EP1767746A1

EP1767746A1 - Turbine blade/vane and turbine section comprising a plurality of such turbine blades/vanes

Info

Publication number: EP1767746A1
Application number: EP05020703A
Authority: EP
Inventors: Jan Dr. Walkenhorst; Armin Dr. De Lazzer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-09-22
Filing date: 2005-09-22
Publication date: 2007-03-28

Abstract

A turbine blade/vane comprising a blade/vane airfoil (40, 42) mounted on a base platform (18, 20) and extending along an elongation axis, said base platform (18, 20) in a first basal direction extending between an upstream surface (46, 48) and a downstream surface (50, 52) is provided that due to its design contributes to minimizing the negative and undesired effects of the leakage flows in the turbine section. For this purpose, in said upstream surface (46, 48) a cavity (60, 62) extending along a second basal direction approximately perpendicular to said elongation axis is provided.

Description

TECHNICAL FIELD

The present invention relates to a turbine blade/vane comprising a blade/vane airfoil mounted on a base platform and extending along an elongation axis, said base platform in a first basal direction extending between an upstream surface and a downstream surface. The invention further relates to a turbine section comprising a plurality of such turbine blades/vanes and a steam turbine or a gas turbine comprising a number of turbine sections of this type.

BACKGROUND OF THE INVENTION

Both gas turbines and steam turbines are employed in many fields for driving generators or machinery. In this process, the energy content of a working medium is used to generate a rotational motion of a turbine shaft. In a steam turbine, hot steam is used as working medium which expands during its passage through turbine sections of the steam turbine. In a gas turbine, in contrast, fuel is burned in a combustion chamber, with compressed air being supplied from an air compressor. The working medium in this case is generated at high pressure and at high temperature in the combustion chamber by the combustion of the fuel and then is conducted to a number of turbine sections connected downstream of the combustion chamber, where the gas expands with an output of work.
In order to generate the rotational motion of the turbine shaft in these processes, in the respective turbine section a number of rotor blades together with a number of guide vanes is provided. The rotor blades, which are usually combined into blade groups or blade rows are arranged on the turbine shaft and drive the turbine shaft by means of a transfer of inertia from the working medium. In order to conduct the working medium within the turbine section, guide vanes connected to the turbine casing are usually arranged in rows between adjacent rotor blade rows.
The rotor blades as well as the guide vanes each typically comprise a blade/vane airfoil mounted on a base platform. The base platform then is mounted onto the rotor shaft (in case of a rotor blade) or to the casing of the turbine section (in case of a guide vane). At the free end or tip of the blade/vane airfoil, a header element may be provided.
Necessarily, the header or blade/vane tip is positioned at a certain distance from its respective counter part in the turbine section, i. e. the turbine inner casing for the rotor blade or the rotor shaft surface for the guide vane, in any case resulting in a certain radial gap of the respective turbine blade row or guide vane row. Through this gap, leakage of the working medium may occur, resulting in a certain small fraction of the working medium bypassing the respective blade row or guide vane row. In order to optimize the efficiency of the inertia transfer from the working medium to the turbine blades and accordingly in order to optimize the efficiency of the turbine in general, it is a common design goal to minimize this leakage of the working medium through the respective radial gaps and to maximize the fraction of the working medium that is actually conducted through the respective turbine blade rows and guide vane rows. For this purpose, specific features such as gaskets or the like may be provided in order to minimize this leakage.
However, in most cases a certain amount of leakage through the respective radial gaps in a turbine section can not be avoided, leading to undesired losses in efficiency. Furthermore, these leakages may result in an undesired impact on the entire flow dynamics within the turbine section since mixing of the leakage flows with the main flow of the working medium within the turbine section may result in undesired contributions to the flow dynamics.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide an improved turbine blade or turbine vane that due to its design contributes to minimizing the negative and undesired effects of the leakage flows in the turbine section. It is another object of the invention to provide a turbine section designed for particularly high efficiency.
According to the present invention, with regard to the turbine blade or turbine vane this object is achieved with a cavity provided in the upstream surface of the base platform of the turbine blade or turbine vane, said cavity extending along a second basal direction approximately perpendicular to the elongation axis of the blade/vane airfoil.
The invention is based upon the concept that even though the leakage effects in the radial gaps in the respective turbine section may not be entirely avoidable, among other things their negative influence on the flow dynamics of the main flow of the working medium should be minimized. In order to achieve this, the effects of re-admixing the leakage flows into the main flow of the working medium should be minimized by establishing a particularly smooth flow path for the partial flows to be re-admixed. Such a smooth flow path may be achieved by designing the structural components in the vicinity of the respective radial gaps such that the leakage flows are smoothly guided back into the main flow. In particular, the leakage flows typically tend to have a flow component in circumferential direction in the turbine, and this component is not significantly reduced by the respective seals or gaskets, and in order to avoid re-admixing losses, in particular these components and their effect on the flow dynamics should be minimized.
As one means for achieving the desired smooth flow path, the invention provides for means for gathering the leakage flows and to dissipate the undesired flow components before re-admixing occurs. As means for dissipating the mentioned flow components within the leakage flow, the upstream surface of the base plate of the turbine blade or turbine vane is provided with an appropriate surface cavity that in response to incoming leakage flows of the working medium generates vortices and turbulences which in turn are used to smoothly guide further inflowing leakage flows back into the main flow of the working medium.
The cavity may be restricted to a part of the width of the respective blade. In order to provide for a particularly beneficial way of conducting the leakage flows, however, in a preferred embodiment the cavity extends over the entire width of the upstream surface of the respective base blade.
The cross section of the cavity may be chosen appropriately in order to optimize the desired influence on the flow dynamics. Among other design choices, the cross section may be polygonal or have other curvatures. In a preferred embodiment, however, the cross section of the cavity is semicircular, allowing for a particularly simplified manufacturing of the respective parts. The radius of this semicircle preferably is chosen comparable to the extension of the respective radial gap. Preferably, the cavity has an open width of approximately 6 mm to 12 mm and an axial depth of approximately 3 mm to 10 mm.
With respect to the turbine section, the object identified above is achieved with a plurality of turbine blades and/or turbine vanes according to the invention, which respectively are combined to form a blade row and/or a vane row. Preferably, the design is chosen such that the cavities of the turbine blades or turbine vanes forming one of said blade/ vane rows jointly form an annular cavity ring circumvening the turbine rotor.
Preferably, the turbine section is part of either a steam turbine or a gas turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained in more detail using the drawings. In this:

FIG 1: shows a half-section through a gas turbine, and
FIG 2: shows an excerpt from a longitudinal section of the gas turbine of FIG 1 with representation of a turbine blade row and a guide vane row.

Similar parts in the two figures are provided with the same designations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG 1 the invention is referred to in the embodiment of a gas turbine 1. However, it is well understood that the invention may also be incorporated into a steam turbine in an entirely analogous manner.
The gas turbine 1 according to FIG 1 has a compressor 2 for combustion air, a combustion chamber 4, and a turbine section 6 for driving the compressor 2 and a generator or a power machine (not shown). For this purpose, the turbine section 6 and the compressor 2 are arranged on a common turbine shaft 8, also designated a turbine rotor to which the generator or this power machine is also connected and which is rotatably supported about its center line 9.
The combustion chamber 4 is equipped with a number of burners 10 for the combustion of the liquid or gaseous fuel. It is, in addition, provided with heat-shield elements (not shown in anymore detail) on its inner wall.
The turbine section 6 has a number of rotor blades 12 which can rotate and which are connected to the turbine shaft 8. The rotor blades 12 are arranged as a as number of rings on the turbine shaft 8 and therefore form a number of rotor blade rows. The turbine section 6 also comprises a number of stationary guide vanes 14 which are likewise fastened rings with the formation of guide vane rows on an inner casing 16 of the turbine section 6. In this arrangement, the rotor blades 12 are used for driving the turbine shaft 8 by use of a transfer of inertia from the working medium M flowing through the turbine section 6 in a main flow direction as indicated by the arrow 17.
The guide vanes 14, on the other hand, are used for conducting the flow of the working medium M between each two rotor blade rows or rotor blade rings, which follow one another viewed in the flow direction of the working medium M. A sequential pair consisting of a ring of guide vanes 14, or a guide vane row, and of a ring of rotor blades 12, or a rotor blade row, is also designated a turbine stage in this arrangement.
Each guide vane 14 has a base platform 18 which is also designated a vane root and which is arranged for fixing the respective guide vane 14 as a wall element on the inner casing 16 of the turbine section 6. In this arrangement, the platform 18 is a thermally comparatively strongly stressed component which forms the outer boundary of a hot gas duct for the working medium M flowing through the turbine section 6. Each rotor blade 12 is fastened, in an analogous manner, by a platform 20, also designated as a blade root, to the turbine shaft 8. A guide ring 21 is respectively arranged on the inner casing 16 of the turbine section 6 between the platforms 18 which are arranged at a distance from one another, of the guide vanes 14 of the adjacent guide vane rows. The outer surface of each guide ring 21 is at a distance in the radial direction from the outer end 22 of the rotor blade 12 located opposite to it, forming a radial gap 24. Likewise, the outer surface of the turbine shaft 8 is at a distance in the radial direction from the outer end 26 of the guide vane 14 located opposite to it, forming a radial gap 28.
As may be seen from the enlarged representation in FIG 2, the radial gaps 24, 28, will cause partial leakage flows of the working medium M as indicated by the arrows 30. Even though the main flow of the working medium M will still be conducted through the respective rows of rotor blades 12 and guide vanes 14, these leakage flows still will occur and reduce the efficiency of the turbine section 6. Beyond potentially limiting these leakage flows by applying appropriate gaskets or the like in order to close the gaps 24, 28, the turbine section 6 is designed in order to minimize the negative effects of the leakage flows on the flow dynamics of the working medium M within the turbine section 6. In order to achieve this, the rotor blades 12 and the guide vanes 14 with respect to their structure are designed such that a particularly smooth flow profile of the leakage flows is achieved and losses due to re-admixing the leakage flows into the main flow of the working medium M are minimized.
As may be seen from the enlarged view in FIG 2, both the rotor blades 12 and the guide vanes 14 comprise a blade airfoil 40 or a vane airfoil 42, respectively, mounted on the respective base platform 20, 18. The blade airfoil 40/the vane airfoil 42 extends along an elongation axis as indicated by the respective arrow 44. The respective base platform 20, 18 furthermore in first basal direction extends between an upstream surface 46, 48 respectively, and a downstream surface 50, 52 respectively, wherein the designations "upstream" and "downstream" refer back to the main flow direction of the working medium M as indicated by the arrow 17.
In order to achieve the desired smooth flow profile with respect to the leakage flows, the platforms 20, 18 on their surfaces facing the inflowing respective leakage flow, i. e. their upstream surfaces 46, 48 are provided with a cavity 60, 62. The cavity 60, 62 is designed in order to catch incoming leakage flow from the preceding gap 28, 24 respectively, and to controllably create turbulences or vortices in the flow medium as indicated by lines 64, 66. These turbulences or vortices will create gas cushions in front of the respective upstream surfaces 46, 48, effectively smoothening the flow dynamics of the leakage flows as indicated by arrows 30. In these vortices or turbulences, an additional mixing process is taking place, efficiently absorbing energy of the respective leakage flow and accordingly minimizing re-admixing losses when the leakage flow re-enters the main flow of the working medium M.
In the embodiment as shown the cavities 66, 62 each have approximately semicircular cross section. However, cross section may be varied according to specific design goals and may have any appropriately chosen curvature. The cavities 60, 62 both extend over the entire width of the respective base platform 20, 18. Consequently, since the turbine blades 12 form a closed ring around the turbine shaft 8, the cavities 60 in this particular blade row also form an annular cavity ring circumvening the turbine rotor 8. Analogously, the cavity 62 of the guide vanes 14 forming a guide vane ring also form an annular cavity ring circumvening the turbine shaft 8.

Claims

Turbine blade/vane comprising a blade/vane airfoil (40, 42) mounted on a base platform (18, 20) and extending along an elongation axis, said base platform (18, 20) in a first basal direction extending between an upstream surface (46, 48) and a downstream surface (50, 52), wherein in said upstream surface (46, 48) a cavity (60, 62) extending along a second basal direction approximately perpendicular to said elongation axis is provided.
Turbine blade/vane according to claim 1, in which said cavity (60, 62) extends over the entire width of said upstream surface (46, 48) .
Turbine blade/vane according to claim 1 or 2, in which said cavity (60, 62) has semicircular cross section.
Turbine blade/vane according to either one of the claims 1 through 3, in which said cavity (60, 62) has an open rapid width of approximately 6 mm to 12 mm and/or an axial depth of approximately 3 mm to 10 mm.
Turbine section, comprising a plurality of turbine blades/vanes according to either one of the claims 1 through 4, respectively combined to form blade/vane rows.
Turbine section according to claim 5, in which said cavities (60, 62) of the turbine blades/vanes forming one of said blade/vane rows jointly form an annular cavity ring circumvening a turbine rotor.
Steam turbine, comprising a number of turbine sections according to claim 5 or 6.
Gas turbine (1), comprising a number of turbine sections according to claim 5 or 6.