Fluid sprinkling – spraying – and diffusing – Reaction motor discharge nozzle – With addition of secondary fluid upstream of outlet
Reexamination Certificate
1999-06-11
2001-10-30
Freay, Charles G. (Department: 3746)
Fluid sprinkling, spraying, and diffusing
Reaction motor discharge nozzle
With addition of secondary fluid upstream of outlet
C060S204000, C060S264000, C060S279000
Reexamination Certificate
active
06308898
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to active flow control of nozzle exhaust plumes and, more particularly, to methods and apparatus for actively controlling behavior of an exhaust plume from a subsonic nozzle in order to enhance mixing within the plume and/or control the cross-sectional shape of the plume.
BACKGROUND OF THE INVENTION
Exhausts from turbojet and turbofan engines are very hot and noisy. The hot exhaust plume from an engine nozzle can create a number of problems. Where the engine is so positioned relative to the airframe that the exhaust plume impinges on parts of the airframe, the hot exhaust can cause undesirable temperature-induced effects on the material properties of the impinged parts. As a result, the impinged parts may have to be constructed of a material capable of tolerating high temperatures, such as titanium, which can lead to increased cost of the airframe. In some cases, even such high-temperature materials may not be adequate to insure sufficient structural strength at the elevated temperatures caused by impingement of the exhaust gases, and thus steps must be taken to prevent impingement or to mitigate the effect of impingement.
A number of different approaches have been used in turbofan-powered aircraft in an attempt to prevent impingement or to mitigate the effect of impingement of hot core exhaust gases on airframe surfaces. One attempted solution has been to forcibly mix the hot core nozzle exhaust with relatively lower-temperature fan bypass air prior to exhausting the mixed exhaust stream out the back end of the engine, so that the resulting exhaust stream has a lower temperature. This approach requires a long, costly, and heavy bypass duct nacelle configuration in order to accommodate the mixing structure that joins and mixes the core stream with the bypass stream. A further disadvantage of this approach is that substantial losses in efficiency occur in the course of mixing the two streams, and because the streams are always mixed before being exhausted, these losses occur during all parts of an engine mission cycle, even though the exhaust gas temperature-induced problems being solved may occur during only some parts of a mission cycle such as ground and takeoff operations. Another disadvantage of this approach is that during activation of the engine fan reverser, the hot core exhaust is not mixed with fan bypass air, and thus any temperature-induced problems during fan reverser operation would not be solved.
Another attempted solution to the exhaust plume temperature problem has been to attempt to prevent impingement by use of a core exhaust thrust reverser that can be deployed when desired so as to redirect the core exhaust plume outwardly and forward. This approach has been used, for example, in cases where the hot core exhaust causes its most severe problems during activation of the engine fan thrust reverser. The core reverser hardware is costly and heavy, and requires frequent inspection and maintenance. A further shortcoming of this approach is that the core reverser is activated only during reverse-thrust operation, and thus exhaust temperature-induced problems during forward-thrust operations are not solved. Additionally, the reversed core exhaust can still impinge on airframe surfaces and cause its own temperature-induced problems. Furthermore, as with all variable-geometry reverser devices, the core exhaust thrust reverser raises safety and reliability concerns in terms of accidental deployment, failure to deploy, and/or failure to stow after deployment.
SUMMARY OF THE INVENTION
The above needs are met and other advantages are achieved by the present invention, which provides methods and apparatus for inducing and enhancing mixing of an exhaust plume and/or for controlling the shape of the plume, wherein the mechanism responsible for mixing and/or shaping can readily be activated when needed and deactivated when not needed. The apparatus does not require any costly and heavy components. The mixing of the exhaust plume occurs external to and downstream of the exhaust nozzle, and thus does not depend on mixer hardware for internally mixing bypass and core streams. Thus, the invention alleviates the problem of continuous efficiency degradation caused by conventional forced mixing of bypass and core streams, and substantially eliminates the significant cost and weight penalties associated with long duct nacelles, bypass-core mixing devices, and core reversers. A further benefit of the invention is that if the apparatus is accidentally activated or fails to deactivate, the only undesirable consequence is a small degradation in engine efficiency, and hence the invention facilitates improved safety and reliability of the engine system.
To these ends, the invention in one embodiment provides a method for inducing mixing of an exhaust plume from a nozzle, comprising directing periodically recurring pulsed jets of fluid inwardly into the exhaust plume from at least two locations that are circumferentially spaced apart about the plume, with pulses directed from one of the locations being out of phase relative to pulses directed from the other location. The pulsed jets cause excitation of the exhaust plume shear layer, which results in a flow instability occurring about one to three nozzle diameters downstream of the nozzle exit plane. This flow instability causes the plume to “flap” back and forth, thereby creating mixing of fluid in the plume with fluid outside of the plume. The behavior of the plume can also be controlled by suitable location of the pulsed jets so as to control the cross-sectional shape of the plume. The mixing of the plume results in a decrease in the average and peak temperatures in the plume downstream of the nozzle exit. Based on CFD model predictions and experimental testing with two different engine nozzle configurations, the invention enables exhaust temperatures downstream of the nozzle to be reduced by up to 50 percent or more.
The pulsed jets in one preferred embodiment of the invention are arranged such that they are directed into the exhaust plume from diametrically opposite locations, i.e., circumferentially spaced about 180° apart, and are timed such that the pulses from one side of the plume are approximately 180° out of phase relative to the pulses from the opposite side. The pulsed jets can be positioned either at or slightly upstream or downstream of the exit plane of the nozzle. In one preferred embodiment of the invention, each of the pulsed jets is elongated in a circumferential direction of the nozzle. For example, each of the pulsed jets advantageously covers about 90° of circumferential arc.
As noted above, the invention can also enable the shape of the exhaust plume to be controlled. More particularly, the pulsed jets cause an alteration in the shape of the cross-section of the exhaust plume, tending to “spread” or elongate the plume along an axis whose orientation is dictated by the circumferential location of the pulsed jets. Thus, the orientation of the plume spreading can be controlled by suitable location of the pulsed jets. For example, where the pulsed jets are located at 6 o'clock and 12 o'clock circumferential positions, the plume downstream of the nozzle exit tends to spread along a horizontal axis passing through 3 o'clock and 9 o'clock positions. This plume spreading can be advantageous in some applications. For example, for “powered lift” operation where the nozzle exhaust gases flow over wing flaps to enhance the lift performance of the wings, the spreading of the exhaust plume can result in increased flap area wetted by the plume, thus improving the powered lift performance. Moreover, since the plume mixing results in lower temperature of the flow over the flaps, the flaps can potentially be constructed of lower-cost and lighter-weight materials than those that may be required in order to tolerate the higher-temperature exhaust gases from a nozzle not employing the present invention.
In another preferred embodiment of the invention, a rotational motion
Dorris, III John
Kibens Valdis
Parekh David Espineli
Smith David Michael
Alston & Bird LLP
Freay Charles G.
The Boeing Company
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