Turbine Blade With Recessed Tip
A turbine blade (1) with a side surface (7) having an aerodynamic profile. The turbine blade (1) further comprises an end surface (6) and is mounted in a turbine, whereby the end surface (6) is delimited by a gap from a casing (8) of the turbine. The end surface (6) comprises a recess (2) which is shaped such that it acts as an improved aerodynamic seal.
The invention lays in the field of turbine blades for highly loaded axial rotor turbines as e.g. used in aero engines or for power generation.
DESCRIPTION OF THE ARTIn axial turbine the tip clearance flow occurring in rotor blade rows is responsible for about one third of the aerodynamic losses in the blade row and in many cases is the limiting factor for the blade lifetime.
The tip leakage vortex forms when the leaking fluid crosses the gap between the rotor blade tip and the casing from pressure to suction side and rolls up into a vortex on the blade suction side. The flow through the tip gap is both of high velocity and high temperature, with the heat transfer to the blade from the hot fluid being very high in the blade tip area. In order to avoid blade tip burnout and a failure of the machine, blade tip cooling is commonly used.
The tip clearance flow has been investigated recently with a number of contributions in the open literature. An important contribution always referred to is the work by Rains [1] (see subsequent list of references), who studied tip clearance flow for axial flow pump motivated by concerns of cavitation. Moore & Tilton [2] investigate the tip leakage flow both experimentally and analytically. The flow structure inside the gap and heat transfer to the blade have been discussed. A flow model assuming the gap losses coming from complete mixing behind the vena contracta (in general, point in a fluid stream where the diameter of the stream is the least) leading to uniform flow conditions at the gap outlet is presented. Bindon [3] measured and investigated the tip clearance loss formation. He could divide the total endwall loss into loss generated inside the tip gap, mixing loss of the tip leakage vortex, and secondary and endwall losses. He concluded that not only tip leakage mass flow is important for loss generation (48% of overall loss seen in mixing loss), but also the flow structure inside the gap would play a significant role (39% of overall loss generated inside the gap). Furthermore, he showed a conceptual model for tip clearance loss formation. Bindon & Morphis [4] investigated loss for different blade tip geometries. They found that the overall loss remained unchanged although gap losses strongly varied between the base line sharp edged flat tip and differently contoured blade tips. Whereas the sharp edge case showed high losses inside the gap with a strong separation bubble at the pressure side lip, the contoured cases showed less losses since no separation bubble was formed on the gap inlet but in turn an increased tip gap mass flow was found.
In a study of different squealer tips by Heyes, Hodson & Dailey [5] it was also concluded that the separation bubble with the associated vena contracta is effectively sealing the gap and by reducing tip mass flow the tip clearance losses may be decreased. In this study also a flow model for squealer tips is included as well as a model for the flow at the gap exit which is represented as a combination of an isentropic jet between the casing and gap mid height and a wake formed behind the separation bubble. A computational study by Ameri [6] on heat transfer on the blade tip showed that a flat tip with sharp edges performs best in terms of efficiency and total pressure loss compared to a mean camberline squealer tip and a flat tip with radiused blade tips. Further computational studies by Tallman [7], [8] on the experimentally investigated linear cascade by Bindon & Morphis [4] discuss the effect of tip clearance height and relative casing wall movement on the flow physics in the tip gap. A further experimental investigation on the tip clearance flow physics due to moving casing wall is presented in a two part study by Yaras & Sjolander [9,10]. It was found that the moving belt simulating relative casing motion significantly decreased tip gap mass flow. Also the tip passage vortex is drawn to the suction side, providing a throttling effect. Furthermore a reduced pressure difference driving the flow into the gap was observed.
In a recent study, detailed heat transfer to recessed blade tip was first investigated by Dunn et al. [12]. A recessed blade tip was equipped with heat flux gauges and experimentally investigated in a full stage rotating turbine. Nusselt Number was shown for different vane/blade spacings. It was found that the leading edge Nusselt Number on the cavity bottom were in excess of the blade stagnation value.
LIST OF REFERENCES
- [1] Rains, D. A., 1954, “Tip Clearance Flows in Axial Flow Compressors and Pumps”, Califormia Institute of Technology, Hydrodynamics and Mechanical Engineering Laboratories, Report No. 5, June 1954.
- [2] Moore, J. & Tilton, J. S., 1988, “Tip Leakage Flow in a Linear Turbine Cascade,”, ASME Journal of Turbomachinery, Vol 110, pp. 18-26.
- [3] Bindon, J. P., 1989, “The Measurement and Foramtion of Tip Leakage Loss,” ASME Journal of Turbomachinery, Vol 111, pp. 257-263.
- [4] Morphis, G. & Bindon, J. P., 1992, “The Development of Axial Turbine Leakage Loss for Two Profiled Tip Geometries Using Linear Cascade Data,” ASME Journal of Turbomachinery, Vol 114, pp. 198-203.
- [5] Heyes, F. J. G., Hodson, H. P., & Dailey, G. M., 1992, “The Effect of Blade Tip Geometry on the Tip Leakage Flow in Axial Turbine Cascades,” ASME Journal of Turbomachinery, Vol 114, pp. 643-651.
- [6] Ameri Ali, A., 2001, “Heat Transfer and Flow on the Blade Tip of a Gas Turbine Equipped with a Mean-Camberline Strip,” ASME Paper 2001-GT-0156.
- [7] Tallman, J. & Lakshminarayana B., 2000, “Numerical Simulation of Tip Clearance Flows in Axial Flow Turbines, With Emphasis on Flow Physics, Part I—Effect of Tip Clearance Height,” ASME Journal of Turbomachinery, Vol 123, pp. 314-323.
- [8] Tallman, J. & Lakshminarayana B., 2000, “Numerical Simulation of Tip Clearance Flows in Axial Flow Turbines, With Emphasis on Flow Physics, Part II—Effect of Outer Casing Relative Motion,” ASME Journal of Turbomachinery, Vol 123, pp. 324-333.
- [9] Yaras, M. I. & Sjolander, S. A., 1992, “Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part I—Tip Gap Flow,” ASME Journal of Turbomachinery, Vol 114, pp. 652-659.
- [10] Yaras, M. I. & Sjolander, S. A., 1992, “Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part II—Downstream Flow Field and Blade Loading,” ASME Journal of Turbomachinery, Vol 114, pp. 660-667.
- [11] Basson, A. H. & Lakshminarayana, B., 1995, “Numerical Simulation of Tip Clearance Effects in Turbomachinery,” ASME Journal of Turbomachinery, Vol 109, pp. 545-549.
- [12] Dunn, M. G. & Haldemann, C. W., 2000, “Time Averaged Heat Flux for a Recessed Blade Tip, Lip and Platform of a Transonic Turbine Blade”, ASME Paper GT2000-0197.
- [13] Behr, T., Kalfas, A. I., Abhari, R. S., “Unsteady Aerodynamics in Casing Injection for Tip Leakage Treatment in an Oneand-½-Stage Unshrouded Turbine”, ASME Paper No. GT2006-90959.
- [14] Sell M., Schlienger J., Pfau A., Treiber M., Abhari R. S., 2001, “The 2-stage Axial Turbine Test Facility LISA”, ASME Paper No. 2001-GT-049.
The invention is directed to a recessed blade tip for a highly loaded axial rotor turbine blade with application in high pressure axial turbines in aero engine or power generation.
To overcome the problems known from the prior art a blade tip design is suggested with a recess in the blade tip instead of a simple flat blade tip. The recess (cavity) inside the blade tip acts as an aerodynamic seal which improves the performance of the turbine and/or reduces the heat load of the turbine tip, in that it takes influence on the flows distribution. Since material at the upper surface of the blade is moved to a lower radius from the axis of is rotation, blade root mechanical stresses can be lowered. Also in case of a tip rub, i.e. when the rotor blade touches the casing during rotation, only the thin cavity rim is damaged. Wear damage to the casing is also limited and since the purge holes for the blade tip cooling are located inside the cavity, the rubbing does not damage the outlet of the holes. Efficient cooling is hence assured even if rubbing occurs. Finally, the recess cavity may act as a labyrinth seal, which could be beneficial in reducing tip clearance mass flow.
It has been observed that by an appropriate profiling of the recess shape, the total tip heat transfer Nusselt Number can significantly reduced, e.g. being 15% lower than the flat tip and 7% lower than the baseline recess shape. Experimental results also showed an overall improvement of 0.3% in the overall turbine total efficiency with the improved recess deign compared to the flat tip case, validating a 0.38% prediction from the CFD analysis.
With use of a three dimensional Computational Fluid Dynamics (CFD), the flow field near the tip of the blade for different shapes of the recess cavities is investigated. Through control of cavity vertical structures, an improved design is achieved and the differences to the blade tips as common in prior art are highlighted.
Tip clearance between the blade tip of a rotor and the casing is necessary for a free rotation of the rotor blade row. The gap however allows fluid to cross the blade tip from the pressure side of the blade to the suction side due to the pressure difference on the pressure and the suction side. This flow is associated with two main problems. Firstly, roughly one third of all the aerodynamical losses in a rotor row are related to the tip leakage vortex, which forms when the tip leakage over the blade tip enters the passage flow again on the blade suction side. It creates both mixing loss when it mixes out with the main flow and perturbs the pressure field on the blade tip wall that is responsible for the blade lift. Furthermore, the fluid crossing the gap is not turned by the blade and therefore no work is extracted from it. It is therefore interpreted as lost work extraction. Secondly, the fluid crossing the tip clearance has a relatively high temperature due to hot streak migration, resulting in a high thermal load for the blade tip. In fact, blade tips burn away if not adequately cooled and are hence one of the limiting factor for the blade lifetime.
Additionally, it is desirable to minimize the tip clearance gap height in order to improve the performance through reduction of the tip leakage mass flow. This reduced gap height, however, increases the risk of the rotor blade rubbing at the casing sometime during the operational envelope. This can occur for example if the rotor expands further than the casing due to transients, a rotor dynamic excursion, an ovalization of the casing, or through casing thermal distortions. In the case that a blade with a flat tip rubs severely at the casing, catastrophic coolant loss could occur if the tip wears off. Even in a case of a relatively minor rub for a flat tip, any cooling holes located on the tip may be damaged resulting in an inadequate cooling eventually leading to blade tip burnout.
Unlike for the case of a flat blade tips, the more complex flow physics for a recessed blade tip is more difficult to understand it's complexity. Also systematic design procedures for cavity size and shape are not available. By research it was possible to overcome this problem and to better understand aerodynamics and heat transfer physics of recess cavities and to provide new design boundaries for a standard, highly loaded rotor blade representative of a high pressure turbine. A special three dimensional CFD tool has been extensively used for this purpose.
Nomenclature
The invention as such and computational tools to improve the results are described in general in accordance with the drawings. Because not available on the marked the computational tools for pre-processing and the solver have been developed by the inventors. These tools may interact in parts with commercial products for post-processing.
In order to perform the intended computational and experimental study, a previously designed axial turbine test case has been utilized. The geometry of the one-and-½-stage, unshrouded turbine models a highly loaded (DH/U2=2.36), low aspect ratio gas turbine environment. The air-loop of the test rig is of a quasi-closed type and includes a radial compressor, a two-stage water to air heat exchanger and a calibrated venturi nozzle for mass flow measurements. Before the flow enters the turbine section, it passes through a 3 Meter long straight duct, which contains flow straighteners to ensure an evenly distributed inlet is, flow field. Downstream of the turbine the air-loop is open to atmospheric conditions. A DC generator absorbs the turbine power and controls the rotational speed of the turbine. An accurate torque meter measures the torque that is transmitted by the rotor shaft to the generator. The TET (turbine entry temperature) is controlled to an accuracy of 0.3% and the RPM (Rounds Per Minute) is kept constant within ±0.5 min−1 by the DC generator. More information on the turbine design (Behr et al. [13]) as well as on the operation of the experimental facility (Sell et al. [14]) can be found in the open literature.
The following table shows the main parameter of “LISA” 1.5-stages axial turbine research facility at design operating point (Table 1):
A computational design optimization for a nominal recess cavity commonly used in axial turbine rotor blades has been presented. From extensive parametric study, an improved recess cavity design is presented. Extensive aerodynamic and heat transfer comparisons between the new design and the flat tip blade and the nominal recess tip are presented. The computational data was compared to experimental data of the Swiss Federal Institute of Technology (ETHZ) where the 3D flow structures and the performance of rotor blades with flat tip and the new recess design were measured. Qualitative comparisons to the experimental data from OSU have also been used to validate the predicted heat transfer data. The following concluding statements can be drawn from this study.
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- A better understanding of the three dimensional flow inside recess cavities was gained. Three cavity vortices were found to govern the leakage flow through the cavity.
- Change of the cavity geometry influences the generation and the interaction of the main recess vortices. A particular recirculation at the suction side front responsible for high heat transfer could be eliminated and lead to a new design with improved heat transfer behaviour.
- The beneficial effect of creating an aerodynamic seal has been shown for both recess designs. Tip leakage mass flow could be lowered by as much as 25% in the new recess design according to the present invention compared to the flat tip. CFD showed increased power output for the new design too. Experimental measurements showed a 0.3% increase in the turbine efficiency between a flat tip and the new recess tip at design point.
- The heat load on the blade tip is found to be a balance between the heat load on the different blade tip components, i.e. the tip rim, the cavity rim walls, the cavity bottom and the rear flat blade tip. The new recessed design is about 7% lower on the overall heat load compared to the base line recessed design and 15% lower compared to the flat tip.
- To the best of the author's knowledge, this is the first time that detailed profiling of blade tip recess cavity is shown to improve performance and reduce heat load.
- Three-dimensional geometric profiling of blade tip recess cavity walls significantly improves overall efficiency and effectively reduces in the same time both heat load at the blade tip and mechanical stress.
- Three-dimensional geometric profiling of recess cavity walls can be achieved by using non-uniform rim wall thickness as well as three-dimensional shaping of the inside of the cavity recess volume.
- Three-dimensional geometric profiling occurs through varying the recess rim thickness and cavity depth either separately or combine.
- Three-dimensional geometric profiling of recess cavity optimize leakage flow and its interaction with vortices within the cavity and suppresses vertical flow formation leading to loss in the cavity through flow and high heat load on the cavity walls.
- Three-dimensional geometric profiling of blade tip recess cavities showing the above features attenuates and suppresses the secondary vortex formation and by restraining the available space required for vortex formation both circumferentially and radially.
- Three-dimensional profiling of recess cavity walls leads to higher work output of the blade because of additional blade surface of the cavity walls in case of a favourable cavity pressure gradient.
- Three-dimensional geometric profiling according to the above features define an optimum cavity volume to combine.
- Three-dimensional geometric profiling exhibiting the above features reduces the number of circumferentially aligned vortices.
- Three-dimensional geometric profiling exhibiting the above features leads to less dissipative vortex patterns inside the cavity.
- Three-dimensional geometric profiling of blade tip recess cavities showing the above features keeps the advantages of non-profiled, constant rim thickness cavities, such as reduced rubbing surface area, cooling hole protection, lower mechanical stresses.
- Three-dimensional geometric profiling of blade tip recess cavities showing the above features is applicable for unshrouded and certain partially shrouded turbine blades.
- Three-dimensional geometrically profiled tip recess cavity walls showing the above features provide passive flow control of leakage flow by acting as a throttling mechanism.
- Three-dimensional geometrically profiled tip recess cavity walls based on the three-dimensional flow structure showing the above features can be used to re-design the blade tips of both existing blades for the upgrade and replacement blades as well as being incorporated into new design configurations.
The invention is directed to a turbine blade with a side surface having an aerodynamic profile. The turbine blade has an end surface arranged in a mounted position in a turbine delimited by a gap from a casing of the turbine. The end surface comprises a recess which is shaped such that it acts as an aerodynamic seal and/or reduces the blade tip heat load. The recess is delimited by a side wall which has a variable wall thickness in circumferential direction. The side wall may have an in general constant wall thickness in height direction (in the direction of the length of the turbine blade). In certain embodiments the wall thickness of the side wall has an overall maximum in the area where the turbine blade has its maximum thickness. In a further embodiment the wall thickness of the side wall has a maximum on the suction side of the turbine blade between +0% and +50% relative length with respect to the blade leading edge (trailing edge +/−100%). In certain embodiments this maximum is an overall maximum. However, in certain other embodiments the wall thickness of the side wall has on the pressure side of the turbine blade a minima. Depending on the field of application this may be located in the range between −0% and −70% relative length with respect to the blade leading edge stagnation point (0%). The wall thickness on the pressure side may be at least partially constant. Good results may be achieved in that the overall maximum of the wall thickness of the side wall is about 5.5 to 6.5 times bigger then the overall minima. In an embodiment the recess has an in general constant depth.
The herein described invention will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be considered limiting to the invention described in the appended claims. The drawings show in a simplified and schematic manner
Subsequent embodiments of the invention are described in more detail. Similar features are in the different drawings marked with the same numbers.
The analytical models applied are in general based on a numerical grid (mesh) of a turbine blade 1. The numerical grids used were generated with an in-house developed grid generator called MELLIP. A multi block structured grid generator uses a two dimensional NURBS library as input data to mesh the computational domain boundaries. Using a set of geometrical transformations the interior block boundaries are defined according to the intended grid topology. High grid quality, i.e. smooth gridlines, limited aspect ratio, skewness and cell to cell ratios are achieved using both non linear interpolation algorithms with flexible clustering specification and two dimensional Poisson type elliptic partial differential equations during the meshing of each block. Several topologies are implemented and partition the computational domain for a blade tip with recess area in 18 blocks for the blade recess case. Especially the use of up- and downstream wake blocks with adjustable sizes and grid density helps to keep low grid skewness in the trailing edge area and prevents the numerical diffusion of the shed wake. The grids used for this study show a high resolution in the blade tip area in order to capture the flow gradients in this region.
This helps in keeping the number of grid points at about 900'000 points, since clustering near walls does not need to be as aggressive as in two layer turbulence model computations. Hence the high number of grid points in the blade tip area leads to homogeneous mesh density with smooth cell to cell ratios distribution. The densely packed tip region grid block spans over about the top 10% the blade span.
A numerical flow solver preferably used is called MBStage3D, a three-dimensional, structured Navier-Stokes solver for multistage turbomachinery applications. The time marching algorithm preferably used in MBStage3D is a Jameson-type algorithm, i.e. an explicit method with a residual-averaging technique applied for improving stability. The time discretization is preferably accomplished by a five stage Runge-Kutta technique, which is of fourth-order accuracy. All computations discussed here were conducted with the algebraic Baldwin-Lomax turbulence model together with the Sommerfeld logarithmic wall function to compute the turbulent viscosity at the wall.
Extensive post processing necessary to gain understanding of flow physics is achieved through 3D, 2D, 1D, and scalar investigation of the flow fields of interest. The 3D visualizing is done with TECPLOT, a collection of integrators and the 3D data generation subroutines for TECPLOT are developed in-house.
The geometry of the tip recess 52 and its impact on the distribution of the flow field around the blade tip 53 was investigated based on a standard (nominal) recess design 52 (see
The cavity walls of the recess 2 (see
The understanding of the detailed flow physics is therefore particularly important in the design process and will be investigated next on behalf of three major test cases. The first case is a flat tip blade. The second test case is a nominal recess cavity as known from the prior art with a length of 80% axial chord and twice as deep than the tip gap, the rim thickness being kept constant. This test case represents a current design for recess cavities. The final test case is the newly designed recess geometry based on the extensive physical modelling and geometric perturbation.
The second main flow feature observed is the tip leakage vortex 103 that forms from the tip leakage flow crossing the gap from the pressure side starting at approx. 15% axial chord. The dividing streamline between the pressure side leakage feeding the tip passage vortex and the tip leakage vortex outer fluid layer can be identified. The outer fluid layers in the tip leakage vortex 103 result from the main part of the pressure driven, low gap shear loss generating leakage jet. The tip leakage vortex core is formed by blade tip boundary layer fluid.
A cutting plane orthogonal to the blade mean camberline reveals the well known gap flow structure. When the tip leakage flow enters the gap from the pressure side, a separation bubble is formed, leading to a vena contracta. The leakage jet leaving the vena contracta would then form the wake fluid in the lower part of the gap. This wake creates mixing loss and is found later in the tip leakage vortex core. The leakage jet above the wake part is often modelled as an isentropic jet, it forms the outer fluid layers around the tip leakage vortex core depending on the axial position when it left the gap on the suction side.
Downstream of the 20% axial chord, the flow behaviour of the pressure side leakage is similar to the flat tip case with the difference that the leakage is deflected by the cavity vortices and interacts with them. After leaving the gap on the suction side, this fluid forms again the outer layer of the tip passage vortex and the tip leakage vortex. The core of the tip passage vortex is formed by the same incidence tip leakage that lifts off the cavity corner vortex when entering and leaving the cavity between 10% and 20% axial chord. The core of the tip leakage vortex is wake fluid behind the separation bubble on the suction side rim that forms when the pressure side leakage jet leaves the cavity.
To additionally clarify the flow features inside the cavity a cutting plane orthogonal to the camberline located downstream of the formation of the vortex formed by the pressure side leading edge jet is shown in
The nominal design showed many vortical structures inside the recess cavity. Particularly the front part of the cavity is affected by these structures. As seen above, the boundary layer fluid leaking from the rim into the cavity rolls up in a vortex along the corner between cavity bottom and cavity rim wall. The aim of the new design was to eliminate the recirculation zone in the front part of the blade to minimize aerodynamic losses and reduce the head transfer coefficient.
One effect of the improved design is that the streamline that separates the recirculation zone from the pressure side leading edge jet is moved. In
Subsequent the results regarding aerothermal performance of three test cases are introduced. For the aerodynamic performance, the tip leakage mass flow is investigated since it is intensively related to the total pressure loss. Nusselt Number distribution and integrated heat flux vector on the blade tip walls are compared to assess the impact of the new design on heat transfer.
As shown in
From
In the
In
Experimentally measured performance data shows that for the turbine used the “new” recess design has a 0.3% total efficiency when compared to the flat tip at exactly the same overall turbine operating conditions. The predicted difference between both efficiencies was 0.38%, which is a good quantitative agreement with the experimental data.
The predicted heat transfer data is qualitatively compared to data presented by the Ohio State University Gas Turbine Laboratory [12]. A turbine blade with a recess cavity similar to the nominal design presented here was equipped with heat transfer gauges to measure heat transfer on the cavity bottom near leading edge, trailing edge and in the middle. Also the rim was equipped with several gauges. Nusselt Numbers were reported for different vane/blade spacings. The trend in the variation of Nu Number according to the investigated location is similar. The highest Nu Number is found in the leading edge region. The second heat flux gauge was positioned 12.5% blade axial chord from peak suction downstream, reporting almost half of the Nu Number at leading edge. This can also be observed in the nominal recess case from
On the pressure side the wall thickness is in certain embodiments constant which is indicated by the in general horizontal progression of the graph in this area. However, certain embodiments (see profile 3) may also have a local maximum 18 at the pressure side.
Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.
Claims
1. A turbine blade (1) comprising:
- a side surface (7) having an aerodynamic profile and an end surface (6) arranged in a mounted position in a turbine delimited by a gap (12) from a casing (8) of the turbine, the end surface (6) comprising a recess (2) which is shaped such that it acts as an aerodynamic seal, wherein the recess (2) is delimited by a side wall (4) which has a variable wall thickness (t) in a circumferential direction of the turbine blade (1).
2. The turbine blade (1) according to claim 1, wherein the side wall (4) has a generally constant wall thickness (t) in a height direction (0).
3. The turbine blade (1) according to claim 1 wherein the wall thickness (t) of the side wall (4) has an overall maximum (15) on a suction side of the turbine blade (1) in an area where the turbine blade (1) has its maximum thickness (14).
4. The turbine blade (1) according to claim 1 wherein the wall thickness (t) of the side wall (4) has a maximum (15) on a suction side of the turbine blade (1) between +0% and +50% relative length with respect to the blade leading edge (0).
5. The turbine blade (1) according to claim 4, wherein the maximum (15) is arranged between +10% and +40% relative length with respect to the blade leading edge (0).
6. The turbine blade (1) according to claim 4 wherein the maximum (15) is an overall maximum.
7. The turbine blade (1) according to claim 4 wherein the wall thickness (t) is on the suction side of the turbine blade (1) on both side of the maximum (15) continuously decreasing.
8. The turbine blade (1) according to claim 1 wherein a wall thickness (t) of the side wall (4) has on the pressure side of the turbine blade (1) a minima in the range between −0% and −70% relative length with respect to the blade leading edge (0).
9. The turbine blade (1) according to claim 8 wherein the wall thickness (t) on the suction side of the turbine blade (1) is at least partially constant.
10. The turbine blade (1) according to claim 8 wherein the wall thickness (t) on the pressure side of the turbine blade (1) is at least partially constant.
11. The turbine blade (1) according to claim 10, wherein the wall thickness (t) on the pressure side is constant in the range between −5% and −50% relative length with respect to the blade leading edge (0).
12. The turbine blade (1) according to claim 1 wherein an overall maximum (15) of the wall thickness (t) of the side wall (4) is about 2 to 8 times bigger then an overall minima.
13. The turbine blade (1) according to claim 12, wherein the overall maximum (15) of the wall thickness (t) of the side wall (4) is about 5.5 to 6.5 times bigger then the overall minima.
14. The turbine blade (1) according to claim 1 wherein the recess (2) has a generally constant depth (0).
15. A turbine formed with the turbine blade (1) of claim 1.
Type: Application
Filed: Jan 15, 2007
Publication Date: Jul 16, 2009
Inventors: Bob Mischo (Zürich), Reza Abhari (Forch), Thomas Behr (Zurich)
Application Number: 12/087,761
International Classification: F01D 5/14 (20060101);