestion. Referring now to FIGS. 5 a  and  5   b , the effectiveness of the present method in reducing/eliminating engine ingestion of the ground vortex has been evaluated and is illustrated for an engine  12  placed at equal distances from the ground plane  6  and a vertical side plane  60 . Tail wind onset flow is applied in this simulation since increased vortex susceptibility has been observed at this condition. For a high power setting the simulation results in a flow field which is symmetrical with respect to a 45° plane defined by the engine axis and the intersection line  61  between the ground  6  and the vertical planes  60 . Specifically, the simulation results in a vortex system which consists of two elements with opposite swirl directions; one vortex  62  originates at the ground plane  6  and the other vortex element  64  forms at the side wall  60 . The flow structure of FIG. 5 a  shows engine vortex ingestion, which is represented by the streaklines that terminate in the inlet  66 . The vortex elements  62  and  64  show similar inlet ingestion patterns due to the ground  6  and the vertical plane  60 , respectively.  
         [0033]    When the active system of the present invention  10  is applied at the bottom side of the engine cowl, the flow field is no longer symmetrical. In this case the jet nozzle moves side-to-side within a ±20° range. This scanning pattern is described FIG. 4 a . The resulting flow is shown in FIG. 5 b . The intermittent mixing provided by the periodic side motion of the jet perturbs the flow in front of the engine and alters the shape of the vortex filament  62 A from the ground plane  6  by reducing its strength and expelling it away from the engine. The vortex  64 A from the vertical plane  60  is only slightly affected. Diagnostics of the flow field indicates that engine ingestion from the bottom side has been curbed while ingestion from the side wall still exists.  
         [0034]    [0034]FIG. 6 is a side view of the engine  12  showing the jet flow pattern  34  after activation of the system  10 .  
         [0035]    [0035]FIGS. 7 a ,  7   b ,  7   c  and  7   d  depict a sequence of snapshots taken during the evolution of the flow pattern at 0, 0.38, 0.76 and 1.14 seconds from the instant of jet application, respectively. At the ground plane  6 , the jet has resulted in reduced suction power. This analysis demonstrates that the present invention is very effective in reducing ground vortex ingestion and its concomitant, the risk of FOD.  
         [0036]    Another potential shortfall of many inlet vortex mitigation schemes is ground impingement of the control jet. Ground impingement can create FOD by lifting debris from the ground that is then ingested into the engine. This invention reduces this effect by aiming the nozzle at the near horizontal plane (i.e., its nominal angular position about which the periodic motion is superimposed) and by constantly moving the control jet so that extended periods of ground impingement do not occur. Usually, the nozzle is directed at an angle of up to 40° off the horizontal plane.  
         [0037]    This benefit is illustrated in FIGS. 8 a ,  8   b ,  8   c  and  8   d  for the case described in FIGS. 5, 6 and  7   a - d . The envelope of the ensemble of streamlines  71  represents the capture streamtube  72 , which designates the domain of all the fluid particles ingested by the engine  12 . The front views in FIGS. 8 a  and  8   b  (before and after jet activation, respectively) show that after activating the control jet the nearly symmetrical shape of the capture streamtube  72  is altered (into  72 A) and the flow adjacent to the ground plane  6  is profoundly affected. More specifically, the capture streamtube  72 A is being pushed upward with a large depression occurring just under the engine  12  in region  74 . The implication is that there is no debris ingestion from the ground. The side view of the flow structure is shown in FIGS. 8 c  and  8   d  (before and after jet activation, respectively). Note that since the power setting of the engine is constant, the engine  12  makes up for the mass flow depletion from underneath by expanding the capture streamtube in the region  76  above it.  
         [0038]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.