EP3204614B1 - Device for influencing the flow in a turbomachine - Google Patents

Description

The invention relates to a device for influencing the flow in a turbomachine, having a housing and having at least one blade ring rotating within the housing and having several blades, according to the type defined in more detail in the preamble of claim 1. The invention also relates to a turbomachine with such a device.

The term "turbo machine" in the sense of the present patent application includes turbines and compressors. Diffusers are often used downstream of turbines, which have the task of slowing down the flow at the outlet of the turbine in order to convert the kinetic energy of the flow still present in this area, for example an air or steam flow, into potential energy in the form of to static pressure, which is called pressure recovery. In order to achieve this, in known solutions the flow cross section is widened from the inlet of the diffuser in the direction of its outlet. This enlargement of the cross section of the diffuser results in a deceleration of the flow. The diffuser causes the back pressure at the outlet to drop, so that a higher enthalpy gradient is available, i. H. more work is implemented, thereby increasing the efficiency of the turbine.

A maximum pressure recovery in a diffuser is achieved at an opening angle at which flow separation just does not occur. Such a flow separation can occur because the boundary layer on the wall of the diffuser loses more and more energy with increasing run length and at the same time the deceleration of the flow causes an increase in pressure, which causes a flow reversal within the boundary layer and thus a separation of the flow from the wall can. Increasing the opening angle of the turbine increases the risk of flow separation. The occurrence of flow separation leads to large-area backflows within the diffuser, which ultimately results in insufficient deceleration of the flow. This reduces the pressure recovery and can sometimes even be negative. The backflow areas described, which occur in the event of flow separation, are usually not stationary, but can trigger significant pressure and velocity fluctuations within the diffuser, which can also lead to structural-mechanical problems within the diffuser.

Due to the risks described, diffusers are usually designed very carefully nowadays, in that the diffuser is either quite long or has a small opening angle, which means that a lower pressure recovery is accepted. However, this leads either to very high costs or to non-optimal efficiency of the turbine.

Since turbines in power plants are usually operated in a very wide load range from very low partial load to extreme overload due to the strongly fluctuating feed-in of regenerative energies, the occurrence of flow separation in the diffuser can be determined on the basis of the geometric parameters, i.e. the length and the area ratio between entry and exit can hardly be avoided. This is another reason why diffusers are often designed very carefully or conservatively in order to achieve a compromise between the highest possible pressure recovery, a large operating range and an economically acceptable diffuser length.

Various approaches for passively influencing the flow in turbines are known from the general state of the art, which are intended in particular to bring about an energization of the boundary layer in the area of the diffuser by artificially generating vortices or increasing the degree of turbulence of the flow, thereby increasing the exchange of energy and momentum takes place between the main flow and the boundary layer. However, these passively working methods have the disadvantage that they are constantly in the flow channel and therefore cause additional losses in those operating ranges in which the diffuser is working stably. An example of this is in " Improving curved subsonic diffuser performance with vortex generators" by BA Reichert and BJ Wendt in AIAA-Journal 34(1), 1996 described.

Furthermore, from " Control of separation in a conical diffuser by vortex generator jets" by M Nishi, Y Kouichi and M Keisuke in JSME Series B, 41(1), 1998 An active method is known in which an additional working fluid, eg air, is blown into the diffuser in order to energize the boundary layer or to increase the degree of turbulence. However, the problem of additionally blowing in working fluid is that it has to be taken from a higher pressure area within the turbine and in particular from the compressor in gas turbine systems. However, since the mass flow taken does not participate in the conversion of work, the power output is reduced in this way of the turbine and thus the efficiency. In addition, the active processes are usually relatively energy-intensive and expensive.

A generic device and a corresponding turbine are from US 2012/0102956 A1 known. A gap of approximately 2.3 to 3.8 mm (90 to 150 mils) in height is provided between the casing and the turbine blades and is intended to create leakage flow around a boundary layer along an outer wall of a subsequent diffuser to energize.

An increase in the gap mass flow by increasing the gap between the rotor blades and the housing, as shown in US 2012/0102956 A1 is described, can contribute to the stabilization of the diffuser, since the gap mass flow does not participate in the work conversion within the moving blade and since there can be an interaction between the main flow and the gap flow, this can also lead to a drop in the efficiency and performance of the turbine . Due to the relatively large gap present in this solution, which leads to a very high leakage flow, the efficiency of the turbine is reduced in most areas of application. These losses due to the gap mass flow far outweigh the higher pressure recovery in the diffuser. A similar state of the art is also described by " A Trade-Off Study of Rotor Tip Clearance Flow in a Turbine/Exhaust Diffuser System" by S. Farokhi in ASME Paper No. 87-GT-214, 1989 .

A gap between the rotating parts of the turbomachinery on the one hand, i.e. the shaft and blades, and the stationary parts on the other hand, i.e. the casing, is necessary to allow the relative movement between the components. In order to minimize the losses caused by the gap flow, an attempt is usually made to keep the radial gap, i.e. the distance between the blade ends and the casing in the case of free-standing blades or the free area between the shroud of the blade ring and the casing, as small as possible .

As a rule of thumb, it is often stated that the radial gap should be at least 1/1000 of the blade ring diameter. It should be noted that the gap is reduced during operation of the turbomachine, for example due to the centrifugal expansion and the different thermal expansion of the housing and rotor blades. A radial movement due to shaft vibrations is also superimposed on these static expansions. If the gap is too small, there is a risk that touch the rotating components of the turbomachine on the housing. This can lead to permanently higher losses or even to the destruction of the turbomachine.

In order to minimize the risk of rubbing with the smallest possible gap and the damage resulting therefrom, various methods are used according to the prior art.

First of all, the minimum gap height is usually not set over the entire width of the blade tip or the axial length of the shroud, as this could lead to a large-scale tarnishing. Rather, structures that are as thin as possible are usually used, which can be damaged in the event of rubbing, which reduces the sealing effect, but this does not usually result in major damage or even failure of the turbomachine. Such a device for free-standing blades is for example in US2007/02376237 described.

In the case of blade rings with a shroud, the latter is usually fitted with one or more sealing tips or ribs, which as a result form one or more turbulence chambers in the axial direction and thus increase the sealing effect. This design is also referred to as a labyrinth seal. In order to further improve the sealing effect, these sealing tips and the counter surfaces in the housing are often offset radially in order to create a stepped labyrinth.

In order to reduce the mechanical loads occurring in such sealing ribs during operation, they are designed in part geometrically in such a way that the rib cross section is expanded in the radial direction, as for example in FIG EP 1 413 712 A1 described. In addition, individual small separating slits serve to reduce the compressive stresses in the ribs that occur due to centrifugal force.

Furthermore, the counter surface in the housing is usually provided with a soft coating, which is removed in the event of rubbing. To promote this process, the blade tips of free-standing blades, such as in the EP 0 702 130 A2 described, be performed with a cuttable abradable coating, while the sealing tips of shroud blades can be provided with a blade-shaped geometry, such as in WO 02/25065 A1 is presented. Another possibility is to arrange the seals in the housing in radially flexible segments, as is the case, for example, in FIG US 5,603,510A or the US 6,502,823 B1 is revealed.

Since the gap flow does not take part in the deflection within the blade ring and therefore has a different flow direction than the main mass flow, in the DE 10 2012 106 175 A1 In addition, attempts are made to adjust the flow direction of the gap mass flow similarly to that of the main mass flow by means of spin-breaking structures within the abradable coating or by upstream and downstream spin-breaking elements, in order to reduce the mixing losses that arise through the interaction of the gap and main mass flow.

Approaches are known for free-standing blades in which an attempt is made to weaken the gap vortex as such with the aid of recesses between the suction and pressure sides that partially extend over the blade. Such an approach is in EP 2 538 024 A1 described.

All of these measures are based on the idea of reducing the gap mass flow in its entirety in order to improve the efficiency of the individual turbine stages. However, this also eliminates the beneficial effect of the gap flow on the flow in the diffuser, which inevitably leads to the very careful design of diffusers discussed above.

It is the object of the present invention to create a device for influencing the flow in a turbomachine, with which flow separations can be avoided and the efficiency of the turbomachine can be improved.

According to the invention, this object is achieved by the features mentioned in claim 1.

The invention is set out in the appended set of claims.

A local increase in the gap flow over the blade ring is achieved by the gap according to the invention, which has a discontinuous height due to individual recesses around the circumference of the blade ring and is continuous in the axial direction. In the case of a diffuser downstream of the turbine blade ring of the turbomachine, the energization of the boundary layer on the wall of the diffuser, i.e. the introduction of energy into this boundary layer, can be improved, which leads to a stabilization of the boundary layer flow and ultimately to higher pressure recovery or a shortening of the diffuser with constant pressure recovery. The inventive The solution thus makes it possible to build significantly more "aggressive" diffusers, ie shorter diffusers with the same ratio of entry to exit area, so that the system costs can be significantly reduced. Furthermore, the gap according to the invention makes it possible to avoid the formation of large backflow areas in a region downstream of the blade ring, which areas can otherwise cause structural mechanical problems due to low-frequency pulsations.

Due to the fact that the height of the gap is discontinuous around the circumference of the blade ring, a sufficiently large mass flow can be achieved in the areas in which the gap has a greater height, which ensures the energization of the boundary layer described above, while at the same time by the restriction of such a gap on individual sections of the circumference of the blade ring, an excessive gap loss, which would reduce the efficiency of the turbomachine too much, is avoided.

The gap area of the original design is defined by the free area between the vane ring and the casing in the design with a continuous gap. This gap area is therefore sometimes also referred to as the free area between the blade ring and the housing.

Since the solutions known from the prior art, in contrast to the solution according to the invention, have a uniformly high gap around the circumference of the blade ring, the mass flow in the same is either too low, with which an energization of the boundary layer cannot be achieved, or too high Reducing the efficiency of the turbomachine. In other versions with a changing gap height, in which the variation of the gap height, for example, in an embodiment of the blade tip as in the EP 0 702 130 A2 or the shroud as in the WO 02/25065 A1 is only slight, and the purpose of which is to improve the overall sealing effect, the mass flow in the gap is also too low, so that the boundary layer cannot be energized.

A further advantage of the solution according to the invention is that due to the relatively large gap in certain sections on the circumference of the blade ring, the problem of manufacturing tolerances and the elongation of the turbine blades and the associated change in size of the gap can be avoided.

Another well-known problem in turbomachinery is blade flutter, particularly when blade rings without shrouds are used. This blade flutter can occur in blade rings used in compressors as well as in turbines.

If the device according to the invention is used in a compressor or a turbine, an interaction of flow and blades that would otherwise occur and lead to flapping of the turbine blades can be avoided. By changing the gap flow in the circumferential direction and the associated variation in the gap flow, it is possible to specifically disrupt and thus prevent the build-up of such an interaction.

A turbomachine with a device according to the invention arranged in a region in front of a diffuser is specified in claim 4 .

Claim 5 results in a turbomachine with a device according to the invention arranged in a compressor section. In the following, exemplary embodiments of the invention are shown in principle with reference to the drawing.

Fig. 1

eine sehr schematische Darstellung einer Turbomaschine;

Fig. 2

eine nicht zu der Erfindung gehörende Ausführungsform der Vorrichtung;

Fig. 3

einen Schnitt nach der Linie III-III aus Fig. 2;

Fig. 4

einen Schnitt nach der Linie IV-IV aus Fig. 2;

Fig. 5

eine nicht zu der Erfindung gehörende Ausführungsform der Vorrichtung;

Fig. 6

eine nicht zu der Erfindung gehörende Ausführungsform der Vorrichtung;

Fig. 7

eine erste Ausführungsform der erfindungsgemäßen Vorrichtung; und

Fig. 8

eine zweite Ausführungsform der erfindungsgemäßen Vorrichtung.

It shows:

1

a very schematic representation of a turbomachine;

2

an embodiment of the device not belonging to the invention;

3

make a cut along line III-III 2 ;

4

cut along line IV-IV 2 ;

figure 5

an embodiment of the device not belonging to the invention;

6

an embodiment of the device not belonging to the invention;

7

a first embodiment of the device according to the invention; and

8

a second embodiment of the device according to the invention.

1 1 shows, in a very schematic manner, a turbomachine 1, which in the present case is designed as a gas turbine and has a housing 1a, an inlet opening 2 and an outlet opening 3. In a manner known per se, a working fluid, in this case a gas, flows through the turbomachine 1 in the axial direction denoted by "x" with the aim of driving a shaft 4 mounted in the housing 1a, in order to, when the turbomachine 1 to generate electricity in a power plant.

As is also known per se, the turbomachine 1 has a compressor section 5, a turbine section 6, a diffuser 7 adjoining the turbine section 6, and a combustion chamber 8 arranged between the compressor section 5 and the turbine section 6, one behind the other in the axial direction x of the working fluid. The compressor section 5, the turbine section 6, the diffuser 7 and the combustor 8, which are in 1 are indicated only very schematically are surrounded by the housing 1a. In the present case, the turbomachine 1 is a gas turbine. However, the term “turbomachine” also encompasses other configurations, such as a steam turbine that does not have a compressor and combustor. Both the compressor section 5 and the turbine section 6 have a large number of blade rings 9 which are set in rotation by the gas flowing through and thus drive the shaft 4 . Since the basic mode of operation of the turbomachine 1 is known, it will not be discussed in detail here.

In the Figures 2 to 8 various embodiments of a device 10 are shown, which are used to influence the flow in the turbomachine 1. All embodiments of the device 10 have in common that between the housing 1a and the blade ring 9 there is a gap 11 which is continuous in the axial direction x and has a discontinuous height around the circumference of the blade ring 9 . Although the gap 11 can be designed in different ways, as will become clear below, it is designed in such a way that it results in a local increase in the gap flow over the blade ring 9 and a stabilization of the flow in the boundary layer to the housing 1a.

It is fundamentally preferable if the gap 11 is of such a size that it increases the free area between the blade ring 9 and the housing 1a compared to a surface area that is not shown in the figures. for the expert, however, very easily comprehensible design with a continuous gap of 5% - 50% results.

In the embodiment of FIG 2 , which shows a simplified front view of a bladed ring 9, the gap 11 is formed by a plurality of recesses 12 on the bladed ring 9. In principle, it would also be conceivable to provide only one recess 12 . According to 2 the vane ring 9 has a shroud 13 with a circumferential sealing tip 14 which is interrupted by the recesses 12 in order to form the gap 11 . The shroud 13 stiffens individual blades 15 of the blade ring 9, some of which have been omitted from the figures for reasons of clarity. The alternating presence of the sealing tip 14 and the recesses 12 in the sealing tip 14 leads to the described discontinuity in the height of the gap 11 around the circumference of the blade ring 9. The statement "in the axial direction x continuous" means that in the case of two offset in the axial direction x Sealing tips 14 have both sealing tips 14 respective recesses 12, which allow the blade row to flow through the gap flow.

At the in 2 illustrated embodiment, which does not belong to the invention, several recesses 12 are provided. The size of the same is to be regarded as purely exemplary. The recesses 12 pass completely through the sealing tip 14 in the axial direction x, the size and number of the recesses 12 being selected such that the gap 11 increases the free area between the sealing tip 14 and the housing 1a compared to an embodiment with a continuous gap of 5% - 50%.

Each individual recess 12 has such a size that the increase in the free area per recess 12 is at least 1%, preferably at least 2%, more preferably at least 3%, more preferably at least 4% and more preferably at least 5% of the total free area between the sealing tip 14 and the housing 1a without recesses.

In 2 it can also be seen that each of the recesses 12 runs over the entire height of the sealing tip. Basically, it is preferable that the area of the at least one recess 12 is at least 50% of the area of the sealing tip 14 over the length of the recess 12 in the circumferential direction.

The discontinuity described in the height of the gap 11 is in the two sections Figures 3 and 4 also very clearly visible. While 3 shows a section through the area in which the sealing tip 14 is present and the gap 11 between the blade ring 9 and the housing 1a has a small height 4 a section through an area of the blade ring 9 in which the sealing tip 14 has one of the recesses 12, so that the gap 11 between the blade ring 9 and the housing 1a is much larger than in the 3 shown area. While according to the Figures 3 and 4 If the recesses 12 are each of such a size that the sealing tip 14 is not present in the area of the recesses 12, it would also be possible, as already mentioned, to design the recesses 12 in such a way that the sealing tip 14 in the area of the recesses 12 has a smaller Has height than in the areas where the recesses 12 are not present.

The discontinuous height of the gap 11 leads to an increased mass flow in the areas in which the gap 11 has a greater height than in the areas in which it has a lower height. Due to this increased mass flow resulting from the enlarged gap 11 or the enlargement of the free area between the blade ring 9 and the housing 1a compared to an embodiment with a continuous gap, which does not flow through the blade ring 9 and is therefore not involved in the work conversion within the Turbomachine 1 participates, an improvement in the energization of the boundary layer flowing along the housing 1a and into the diffuser 7 can be achieved. By enlarging the gap 11 due to the local reduction in the diameter of the blade ring 9 or the sealing tip 14 of the blade ring 9 by means of the recesses 12 in the embodiment of FIG 2 the result is a gap mass flow that rotates with the rotation of the blade ring 9 within the diffuser 7 that follows the turbine section 6 . Due to this flow, which has a certain twist, the entire diffuser 7 is subjected to the changed gap flow. This avoids an uneven loading of the diffuser 7 .

In the embodiment of FIG figure 5 the gap 11 having the discontinuous height is formed by shortening individual free-standing blades 15 of the blade ring 9, as a result of which the recesses 12 are formed. This variant lends itself when the blade ring 9 does not have the shroud 13, ie when the blades 15 are free-standing blades.

It is preferable that at least one and at most half of the free-standing blades 15 have a length that is less than the average length of the remaining unabridged blades 15, so that an increase in the free area between the respective blade 15 and the Housing 1a compared to an embodiment with a continuous gap, ie in an embodiment in which all blades 15 are of equal length, of 5% - 50% results.

The free-standing blades 15 are shortened in such a way that the increase in the free area due to the shortening per free-standing blade 15 is at least 1%, preferably at least 2%, even more preferably at least 3%, even more preferably at least 4% and even more preferably at least 5%. of the total free area between each free-standing blade 15 and the casing 1a without recesses.

At the in 6 In the illustrated embodiment of the device 10 not belonging to the invention, the gap 11 having a discontinuous height is formed by a plurality of recesses 16, each spaced apart, on the inner periphery of the housing 1a. This also results in the areas in which the gap 11 has a greater height due to the recesses 16, a larger mass flow, which does not flow through the blade ring 9, but between the blade ring 9 and the housing 1a and thus to a Energizing the boundary layer contributes. In contrast to the embodiments of 2 and figure 5 However, this mass flow is stationary, since the recesses 16 are always located at the same point. Although the vane ring 9 in the embodiment of 6 the shroud 13 with the sealing tip 14, it is also possible to use a vane ring 9 without the shroud 13.

In one of the in 6 In the embodiment of the device 10 modified in the illustrated embodiment, a rotatable ring is mounted in the housing 1a, which ring has recesses with which the above-described discontinuous height of the gap 11 is produced. If this ring is held stationary, the increased mass flows also remain at the same locations around the inner circumference of the housing 1a. In this case, however, it is possible by turning the ring to generate the increased mass flows at other points on the inner circumference of the housing 1a.

In the 7 The embodiment of the device 10 according to the invention shown is also a further development of that in 6 illustrated embodiment. Again, the recesses 16 are provided in the housing 1a to provide the discontinuous height of the gap 11 to generate. In addition, a rotatable ring 17 is mounted in the housing 1a, with which the recesses 16 can be closed at least partially. For this purpose, the ring 17 has alternating recesses 17a and projections 17b, so that the recesses 16 located in the housing 1a can be closed by rotating the ring 17 . Depending on the size of the recesses 17a or the projections 17b of the ring 17 in 7 In this way, the recesses 16 can be completely opened or, if the length of the projections 17b of the ring 17 is at least as great as the length of the recesses 16 in the housing 1a, also completely closed. In such a case, the gap 11 would have the same small height around the entire circumference. The height of the gap 11 in the area of the recesses 16 can only be reduced and not increased by the ring 17 . These recesses could also be provided in a manner that is not shown in a second ring that can also be rotated with respect to the housing 1a. In this case, two rings that can be rotated relative to the housing 1a would be provided. The size of the overall recess resulting from the overlapping of the two recesses can be changed by appropriately rotating the two rings relative to one another.

In the embodiment of 7 the vane ring 9 has no shroud. Nevertheless, it is also possible to use a bladed ring 9 with the shroud 13 . Such an embodiment of the device 10, which differs from that in 7 illustrated embodiment differs only in that the shroud 13 is provided is in 8 shown.

The size of the recesses 16 and 17a, which are continuous in the axial direction x, are based on the above-described embodiments of such a size that they increase the free area between the blade ring 9 and the housing 1a compared to an embodiment with a continuous gap of 5% - 50% results.

In this embodiment, too, it is preferable if each individual recess 16 or 17a in turn has such a size that the enlargement of the free area per recess 16 or 17a is at least 1%, preferably at least 2%, more preferably at least 3%. more preferably at least 4%, and even more preferably at least 5%, of the total open area between each cantilever blade 15 and the uncavity casing 1a.

The recesses 12 or 16 or 17a are evenly distributed around the circumference of the housing 1a or the blade ring 9 or the ring 17 with small deviations, so that on the one hand an even distribution of the areas with an increased gap mass flow and the circumference of the blade ring 9 achieved and on the other hand mutual swinging open of the blades 15 can be prevented.

The gap 11 described, having a discontinuous height, between the blade ring 9 and the housing 1a can, in principle, be used at any point of the turbomachine 1. However, since the mass flow of air, steam or the like flowing over the blade ring 9 and through the gap 11 does not participate in the work conversion within the respective impeller, this gap 11 is only used on that blade ring 9 which is immediately in front of the diffuser in the direction of flow x 7 is located. In particular, the device 10 can be used both in turbines with downstream axial diffusers and downstream axial-radial diffusers.

A further possibility for using the device 10 is in the compressor section 5 in order to prevent the blades 15 of the blade ring 9 from fluttering.

Claims (5)

1. Device for influencing the flow in a turbomachine (1), having a housing (1a) and at least one blade ring (9) which has a plurality of blades (15) and rotates within the housing (1a), wherein

   between the housing (1a) and the blade ring (9) there is a gap (11) which is continuous in the axial direction (x) and has a discontinuous height around the circumference of the blade ring (9) and by means of which there is a local increase in the gap flow over the blade ring (9) and a stabilization of the flow in the boundary layer to the housing (1a), and wherein

   the gap (11) having the discontinuous height is formed by recesses (16, 17a) on the housing (1a) or a component connected to the housing (1a),

   characterized in that

   a rotatable ring (17) is supported in the housing (1a), by means of which ring the recesses (16) can be at least partially closed, or in that

   the housing (1a) has two rings which can be rotated relative to one another and which each have recesses, at least one of the rings being rotatably supported by the housing (1a).
2. Device according to claim 1,
   characterized in that
   the housing (1a) or a component connected to the housing (1a) has one or more recesses (16, 17a) radially outside the blade ring (9) passing through in the axial direction (x), so that there is an increase in the free area between the blade ring (9) and the housing (1a) of 5% - 50% compared with a design with a continuous gap.
3. Device according to claim 1 or 2,
   characterized in that
   the gap (11) having the discontinuous height is formed by a plurality of recesses (12, 16, 17a) which are equally distributed with slight deviations around the circumference of the housing (1a) or of the blade ring (9).
4. Turbomachine having a device according to one of claims 1 to 3, which is arranged in an area in front of a diffuser (7).
5. Turbomachine having a device according to one of claims 1 to 3, which is arranged in a compressor section (5).

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