EP0990770A1 - Blading for highly loaded turbines - Google Patents

Abstract

The turbine has an axial turbine stage of guide blade row (LE) and rotor blade row (LA) in a common housing (30) with intake section (31) and outlet section (32). The ratio of axial chord length (Sax) to height (h) of the blade rows for a turbine part located between intake and outlet sections, is chosen, so that a figure RSH is larger than 1. RSH is.................. P (W) = turbine output p (Pa) = arithmetical mean between intake and outlet pressure of turbine z (-) = number of stages m (kg/s) = working medium mass flow rate through turbine N (1/s) = RPM hi (m) = height of blade in row i, on outlet side of blade DM,i(m)= average mean of outer hub diameter and inner housing diameter measured on outlet side of blade in row i, sax,i (m) = max. axial chord length of blade in same row.

Description

Technical field

The invention relates to a turbine according to the preamble of claim 1.

State of the art

When designing axially flowed stages of turbines today in pursued two main approaches. So, on the one hand, with a high Work turnover in the stage the chord length of the blades and the Hub cut diameter is large, but at the same time smaller Bucket height. However, this interpretation contradicts the fluid mechanical Realization that to reduce leakage and wall friction losses the bucket height should be large, while at the same time being small Hub diameter, and further that at a small ratio of Bucket height to chord length the secondary flow losses drastically increase.

With this arrangement of the blades on large hub diameters, the Turbine mostly built in chamber design, with the low blade height limit the gap losses at the blade tips. With that, however wheel friction losses increase sharply. Furthermore, the chamber construction very expensive. On the other hand, large impulses can be used Hardly avoid hub diameter, otherwise the deflection in Hub proximity rises in such a way that the flow detaches and not closes would generate responsible losses.

Therefore, as a further approach, the choice is made to reduce the work turnover relatively low hold, and to place large blade lengths on small diameters, the blades with a small flow deflection a small one Preserve tendon length. Due to the much smaller Hub diameter can be the much cheaper drum design Find use. However, for a machine with given inputs and results Leaving states of the working medium a large number of stages. Thus in turn, the overall length of a machine increased, which on the one hand negatively affects rotor dynamics; on the other hand, the advantage of lower losses of a single vane grille due to the necessary high Number of levels at least partially canceled. In addition, one drives Construction with a high number of stages in turn increases the costs.

For the reasons given, for example, are executed in real Steam turbo sets usually combine both versions. Far for example, the use of one or more stages is less common Reaction and with high work turnover at highest pressures, and low stressed repetition stages of high reaction in the further course of the expansion of the work equipment. Due to this design, a high pressure in the first Steps dismantled quickly without significant axial thrust towards the rotor transmitted, with a shorter length for a certain degree of expansion of the runner is necessary. Here, for reasons in particular aerodynamic load the chord length of the blades is large, the necessary to achieve the high turnover of work Flow deflection not to be too blatant. Likewise, the Paddles placed on large diameters to the deflection in the Limit hub cut. The further enthalpy degradation then takes place in stages high response.

With this, in today's usual real-life machines, the advantages, however in particular, the disadvantages of both designs combined. A Blading, which combines the features of the design variants, So far, it has been known in the United States that their advantages are fully exploited Technology not known.

Presentation of the invention

The invention seeks to remedy this. The object of the invention is in a Heat engine of the type mentioned a blading specify the high step enthalpy conversion with low losses combined.

This is achieved by the characterizing features of claim 1.

The essence of the invention is, therefore, with an essentially axial flow Turbine to design the blading so that at a given Mass flow and predetermined entry and exit states of the Working medium as small a number of stages is required, and the Enthalpy turnover with little loss. This will be a big one Flow deflection is provided, and at the same time the chord length of the Shovels kept small. Furthermore, large height buckets are chosen, and placed on a large diameter. For the specialist is without it can also be seen that these variables are used when assessing a degree of Fulfillment of tasks in a very complex context stand so that the simple specification of geometric indicators for themselves taken to characterize the blading according to the invention is unsuitable. Therefore, the features of the subject matter of the invention a dimensionless figure to be explained below, previously called RSH based.

Advantageous configurations and uses result from the Subclaims.

The importance of a so-called HRSH turbine (high Relative blade load height) will be explained with reference to the drawing.

Brief description of the drawing

Fig. 1 shows an example of a turbine with four axially flow stages, and explains the key factors for the formation of the load parameter RSH geometric sizes.

2 characterizes different machine types on the basis of typical RSH ranges.

3 exemplarily illustrates the deflection and outflow angles of a guide and a blade.

Way of carrying out the invention

1 shows a turbine with four stages, the blades LA of which are fastened to a shaft 20 and the guide blades LE of which are fastened in a housing 30. The stages are arranged between an inflow section 31 and an outflow section 32, in which the pressure p ₀ or p ₁ prevails. The rows of blades are numbered from the inflow section 31 to the outflow section 32 of the housing 30; if z is the number of stages, there are 2z rows of blades, in the case shown four rows of four blades. Furthermore, geometrical quantities relevant to the invention are shown in FIG. 1. These are the bucket height h, the average diameter D _M , and the axial chord length of a bucket s _ax .

The single-flow turbine shown here is by no means restrictive To understand the meaning, in particular it could also be part of a large steam turbine set. Several turbines could also be used with own or common inflow and outflow sections in one Housing.

Of course, as mentioned above, when assessing a Turbine blading according to the invention the flow deflection in the Blade channels of great importance; however, this can initially completely equivalent also over their mass flow and speed-specific enthalpy conversion, or at a given Machine also by a step and mass flow specific performance, are expressed, as is readily apparent to those skilled in the art.

Now to compare the blades of different turbines or stages a key figure is required that enables such blades in machines different power and mass flow classes, as well as at characterize different pressure levels. Furthermore, the Optimization task described above blade load and Loss parameters are sensibly related.

• Leistung P
• Drehzahl N
• Stufenanzahl z
• Druck p
• Massenstrom m ˙
• Schaufelhöhe h
• axiale Sehnenlänge s_ax
• Mittelschnittdurchmesser D_M, definiert als Mittelwert von Gehäuse-Innen- und Naben-Aussendurchmesser

An essentially axially flowed stage or turbine is essentially described in terms of the invention by the following sizes:

• Power P
• Speed N
• Number of steps z
• Pressure p
• Mass flow m ˙
• Bucket height h
• axial chord length s _ax
• Center cut diameter D _M , defined as the mean value of the inside and hub outer diameters

These dimensional variables are initially reasonable undimension.

First, the specific performance is treated as a blade load parameter. The performance of a turbomachine is proportional to the mass flow and the square of the speed. The relationship is thus obtained for the dimensionless level-specific performance P'∝ P z m · N 2nd · L 2nd L is a characteristic length scale of one or more turbine stages, or a turbine. The step kinematics suggests to choose the middle section diameter as a characteristic length scale; thus the dimensionless specific performance becomes P '= P z m · N 2nd · D M 2nd

Another characteristic variable is the average pressure level, which can now also be converted into a dimensionless load parameter. Physical insight teaches that the pressure drop across a row of blades or step is a significant factor in the present context. This is for printing p'∝ P e.g. kg s 2nd · M

The dimension shown shows which sizes are still necessary to undimension the pressure. These are a characteristic mass, a time scale, and a length scale. Therefore, the mass flow and the speed are used to undimension the size with respect to mass and time. Furthermore, the physical insight shows that with the aim of forming a load parameter as a length scale, a lever is to be selected via which the pressure forces act on the blade. Ultimately, the dimensionless pressure gradient increases p '= p z m · N ·H

One aspect on which the invention is essentially based is the minimization of the secondary flow losses, which are largely determined by the ratio of the blade height to the axial chord length. Therefore, the geometric parameter must also h '= H s ax are taken into account, which can also be understood as a parameter for the secondary losses.

As mentioned above, increasing the level load and the associated reduction in the number of levels is not an end in itself; on the other hand, the rotor vibrations can be controlled more easily by reducing the rotor length. The vibration behavior is largely dependent on the ratio of the rotor mass and bending length, essentially reflected by z · s _ax , and the area moment of inertia of the rotor, given the other geometry, essentially characterized by D _M ² . This defines a dimensionless quantity that describes the rotor vibration behavior: S '= D M 2nd (zs ax ) 2nd In a way, S 'reflects the rigidity of the rotor.

In order to identify the turbine blades according to the invention with high lattice load and low losses, while at the same time resulting in a favorable rotor vibration behavior, the size RSH (“relative blade load height”) is in the form RSH = K · P ' A · P ' B ·H' C. · S ' D formed from the dimensionless load, loss and vibration parameters. K is a constant with which RSH can be adjusted to a reasonable size.

The exponents A, B, C and D are now to be selected such that the parameter RSH best characterizes a blading according to the invention with a high step enthalpy conversion and low secondary flow losses due to a large ratio of blade height to chord length. It is elected RSH = K · P ' 2nd · P ' 4th ·H' 4th · S '

This choice of exponents is made in order to weight a large circumferential work with a high ratio of blade height to chord length, which is the essence of the invention. Expressed in the dimension-based basic sizes, RSH results as RSH = K P 2nd · P 4th ·H 8th e.g. 8th · S ax 6 · D M 2nd · N 8th · m 6

The characterization of a turbine, in which the pressure as well as the geometric data vary greatly, is used according to the invention RSH = 1.1 · π · 10 -15 · P 2nd · p 4th e.g. 8th · m 6 · N 8th · i = 1 2 · z H 8th i D 2nd M, i · S 6 ax, i

It is p the arithmetic mean of inlet and outlet pressure, and the geometric data are summed up over all rows of blades. The mean cut diameter and the blade height are determined on the outflow side of a blade, while the value of the maximum chord length is taken for the axial chord length. With the chosen constant pre-factor, RSH is of the order of magnitude using SI base units.

The assessment of the blading of a machine using the RSH key figure can be useful for any turbine with essentially axial flow be made. The turbine is defined as all in one common housing between an inflow section and a Outflow section alternately arranged as guide and run rows Shovels; it can therefore also be a partial turbine of one Steam turbine set, such as the medium pressure turbine Three-pressure system, act.

Fig. 2 shows the RSH areas in which are usually executed today Turbines typically lie. The RSH area in which today's gas turbines typically work is marked GT and is less than 0.1. Executed steam turbines can be found in the area marked with DT, from about 0.1 to 0.7. The execution of a turbine with the Highly loaded HRSH blading according to the invention leads to a RSH that is greater than 1.

The essence of the invention is thus to be seen in given thermodynamic data at the turbine inlet and outlet, as well as predefined Power, mass flow and speed, to design the blade geometry so that RSH of the turbine is greater than 1. In contrast to the previous one Executed turbines use long, slim blades with at the same time great diversion.

Significant advantages of the invention are that the number of stages and thus the overall length with the same mass flow specific power and specified pressure level is significantly lower than in conventional Construction methods. Due to the invention, even with a low degree of reaction large blade heights on a comparatively small hub diameter when using the blading according to the invention also at the transition to large step enthalpy sales low-loss and inexpensive Drum construction are retained. In addition, the big Ratio of blade height and axial chord length compared to conventional Blade design with enthalpy turnover increasing sharply Secondary flow losses kept within limits.

However, it should also be noted that when using the HRSH blading according to the invention, the mechanical as well as the No aerodynamic load on the blades in a yet realized mass is driven to the permissible limits, so that the provided tolerance range in which an incorrect interpretation without harmful consequences remains, is very narrowly limited. As from the calculation rule visible for RSH, have very slim blades with a high Redirection can be realized on a short axial flow path. The Blading according to the invention therefore requires the highest currently and until recently unimaginable standards in the design, especially when calculating the mechanical blade load and the aerodynamic flow load if used successfully shall be.

Fig. 3 shows the top view of a guide and a rotor blade, in the hub section. When designing a blading according to the invention, the outflow angle β to the circumferential direction U is advantageously kept greater than 8 °, despite the desired large flow deflection γ, which applies both to the outflow angle of a guide vane β _LE and to the outflow angle of a moving blade β _LA . On the one hand, this is advantageous in order to limit the swirl of the grating outflow, and on the other hand in order not to obtain an excessive blockage of the flow channels. Furthermore, it is advantageous to limit the maximum deflection γ _LE and γ _{LA of} a guide or rotor blade in the hub cut to less than 150 ° in each case in order to avoid strong loss-generating flow separations in this area.

Reference list

20th

Turbine shaft

30th

Turbine casing

31

Inflow section

32

Outflow section

H

Bucket height

i

Indexing the rows of blades

p ₀

Turbine inlet pressure

p ₁

Turbine outlet pressure

s _ax

greatest axial chord length of a blade

e.g.

Number of steps

D _M

Center cut diameter of a row of blades

U

Circumferential direction

β _LE , β _LA

Outflow angle of a guide or rotor blade against the circumference

γ _LE , γ _LA

Flow deflection angle of a guide or rotor blade

Claims (4)

Turbine with at least one essentially axially flowed stage, which stage consists of a row of guide vanes (LE) and a row of rotor blades (LA), which are housed in a common housing (30), which housing has at least one inflow section (31) and at least one outflow section ( 32), and furthermore the degree of reaction of a stage is greater than 0.15, characterized in that for a part of the turbine which lies between an inflow section (31) and an outflow section (32) of the housing (30), for the substantially axial through which the blade rows (LE, LA) flow, the ratio of their axial chord length (s _ax ) and their height (h) is selected such that a characteristic number RSH is greater than 1, RSH being defined by RSH = 1.1 · π · 10 -15 · P 2nd · p 4th e.g. 8th · m 6 · N 8th · i = 1 2 · z H 8th i D 2nd M, i · S 6 ax, i in which calculation rule mean P [W] power of the turbine p [Pa] arithmetic mean between inlet and outlet pressure of the turbine z [-] number of steps m ˙ [kg / s] mass flow of the working medium flowing through the turbine N [1 / s] speed h _i [m] blade height of a blade of blade row i, measured on the downstream side of the blade D _{M, i} [m] Average value of hub outer diameter and housing inner diameter measured on the downstream side of a blade of the blade row i s _{ax, i} [m] axial chord length of a blade in blade row i, measured at the location of the greatest axial chord length Turbine according to claim 1, characterized in that an outflow angle (β _LE , β _LA ) of each blade to a circumferential direction (U) is greater than 8 °. Turbine according to claim 1, characterized in that the turbine in Drum type is built. Turbine according to claim 1, characterized in that a maximum flow deflection (γ _LE , γ _LA ) in the hub section of each row of blades is less than 150 °.

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