Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
2002-10-25
2004-07-20
Dinh, Tien (Department: 3644)
Power plants
Combustion products used as motive fluid
With safety device
C244S05300R
Reexamination Certificate
active
06763651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
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.
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.
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.
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.
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.
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's visibility.
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.
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.
The existing techniques target specific flow situations and they do not provide effec
Clark Roger W.
Shmilovich Arvin
Smith David M.
Yadlin Yoram
Alston & Bird LLP
Dinh Tien
The Boeing Company
LandOfFree
Active system for wide area suppression of engine vortex does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Active system for wide area suppression of engine vortex, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Active system for wide area suppression of engine vortex will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3185970