Power plants – Reaction motor – Air passage bypasses combustion chamber
Reexamination Certificate
1998-06-24
2001-01-30
Thorpe, Timothy S. (Department: 3746)
Power plants
Reaction motor
Air passage bypasses combustion chamber
C239S265170
Reexamination Certificate
active
06178742
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a rear mixer ejector for a turbomachine intended for propelling supersonic civil aircraft.
The noise level caused by the exhaust gases from the nozzle of a turbojet engine increases as the gas ejection speed increases. This noise, known as jet noise, is very noticeable in the case of a single flow, or straight, turbojet engine.
In order to reduce the noise level of jet aircraft near airports and at low and medium heights their engines must be provided with means for attenuating exhaust gas noise, and an effective technique for reducing jet noise is to mix the primary highvelocity hot gas flow from the gas generator, or combustor, of the turbojet engine with low-velocity cold air delivered from a secondary flow path outside the primary flow path in order to produce a relatively uniform mixture of intermediate velocity at the exhaust nozzle exit.
2. Summary of the Prior Art
Various fixed means for achieving this mixture are known, such as organ pipe devices, daisy devices or lobed devices. However, they are permanently present in the flow path of the hot gases leaving the combustor, and this impairs the performance of the engine since it leads to excessive fuel consumption in some flight conditions.
The ejection nozzle of supersonic aircraft has a variable configuration which is adaptable to flight conditions and aircraft speed. Reducing noise from the jet engines of such aircraft is unnecessary during supersonic cruising, descent, approach and landing, since the aircraft flies at a very high altitude when cruising at supersonic speeds, and engine speeds are low during the other flight regimes. During take-off and climbing, however, attenuation of the engine noise is particularly necessary, and temporary cold air feeds must therefore be available for mixing with the hot gases from the combustor in order to lower the hot gas temperature and thus reduce the speed of the gases ejected from the nozzle.
U.S. Pat. Nos. 5,154,052 and 5,291,672 disclose rear mixer ejectors for supersonic aircraft engines wherein the ejector casing has a rectangular cross-section in which the opposed top and bottom walls are provided with variable-geometry convergent-divergent flaps and pivotable mixing devices comprising a number of spaced-apart chutes movable between a deployed position, in which they channel cold air from the outside into the hot gas flow path, and an inoperative retracted position. The chutes each comprise two spaced-apart lateral walls which are of triangular shape and which are interconnected along one of their edges by a transverse wall forming a chute bottom which extends inwards into the hot gas flow path and in the downstream direction when the chutes are in the deployed position. In the inoperative position the chutes are retracted into the thickness of the casing and the chute bottoms close the air inlet apertures which are provided in the casing walls in correspondence with the chutes. This arrangement makes it necessary to increase the casing wall thickness, and results in an undesirable increase in aerodynamic drag and excessive fuel consumption.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome this problem and to provide a rear mixer ejector for a supersonic aircraft engine wherein the mixing devices remain in the hot gas flow path of the turbomachine when in the inoperative position but without causing excessive losses.
To this end, according to the invention there is provided a rear mixer ejector of a turbomachine for supersonic aircraft, comprising a casing having opposed top and bottom walls and opposed side walls defining a substantially rectangular cross-section, said casing having a central axis and defining a flow path for the gases exhausted from the gas generator of said turbomachine, movable variable geometry flaps in said top and bottom walls of said casing forming a variable geometry gas exhaust nozzle, air inlet apertures provided in said side walls of said casing upstream of said exhaust nozzle, and mixer means which are mounted on said side walls adjacent said air inlet apertures and are adjustable between an inoperative position and a deployed position wherein said mixer means are operative to channel into said gas flow path cold air which enters said casing from outside through said air inlet apertures, said mixer means on each of said side walls comprising a plurality of spaced apart chutes each mounted adjacent a respective air inlet aperture, each chute comprising two spaced lateral walls of substantially triangular shape and a transverse wall extending between said lateral walls to define a chute bottom which extends angularly into said gas flow path in the downstream direction when said mixer means are in the deployed position, said chutes on each of said side walls being of unitary construction and mounted to pivot between said inoperative position and said deployed position about an axis which is disposed at the downstream edge of the respective air inlet apertures and remote from said chute bottoms, whereby said chutes are disposed in said gas flow path in both said inoperative and deployed positions with said chute bottoms extending parallel to said central axis in said inoperative position, means being provided for closing said air inlet apertures when said chutes are in said inoperative position.
Preferably, said means for closing said air inlet apertures comprises a door which is disposed outside said gas flow path and which is mounted to pivot about said axis at said downstream edge of said air inlet apertures, said door pivoting to close said air inlet apertures when said chutes pivot to said inoperative position.
As an equivalent variant, the invention also provides a rear mixer ejector of a turbomachine for a supersonic aircraft, comprising a casing having opposed top and bottom walls and opposed side walls defining a substantially rectangular cross-section, said casing having a central axis and defining a flow path for the gases exhausted from the gas generator of said turbomachine, movable variable geometry flaps in said top and bottom walls of said casing forming a variable geometry gas exhaust nozzle, air inlet apertures provided in said side walls of said casing upstream of said exhaust nozzle, and mixer means which are mounted on said side walls adjacent said air inlet apertures and are adjustable between an inoperative position and a deployed position wherein said mixer means are operative to channel into said gas flow path cold air which enters said casing from outside through said air inlet apertures, said mixer means on each of said side walls comprising a plurality of spaced apart chutes each mounted adjacent a respective air inlet aperture, each chute comprising two spaced lateral walls of substantially triangular shape and a transverse wall which extends between said lateral walls and defines a chute bottom extending angularly into said gas flow path in the downstream direction when said mixer means are in the deployed position, said lateral walls of each chute being fixed to the respective side wall of said casing adjacent the respective air inlet aperture and projecting permanently into said gas flow path, and said transverse wall of each chute being in the form of a flap which is hinged at the upstream edge of said respective air inlet aperture and is pivotable between the deployed position, in which said flap defines the chute bottom extending angularly into said gas flow path, and the inoperative position, in which said flap extends parallel to said central axis and closes said air inlet aperture.
Thus, in both constructions in accordance with the invention the mixing means remain permanently in the hot gas flow path of the turbomachine. However, when the chutes are in the inoperative position their constituent walls are all parallel to the casing axis and are thus disposed in the flow path so as not to cause excessive disturbance of the exhaust gas flow.
Other advantages and preferred features of the invention will becom
Guyonnet Xavier Jean Michel Andr{acute over (e)}
Wurniestky Pascal Claude
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Societe Nationale d'Etude et de Construction de Moteurs d&a
Thorpe Timothy S.
Torrente David J.
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