WO2008110543A1 - Covering strip connection of a turbine blade - Google Patents

Abstract

The turbine blade comprises a plurality of rotating blades (10), arranged on a hub that can be rotated about an axis. Said rotating blades comprise covering plates (20) at the radial outer ends thereof. The transition between two rotating blades arranged next to each other in the region of the covering plates is formed by a first, uneven contact surface (21) and a second, even contact surface (25). The uneven contact surface comprises a toroidal elevation with a radius of curvature R and a cross-sectional radius r, wherein R is greater than r. The contact between an uneven surface and an even surface provides for better control of the contact position and undesired stress concentrations can be avoided.

Description

 DECKBAND CONNECTION OF A TURBINE BUCKET

DESCRIPTION

Technical area

The invention relates to the field of turbomachines, in particular exhaust gas turbocharger for supercharged internal combustion engines, steam and gas turbines.

It relates to a turbine wheel with a plurality of blades, which each have at their free ends cover plates and a blade of such a turbine wheel.

Prior art impellers of thermal turbomachines, such as steam turbines, gas turbines or turbines of exhaust gas turbochargers, have a plurality of blades, which are arranged on a hub which is rotatably mounted about a shaft. The impellers often have shrouds - referred to in technical language as "Shroud" - at their radially outer, free ends. A shroud is composed of individual segments (hereinafter referred to as cover plates), which are integrally connected to one blade each.

The cover plates are braced against each other by a torsional bias of the blades during assembly or in operation by the natural unwinding of the blades under the influence of centrifugal force. The function of the cover plates is to improve the thermodynamic efficiency by minimizing the gap losses, as well as in the optimization of the vibration behavior by their damping and stiffening effect. The design of the transition between the cover plates of two adjacent blades arranged according to various criteria in terms of thermodynamics, durability, surface pressure, assembly and manufacturing.

Since the nominal contact surfaces in the region of the transition between cover plates of two adjacently arranged blades of a conventional Turbine wheel are flat, correspond to the effective contact surfaces thin strips or even small points. These small contact surfaces can hardly transmit moments during operation and provide for a lower coupling than expected in the development phase. Furthermore, these small contact zones can lead to extreme stress concentrations in the cover plates and, in the case of micro friction, cause fretting corrosion damage - in technical language called "fretting" - at the contact surface Fretting caused by fretting is a consequence of static and dynamic stresses in the material below the contact surface and In the development phase, they are numerically predictable - for example with the finite element (FE) method - only partially or not at all, because their estimation requires extremely high FE mesh densities.

An exemplary form of transition between the cover plates of adjacent gas turbine rotor blades is shown in US 5,593,282, FIG. 4.

Summary of the Invention The object of the present invention is to improve the transition between the cover plates of adjacently disposed blades of a turbine wheel.

According to the invention, the transition between the cover plates of adjacently arranged rotor blades of a turbine wheel with a flat and an uneven contact surface is designed for this purpose.

The contact between an uneven surface and a flat surface allows better control of the contact position. At any angle of incidence of the mating surface, a Hertzian pressure sets and it can unwanted concentrations of stress can be avoided. Especially in turbine stages, which are exposed to impulse excitations, thus loads can be greatly reduced.

Instead of the conventional, planar contact is provided at one of the ends of the cover plate, the contact surface with at least two semi-cylindrical elevations (wrinkles) with radius r. These semi-cylindrical protrusions optionally have along their axis a curvature of radius R. The mating contact surface of the cover plate, however, is flat. By changing the cylinder radius r, the surface pressure can be varied and adapted to the cover plate size. In the case of purely level contact, uncontrolled local stress concentrations and misplacement of contact zones occur. This results in a different design of the wear on the cover plates of the same blade wreath. Small manufacturing differences between blade to blade within the tolerance have great effects on the formation of the contact on flat cover plate surfaces and lead to a detuning of the blade ring with it.

Whether fretting damage is to be expected at the contact points depends on the effective surface pressure. In contrast to uncontrolled plane-to-edge contact on conventional shrouds, Hetzscher contact always sets in on uneven, folded cover plates. This allows to determine the surface pressure on the basis of the Hertz formulas and to predict the probability of a damage by fretting with the help of a failure criterion.

Pleated cover panels reduce the likelihood of misplacement. Because of the controllability of the contact, the blade kranzverstimmung and thus the scattering of the blade natural frequencies is reduced. If the folded contact surface is provided with several, ie at least two rows of folds, forces and moments can be transmitted well at any time and a strong coupling between blades is ensured.

Brief description of the drawings

Subsequently, an embodiment of the inventive transition between the cover plates adjacently arranged blades of a turbine wheel is described with reference to the drawings. This shows

1 is a view - perpendicular to the axis and directed radially inward - on a blade assembly according to the invention designed cover plate

Transitions

FIG. 2 shows a section along M-II through a cover plate transition of the blade group according to FIG. 1, FIG.

Fig. 3 shows a guided along Ml-Ml section through the cover plate transition of Fig. 2, and 4 shows a section along IV-IV through the cover plate transition according to FIG. 2.

Way to carry out the invention

Fig. 1 shows an application example of the invention, a part of the blades of an axial turbine of a turbocharger. The blades are arranged with blade roots in a blade carrier, the hub of the turbine wheel. The hub of the turbine wheel is rotatably mounted on a shaft about an axis. As used herein, the terms "radial," "axial," and "circumferential direction" refer to this axis, and typically the blade roots are fir-tree shaped and axially inserted into oppositely-shaped grooves and axially secured body 10, which is exposed to the flow, that is to say the hot exhaust gases or the steam in the case of a steam turbine At their radially outer, free ends, the rotor blades have a shroud which projects at least in sections in the axial direction over the blade body divided into many short segments, the cover plates 20, which are each integrally connected to a blade.

Between the cover plates of two adjacently arranged blades at least one contact area is present. The cover plate of the ith blade has an uneven contact surface 21 in the contact region according to the invention. In contrast, the cover plate of the (i-1) -th blade has a flat contact surface 25.

How exactly the uneven contact surface 21 is designed will be explained in more detail with reference to FIGS. 2 to 4.

Fig. 2 shows a view in the arrow direction on the section, which is guided along the designated M-Il, dashed line. The uneven contact surface 21 has a plurality of elevations 22. As shown in Fig. 3 - a view in the radial direction of the section, which is guided along the designated IM-III, dashed line - is shown - the elevations have a round, semicircular or semi-elliptical cross-section. Depending on the angular position of the two adjacent cover plates, the flat contact surface 25 and one or more of the elevations 22 touch. It can be seen from the section in FIG. 4 taken along the broken line indicated by IV-IV that the elevations 22, or the underlying surface, has a curvature. The curvature - exaggerated in FIG. 4 - extends radially from the view of the rotor blades, so that contact between the two contact surfaces of the two cover plates, regardless of any slight relative skew, certainly takes place. As the turbine speed increases, a protrusion curved with radius R is pressed more and more against its planar counterpart, so that the "cylinder plane" contact with Hertz sets in. The curvature of the elevation is denoted by R in the figures, where R is smaller than the radius r the individual surveys is significantly larger.

Thus, the surface of the protuberances has the surface shape of a tome, where a toms is a geometric body in which the points on the surface of a circle of radius R are the distance r, where r is less than R.

Such toroidal elevations with a radius of curvature R and a cylinder radius r on one of the contact surfaces of the cover plate avoid stress concentrations under load of the blade. By changing the cylinder radius r, the surface pressure can be varied - a larger cylinder radius leads to a lower surface pressure - and an adaptation to the cover plate size can be made. To reinforce or instead of the curvature defined by the radius R, the cross-sectional radii r of the bumps in the radial direction, i. towards the root of the blade, decrease, so that instead of the semi-cylindrical elevations, semi-conical elevations now result. The corresponding Toms thus has along the radius of curvature R a variable cross-sectional radius r. In the preparation of the uneven contact surface at each end of the cover plates, a curvature with the radius R is ground in the plane just configured surface in a first step. Subsequently, the individual elevations with the cross-sectional radius r are produced on the curved surface by means of profile grinding. Finally, the contact surfaces are polished to ensure a clean contact.

In a second, not shown embodiment, the elevations are made without the curvature defined by the radius R. For this purpose, several surveys with different radius r are provided, which is maximum at the middle elevation and decreases towards the edge elevations. In a third variant, a plurality of elevations of the same radius r are placed on a curved surface 21. The axis of this curvature points in the radial direction.

LIST OF REFERENCE NUMBERS

10 blades

20 cover plate (shroud segment)

21 Uneven contact surface

22 Survey

25 plane contact area i-1, i, i + 1 blade numbering

R Radius of curvature r Radius of elevation

Claims

PAT EN TA NSPR O CHE A turbine wheel comprising a plurality of blades (10) disposed on a hub rotatable about an axis and each having at its radially outer ends cover plates (20) which, lined up in the circumferential direction, form an annular shroud, the transition between two adjacently arranged moving blades in the region of the shroud is formed by a first, uneven contact surface (21) and a second, planar contact surface (25), characterized in that the uneven contact surface (21) has at least one torus-shaped elevation (22), which has a radius of curvature (R) and a cross-sectional radius (r), wherein the radius of curvature (R) of the curvature is greater than the cross-sectional radius (r) of the at least one elevation (22), and in that the uneven contact surface (21) with the at least one Toroidal elevation (22) rests on the flat contact surface (25). 2. turbine wheel according to claim 1, wherein the cross-sectional radius (r) of the at least one elevation (22) along the radius of curvature (R) is different in size. 3. Turbine wheel according to one of claims 1 or 2, wherein the uneven contact surface (21) has a plurality of toroidal projections (22), and the plurality of elevations (22) each have different cross-sectional radii (r). 4. Turbine of an exhaust gas turbocharger, comprising a turbine wheel according to one of the preceding claims. 5. Exhaust gas turbocharger, comprising a turbine according to claim 4. 6. Gas or steam turbine, comprising a turbine wheel according to one of claims 1 to 3. A rotor blade (10) which can be arranged in a plurality on a hub of a turbine wheel, comprising at its radially outer end a A cover plate (20) which, when a plurality of blades (10) are circumferentially aligned with the cover plates of the other vanes, forms an annular shroud with the plurality of vanes (10) arranged to transition between two adjacently disposed blades in the area of the shroud a first, uneven Contact surface (21) and a second, planar contact surface (25), characterized in that the uneven contact surface (21) has at least one torus-shaped elevation (22) which has a radius of curvature (R) and a cross-sectional radius (r), the radius of curvature (R) of the curvature being greater than the cross-sectional radius (r) of the curvature at least one survey (22). 8. Blade according to claim 7, wherein the cross-sectional radius (r) of the at least one elevation (22) along the radius of curvature (R) is different in size. 9. Blade according to one of claims 7 or 8, wherein the uneven contact surface (21) has a plurality of toroidal projections (22), and the plurality of elevations (22) each have different cross-sectional radii (r).