EP0581978B1 - Multi-zone diffuser for turbomachine - Google Patents

Description

Technical field

• wobei die Knickwinkel des Diffusoreintritts sowohl an der Nabe als auch am Zylinder der Turbomaschine ausschliesslich zwecks Vergleichmässigung des Totaldruckprofils über der Kanalhöhe am Austritt der letzten Schaufelreihe festgelegt sind,
• wobei innerhalb der Verzögerungszone des Diffusors Mittel zur Drallwegnahme der drallbehafteten Strömung in Form von Strömungsrippen vorgesehen sind,
• und wobei strömungsführende Leitringe den Diffusor mehrkanalig unterteilen.

The invention relates to a multi-zone diffuser for an axially flow-through turbomachine.

• the kink angles of the diffuser inlet both on the hub and on the cylinder of the turbomachine being determined exclusively for the purpose of making the total pressure profile uniform over the channel height at the outlet of the last row of blades,
• wherein means for removing the swirl of the swirled flow in the form of flow ribs are provided within the delay zone of the diffuser,
• and flow-guiding rings divide the diffuser into multiple channels.

State of the art

Such multi-zone diffusers for turbomachinery are known from EP-A 265 633. In order to meet the demand there for the best possible pressure recovery and swirl-free diffuser outflow at part load, a rectifying grating is provided within the diffuser, which extends over the entire height of the channel through which flow passes . These means for swirl removal are cylindrical flow ribs arranged uniformly over the circumference with thick straight profiles, which are designed according to the knowledge of turbomachine construction and which should be as insensitive as possible to oblique flow. The leading edge of these ribs is located relatively far behind the trailing edge of the last blades in order to avoid excitation of the last row of blades caused by the pressure field of the ribs. This distance is dimensioned such that the front edge of the ribs is in a plane in which a diffuser area ratio of preferably three predominates. This first diffusion zone between the blading and the flow ribs should thus remain undisturbed due to total rotational symmetry. The fact that no interference effects between the ribs and the blades are to be expected is due to the fact that the ribs only become effective in a plane in which a relatively low speed level already prevails.

Since, in the case of customary, heavily loaded blades of turbines, their opening angle far exceeds that of a good diffuser, the known diffuser for supporting the flow in the radial direction is divided into several partial diffusers by means of flow-guiding rings. These guide rings extend from a level directly at the exit of the blading to a level at which a diffusion ratio of three has been reached, i.e. over the entire first diffusion zone. For reasons of vibration, these guide rings should preferably be formed in one piece. This leads to a solution which is disadvantageous for assembly reasons, without a parting plane. In addition, the guide rings lead to large diameters, so that transport problems can arise.

A second diffusion zone extends from the front edge of the thick flow ribs to the greatest profile thickness of the ribs. In this second zone, the swirling of the flow is to be carried out for the most part, largely without delay. In a third subsequent diffusion zone in the form of a straight diffuser there is a further delay in the flow, which at the time was almost swirl-free.

With all of these measures, in addition to maximum pressure recovery, in particular at partial load, the overall length of the system is to be shortened.

In conventional gas turbines, the diffuser is flowed at at idle under a speed ratio c _t / c _n of approximately 1.2, where c _{t means} the tangential speed and c _n the axial speed of the medium. This oblique flow leads to a drop in the pressure recovery C _p .

With other machine types, such as steam turbines or gas turbines for fluidized bed combustion, it is quite possible that the volume flow is reduced to 40% and thus there are c _t / c _n ratios of up to 3. With such machine types, a fixed diffuser geometry is not recommended, since the pressure recovery could even become negative. This applies even in the case where the ratio of pitch to chord of the flow ribs is 0.5. Flow ribs with pitch / chord ratios of about 1, which would result in a somewhat greater pressure recovery at full load, ie c _t / c _n = approx. 0, cannot be used at all in such machines.

The large drop in pressure recovery can be attributed to the fact that, under the extreme conditions mentioned, a strong vortex is formed between the outlet blades and flow ribs. The vortex is limited by the flow ribs on which the tangential component of the velocity is dissipated. If solid particles, for example in gas turbines or water droplets, for example in steam turbines, are carried along with the return flow, an acute risk of foot erosion can arise on the blades of the last run row.

To remedy this, it is known from EP 0 417 433 A1, in the case of a turbomachine of the axial type in the diffuser to arrange at least one row with adjustable guide vanes between the means for swirl removal and the outlet rotor blades. The means for swirl removal within the diffuser are here also flow ribs arranged uniformly over the circumference with a straight skeleton line and a symmetrical profile and with a ratio of division to chord between 0.5 and 1 in the middle section of the flowed channel. These flow ribs are tapered in the radial direction. These measures of diffusion design are intended to further improve the part-load behavior of the machine.

Presentation of the invention

On the basis of a 3D optimization using Navier-Stokes computing methods, the object of the invention is for a multi-zone diffuser of the type mentioned at the given diffuser area ratio, which is understood to mean the ratio of the flow cross sections at the outlet to the inlet of the diffuser, and with the smallest possible diameter in the first diffusion zone, as well as with the physically greatest possible pressure recovery and swirl-free outflow, to keep the total length of the diffuser to a minimum.

• dass eine erste Diffusionszone sich von der Austrittsebene der letzten Schaufelreihe bis zu einer Ebene am Austritt der Strömungsrippen erstreckt und einkanalig ausgebildet ist, wobei der äquivalente Öffnungswinkel der Meridiankonturen stromabwärts der Knickwinkel zur Vermeidung von Strömungsablösung reduziert wird, so dass eine Art Glockendiffusor entsteht;
• und dass eine zweite Diffusionszone in Form eines mehrkanaligen Diffusorteils gebildet wird, wobei die strömungsführenden Leitringe stromabwärts der Strömungsrippen angeordnet sind.

According to the invention, this is achieved by

• that a first diffusion zone extends from the exit plane of the last row of blades to a plane at the exit of the flow ribs and is of single-channel design, the equivalent opening angle of the meridian contours downstream of the kink angle being reduced to avoid flow separation, so that a kind of bell diffuser is formed;
• and that a second diffusion zone is formed in the form of a multi-channel diffuser part, the flow-conducting guide rings being arranged downstream of the flow ribs.

The advantage of the invention is to be seen, inter alia, in the fact that the bend angle idea can be implemented for the first time by means of a single-channel diffuser in the case of a strongly divergent flow. The fact that the previous multi-channel system in the first diffusion zone can be dispensed with results in the desired small diameter of this zone. This diameter is decisive for the portability of the assembled machine on railways. This applies even to the largest unit outputs currently customary in gas turbines, for example.

It is particularly expedient if a third diffusion zone in the form of an impact diffuser is formed downstream of the second diffusion zone, the axial length of which is essentially L = D / n, where D is the diameter of the flowed-through channel (in the exhaust pipe) and n the number of channels in the second diffusion zone. As a result, flow inhomogeneities after the second diffusion zone can be compensated for and the pressure recovery can be increased further. In addition, interference effects with downstream flow components such as silencers, boilers etc. can be avoided. In addition, such a compensation zone reduces the sensitivity of the pressure recovery to partial load conditions.

It is useful if, in order to largely avoid interference with the last row of the blades, the ratio of the rib spacing a from the exit of the blades to the rib pitch t is at least 0.5. This measure also results in a full utilization of the working ability of the fluid.

If the ratio of rib chord s to rib pitch t is at least 1, it is ensured that the sensitive diffuser flow is free of detachment in the axial outflow direction is redirected and that a contribution to the desired delay is made.

Provided that the ratio of the greatest profile thickness d _{max of} the flow ribs to the rib chord s is at most 0.15 and is largely constant over the rib height, overspeeds, local Mach number problems and different displacement effects are minimized.

It is also appropriate if the leading edges of the ribs are oriented above the rib height so that they are cut perpendicularly by the streamlines. Together with the measure d _max / s = constant, this ensures that the flow is not pushed radially outwards and hub separation is formed.

The curvature of the Velcro line of the ribs is advantageously chosen with regard to a smooth entry and an axial outflow. This guarantees the desired high pressure recovery as well as a certain insensitivity to partial load.

It is expedient if the meridian contour of the diffuser in the region of the ribs is additionally expanded in order to avoid overspeeds on the ribs. With this measure, the displacement effect caused by the ribs is compensated for at least in the peripheral zones.

It is particularly favorable if the diffuser is provided with a horizontal parting plane in the first diffusion zone. Due to the fact that, in contrast to the solution mentioned at the beginning, the first diffusion zone is not equipped with guide rings, which are usually made in one piece for reasons of vibration, thanks to the parting plane it is possible to cover the first zone and thus easy assembly and disassembly of the blading, for example guaranteed without auxiliary devices and without axial displacement.

In the case of a parting plane in the first diffusion zone, an even number of ribs is provided, ribs being arranged in the vertical plane, but not in the horizontal plane. The lower vertical rib can thus be used to support the diffuser and there is no need for split ribs.

It is advisable to provide several profiled hollow ribs with defined tear-off edges in the second diffusion zone, which are distributed uniformly over the circumference and arranged symmetrically to the vertical plane. This makes it possible to ventilate the hub body using natural convection. The necessary supply lines for the storage and the rotor and housing cooling can be led through these hollow ribs. If necessary, the blow-out quantities required for the compressor of a gas turbine system can also be mixed into the exhaust gas through these hollow ribs.

It is expedient to provide the inner ring wall of the diffuser with a defined tear-off edge at the outlet of the second diffusion zone. On the one hand, this minimizes the cross-section of the demolition and, on the other hand, speeds up the compensation of the flow inhomogeneities.

Brief description of the drawing

Fig. 1

einen Teillängsschnitt einer Gasturbine mit erfindungsgemässem Diffusor;

Fig. 2

das Detail 2 gemäss Fig. 1 in vergrössertem Massstab;

Fig. 3

eine perspektivische Ansicht einer strömungsorientierten Rippe in Form von Netzlinien;

Fig. 4

einen Teillängsschnitt einer Gasturbine mit axial/radialem Abgasdiffusor;

Fig. 5

einen Teillängsschnitt des Verdichters einer Gasturbinenanlage mit stehender Einzelbrennkammer;

Fig. 6

einen Teillängsschnitt des Verdichters einer Gasturbinenanlage mit ringförmiger Brennkammer.

In the drawing, several embodiments of the invention are shown schematically and in a simplified manner. Show it:

Fig. 1

a partial longitudinal section of a gas turbine with a diffuser according to the invention;

Fig. 2

detail 2 according to FIG. 1 on an enlarged scale;

Fig. 3

a perspective view of a flow-oriented rib in the form of net lines;

Fig. 4

a partial longitudinal section of a gas turbine with axial / radial exhaust gas diffuser;

Fig. 5

a partial longitudinal section of the compressor of a gas turbine system with a standing single combustion chamber;

Fig. 6

a partial longitudinal section of the compressor of a gas turbine system with an annular combustion chamber.

In the gas turbine according to FIG. 1 with an axial / axial exhaust gas diffuser, only the elements essential for understanding the invention are shown. The system does not show, for example, the compressor section, the combustion chamber and the complete exhaust pipe and chimney.

In the different exemplary embodiments, the same elements are each designated with the same reference symbols, but with different indices. The embodiment shown in FIGS. 1, 2 and 3 has no indices. For the sake of clarity, the articulation angles are designated as such only in FIG. 2. The direction of flow of the working fluid is indicated by arrows.

Way of carrying out the invention

The gas turbine, of which only the last three axially flowed stages are shown in FIG. 1, essentially consists of the bladed rotor 1 and the blade carrier 2 equipped with guide blades. The blade carrier is suspended in the turbine housing 3. The rotor lies in a support bearing 4, which in turn is supported in an exhaust housing. In the example, this exhaust housing essentially consists of a hub-side inner part 6 and an outer part 7, which limit the diffuser 13. Both elements 6 and 7 are pot housings with a horizontal parting plane at shaft height. They are connected to one another by a plurality of welded supporting flow ribs 8, which are evenly distributed over the circumference and whose profile is indicated by 9. The exhaust housing is designed so that it is not in contact with the exhaust gas flow. The actual flow control is taken over by the diffuser, which is designed in its first zone as an insert for the exhaust housing. For this purpose, the outer boundary wall 14 and the inner boundary wall 15 of the diffuser are held over the flow ribs 8. The walls are penetrated by actual support bodies 10 which extend within the flow ribs and hold the exhaust gas housing 6, 7.

The decisive factor for the desired functioning of the diffuser is now the kink angle of its two boundary walls 14 and 15 directly at the exit of the blading. This is a highly loaded reaction blading with a large opening angle. A high Mach number flows through the last row of blades. The channel contour on the blade root is cylindrical, that on the blade tip runs obliquely at an angle of approx. 30 °. If this conicity were to be continued in the diffuser, the angle of 30 ° mentioned would be completely unsuitable in order to delay the flow and to achieve the desired pressure increase. The current would detach from the walls. Purely constructive considerations would normally lead to a reduction of the diffuser angle from 30 ° to 7 °. The resulting deflection of the streamlines at the kinks at the diffuser inlet and the associated harmful pressure build-up meanwhile reduce the gradient, ie the gas work above the blading. This results in lower performance. The energy not used leads locally to excess speeds at the diffuser outlet and subsequently dissipates in the exhaust pipe.

The diffuser is therefore designed solely on the basis of fluid dynamics. The considerations must lead to achieving the most homogeneous possible total pressure profile over the entire channel height, i.e. also on the hub and on the cylinder. The two bending angles are therefore determined on the basis of the entire flow in the blading and in the diffuser.

The equation for the radial equilibrium teaches that the meridian curvature of the streamlines is primarily responsible for the extent of the pressure increase mentioned above. This must therefore be primarily influenced by adjusting the angle of attack in order to achieve a homogeneous total pressure distribution. With this consideration, the kink angle α _N (FIG. 2) of the inner boundary wall 14 at the diffuser inlet is in principle determined. In the present case, this leads to an angle α _N which rises from the horizontal in a positive direction, namely by almost 15 °. This is due, among other things, to the influence of cooling air. As is well known, the hub, ie the rotor surface and the blade roots, are usually cooled down to a tolerable level with cooling air. Part of this cooling air now flows into the main duct along the rotor surface. This cooling air has a lower temperature than the main flow, which causes low-energy zones directly on the hub behind the last rotor blade. This gas turbine-specific fact now leads to the fact that the pressure gradient mentioned must be enforced here at the point of the lack of energy. And this is achieved by increasing the inner boundary wall 15 and a meridional deflection of the flow caused thereby. The energy built up in this way prevents the flow at the hub of the diffuser from becoming detached. From all this it can be seen that an arbitrary, for example cylindrical, continuation of the inner boundary wall of the diffuser would in any case be unsuitable to compensate for the typical leakage defects.

The same considerations are now also to be made with regard to the articulation angle α _z on the cylinder, ie on the outer boundary wall 14. Here, however, it is important to take into account that the flow is very high in energy due to the gap flow between the blade tip and blade carrier 2. In addition, it has a strong swirl. A homogeneous energy distribution can only be achieved here if the kink angle α _Z on the cylinder opens towards the outside in any case with respect to the inclines of the blading channel. In the example, this is done by an additional 10 °.

The result shows that the total opening angle of the diffuser is in the range of the opening angle of the blading, and may even be greater than this. Under no circumstances does it assume a value that would correspond to purely constructive considerations.

This creates the conditions for the pressure to be converted in the downstream diffuser in such a way that a homogeneous, uniform outflow is present at the outlet thereof.

However, it is now clear that a diffuser with a 30 ° opening angle is unsuitable to delay the flow. In the known diffuser mentioned at the outset, the channel is therefore divided in the radial direction by means of flow-guiding rings into a plurality of partial diffusers which are dimensioned according to the known rules.

worin

• U = der lokale Umfang des Strömungsquerschnittes;
• dA = die lokale Änderung des Strömungsquerschnittes;
• ds = die lokale Änderung des Strömungsweges entlang des Diffusors.

However, the present invention is based on the idea of designing the first diffusion zone 50 as a single channel. The flow-carrying parts of this first diffusion zone 50 are shown in FIG. 2. A so-called bell-shaped diffuser 26 (bell-shaped diffuser) is used to achieve the single-channel configuration. This means that the equivalent opening angle θ of the meridian contours downstream of the kink angles α _Z and α _N determined according to the above criteria is reduced in order to avoid flow separation. this happens first to a greater extent and then to a lesser extent, which leads to the bell shape shown. The equivalent opening angle Θ is understood here: $$\text{tan Θ / 2 =}\frac{\text{1}}{\text{U}}\text{·}\frac{\text{there}}{\text{ds}}$$

wherein

• U = the local circumference of the flow cross-section;
• dA = the local change in the flow cross-section;
• ds = the local change in the flow path along the diffuser.

Also in contrast to the known diffuser mentioned at the outset, in the present case the first diffusion zone 50 extends from the exit plane of the last row of blades to a plane at the outlet of the flow ribs 8. The latter are therefore included and their type, their design, their arrangement and their number based on the following considerations.

First, the distance a from the leading edge 24 of the flow ribs 8 to the exit of the blading is set in relation to the rib pitch t - which is the measure for the number of ribs. If this ratio is at least 0.5, interference with the last row 12 of the blading can be largely avoided.

In the present case, two things have to be taken into account when determining the tendon length of the flow rib. If the flow rib has a supporting function, the minimum cross-section should not be undercut. Sufficient space must be created in the interior of the ribs for the arrangement of the supporting bodies 10. With regard to the deflection task of the flow rib - with the help of which the swirled flow is to be rectified - a minimum chord length should also not be undercut. Now the ratio of rib chord s to Rib division t at least 1, so both tasks can be performed.

If the length of the chord and the rib division is also determined via the ratio s / t, the number of flow ribs is also given in principle. The arrangement of these ribs is now subject to the following criteria: In order to allow access to the blading and storage, the first diffusion zone 50 is provided with a horizontal parting plane, i.e. the outer boundary wall 14 and the inner boundary wall 15 of the diffuser are designed to be divided. No flow ribs are preferably installed in this horizontal parting plane in order to avoid a division of the ribs. On the other hand, it is advisable to arrange flow ribs in the vertical plane. The vertically oriented flow rib of the lower half can thus be used for support functions. If you insist on an even number of ribs for reasons of symmetry, there is a minimum number of 6 flow ribs over the circumference, which can be very useful for smaller machines. The next possible number of ribs which is best suited for the present purposes is 10. An even higher number would again impair the cross-section through which the flow passes and considerably increase the effort.

The ratio of the greatest profile thickness d _{max of} the flow ribs to the rib chord s should not exceed 0.15 and is kept largely constant over the rib height. This, in turn, in contrast to the flow ribs in the diffuser mentioned at the outset - relatively thin ribs avoid local Mach number problems and minimize different displacement effects above the blade height.

Again, in contrast to the flow ribs in the diffuser mentioned at the beginning, the flow ribs are curved. The curvature of the Velcro line of the ribs is with regard to a shock-free entry and an axial one Outflow selected, which leads to a variable curvature above the rib height.

As can be seen from FIGS. 1, 2 and in particular from FIG. 3, the ribs have a basic conicity. This is based on the idea of s / t = constant above the height of the ribs. This radius-independent configuration forms the starting position, which is then adapted to the actual flow in sections above the height of the ribs. For this purpose, the front edges 24 of the ribs are oriented above the rib height so that they are cut perpendicularly by the streamlines. This leads to leading edges, which in no way have to be aligned radially, as illustrated in FIG. 3.

In a departure from the bell shape, the meridian contour of the diffuser in the area of the ribs 8 is additionally expanded. At least this measure is taken in the area 25 from the front rib edge 24 to the greatest profile thickness. In this way, overspeeds on the ribs can be largely avoided.

This first diffusion zone 50, which ends at the outlet of the flow ribs, is designed with an area ratio of 1.8.

A second diffusion zone 51 in the form of a multi-channel diffuser part adjoins the first diffusion zone. It is designed with an area ratio of 2.5. For this purpose, two flow-guiding rings 16 are arranged downstream of the ribs 8, which divide the channel into three partial diffusers 17. The partial diffusers are designed as straight diffusers according to the known rules with equivalent opening angles of approximately 7.5 ° each. This measure shortens the second diffusion zone according to the rule L = L _1K / n. Here L is the axial extent of the second diffusion zone, L _{1K is} the axial extent of one single-channel diffuser with the same area ratio, n the number of partial diffusers.

At the end of this second diffusion zone 51 there are three profiled hollow ribs 18 distributed uniformly over the circumference, one of these hollow ribs standing vertically in the upper half. Electrical, air and oil lines can be passed through these hollow ribs. The blunt trailing edges of these hollow ribs are provided with defined tear-off edges 19. The annular inner boundary wall 15 of the diffuser, which ends at the outlet of the second diffusion zone 51 with a blunt section 20, is also provided with such a defined tear-off edge 21. With these measures, the cross-section of the demolition is kept as small as possible, the compensation is accelerated and the hub dead water is reduced.

As a result of the fanning out, this second diffusion zone 51 has a considerably larger diameter than the first diffusion zone 50. However, since the second zone is merely a sheet metal construction which can be assembled from disassembled parts at the installation site of the system, this fact offers in particular no difficulties with the rail transport.

A third diffusion zone 52 in the form of an impact diffuser is provided downstream of the second diffusion zone 51, this being a sudden expansion. The axial length of this Carnot diffuser, which is designed as a compensation zone, is L = D / n, where D is the diameter of the flow-through channel in the cylindrical exhaust pipe 22 and n is the number of channels in the second diffusion zone 51. The area ratio of this third diffusion zone 52 is 1.2, the trailing of the three hollow ribs also having to be taken into account here.

The total area ratio of the diffuser is therefore 5.3.

As a rule, both the cylindrical exhaust pipe 22 and the outer boundary wall 14 of the second diffusion zone 51 are welded together on the construction site to form a one-piece element. In order to ensure free access to the second diffusion zone, the second diffusion zone 51 is designed to be insertable axially into the third diffusion zone 52, as is indicated schematically at 23 in FIG. 1.

• Die Stufenarbeit kann gesteigert werden bei gleichbleibendem Wirkungsgrad oder
• der Wirkungsgrad kann gesteigert werden bei gleichbleibender Stufenarbeit;
• die Schaufeln der letzten Laufreihe könnten weniger verwunden ausgebildet werden, was zu einer Verbilligung führt;
• die Umlenkung in der letzten Turbinenstufe kann reduziert werden, was wegen der Partikelseparation insbesondere bei wirbelschichtgefeuerten Gasturbinen zum Tragen kommt.

The new measure also makes it possible to allow a certain counter-swirl at the outlet from the last blades 12, since an axial alignment takes place downstream in the diffuser through the flow ribs. This counter-swirl offers the following advantages:

• The step work can be increased with the same efficiency or
• the efficiency can be increased with constant step work;
• the blades of the last row could be made less wounded, which leads to a reduction in price;
• the deflection in the last turbine stage can be reduced, which is particularly important in the case of fluidized-bed-fired gas turbines because of the particle separation.

Of course, the invention is not limited to the exemplary embodiment shown and described in FIGS. 1 and 2, which has a diffuser with an axial outlet and thus greatly facilitates the arrangement of the flow ribs. It is particularly applicable in particular to steam turbines or gas turbines in general in turbines of exhaust gas turbochargers, and in compressors of gas turbines, which generally all have a so-called axial-radial or axial-radial-axial diffuser.

Such an example is shown in FIG. 4 using a gas turbine. The first diffusion zone 50B here corresponds to that of FIG. 1. The second diffusion zone 51B, which is divided into three partial diffusers 17B by means of two guide rings 16B, opens into a third diffusion zone 53B, which deflects strongly with only a slight delay. This strong deflection is greatly favored by the arrangement of the guide rings continuing into the diffusion zone 53B. This measure reduces the average radius of curvature of the third diffusion zone according to the rule R = R _1K / n. Here, R is the radius of curvature of the third diffusion zone, R _{1K is} the mean radius of curvature of a single-channel diffusion zone with the same area ratio, n is the number of channels. The third diffusion zone 53B opens radially into the chimney 27. The idea of an impact diffuser is also realized in this transition to the chimney.

In a departure from the solution shown in FIG. 1, the flow ribs can also be made full instead of hollow. This solution is useful if, for example, an actual exhaust housing is not used, i.e. when the exhaust housing takes over the flow-guiding tasks, i.e. when the outer boundary wall 14 of the diffuser forms the end to the outside and is flanged directly to the turbine housing.

FIG. 5 shows how the idea of the invention can be implemented in a compressor diffuser. This could be, for example, the compressor of the gas turbine shown in FIG. 1, it being possible for the system to be equipped with a standing individual combustion chamber (not shown). The latter configuration leads to the almost radial exit from the diffuser shown.

In the present case, both a regular compressor guide row and a follow-up row are provided in the first diffusion zone for swirling the flow. They take over the function of the flow ribs. The compressor guide row acting as the first flow rib 8C is designed according to the above-mentioned criteria, but there is no axial exit from the rib. Because in the flow direction, the rib 8C is followed by a guide line 8'C for further rectification of the flow, which of course can also be designed according to the criteria mentioned. The first diffusion zone extends from the rear edge of the blade 12C to a level behind the guide line 8'C. Of course, the two ribs 8C and 8'C could also be combined into a single flow rib.

The second diffusion zone is divided into two partial diffusers 17C by a guide ring 16C. This guide ring is held in its position in a third diffusion zone 53C, which is not very delaying but strongly deflects, via ribs 28 on a rotor cover 29C and on the outer boundary wall 14C. In this exemplary embodiment, the third diffusion zone merges into a fourth diffusion zone 54C, in which deceleration is continued.

In such a single-shaft, axially flow-through gas turbine, the shaft part located between the turbine and the compressor is designed as a drum 30. This is surrounded by the already mentioned rotor cover 29C. The annular duct 31C formed between the drum and the rotor cover takes over the guidance of the entire rotor cooling air removed on the hub side between the ribs 8C and 8'C of the compressor to the front side of the turbine, from where it reaches the cooling ducts on the rotor side. This cooling air on the rotor side is combined with the their adherent swirl directed into the ring channel 31C. This ensures on the one hand that the heating of the rotor via the cooling air and thus the level of the transient voltages is as small as possible. In addition, the purest possible, almost dust-free air is introduced into the ring channel through the hub-side removal. For the subsequent diffuser, air extraction has the advantage that the low-energy zone on the hub, which is pronounced in the case of compressors, is largely removed, which creates better conditions with regard to the diffuser inlet. It goes without saying that this measure is taken into account when determining the buckling angle at the outlet of the rotor blade 12C and the design of the single-channel bell diffuser in the first diffusion zone.

The variant of the multi-zone diffuser shown in FIG. 6 is suitable for systems which are equipped with an annular combustion chamber. The available space leads to an almost 180 ° deflection of the diffuser flow. In this embodiment, only one compressor guide row is provided, which takes over the function of the flow ribs 8D. They are designed according to the criteria mentioned several times. As a result, the rotor-side cooling air is removed from the hub directly at the outlet of the last rotor blades 12D and conducted into the annular duct 31D. Compared to the embodiment according to FIG. 5, the cooling air thus has less pressure, but more swirl, provided that there are the same conditions on both compressors at the outlet of the blades.

Here, too, the second diffusion zone is divided into two partial diffusers 17D by a guide ring 16D. This guide ring is held in its position in a third diffusion zone 53D, which is not very slow but strongly deflects, via ribs (not shown) on the rotor cover 29D and on the outer boundary wall 14D. In this embodiment the third diffusion zone merges into a single-channel fourth diffusion zone 54D, in which deceleration continues.

The guide ring is made in two parts. In its first section, it consists of a cylindrical sheet metal jacket 16Da, which is held in position on the blade carrier 2D via a plurality of profiled ribs 32 distributed over the circumference. In its second deflecting section 16Db, it consists, for example, of a cast part which is screwed to the first part. To cool the combustion chamber walls, air is branched off from the third diffusion zone via a further annular channel 33.

Reference list

1

rotor

2nd

Shovel carrier

3rd

Turbine casing

4th

Support bearing

5

Exhaust housing

6

inner part of 5

7

outside part of 5

8th

Flow rib

9

Profile of 8

10th

Supporting body

11

vane

12th

Exit blade

13

Diffuser

14

outer boundary wall of the diffuser

15

inner boundary wall of the diffuser

16

Guide ring

17th

Partial diffuser

18th

Hollow rib

19th

Tear-off edge

20th

blunt section

21

Tear-off edge

22

cylindrical exhaust pipe

23

Possibility to move

24th

Leading edge of 8

25th

extended area

26

Bell diffuser

27

stack

28

rib

29

Rotor cover

30th

drum

31

Ring channel

32

rib

33

annular channel

50

first diffusion zone

51

second diffusion zone

52

third diffusion zone

53

third diffusion zone in FIGS. 5 and 6

54

fourth diffusion zone in FIGS. 5 and 6

a

Distance from 12 to 24

d _max

greatest profile thickness of 8

s

Tendon of 8

α _Z

Kink angle at 14

α _N

Articulation angle at 15

Claims (15)

1. Multi-zone diffuser for an axial-flow turbomachine

   - in which the kink angles of the diffuser inlet both at the hub and at the cylinder of the turbomachine are fixed exclusively for the purpose of evening out the total pressure profile over the duct height at the outlet from the last rotor blade row (12),

   - in which means, in the form of streamlined struts (8), are provided within the deceleration zone of the diffuser (13) for the removal of swirl from the swirling flow,

   - and in which flow guide rings (16) subdivide the diffuser in multi-duct fashion,

   - characterized in that a first diffusion zone (50) extends from the outlet plane of the last rotor blade row (12) to a plane at the outlet from the streamlined struts (8) and is configured as one duct in which the equivalent opening angle (θ) of the meridian contours downstream of the kink angles is reduced to avoid flow separation so that a type of bell-shaped diffuser (26) is formed;

   - and in that a second diffusion zone (51) is fashioned in the form of a multi-duct diffuser part (17), the flow guide rings (16) being arranged downstream of the streamlined struts (8).
2. Multi-zone diffuser according to Claim 1, characterized in that a third diffusion zone (52) is formed downstream of the second diffusion zone (51) in the form of a dump diffuser whose axial length is substantially L = D/n, where D is the diameter of the flow duct in the exhaust pipe (22) and n is the number of ducts (17) in the second diffusion zone (51).
3. Multi-zone diffuser according to Claim 1, characterized in that the ratio between the distance (a) between the struts and the outlet from the blading, on the one hand, and the strut pitch (t), on the other, is at least 0.5 in order substantially to avoid interference with the last rotor row (12) of the blading.
4. Multi-zone diffuser according to Claim 1, characterized in that the ratio between the strut chord (s) and the strut pitch (t) is at least 1 and is substantially constant over the height of the struts in order to secure execution of the deflection duty.
5. Multi-zone diffuser according to Claim 1, characterized in that the maximum ratio between the maximum profile thickness (d_max)of the streamlined struts and the strut chord (s) is 0.15 and is substantially constant over the height of the struts.
6. Multi-zone diffuser according to Claim 1, characterized in that the respective curvature of the camber line of the streamlined strut (8) is selected with a view to shock-free entry and axial outlet flow over the whole height of the struts.
7. Multi-zone diffuser according to Claim 1, characterized in that the meridian contour of the diffuser is additionally widened (25) in the region of the struts in order to avoid excessive velocities on the streamlined struts (8).
8. Multi-zone diffuser according to Claim 1, characterized in that the leading edges (24) of the streamlined strut (8) are so oriented over the height of the struts that they are intersected at right angles by the streamlines.
9. Multi-zone diffuser according to Claim 1, characterized in that the diffuser is provided with a horizontal split plane in the first diffusion zone (50).
10. Multi-zone diffuser according to Claim 9, characterized in that an even number of streamlined struts (8) is provided, struts being arranged in the vertical plane but not in the horizontal plane.
11. Multi-zone diffuser according to Claim 1, characterized in that a plurality of hollow profiled struts (18), which have defined separation edges (19), are arranged evenly distributed about the periphery and are arranged symmetrically about the vertical plane, are provided in the second diffusion zone (51).
12. Multi-zone diffuser according to Claim 1, characterized in that the inner boundary wall (15) of the diffuser at the outlet from the second diffusion zone (51) is provided with a defined separation edge (21).
13. Multi-zone diffuser according to Claim 2, characterized in that the second diffusion zone (51) is designed so that it can be pushed axially into the third diffusion zone (52).
14. Multi-zone diffuser according to Claim 1, characterized in that a third, likewise multi-duct diffusion zone (53), in which there is weak deceleration but strong deflection, is arranged downstream of the second diffusion zone (51).
15. Multi-zone diffuser according to Claim 14, characterized in that a fourth, single-duct or multi-duct diffusion zone (54), in which there is strong deceleration but weak deflection, is arranged downstream of the third difusion zone (53).

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