The present invention relates to a stator blade for a turbomachine, especially for a steam turbine with at least one stator blade row.
Curved blades are used especially in steam construction as an embodiment of turbine blades particularly when strong three-dimensional flows occur, which feature pronounced radial differences in the static pressure variation between rotor side and stator side, and which arise as a result of the deflection in the stator blades. The flow of a flow medium in a last stage of a low-pressure turbine with large inflow cross section leads to a radial reaction distribution which acts negatively upon the efficiency of the steam turbine, especially in the case of a large ratio between blade length and hub. The reaction distribution in this case is different in the radial direction, wherein the reaction distribution is low at the hub and high in the region of a casing of the turbine, which is generally regarded as being disadvantageous.
A high reaction in the hub region reduces the gap losses in the stator blade ring and therefore leads to improved efficiency. In order to optimize the radial reaction distribution, curved stator blades are therefore used.
A turbine with stator blades which are curved only in the circumferential direction is known from DE 37 43 738 A1, the blade curvature of which is directed over the height of the blade towards the pressure side of the adjacent stator blade in the circumferential direction in each case. Blades, the curvature of which is directed over the height of the blade towards the pressure side of the adjacent stator blade in the circumferential direction in each case, are additionally known from the aforesaid publication. Consequently, boundary layer pressure gradients which extend both radially and in the circumferential direction are to be reduced in an effective manner and as a result the aerodynamic blade losses are altogether reduced.
Turbines with stator blades which are curved in the axial direction and in the circumferential direction are known for example from DE 42 28 879 A1. Upstream of a rotor cascade, in this case a fixed stator cascade is arranged, the rotor blades of which are fluidically optimized for full load with regard to number and also with regard to their chord-to-pitch ratio. The stator blades impart to the flow the swirl which is necessary for entry into the rotor cascade. The curvature of the blades extends perpendicularly to the chord, which is achieved as a result of displacement of the profile cross section both in the circumferential direction and in the axial direction. The curvature of the stator blades is directed towards the pressure side of the adjacent stator blade in the circumferential direction in each case. As a result of this curvature perpendicularly to the blade chord, the blade surface which is projected in the radial direction is greater than in the case of a known curvature only in the circumferential direction, as a result of which the radial force upon a flow medium is increased so that the flow medium is pressed onto a passage wall and reduces the boundary layer thickness there.
A turbine blade is known from WO 2005/005784 A1, which in the direction of flow is negatively swept on its rotor-side end and on its stator-side end, and in a direction which is radial with regard to the direction of flow is inclined towards the pressure side on its rotor-side end and also on its stator-side end. In this case, therefore, it concerns a turbine with turbine blades which are curved both in the circumferential direction and in the axial direction.
A final stage of a turbine which is exposed to axial throughflow, with a large passage divergence and also with a row of curved stator blades and a row of tapered and twisted rotor blades is known from EP 0 916 812 B1, wherein the stator blades in the axial direction are positively swept on their rotor-side end and negatively swept on their stator-side end, in each case with regard to the run of the rotor-side passage boundary. The positive sweep of the stator blade in this case extends over two thirds of the height of the blade and then merges into the negative sweep, wherein in the region of positive sweep the stator blade trailing edge extends parallel to the stator blade leading edge, and in the region of negative sweep an axial diffuser, which continuously widens towards the wall, is formed between stator blade and rotor blade with increasing deceleration of the axial component of the flow medium.
Further turbines with turbine blades which are curved in the circumferential direction and/or in the radial direction are known for example from U.S. Pat. No. 5,249,922, from U.S. Pat. No. 4,470,755, from U.S. Pat. No. 4,500,256 or from EP 0 425 889 A1.
It is the object of the present invention to provide a stator blade for a turbomachine, which by reducing the aerodynamic blade losses enables an improved efficiency of the turbomachine to be achieved.
This problem is solved by means of the subject of the independent claim. Preferred embodiments are the subject of the dependent claims.
The invention is based on the general idea in the case of a turbomachine of providing at least the stator blades of a stator blade row with a lean curvature, a sweep curvature, a twist, a chord length which varies over the radial extent of the stator blade, and a cross-sectional profile which varies over the radial extent of the stator blade. In addition, the stator blade row has a hub-side circumferential step which in the direction of flow falls away inwards and radially to the rotational axis of the turbomachine. As a result of this, a number of advantages can be combined. On the one hand, a radial distribution of a mass flow which flows through the turbine and also a radial pressure gradient are reduced, while on the other hand a greater mass flow, that is to say, throughflow volume, is induced in the region of the hub. At the same time, the impingement energy of water droplets is reduced, as a result of. which the erosion behavior is favorably influenced. In particular, the reduced impingement energy can be used for reducing the reaction degree at the blade tip, as a result of which lower absolute velocities can be realized on a stator-blade trailing edge so that lower leakage losses are encountered.
Further important features and. advantages of the stator blade according to the invention for a turbomachine result from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.
Preferred embodiments of the invention are represented in the drawings and are explained in more detail in the following description.
In this case, in the drawing, schematically in each case,
According to
As shown in
In
According to the invention, the stator blade 4 also has a twist in the radial direction of the respective blade 4, which is shown in
In
In
In the view in
It is worthy of note in this case that the stator blades 4 are formed in such a way that at least the curvature angle γ of the lean curvature and/or the curvature angle δ of the sweep curvature do not change along the radial blade length provided that the angles are measured with regard to the curvature center line 13 or with regard to the leading edge 16.
According to
An angle Δα is defined according to
1 Flow space
2 Hub of the turbomachine
3 Radial outer wall/casing
4 Stator blade
6 Blade surface
8 Rotational axis of the turbomachine
9 Radial line
10 Blade chord
11 Point of intersection
12 Trailing edge
13 Curvature center line
14 Hub contour
15 Direction of flow
16 Leading edge
17 Point of intersection
18 Center of gravity line
19 Pressure side of the stator blade 4
20 Suction side of the stator blade 4
21 Circumferential line
α1 Metal angle at the blade leading edge
α2 Metal angle at the blade trailing edge
β Angle to the hub contour 14
γ Lean curvature angle
δ Sweep curvature angle
s Chord length
t Blade spacing
q Narrowest flow cross section
WE Wedge angle
Number | Date | Country | Kind |
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102006015532.7 | Mar 2006 | DE | national |
Number | Date | Country | |
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Parent | PCT/EP2007/052828 | Mar 2007 | US |
Child | 12241825 | US |