GB2398046A

GB2398046A - Porous nozzle arrangement

Info

Publication number: GB2398046A
Application number: GB0300865A
Authority: GB
Inventors: Anthony Gregory Smith; David Michael Thomas
Original assignee: S & C Thermofluids Ltd
Current assignee: S & C Thermofluids Ltd
Priority date: 2003-01-15
Filing date: 2003-01-15
Publication date: 2004-08-11
Anticipated expiration: 2023-01-15
Also published as: GB0300865D0; GB2398046B

Abstract

A nozzle arrangement 1,3,4 comprising a porous nozzle surface 3 for affecting the attachment of the jet 2 using the coanda effect. The nozzle arrangement 1,3,4 further comprises means to restrict gas flow through the porous surface 3, and alter the point of detachment 5, which may comprise an impervious material 4 moveable beneath the porous surface 3. A plenum chamber may be located external to the nozzle arrangement 1,3,4, which may introduce a gas through the porous surface 4 to promote detachment of the jet 2. The porosity may be variable along the length of the nozzle. The side plates of the nozzle arrangement may also be porous. There may be provided a two sided nozzle arrangement, the coanda properties of which are independently variable.

Description

The Use of Porous Surfaces with Coanda Effect Coanda effect is the

phenomenon by which a jet of fluid will remain attached to a surface in its proximity. The surface can be turned away from the initial trajectory of the jet such that it is convex in terms of the side to which the jet is attached.

Under the correct conditions, in which the jet entrainment is restricted, the jet will remain attached to the surface even in the presence of this curvature.

Conventionally, the surfaces used to allow attachment of the jet flow according to the Coanda effect are solid, i.e. they can be considered to be impervious to the fluid. This ensures attachment through the appropriate prevention of entrainment.

This invention relates to the use of surfaces involved in the attachment of the jet flow which are porous such that they can allow the fluid to pass through them.

By controlling the flow of fluid through the porous surface, attachment of the jet and its mixing and deflection can be influenced.

For example, in a typical thrust vector application, the exhaust flow from a jet engine is made to flow over a curved plate. The curved plate which forms the Coanda surface is solid (non-porous) and is bounded at its sides of the solid surfaces (side plates) which prevent entrainment into the exhaust jet from the sides. The position at which the side plates end relative to the Coanda surface can be varied. Beyond this position, the exhaust jet is able to entrain surrounding air and is able to separate from the Coanda surface. Thus by varying the position of the end of the side plates, the extent to which the exhaust flow is deflected can be controlled.

However, if the side plates are positioned along the complete length of the Coanda surface and the Coanda surface is made of porous material, the attachment of exhaust flow to the Coanda surface can be controlled by controlling the entrainment through the porous surface. This can be achieved in a number of ways - for example a plenum can be created beneath the Coanda surface. The main exhaust flow will attempt to entrain through the porous Coanda surface from this plenum region. If the supply to this plenum region has a valve, the amount of entrained flow can be controlled. In practice this entrained flow (secondary flow) could be used to supply positive pressure to the plenum and force separation of the jet flow. Alternatively, another impervious surface could be allowed to slide beneath the porous Coanda surface controlling the position over which entrainment takes place. One advantage of this approach is that the sliding surface can be made of thin material which is easy to move and to store and the porous surface can be use to take the load resulting from the pressure difference. A further advantage is that whilst the jet is entraining through the porous surface, that part of the surface will be kept cool.

The invention is more particularly described by way of Figure 1 which is a cross- section through a Coanda device. Fluid leaves the nozzle, 1, to form a jet, 2, which entrains surrounding fluid. A porous Coanda surface, 3, is placed in the proximity of the nozzle. An impervious surface, 4, is able to move beneath the porous surface, 3, so as to block entrainment into the jet to different extents. At the position, 5, where the impervious surface, 4, terminates, flow can be entrained through the porous surface and jet detaches from the porous surface, 3, thus leaving at an angle relative to its initial trajectory.

Variations to this invention include, a two sided Coanda device in which flow is split between the two surfaces and can be made to fully attach to one surface whilst detaching from the other surface. The two surfaces can be connected to each other or can be made opposing so that the two complimentary jet flows are formed. The Coanda surfaces can be curved or made of flat sections at discrete angles to each other. The secondary flow can be provided at positive pressure.

The porosity of the surface can be variable along its length. The side plates of a nozzle can be made porous as well as or instead of the Coanda surface so as to allow entrainment from the side.

Claims

1. A propelling nozzle which produces a jet of fluid which entrains a secondary flow from the surrounding fluid medium and which has a porous surface close to its proximity which, at some point downstream of the nozzle exit, is angled away from the initial trajectory of the jet. The porous surface has some means of closing the porosity so that entrainment into the jet can be controlled. In the region of the porous surface, if the entrainment is restricted, the jet will attach to the porous surface and start to follow the direction of the surface. At the position along the porous surface where entrainment is no longer restricted, the entrainment into the jet will allow separation to occur and the jet will no longer remain attached to the surface and will not necessarily continue to follow its direction.

2. A nozzle according to claim 1 in which the porous Coanda surface is curved in the! direction of the jet flow.

3. A nozzle according to claim 1 in which the Coanda surface is flat but angled away from the initial direction of the jet leaving the nozzle.

4. A nozzle according to claims 1, 2 and 3 in which the edges of the Coanda surface are bounded by solid surfaces at the sides (side plates) to prevent entrainment of flow into the jet from the sides.

5. A nozzle according to claims 1 to 4 in which the Coanda surface is made up of a series of flat segments each of which is progressively angled relative to the previous one in the direction of flow and away from the initial direction of the jet leaving the nozzle.

6. A nozzle according to any of the preceding claims in which the Coanda surface may not be planar in the direction normal to the flow but rather may be angled to provide more than one region of Coanda surface.

7. A nozzle according to any of the preceding claims in which flow through the porous surface is controlled by the use of a solid surface beneath the porous surface.

8. A nozzle according to any of the preceding claims in which secondary flow through the porous surface is controlled by the use of valves feeding discrete chambers beneath the Coanda surface.

9. A nozzle according to any of the preceding claims in which the secondary flow is controlled by using a second porous surface beneath the main Coanda surface which can vary the aperture of the porous regions.

10. A nozzle according to any of the preceding claims in which the secondary flow is supplied at positive pressure relative to the surrounding medium so that it can be forced through the Coanda surfaces.

11. A nozzle according to any of the preceding claims in which the jet is split into two and fed to two Coanda surfaces, either opposing or adjacent to each other.

12. A nozzle according to any of the preceding claims in which the porosity of the Coanda surface can vary along its length, and even reduce to zero.

13. A nozzle according to claim 4 in which the side plates can also be made porous as well as or instead of the Coanda surface in order to allow and control entrainment from the side into the jet.

14. A nozzle according to any of the preceding claims in which the jet is from an air breathing jet engine.

15. A nozzle according to any of the preceding claims in which the jet flow is of water

16. A nozzle according to any of the preceding claims in which the jet flow is of any type of fluid.

17. A nozzle which achieves vectoring of the main thrust component by causing the jet which emanates from the nozzle to attach to a porous surface through which there is a means of preventing entrainment into the jet up to the point along the porous surface where the angle of vector is required.