GB2143598A - Separating particles from leakage gas flows - Google Patents

Abstract

The device (1) incorporates a gap, formed between a wall (3) of a stationary part (2) of the turbo-machine and facing wall (5) on a rotating part (4) of the machine, which extends generally radially and through which gas flow from an adjacent region leaks. In order to avoid foreign particles passing into that region in the reverse gas flow which is induced along the stationary wall (3), that wall is provided with projecting edges (10) directed towards the rotating wall (5) which have the effect of breaking up the reverse flow into eddies which carry the particles into the turbulent flow adjacent the rotating wall from where they are led outwards by centrifugal action. The projecting edges (10) may be formed by equally and oppositely inclined wall surfaces (6 and 7) though in other embodiments the profile may be of saw-tooth or other form. Radial or radially inclined channels and/or projections may be provided on the rotating wall to provide outflow passages for the separated particles. <IMAGE>

Description

SPECIFICATION Device for separating foreign particles from leakage gas flows of turbo engines This invention relates to a device for separating foreign particles or droplets from leakage gas flows of turbo engines, turbo chargers or gas-turbine mechanisms, in which a leakage gas flow is conveyed through a gap between a wall which is stationary during operation of the engine and an oppositely-located wall which rotates.

In sealing or bearing gaps of air bearings of high speed rotors, e.g. gas-turbine mechanisms and exhaust gas turbo chargers, exhaust gas particles or particles of dirt from the air can enter and be deposited. Air bearings are extremely sensitive with regard to the entry of such particles and can thus become unserviceable in a very short time.

The aim of the invention is to produce a device of the type mentioned at the beginning, with which in a comparatively simple way the leakage air or gas flows that can be removed from pressurised areas of the engine should be able to be freed to a great extent from entrained particles before being used again.

According to the present invention, there is provided a device for separating foreign particles or droplets from leakage gas flows of turbo engines, turbo chargers or gas turbine mechanisms, comprising a first wall member connected or connectible with a part of the turbo-machine which is stationary during operation of the engine and a second wall member connected or connectible with a part of the turbo-machine which rotates during operation of the engine, the first and second wall members being adapted to be located in facing relationship to each other adjacent a region of the turbo-machine, such as an aerodynamic or gas dynamic bearing, to define a gap between them through which leakage gas flow is conveyed, the stationary, first wall member having at least one edge which in use projects towards the oppositelylocated region of the rotatable, second wall member so that in operation a leakage flow moving along the stationary wall radially inwards is broken or deflected and hence foreign particles or droplets contained therein reach the rotational turbulence field fed by a portion of the leakage flow and formed by a centrifugal force effect along the rotatable, second wall member, whereby the particles or droplets are centrifuged radially outwards from this and the remaining purified residual leakage gas flow works as a sealing gap medium for the adjacent machine region.

In a plain radially extending gap formed from flat walls without projecting edges, it can be understood that a rotating drag current is superimposed on the leakage flow directed radially inwards through the shearing effect of the border layer remaining on the moving wall. In the gap area there is consequently formed a flow state which is governed by a relative turbulence. The relative turbulence can be described as a ball of fluid whose core rotates with reduced speed round the axis of the rotor. The edge areas of this turbulence have a radial flow speed component, and particularly in the region of the rotating wall, because of the centrifugal force effect, it is directed radially outwards and on the opposite side of the gap at the non moving wall it is directed radially inwards by way of compensation.The inwardly directed (reverse) leakage flow superimposed on this turbulence therefore takes up its path along the non-moving wall. Particles carried and entrained by the leakage flow are thus transported radially inwards on the same path.

The fluid material forming the turbulence is constantly changed from the oncoming leakage flow.

Therefore entrained, solid or liquid particles reach the turbulence zone and there undergo the influences of this intrinsic centrifugal force field. Because of the higher specific mass of the particles with respect to the carried medium, it would therefore at least in theory be conceivable to subjugate latter forces that are working outwards and which are higher under the effect of the centrifugal acceleration, so as to be able to separate them.The proportion of the particles separated in this way depends however, amongst other things, on to what extent the leakage flow is likely to take part in the turbulence movement, and it must therefore be reckoned that a proportionately large amount of the leakage flow - in particular in the immediate vicinity of the non-moving wall - is not subjected to any turbulence effect at all and thus flows radially inwards without the entrained particles being able to be separated.

Even the theoretically possible idea of a reduction in the gap, i.e. the distance between the two functional surfaces forming the gap area, should at best lead to a reduction in the leakage flow, but in principle can alter nothing as regards the fact that particles can be carried radially inwards along the non-moving wall. Not until the gap width is reduced to the order of magnitude of the size of the particles themselves could one reckon on each penetrating particle being able to be satisfactorily caught hold of by the shearing movement of the rotation, so as to be able to be separated outwards under the effect of the centrifugal acceleration. The air film in an air bearing generally has a thickness of a few 1/1000 mm.A particle which can pass through this film without causing any damage would have to be about an order of magnitude smaller than the thickness of the air film in the bearing. Thus it would be required that the gap in the separation device be adjusted to this order of magnitude. However, in practice this is not possible since, for freedom from contact of the working surfaces at this point, a gap of a few 1/10mum up to lmm during operation must be retained in order to be able to compensate manufacturing tolerances of the associated components, different heat expansions and movements from the dynamic processes.

According to the invention it is therefore proposed to construct the non-rotating wall of the gap area in such a way that the entrained particles are caused to depart from the leakage flow near the wall and to come into the influence zone of the rotating turbulence, so that they are centrifuged by this out of the gap region. In accordance with the invention, this effect occurs in particular by the construction of at least one projecting edge on the gap wall of the fixed, i.e. non-rotating, part. The energy required to bring about this effect is derived from the moving wall of the gap and partially also from the inflowing medium. In operation, an axial flow component is induced on the fixed part during the gap wall limit flow, because of the projecting edge.The leakage flow directed radially inwards near the wall is thus broken on the one edge or edges, is deflected and partially eddied.

Owing to their greater specific mass, the entrained particles can not follow these abrupt changes in direction in the same way and thus go deeper into the zone of the described turbulence.

Owing to the fact that the separation device and the adjacent machine region, e.g. an air bearing, can be connected in series, the latter can be constructed and driven completely uninfluenced by any foreign body separation criteria.

One advantageous development of the invention provides for the gap wall of the fixed part to have at least one inclined surface at an angle to the radial cross-section of the rotating part. The inclined surface is combined with the projecting edge of the invention and increases the breaking effect of the leakage flow directed substantially radially inwards.

There can be provided several preferably parallel-inclined surfaces on the gap wall of the fixed part, and adjacent inclined surfaces may be interconnected by oppositely directed surfaces of the same mutual inclination so as to form the edges.

Thus several breaks in the leakage flow may be arranged successively in the radially inward direction.

An advantageous embodiment of the invention provides for there to be several inclined surfaces in a saw tooth profile on the gap wall of the fixed part. The angles formed by the individual areas of the surface of the non-rotating wall broken into axially symmetrical conical surfaces in the meridian section with respect to the axis normal, can also be different from each other and are empirically optimised.

To increase further the particle separation effect, the rotating wall can also be profiled, primarily by radially extending channels. When these lateral channels rotate, they exert a driving effect on the fluid located in the gap. The drive of the above described turbulence no longer takes place only by friction forces of the boundary layer remaining on the rotating wall, but also by surface forces of the rotating channel edges. The width of the mechanically necessary operating gap and the depth of the channels indicated can be adjusted to obtain an optimum effect on each other. Thus it is also possibie, through the construction of channels, to cause a return which drives a feed flow from the inner area radially outwards over the amount of penetrating leakage flow.This could be particularly useful if a radially inwardly situated air bearing is to be permeated by cooling air or closure air.

The open radial channels in the gap wall of the rotating part can, as seen in the circumferential direction, take various forms, as seems to be the most appropriate for the function. In particular there can be provided a saw tooth profile : the runoff edge thus carries a flat angle, the run-up edge is arranged at a right angle or steep angle to the circumferential direction. Also the open radial channels can be constructed in various different ways in the front elevation of the rotating wall. On the one hand radial channels that extend exactly radially and are arranged in star-form are possible.

The generally radial channels, however, can also be arranged to be inclined radially outwards in a straight line or also curved (spiral shaped). A particularly preferred arrangement is when there is provided a constant gap width between the fixed profiled part and the rotating profiled part. Also with the channel construction of the rotating wall the axially outer limit of the channels can be brought near to the mechanically necessary operating gap on the profiled surface of the non-rotating wall.

The projecting edge of the invention in the gap wall of the fixed part can also be constructed, in accordance with the basic principle of the invention, preferably by an axially extending circumferential surface adjoining a radial surface of the fixed wall, whereby the rotating wall has channel walls with radially outward projections which surround the edge on the non-rotating wall. Also the leakage flowing to the wall of the fixed part in the gap which is formed by the distance to the rotating part is sharply deflected at the edge, and hence the entrained particles are delivered to the output of the rotating profiled wall, caught up by the rotation and radially centrifuged.

The invention may be put into practice in a number of ways but certain specific embodiments will now be described, by way of example, with reference to the drawings. These show: Figure 1 a gap construction of a device in accordance with the invention, between a fixed and a rotating component, shown in axial longitudinal section; Figure 2 the gap wall construction of the fixed and rotating parts in another form; Figure 3 a gap construction similar to that of Fig.1 with open radial channels in the rotating wall; Figure 4 a gap construction with profiled gap walls of another form; Figure 5 a partial circumferential view of the gap with saw-tooth profiled radial channels on the rotating wall; Figure 6 a partial front view of a rotating wall with channels extending with a steep inclination to the radial direction; ; Figure 7 an embodiment corresponding to that of Fig.3 with radial channel walls in close proximity to the fixed profiled gap walls; and Figures 8 to 10 further embodiments of gap walls with radial channel construction in the rotating wall.

In Fig.1 there is shown, in axial longitudinal section, a gap construction 1 of the device between a fixed component 2 and a rotating component 4.

The gap includes a section that extends substantially radially with one flat radially extending gap wall 5 on the rotating component 4 and an axially symmetrical, non-flat, gap wall 3 constructed as viewed in axial section in a zig-zag, on the fixed component 2. In particular the gap wall 3 has inclined surfaces 6 which are spaced apart and extend parallel to one another, which are inclined at an angle e to the normal to the rotational axis. The inclined surfaces 6 extend from radially outwards to radially inwards and inclined in a direction towards the gap wall 5 of the rotating component 4.

Between the inclined surfaces 6 there are equally and oppositely directed inclined surfaces 7 formed in the gap wall 3, which produce circular projecting edges 10 and circular set back edges (internal apices) 9. The effect of the projecting edges 10 is that the radial inwardly directed leakage flow is broken or upset in the region of the gap wall 3 in such a way that particles present in the flow reach the turbulence field in the zone of the gap wall 5 of the rotating part 4 and from there are centrifuged radially outwards because of the effects of the centrifugal force field present in operation as produced by the rotating part 4.

In the embodiment according to Fig.1 there are provided two inner break zones with projecting edges 10, so that particles which were not yet separated at the first edge are safely conveyed away at the second edge and hence are kept out of the air bearing which can extend to a radially inner point between the fixed component and the rotat ing component for example in the radial direction.

In the device shown in Fig.2, the axially sym metrical gap wall 3 of the fixed part 2 is differently constructed. Basically there are again inclined surfaces 6 as in the embodiment of Fig.1, but the interconnecting inclined surfaces 6 are short inclined surfaces of a different, steeper, inclination that run parallel to one another and are constructed per pendicularly to the inclined surfaces 6, so that a saw-tooth profile is formed, as viewed in axial section. The projecting edges 10 that result are not obtuse angled as according to the embodiment of Fig.1, but rectangular. An acute angle at each edge is also possible.

The embodiment shown in Fig.3 corresponds basically to that of Fig.1 wherein there are con structed, in the gap wall 5 of the rotating compo nent 4, radial channels 13 which should provide for a better discharge of the particles radially outwards. The radial channels 13 have a radially extending base 12 and are open in the direction of the fixed part 2 so as to be able to receive safely particles that are to be separated.

The walls of the radial channels 13 and of the gap can diverge, as viewed in the meridian section, from the radial direction, as shown in the embodiment according to Fig.4, so as to strengthen the effect of the particle separation.

In the circumferential direction, the radial channels 13 can be constructed in zig-zag form as is shown in Fig.5. The part 4 rotating in the direction of the arrow thus has radial channels 13 with a run-off edge with a flat angle and a run-up edge at right angles to the circumferential direction, so that the particles to be separated are picked up particularly effectively by the rotation.

The radial channels 13 can extend exactly radially outwardly or can extend at an angle inclined to the general radial direction, as is shown in Fig.6, illustrating a front view of the rotating part 4. The radial channels 13 can alternatively be curved.

In a further embodiment, the axially outer limit of the radial channels 13 can be drawn up to the mechanically necessary operating gap onto the broken surface of the non-rotating wall, as is shown in Fig.7. The necessary operating gap thus has a constant width b, even in the kinked areas.

Combinations of different ones of the abovementioned concepts are possible. For example, when sticky particles are to be separated out, it may be advantageous to provide a combination of the arrangements of Figs.4, 6 and 7, so that particles adhering to the working surfaces are released again by centrifugal voices or are peeled off (removed) by the sharp edges.

Another construction in accordance with the basic principle of the invention can be seen in Fig.8. In this, a profile belonging to the gap wall 5 of the rotating part 4 formed by a radially outer surface section 11, overlaps the outer edge 10 of the gap wall 3 belonging to the fixed part 2. The leakage flowing along the gap wall 3 of the fixed part, in the gap formed by the distance to the rotating part 4, is sharply deflected on the "projecting" edge 10 and hence the entrained particles are carried into the working area of the rotating profiled gap wall 5, are picked up by the rotation and are centrifuged radially outwards. The surface section 11 of the radially outer overlapping portion of the rotating part 4 on the rotating part 4 and the adjacent surface 8 on the fixed part 2 extend in the axial direction.

The above-mentioned principle can also be put into effect basically according to the embodiments of Figs.9 and 10, whereby inner axial surface sections 8 are provided on the fixed part 2 so that zigzag shaped gap walls 3 are constructed on the fixed part 2. In the embodiment of Fig.9 there are provided radial channels 13 extending at an inclination to the normal to the rotational axis, whilst the radial channels 13 of Fig.10 lie along the perpendicular to the axis.

As shown in Fig.1 - and representative of all the other embodiments - the residual leakage gas flow that is cleaned by the separation device, and which is therefore free for example of foreign particles, is designated R, and can be supplied for example to an air bearing connected on the outlet side as a sealing gap medium.

Thus, in summary, the device (1) incorporates a gap, formed between a wall (3) fixed to a stationary part (2) of the turbo-machine and a wall (5) on a rotating part (4) of the machine, which extends generally radially and through which gas flow from an adjacent region leaks. In order to avoid foreign particles passing into that region in the reverse gas flow which is induced along the stationary wall (3), that wall is provided with projecting edges (10) directed towards the rotating wall (5) which have the effect of breaking up the reverse flow into eddies which carry the particles into the turbulent flow adjacent the rotating wall from where they are led outwards by centrifugal action. The projecting edges (10) may be formed by equally and oppositely inclined wall surfaces (6 and 7) though in other embodiments the profile may be of sawtooth or other form. Radial or radially inclined channels and/or projections may be provided on the rotating wall to provide outflow passages for the separated particles.

Claims (15)

1. A device for separating foreign particles or droplets from leakage gas flows of turbo engines, turbo chargers or gas turbine mechanisms, comprising a first wall member connected or connectible with a part of the turbo-machine which is stationary during operation of the engine and a second wall member connected or connectible with a part of the turbo-machine which rotates during operation of the engine, the first and second wall members being adapted to be located in facing relationship to each other adjacent a region of the turbo-machine, such as an aerodynamic or gas dynamic bearing, to define a gap between them through which leakage gas flow is conveyed, the stationary, first wall member having at least one edge which in use projects towards the oppositelylocated region of the rotatable, second wall member so that in operation a leakage flow moving along the stationary wall radially inwards is broken or deflected and hence foreign particles or droplets contained therein reach the rotational turbulence field fed by a portion of the leakage flow and formed by a centrifugal force effect along the rotatable, second wall member, whereby the particles or droplets are centrifuged radially outwards from this and the remaining purified residual leakage gas flow works as a sealing gap medium for the adjacent machine region.

2. A device as claimed in claim 1, in which the stationary, first wall member has at least one inclined surface terminating in the or a projecting edge, which surface when the device is installed on a turbo-machine is inclined to the radial crosssection of the rotatable wall member.

3. A device as claimed in claim 2, in which severa! parallel inclined surfaces are provided on the stationary wall member, adjacent inclined surfaces being interconnected by respective oppositely directed surfaces of the same mutual inclination to form a plurality of the said edges.

4. A device as claimed in claim 3, in which on the stationary wall member there are several inclined surfaces in a saw-tooth profile.

5. A device as claimed in any one of claims 1 to 4, in which the stationary wall member component has at least one surface extending in the axial direction of the rotatable wall member.

6. A device as claimed in any one of the preceding claims, in which the surfaces of the stationary wall member are axially symmetrical.

7. A device as claimed in any one of claims 1 to 6, in which the rotatable wall member has at least one radially extending surface section that is axially displaced with respect to another radially extending surface section of that member.

8. A device as claimed in any one of claims 1 to 7, in which the rotatable wall member has at least one axially projecting surface portion.

9. A device as claimed in any one of claims 1 to 8, in which the stationary wall member and the rotatable wall member are adapted so that when installed there is a gap of constant width between them.

10. A device as claimed in any one of claims 1 to 9, in which radial channels open towards the stationary wall member are formed in the rotatable wall member.

11. A turbo-machine having a device according to any one of the preceding claims, in which the rotatable part having connected to it the rotatable wall member is a component of the engine rotor and is directly or indirectly a carrier for a rotating sealing ring of an aerodynamic or gas dynamic bearing that is connected on the outlet side.

12. A turbo-machine having a device according to any one of claims 1 to 10, in which the stationary part to which the stationary wall member is connected, is directly or indirectly the carrier for a stationary sealing ring of an aerodynamic or gas dynamic bearing connected to the outlet side.

13. A turbo-machine having a device according to any one of claims 1 to 10, in which an aerodynamic or gas dynamic bearing is arranged to lie radially inwardly with respect to the device and is constructed between the components that are stationary and rotating in operation.

14. A device for separating foreign particles or droplets from leakage gas flows of a turbo-machine, substantially as specifically described herein with reference to any one of the embodiments shown in the drawings.

15. A turbo-machine having a device as claimed in claim 14.