GB2451261A

GB2451261A - Gas turbine engine with nozzle and porous Coanda surface

Info

Publication number: GB2451261A
Application number: GB0714480A
Authority: GB
Inventors: Anthony Gregory Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-07-25
Filing date: 2007-07-25
Publication date: 2009-01-28
Anticipated expiration: 2027-07-25
Also published as: GB2451261B; GB0714480D0

Abstract

A nozzle 1 is attached to a gas turbine engine 2 and accepts exhaust flow 3 from the engine 2. The nozzle 1 directs the flow at an initial angle to an axial direction of the engine 4 and over a Coanda surface 5 fitted downstream of the exit plane of the nozzle 1. The Coanda surface 5 is porous such that it can allow a tertiary flow 6 to pass from beneath the surface 5 under control of surface valves 7 to separate the exhaust from the surface 5. By rapidly opening and closing the surface valves 7 the exhaust flow can be made to attach and detach repeatedly at high frequency producing significant transfer of momentum and energy from the exhaust to the surrounding ambient flow. The detaching and attaching of the exhaust flow is a thrust vectoring technique for direct transfer of momentum and energy from the exhaust of a gas turbine engine to the surrounding ambient flows in order to improve on propulsive efficiency.

Description

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Improvements to Gas Turbine Propulsive Efficiency This invention relates to improvements to the propulsive efficiency of gas turbine engines by increased mixing of hot engine exhaust flow with surrounding ambient flow.

In gas turbine engines propulsive efficiency is increased by the use of a power turbine and a fan or propeller in order to achieve the transfer of energy from the high velocity high temperature main engine core flow to the surrounding ambient flow.

The resulting higher mass flow at lower speed represents a greater thrust for the same fuel input and so, therefore, specific fuel consumption (SFC) of the engine is improved above that of just using the core flow alone to generate thrust.

Whilst there is the potential to augment the thrust obtained from just the core flow by the use of mixing devices, such devices usually rely purely upon the transfer of momentum and energy through the shear layers of the exhaust flow and the ambient flow. As a result such mixing is at a relatively low rate, is inefficient and can require significant length to be added to the engine system in order to achieve any measurable increase in thrust and, therefore, propulsive efficiency.

Methods exist for redirecting the exhaust flows from gas turbine engines. Such methods are used for vectoring the thrust of such engines in order to provide directional control or lift.

It has been found that certain methods of thrust vector control, which involve the use of the Coanda effect, can be utilised to achieve very high rates of change of the jet direction.

The current invention reiates to the use of such thrust vectoring techniques to achieve direct transfer of momentum and energy from the exhaust to the surrounding ambient flows rather than relying mainly on shear.

By rapidly pulsing the exhaust flow onto and away from a Coanda surface the exhaust flow can be made to sweep through an angle repeatedly washing backwards and forwards into the ambient stream transferring momentum directly (i.e. pushing into the ambient or secondary flow) and at a high rate when compared with transfer through shear alone.

One particular embodiment of the invention is shown in Figure 1 and involves the use of a nozzle, 1, attached to a gas turbine engine, 2, to accept all of the exhaust flow, 3, from the engine itself. The nozzle directs the flow at an initial angle to the axial direction of the engine, 4. A planar Coanda surface, 5, is fitted downstream of the exit plane of the nozzle and in close proximity to it such that in practice the exhaust flow leaving the nozzle exit plane attaches to the Coanda surface according to the Coanda effect.

The Coanda surface, 5, is curved away from the initial trajectory of the exhaust flow passing through an angle at which it is then parallel with the axial direction of the engine. 4, and through a further angle beyond that axis. The Coanda surface is porous or perforated such that it can allow a tertiary flow, 6, to pass from beneath the surface and in to the main exhaust flow itself, separating the exhaust from the surface as it does so.

During normal operation flow is intermittently allowed to pass through the porous surface and is then shut off using the surface valves, 7. When the tertiary flow, 6, passes through the porous surface the main exhaust flow detaches from the Coanda surface and travels towards the outer boundary, 8, of the exhaust system pushing into the ambient secondary flow ahead of it as it does so.

After a short time interval, flow through the porous surface is stopped by closing the surface valves, 7, and the exhaust flow attaches to the Coanda surface, 5, again and travels around the surface and off the trailing edge of the Coanda surface, 5. As it does so it entrains ambient secondary air, 9, into the main exhaust system.

The repeated flapping of the exhaust flow in the main exhaust system at high frequency produces significant transfer of energy from the high velocity, high temperature, low mass flow exhaust to the surrounding ambient flow creating a larger mass flow at lower velocity, but with a higher overall thrust -thus improving the propulsive efficiency and lowering the specific fuel consumption of the engine compared to using the primary exhaust flow alone for propulsion.

Several variations upon this form of the invention are possible. For example the exhaust flow can be split to be taken to two opposing Coanda surfaces. The exhaust flows would be attached and detached on each side of the Coanda surface, either out of phase or in phase according to the requirements for additional thrust.

The exhaust càuld consist of an annular outlet with an axisymmetric external Coanda surface, the flow being repeatedly attached to and detached from this Coanda surface.

The axisymmetric surface could be subdivided into a series of channels and each of the channels separated and attached at different phase intervals.

These channels themselves could be made to spiral around the main axis of the engine to increase further the mixing between the exhaust flow and the ambient air.

If the exhaust flow did follow spiralled channels, a final set of vanes could be used to ensure that the flow was bought parallel with the engine axis and to remove swirl before leaving the exhaust mixing duct.

Other fluidic thrust vector designs could be used to achieve the same momentum and energy transfer.

Not all of the engine flow needs to travel through the thrust vectoring nozzle.

Flow introduced through the porous Coanda surface and other parts of the nozzle could be from different sources. Compressor or fan air could be used as the source.

Free stream (ambient air) might be used. Alternatively, this flow could be in the form of a liquid such as water or glycol (or a mixture of liquid and gas). The intention would be that the liquids would evaporate as they passed through the Coanda surface thus converting some of the thermal energy in the exhaust flow into the momentum energy of the resulting vapour, and helping to enhance the transfer of energy with the surrounding flow.

The Coanda surface might not be porous but be continuous. In this case the flow controlling vector could be admitted from the sides of the Coanda surface.

The orientation of the engine relative to the vehicle could be reversed from the conventional sense such that the intake would be at the downstream end of the vehicle and supplied using a plenum intake and the primary nozzle exit plane could be placed at the upstream end of the vehicle. The nozzle and the Coanda surface would then turn the exhaust flow through a greater angle in order to bring the flow around to the downstream direction. The aim would then be to allow the transfer of momentum and energy to place along the length of the engine thus minimising any increase in footprint of the propulsion system as a whole.

Claims

Improvements to Gas Turbine Propulsive Efficiency CLAIMS

1. A gas turbine engine comprising a nozzle to direct exhaust flow from the engine away from the engine's axis, and a Coanda surface immediately downstream of said nozzle arranged such that the exhaust flow will attach to the surface according to the Coanda effect, and with a means for controlling attachment such that by repeatedly attaching and detaching the exhaust flow, momentum and energy is transferred into the surrounding flow stream.

2. A gas turbine engine as in claim 1 in which the Coanda surface is curved in the direction of the flow.

3. A gas turbine engine as in claim 1 in which the Coanda surface is made up of series of discrete flat sections, each angle away from each other so as to turn the exhaust flow away from initial trajectory under the action of the Coanda effect.

4. A gas turbine engine according to any of the preceding claims in which the nozzle is rectangular in cross section.

5. A gas turbine engine according to any of the preceding claims in which the nozzle splits into two halves which are angled away from each other in order to produce two exhaust streams.

6. A gas turbine engine according to claims 1, 2 and 3 in which the nozzle is axisymmetric in cross section and which creates an annular exhaust flow.

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7. A gas turbine engine according to claim 6 in which the Coanda surface is also axisymmetric *

8. A gas turbine engine according to any of the preceding daims in which the nozzle exit is arranged such the exhaust flow is caused to swirl as it leaves the : :** nozzle exit plane. S..

9. A gas turbine engine according to any of the preceding claims in which fences are used along the Coanda surface in order to channel the exhaust flow into separate streams.

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1O.A gas turbine engine according to claim 9 in which the fences are twisted in the direction of the flow in order to encourage the exhaust flow to swirl as it flows over the Coanda surface

11. A gas turbine engine according to any of the preceding claims in which the nozzle and Coanda surface are enclosed inside an outer shroud whose purpose is to bound and direct the surrounding flow stream.

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12. A gas turbine engine according to claim 11 in which the outer shroud is shaped to take advantage of the thrust generated by the momentum and energy transfer from the exhaust stream to the surrounding flow stream.

13. A gas turbine engine according to any of the preceding claims in which the Coanda surface is porous in order to admit flow to control separation of the exhaust stream.

14.A gas turbine engine according to any of the preceding claims in which side walls are used to control the separation of the exhaust stream.

15. A gas turbine engine according to claim 13 in which a liquid is admitted through the Coanda surface with the purpose of enhancing momentum and energy transfer from the exhaust flow to the surrounding flow stream.

16.A gas turbine engine according to any of the preceding claims in which not all of the engine exhaust flow travels through the nozzle but has some exhaust ducted away separately.

17. A gas turbine engine according to any of the preceding claims in which the surrounng flow stream is controlled in order to affect the movement of the AI idUI I,uwy.

18. A gas turbine engine according to any of the preceding claims in which the engine intake is arranged downstream of engine's nozzle and the Coanda surface or surfaces are arranged so as to turn the exhaust flow from the upstream to the downstream direction.

19. A gas turbine which uses continuous vectoring of the exhaust stream in order * .. to enhance mixing between the exhaust stream and the surrounding flow stream for the purposes of achieving improved propulsive efficiency. S... * S * S.. S. * I * ***

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