Power plants – Reaction motor – Interrelated reaction motors
Reexamination Certificate
2002-02-12
2004-11-09
Yu, Justine R. (Department: 3746)
Power plants
Reaction motor
Interrelated reaction motors
C060S262000, C415S211200
Reexamination Certificate
active
06813877
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to gas turbine engine exhaust nozzles, and in particular to noise reduction and performance improvements to nozzle arrangements used for gas turbine engines suited to aircraft propulsion.
BACKGROUND OF THE INVENTION
Gas turbine engines are widely used to power aircraft. As is well known, the engine basically provides propulsive power by generating a high velocity stream of gas which is exhausted rearwards through an exhaust nozzle. A single high velocity gas stream is produced by a turbojet gas turbine engine. More commonly nowadays however two streams, a core exhaust and a bypass exhaust, are generated by a ducted fan gas turbine engine or bypass gas turbine engine.
The high velocity gas stream produced by gas turbine engines generates a significant amount of noise, which is referred to as exhaust or jet noise. This noise is generated due to the high velocity of the exhaust stream, or streams, and the mixing of the streams with the surrounding atmosphere, and in the case of two streams, as the bypass and core streams mix. The degree of noise generated is determined by the velocity of the stream and how the streams mix as they exhaust through the exhaust nozzle.
Increasing environmental concerns require that the noise produced by gas turbine engines, and in particular aircraft gas turbine engines, is reduced and there has been considerable work carried out to reduce the noise produced by the mixing of the high velocity gas stream(s). A large number of various exhaust nozzle designs have been used and proposed to control and modify how the high velocity exhaust gas streams mix. With ducted fan gas turbine engines particular attention has been paid to the core stream and the mixing of the core and bypass exhaust streams. This is because the core stream velocity is considerably greater than the bypass stream and also the surrounding atmosphere and consequently the core exhaust stream generates a significant amount of the exhaust noise. Mixing of the core stream with the bypass stream has also been found to generate a significant proportion of the exhaust noise due to the difference in velocity of the core and bypass streams.
One common current exhaust nozzle design that is widely used is a lobed type nozzle which comprises a convoluted lobed core nozzle as known in the art. However, this adds considerable weight, drag, and cost to the installation and nowadays short bypass nozzles are favoured with which the lobed type core nozzles are less effective and are also more detrimental to the engine performance than when used on a long cowl arrangement.
An alternative nozzle design that is directed to reducing exhaust noise is proposed and described in GB 2,289,921. In this design, a number of circumferentially spaced notches, of various specified configurations, sizes, spacing and shapes, are provided in the downstream periphery of a generally circular core exhaust nozzle. Such a nozzle design is considerably simpler to manufacture than the conventional lobed designs. This prior proposal describes that the notches generate vortices in the exhaust streams. These vortices enhance and control the mixing of the core and bypass streams which it is claimed reduces the exhaust noise.
Model testing of nozzles similar to those described in GB 2,289,921 has shown that significant noise reduction and suppression can be achieved. However the parameters and details of the design proposed in GB 2,289,921 are not optimal and there is a continual desire to improve the nozzle design further.
A further design, and that of the present Assignee, is proposed in UK Application GB 0025727.9. This application discloses trapezoidal shaped tabs disposed to the axially rearward exhaust ducts of the bypass and core and which are inclined radially inward to impart vortices to the exhaust streams.
However, the main requirement of reducing exhaust noise is during aircraft take-off and landing. At higher altitudes where the majority of the duration of the flight is, exhaust noise is not a problem. It is therefore not necessary to have noise reduction means operational at higher altitudes especially when one considers the noise reduction means inherently introduces aerodynamic inefficiencies.
SUMMARY OF THE INVENTION
It is therefore desirable and is an object of the present invention to provide an improved gas turbine engine exhaust nozzle which is quieter than conventional exhaust nozzles and/or which offers improvements generally.
According to a first aspect of the present invention there is provided a gas turbine engine exhaust nozzle arrangement for the flow of exhaust gases therethrough between an upstream end and a downstream end thereof comprising a nozzle, a downstream portion and a plurality of tabs, each tab extends in a generally axial direction from the downstream portion of the nozzle wherein the nozzle further comprises an actuation mechanism capable of moving the tabs between a first deployed position, in the first position the tabs interact with a gas stream to reduce exhaust noise thereof, and a second non-deployed position, in the second position the tabs are substantially aerodynamically unobtrusive.
Preferably, the plurality of tabs is circumferentially disposed about the nozzle.
Preferably, the actuation mechanism comprises a shape memory material element.
Preferably, the nozzle further comprises a radially inner position and a radially outer part, wherein the tabs are rotatably attached to the nozzle at the radially inner position, the actuation mechanism comprises the shape memory element mounted at a first end to a radially outer part of the nozzle and mounted at a distal end to a radially outer part of the tab, such that in use, the element in a first shape maintains the tab in the second non-deployed position and in a second shape maintains the tab in the first deployed position.
Preferably, the periphery of the nozzle defines a pocket therein and at least a part of the element is generally disposed within the pocket.
Preferably, the tab defines a recess therein and at least a part of the element is generally disposed within the recess.
Alternatively, the element is in the form of a spring.
Preferably, the nozzle arrangement comprises a resilient member having a first end and a distal end, the resilient member is attached at the first end to the tab and at the distal end to the nozzle and is arranged to provide a returning force to the tab.
Preferably, the nozzle defines an orifice and a passage, the orifice is exposed to a gas stream and the passage extends from the orifice to the pocket and thereby provides a conduit for transmitting the thermal flux of the gas stream to the actuation mechanism.
Alternatively, the tab comprises shape memory material and the tab further comprises a flexural element, the flexural element, in use, is arranged to provide a returning force to the tab.
Preferably, the tab defines an orifice, the orifice exposed to a gas stream, and a passage, the passage extending from the orifice, to the shape memory material and thereby provides a conduit for rapidly transmitting changes in the thermal flux of the gas stream to and throughout the memory shape material element.
Preferably, the actuation mechanism is actuated in a response to an applied field and the field is a temperature flux. Alternatively, the field is an electric current.
Preferably, the temperature flux is provided by the gas stream and the gas stream is any one chosen from the group comprising an ambient gas flow, a bypass flow, a core flow.
Preferably, the shape memory material element comprises any one of a group comprising Titanium, Manganese, Iron, Aluminium, Silicon, Nickel, Copper, Zinc, Silver, Cadmium, Indium, Tin, Lead, Thallium, Platinum.
Alternatively, the shape memory material element comprises an electrostrictive material and the actuation mechanism further comprises an electrical circuit, the electrical circuit comprising control apparatus, an electric generating means and electrical contact means, the electrical contact means a
Birch Nigel T
Webster John R
Manelli Denison & Selter PLLC
Rodriguez William H
Rolls-Royce plc
Taltavull W. Warren
Yu Justine R.
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