WO2001036791A1

WO2001036791A1 - Turbine blade and method for production thereof

Info

Publication number: WO2001036791A1
Application number: PCT/EP2000/010947
Authority: WO
Inventors: Roland Liebe; Harald HÖLL; Günther WALZ
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-11-16
Filing date: 2000-11-06
Publication date: 2001-05-25
Also published as: EP1101901A1

Abstract

The aim of the invention is to produce a turbine blade (1), comprising an outer wall (4), surrounding a hollow cavity, through which a cooling fluid (6) flows and which has an increased life expectancy, even under heavy loading and is simple to produce. The aim of the invention is achieved, whereby the thickness (8) of the outer wall (4), at least over an extent of the blade leading-edge region (7), is such that, at least in pre-determined areas of the external wall (4), pre-determined temperature thresholds (TM) and/or pre-determined temperature gradients (ΔTM) are not exceeded.

Description

Turbine blade and method for producing a turbine blade

The invention relates to a turbine blade, in particular a gas turbine blade, which has an outer wall against which a hot action fluid flows, which surrounds a possibly multi-part cavity through which a cooling fluid flows, the outer wall having a cross-section through the blade area of the blade area Turbine blade is of different thickness, and a method for producing a cast turbine blade, in particular gas turbine blade, according to the preamble of claim 27.

In order to achieve high levels of efficiency and performance when operating a turbine, in particular a gas turbine, which is operated with an action fluid, in particular a hot gas, the action fluid is heated to a high temperature. The guide vanes and rotor blades that are first flowed onto by the hot action fluid are therefore internally cooled to avoid damage, in particular by flowing through a cooling fluid, for example a cooling gas or a slightly overheated cooling steam.

US Pat. No. 5,320,483 discloses how the cooling fluid in the form of cow vapor is introduced into the turbine blade in a closed circuit and is led out again after flowing through an internal cavity of the turbine blade which is equipped with different flow chambers and inner walls. The cavity is surrounded by the outer wall of the turbine blade, which is flowed against by the hot action fluid of the turbine. The outer wall has a substantially constant thickness by viewing a cross section through the airfoil area. Despite the formation of complex and quite complex to produce channels and turbulators within the cavity of the turbine blade With this type of construction of a turbine blade, however, it does not ensure that the cooling takes place everywhere homogeneously and to the required extent, which greatly reduces the lifespan of the blade.

The object of the present invention is to provide an internally cooled turbine blade with the above-mentioned features, which has a longer service life than conventional turbine blades, even under very high loads, can be produced with little effort, and high performance and efficiency at low levels in a turbine NOx emissions and, as a sub-task, a suitable manufacturing process.

The object directed to the turbine blade is achieved in that the thickness of the outer wall, at least over a partial circumference of the airfoil region, is such that predetermined ones occur in accordance with the course of the external heat transfer number on the outside of the outer wall and the course of the internal heat transfer number on the inside of the outer wall Temperature threshold values on the outer wall and / or predetermined temperature gradients between predetermined locations on the outer wall are not exceeded.

The hot action fluid does not flow around the outer wall of the turbine blade equally quickly and equally everywhere, which leads to locally different heat input or heat transfer action fluid / outer wall. The external heat transfer coefficient is a measure of this heat transfer. A heat transfer number indicates the amount of heat that is transferred per unit of time and area. The higher the heat transfer number, the greater the heat transfer of the heat introduced into the material, for example by convection or radiation. With an increased external heat transfer, the cooling requirement increases at this point on the airfoil. This locally increased cooling requirement is met according to the invention in that the thickness of the metal wall and thus the outer wall is reduced at points with a high external heat transfer number. This results from the inclusion of the solution of an equation system that describes the heat transfer within the different areas of the turbine airfoil. The heat transfer comprises the heat transfer from the hot action fluid to the outside of the outer wall and from the inside of the outer wall to the cooling fluid. Furthermore, the heat conduction within the outer wall is described in the system of equations. A thinner outer wall increases the heat conduction. The temperature threshold values and the temperature gradients are set as boundary conditions for the solution of the system of equations. They are characteristic of the outer wall and essentially represent an upper limit for the action fluid temperatures. Compliance with these values ensures that no temperatures are exceeded on the blade which could lead to local damage and ultimately to the early failure of the turbine blade. The temperature threshold generally corresponds to an oxidation limit of the outer wall material, the temperature gradient is a measure of the thermal stresses that arise between two points of the outer wall due to different temperatures. To ensure a long lifespan for the turbine blade, it must not exceed a critical value that depends on the material, the composition of all the voltages involved and the operating load spectrum.

The solution to the system of equations shows that thinning the outer wall in a kind of dynamic equilibrium reduces the temperature level and the temperature gradients. In principle, a thinner design of the outer wall leads to an improved cooling effect due to the increased heat dissipation through the blade outer wall material. However, this is still subject to the requirements for stability, which is the thickness of the outer wall set lower limit. If the interior is skillfully designed, for example by inserting ribs, as described below, this lower limit is shifted a little to smaller thicknesses h.

By locally varying the thickness, the locally increased cooling requirements at locations with high external heat transfer numbers can thus be met in a simple manner. In places with a low external heat transfer number, the outer wall can be made even thicker, which increases stability. Due to the individually adapted cooling effect achieved by adjusting the outer wall thickness, it is possible to dispense with complicated channels within the cavity. This simplifies the manufacture of the Turbmenschaufei and lowers the costs. In addition, the required cooling fluid mass flow is reduced by the adapted cooling, which improves the efficiency and the performance of the turbine.

It is advantageous if the outer wall has a multilayer structure and has a thin ceramic protective layer on the outside of the outer wall and a metal wall on the inside and that the temperature gradient that is present between the outside and the inside of the metal wall is decisive. Due to the multi-layer structure, the outer wall can fulfill various tasks and requirements with a suitable choice of layers. The metal wall, in particular made of a high-temperature metal alloy, ensures sufficient mechanical strength and good thermal elasticity, which is necessary due to the changing mechanical loads and temperatures. A ceramic protective layer protects the metal wall from excessive temperature loads and prevents oxidation or corrosion. The protective layer is intended, inter alia, to prevent the highest temperature caused by the inflow of hot action fluid on the outer wall of the blade from exceeding a material-specific maximum value or from an established temperature turgradient between the outside of the outer wall and the inside of the outer wall exceeds a certain critical value. Usual high-performance blades depend on sufficiently thick ceramic protective layers for thermal insulation so that temperature and voltage limits can be maintained. Due to the high loads during the operation of the turbine, in particular due to rapid temperature changes or large voltage differences between different areas of the outer wall and due to the lattice parameter differences already existing in the cold state between the ceramic protective layer and the metal wall and different coefficients of thermal expansion, ceramic thermal insulation layers burst prematurely from the metal wall from. This is followed by a failure of the blade. This is prevented according to the invention in that the thickness of the metal wall is set in accordance with the heat transfer coefficients and the temperature threshold and the temperature gradient between the outside and the inside of the metal wall do not exceed predetermined values. These values are designed according to the corresponding requirements of the protective layer or the boundary layer between the protective layer and the metal wall. It is therefore sufficient to apply a much thinner protective layer to the metal wall than conventional protective layer thicknesses. The thinner layer also improves the adhesion of the protective layer to the blade surface and prevents local flaking, because the different thermal expansions of the materials no longer have such an impact due to the small layer thickness. At the same time, this thin layer is much easier to apply, among other things because it has to meet less stringent homogeneity requirements. This reduces the manufacturing costs and at the same time increases the lifespan of the blade.

If the temperature threshold value on the entire outer wall and / or predetermined temperature gradients over the entire outer wall are not exceeded, particularly good values are conditions for a low thermal or stress load of a turbine blade. This is particularly important with coated turbo showers. Due to a more uniform, lower temperature of the outer wall due to the setting of the thickness of the outer wall according to the invention, good adhesion of the ceramic protective layer to the metal wall is ensured without further manufacturing measures having to be taken or the hot gas temperature having to be reduced, which would reduce the efficiency.

For thermal reasons, it is possible to completely omit the ceramic protective layer if the temperature threshold value and the temperature gradient correspond to critical material-dependent values. In this case, a possible protective layer essentially still serves to prevent corrosion or oxidation attacks and can thus be at least thinner than conventional ceramic protective layers. This reduces the manufacturing costs and increases the lifespan of the blade.

It is particularly advantageous if the outer wall is single-layer and consists of metal. The metal is still stable even at relatively high temperatures and at the same time dissipates the heat well, so that the temperature threshold values and the temperature gradients can be maintained by the cooling inside and the adapted thicknesses of the outer wall.

In order to counter increased stresses in the outer wall, in particular in the case of thin metal wall sections, for example due to increased primary stresses due to a high internal pressure, it is proposed that a field of ribs be provided in the cavity where there is an outer wall region of reduced thickness. In this way, thinner areas of the outer wall are strengthened in such a way that they have approximately the same stability as thicker areas. This makes it possible to achieve a homogeneous stress on the outer wall of the turbine blade and a uniform material utilization. Because of the homogeneous Stress and strain distribution result in better long-term adhesion of the ceramic protective layer on the base material, which leads to an extension of the blade life. By limiting the primary stresses caused by internal pressure by attaching ribbed fields dependent on the wall thickness in the cavity and limiting the thermal stresses by adhering to a limit value for the temperature gradient, damage to the material is caused by excessive cycle numbers of the resulting total van Mises comparative stress, the primary stress, the hot voltage and other voltages reliably prevented. In the case of leading and moving vane, the thermal conductance values, ie the thickness variation, are calculated approximately the same. When designing the rib fields, it is important to take into account that centrifugal stresses are added, as well as additional secondary currents.

These aforementioned advantages are achieved in particular in that the ribs of the field have dimensions, distances and spatial arrangements predetermined in accordance with the thickness of the outer wall, the temperature threshold and / or the temperature gradient and / or the Mises reference stress. An optimal combination of parameters enables the temperature target sizes to be maintained over a wide range, so that the material is subjected to a homogeneous load and uniform

Material utilization can be achieved. The thermal stresses are essentially limited by adhering to the predetermined temperature gradient by adjusting the thickness of the metal wall and thus the outer wall. The primary tension is limited by the rib thickness fields on the inside of the outer wall, which are dependent on the wall thickness. If predetermined distances between the ribs are observed, an optimal cooling effect can be achieved on the one hand, but at the same time, however, an optimal stability of the material can be achieved. Other parameters are the height and width of the ribs, as well as their spatial arrangement. By a certain arrangement of ribs in ribbed fields it is possible to produce thin and at the same time durable outer walls for optimal thermal wall design with or without ceramic protective layers. As a rule, these measures can be used for both guide and moving displays.

If, in particular, the field of the ribs runs at least in sections transversely to the flow of the cooling fluid, the turbulence of the cooling fluid is increased, which improves the cooling effect without the need to use additional turbulators. Due to the rib fields arranged transversely to the direction of flow of the cooling fluid, a desired higher cooling effect is achieved especially in the areas with thin wall thickness where a higher internal heat transfer number is required. In order to achieve the desired swirling, care must be taken that the ribs are neither too narrow nor too far apart, because otherwise either insufficient swirling or insufficient stability will be achieved.

If the ribs have transverse openings, the cooling fluid becomes more turbulent as it flows through the interior. This in turn improves the cooling effect. The openings are designed so that they do not affect the stability of the ribs.

It is advantageous if the cavity is traversed by inner walls from the pressure side to the suction side in the longitudinal direction of the turbine blade, the inner walls being connected to the pressure-side or suction-side outer wall with a continuous course to the continuous course of the thickness of the outer wall. The division of the cavity from the pressure side to the suction side ensures that the stability of the turbine blade is maintained or improved. At the same time, the cavity is divided into several chambers. The shape and number of the inner walls used for this purpose are chosen depending on the type of cooling and cooling fluid properties so that the cavity is as simple as possible. consulted. This means that an inexpensive, conventional investment casting technique can be used. If the inner walls are connected to the pressure-side or suction-side outer wall with a continuous course to the continuous course of the thickness of the outer wall, stress peaks in the outer wall are reduced. The inner walls reinforce the outer wall areas and thus absorb tensions caused by a changing thickness and different temperatures in the outer wall and thus different heat transport. In addition, it is taken into account that there is an optimal speed level of the cooling fluid everywhere and thus an optimal internal heat transfer number. Due to the division of the cavity, only slight pressure losses occur. Therefore, a high proportion of energy can be recovered from the heated cooling fluid.

An additional improvement in the corrosion resistance is given by the fact that the cavity is provided with an aluminizing layer, in particular the steam-wetted inner surfaces.

The efficiency of the turbine is hardly or only minimally reduced by the cooling fluid if the cooling fluid is passed through the turbine blade in a closed circuit. The guidance in a circuit can also comprise further turbine blades, whereby additional cooling fluid is saved. Because no cooling mixture is created by the cooling fluid exiting the action fluid, the efficiency and thus the performance of the turbine are retained. No cooling fluid is consumed, which reduces the operating costs of the

Turbine lowers. The heat absorbed by the cooling fluid within the turbine blade can largely be reused. This improves energy utilization and increases efficiency.

An advantageous spatial arrangement of the cavity of the turbine blade is supported in that the inlet and the outlet of the cooling fluid are arranged in the foot area. The cooling fluid is then directed from the foot area to the various other cooling areas. The foot area is more easily accessible for cooling fluid supply lines.

The cooling fluid is used economically in that the top and bottom region of the turbine blade is cooled at the same time as the cooling fluid of the airfoil region. This simplifies the structure of the head, foot and blade area and in particular the transitions between the areas.

A more precise adaptation to the cooling actually required is given in that the turbine blade is a moving blade and the wall thickness of cooling chambers in the cavity varies locally in accordance with a local heat transfer number. Due to the rotating movement of the rotor blade, the cooling fluid is pressed more strongly against the inner walls or against the outer walls in some areas of the cooling chambers. This causes an inhomogeneous internal heat transfer coefficient. This is compensated for by the change in the wall thicknesses of the inner walls or the outer wall according to the invention. By adjusting the wall thicknesses, only the quantity of material that is absolutely necessary is used and, at the same time, a more precisely adapted coolant consumption is achieved. This increases the efficiency of the turbine and at the same time ensures sufficient cooling in all areas of the Scahuefl.

It is advantageous if in the central region of the airfoil region there are provided central cooling chambers which are flowed through in series by the cooling fluid. The central cooling ducts are located in the areas of the turbine blade that are most heavily loaded with high heat input. They therefore carry a large proportion of the heat registered. The serial flow ensures a long, meandering path of the cooling fluid through the turbine blade and thus a good utilization of the heat capacity of the cooling fluid. In particular at deflection points, the cooling fluid is strongly swirled and the cooling effect is thus improved. The amount of cooling fluid required is reduced.

A rapid flow of the cooling fluid and thus an improved heat removal is provided in that central cooling chambers formed by inner walls are provided in the central region of the airfoil region and the cooling fluid flows through them in parallel. At the same time, this simplifies the construction of the cavity in which the cooling chambers are located, thus making it possible to cast with less scrap during manufacture.

The flow rate of the cooling fluid shortly before the impact on the outer wall is increased if at least one of the central cooling chambers has an impact cooling insert with outward directed impingement cooling bores, which are arranged at a distance from the inside of the outer wall and through which the cooling fluid flows. The cooling effect is significantly improved by the increased flow rate of the cooling fluid hitting the inside of the outer wall. This makes it possible to achieve a good cooling effect even by means of a coolant with low pressure without stressing the outer wall due to high primary stresses due to the internal pressure.

A simple, safe and inexpensive way of holding the baffle insert is provided if the baffle insert is held by on the inside of the outer wall and / or by spacers attached to the inside wall and / or by ribs.

A further improvement of the cooling is given by the fact that additional cooling is provided on the rear edge of the turbine blade. This is particularly advantageous because the outer walls converge more closely there, and a connection to the other cooling chambers is therefore often difficult. In particular, it is a separate, closed steam cooling.

If, alternatively, there is open air cooling with a free outlet at the rear edge of the turbine blade, no return line is required. The air used is fed freely into the action fluid space. Since it is only a relatively small amount of cooling air, the efficiency of the turbine is not reduced as a result.

To achieve a higher internal heat transfer number, it is advantageous if the cooling fluid is steam. The scarce compressor air required for low pollutant emissions during pulsation-free operation does not have to be used. Closed air cooling requires a lot of air and causes high pressure drops. When steam is used as the cooling fluid, internal heat transfer numbers 1.5 to three times higher than that of air can be achieved. The use of steam thus enables the turbine to be operated with a hotter action fluid, which in turn increases efficiency. When cooling air is introduced into the action fluid, there are high efficiency losses. If the temperature of the action fluid is maintained, the use of cow steam makes it possible to make the turbine blade outer wall thicker, which increases the stability of the blade and reduces the demands on the fin fields. Solutions without rib fields are also possible. At the same time, cow steam has a higher heat capacity than air, which leads to improved heat removal from the turbine blade.

When using a low-pressure steam, it is possible to design the cavity with a few cooling chambers in the blade area. This low pressure steam is characterized by an inlet pressure of 15 bar or an inlet temperature of approximately 250 ° C. Due to the low pressure, the load on the outer wall due to primary stresses caused by internal pressure is reduced and there are fewer ribs to stabilize the Outside wall needed. The interior can, for example, be designed such that two cooling chambers formed by an inner wall have cooling fluid flowing through them in series. Advantageously, at least in one of the cooling chambers there is an impingement insert which has impingement cooling bores through which the cooling fluid flows and which is held by webs arranged on the inside of the outside wall and / or on the inside wall and / or on some of the ribs. The use of impingement cooling bores accelerates the local cow steam considerably and thus increases its cooling effect. Acceleration takes place through the baffle cooling holes on the inside of the outer wall, thus increasing the internal heat transfer rate.

The steam has particularly good cow properties when it is a medium pressure steam. Medium pressure steam is characterized by inlet data of approximately 30 bar pressure and 350 ° C inlet temperature. At the same time, the internal compressive stress level is not yet very high, so that the resulting stresses can still be controlled. The medium-pressure steam is directly available in modern combined cycle power plants and does not have to be additionally provided with loss of energy. The higher steam pressure results in higher heat transfer numbers and better heat transport compared to low-pressure steam. While ensuring a constant cooling effect, the wall thickness of the turbine blade can thus be made thicker, which increases the stability of the turbine blade and the wall is better able to withstand the primary stresses increased by the high pressure of the medium-pressure steam. In addition, the cavity has only cooling chambers when using a medium-pressure cooling steam. Baffle inserts can be dispensed with. This simplifies production and reduces costs.

The outer contour of the turbine blade advantageously corresponds to the shape of an aerodynamically predetermined shape, the

The thickness of the outer wall towards the cavity varies. The shape thus has the advantage of maintaining the temperature threshold values on and at the same time does not deviate from its outer shape from the usual profiles, so that the turbine blade can be used in conventional turbines and has the already known flow properties.

The sub-task relating to the manufacturing process is solved in that the casting mold is arranged in such a way that the profile profile of the outer contour of the casting core is the difference between an aerodynamically predetermined, in particular the external profile profile of a turbine airfoil and one

Corresponds to function which, in accordance with the profile of the external heat transfer number on the outside of the outer wall of the turbine blade and the profile of the internal heat transfer number on the inside of the outer wall of the turbine blade, is such that predetermined temperature threshold values and / or predetermined values are present at least at predetermined locations on the outer wall Temperature gradients between predetermined locations on the outer wall are not exceeded. In particular, the outer profile profile corresponds to a standardized profile profile.

Thus, only one casting core is used, the outer curvature or geometry of which can be changed relative to a surrounding casting mold or outer contour with the variable thickness of the outer wall and possibly with the geometries of the associated rib fields. This cast core is compact, has an easy-to-manufacture shape that can be easily supported and is not subject to excessively tight tolerance requirements. This means that conventional investment casting processes as well as processes with directional solidification or single crystal solidification can be carried out at no additional cost. The turbine blade can be cast in one piece in its blade area. The waste in casting is reduced by the simple shape. Due to the outer curvatures, the outer wall of the cast product of the turbine blade is made of different thicknesses, with essentially no post-processing being necessary. By simply taking the different thickness trained outer walls, temperature limit values can be maintained without the need for complex coatings which also easily flake off again.

Common low-reject methods are used for both low-pressure and medium-pressure steam constructions, since the minimum outer wall thicknesses of approximately 1 to 2 mm are almost twice as large as the usual outer wall thicknesses of steam-cooled turbine blades and the casting tolerances are approximately 0 , 15 mm, which is in a range that is problem-free for conventional casting processes. This simplifies manufacture and considerably reduces manufacturing costs.

The invention is explained in more detail with reference to the exemplary embodiments shown in the figures.

Show it:

1 shows a cross section through a low-pressure steam-cooled turbine guide vane with a varying outer wall thickness,

Fig.2 is a schematic enlarged detail of the outer wall to show the heat transfer mechanism in the

Outer wall,

3 shows a schematic section through an airfoil area and a foot area of a low-pressure steam-cooled turbine guide vane from FIG. 1,

4 shows a flow diagram of the cow vapor through a low-pressure steam-cooled turbine guide vane in the longitudinal section of FIG. 1, FIG. 5 shows a section through a fin field, FIG. 6 transverse openings of the fins,

7 shows a cross section through a medium-pressure steam-cooled turbine guide vane,

8 shows a schematic section through an airfoil area and a foot area of a medium-pressure steam-cooled turbine guide vane from FIG. 7,

9 shows a flow diagram of the cooling steam of a low-pressure steam-cooled turbine guide vane in the longitudinal section of FIG. 7, 10 shows a flow diagram with flow resistances of the blade, FIG. 11 shows a schematic section through a medium-pressure steam-cooled turbine guide blade and

12 shows a flow diagram of the turbine guide vane from FIG. 11.

1 shows a cross section through an airfoil area 7 of a low-pressure steam-cooled turbine guide vane 1 with a varying outer wall thickness 34. A hot action fluid 2, in particular a hot gas, flows against the turbine vane 1 on the outer side 9 of the outer wall 4. For cooling, the turbine blade 1 in its interior, generally multi-part cavity 5, which is surrounded by the outer wall 4, flows through a cow vapor 6, namely a low pressure cow vapor. The cavity 5 is traversed in the longitudinal direction of the turbine blade 1 by inner walls 20, which traverse the blade profile in the direction from the pressure side 46 to the suction side 45 in such a way that several central cooling chambers 21 are created, in this case two, the inner walls 20 being connected to the pressure side or suction-side outer wall 4 are continuously connected to the continuous course of the thickness 34 of the outer wall 4. The central cooling chambers 21 have baffle insert 22, the walls of which are pierced by a large number of small baffle bores 23. The low-pressure cow steam is pressed through the impingement cooling holes 23 and onto the inside 13 of the

Outer wall 4 accelerated. Due to the rapid impact, the inside 13 of the outer wall 4 is then cooled uniformly intensively. In the leading edge area 32, the cavity 5 has two front cooling chambers 31, through which cow steam also flows and the inside 13 of the outer wall 4 is cooled. The cooling takes place here by convection.

The outer wall 4 is optionally constructed in multiple layers and has a metal wall 3, if necessary a ceramic protective layer 15 on the outside and an aluminum alloy layer 54 on the inside, as shown in FIG. The metal wall 3 has a cross section through the blade sheet area 7 different thicknesses 8. The thickness 8 of the metal wall 3 varies continuously, ie without cracks or continuously in order not to cause stress peaks, in accordance with the external heat transfer coefficient W _ex on the outside 9 of the outer wall 4. The thickness 33 of the ceramic protective layer 15 is approximately constant. The thickness 34 of the outer wall 4 thus also varies with the thickness 8 of the metal wall 3. The external heat transfer number W _ex is given by the size of the heat transfer from the hot gas 2 into the outer wall 4. The principle of heat transfer through the outer wall 4 is illustrated in Fig.2. The external heat transfer takes place with a locally different size, indicated by the external heat transfer number W _ex , to which the thickness 8 of the metal wall 3 or the thickness 34 of the outer wall 4 is adapted.

The thickness 34 of the outer wall 4 or the thickness 8 of the metal wall 3 is also set according to the invention in accordance with the internal heat transfer number W _ιnt on the inside 13 of the outer wall 4. The type and the physical parameters of the cooling fluid 6 have a decisive influence on the internal heat transfer number W _ιnt . The internal heat transfer number W _{ιnt can also be} changed by the construction of the cavity 5 on the inside 13 of the outer wall 4, for example by means of ribs 16.

The cavity 5 has ribs 16 in the areas 14 of the outer wall 4 which are particularly thin or which are subjected to particularly heavy loads and therefore have to be stabilized. Ribs 16 are mounted, for example, on both inner sides 13 of the outer wall 4 of a central cooling chamber 21 provided with impingement cooling inserts 22, running transverse to the flow 18 of the cooling fluid 6. The middle center cooling chamber 21 has only ribs 16 on the inside 13 of the outer wall 4 on the suction side 45 of the turbine guide vane 1, on the other hand only spacers 44 on the pressure side 46, which the

Hold the baffle insert 22 in position. On some of the ribs 16 there are also spacers 44 for positioning the baffle insert 22.

The ribs 16 have predetermined dimensions, such as the thickness 37, the height 41, their base radius 39, their head radius 40, their load-bearing width 38 and spatial arrangements which are particularly suitable for contributing to the swirling of the cooling fluid flow 18 or a sufficient cooling surface on the To deliver inside 13 of the outer wall 4. A representation can be found in FIGS. 5 and 6, respectively. A good swirl is given in particular when the ribs 16, which are arranged in rib fields, lie transversely to the direction of flow 18 of the cooling fluid 6.

The thickness 8 of the metal wall 3 or the thickness 34 of the outer wall 4 ranges from approximately 0.6 mm to 1.0 mm in the rear edge region 36 to approximately 2 mm in the pressure region 46. The changes between the individual thickness regions caused by inner walls 20 are delimited, have continuous transitions 10 to reduce voltage peaks, calculated for example by means of a linear interpolation between the different target thicknesses.

2 shows schematically the heat transfer from an action fluid 2 to a cooling fluid 6 via an outer wall 4 and a schematic profile of the temperature T. The outer wall 4 of the thickness 34 is constructed in several layers. It has an external ceramic protective layer 15 with a thickness of 33 and a load-bearing metal wall 3 with a thickness of 8. An aluminization layer 54 against corrosion is optionally provided in the cavity 5 and in particular on the inside 13 of the outer wall 4. The coating 54 can be made very thin. If the coating 54 is not applied, the inside 13 of the outer wall 4 is identical to the inside 12 of the metal wall.

The hot action fluid 2 flowing on the outside has a temperature T which is higher than that of the outer wall 4. Page 9 of the ceramic protective layer 15 there is heat transfer to the outer wall 4. The external heat transfer is characterized by the external heat transfer number W _ex , the size of which indicates how strongly heat transfers to the outer wall 4. The local heat transfer between the action fluid 2 and the outer wall 4 has different external heat transfer coefficients W _ex for different outer wall sections 14 of the airfoil area 7 of the turbine blade 1 and thus different thicknesses 8 of the metal wall 3.

After the heat has entered the outer wall 4, there is first a heat conduction through the ceramic protective layer 15 and then through the metal wall 3. The heat conduction of the ceramic protective layer 15 is different from that of the metal wall 3. Thus, the temperature profile T at the transition from the inside 35 has ceramic protective layer 15 on the outside 11 of the metal wall 3 eme discontinuity. On the inside 12 of the metal wall 3, which in this case corresponds to the inside 13 of the outside wall 4, the heat emerges from the outside wall 4, which is described by the internal heat transfer coefficient W _ιnt . On the inside 13, the cooling fluid 6 flowing past takes the heat with it. The temperature curve T shows a sharp drop in this area.

In the area of the transition from the ceramic protective layer 15 to the metal wall 3, a temperature threshold value T _{M is} defined which is characteristic of the temperature resistance of the outer wall material, inter alia for the adhesive quality of the ceramic protective layer 15 on the metal wall 3. Between the maximum metal temperature < / = T _M and the temperature on the inside 12 of the metal wall 3, a temperature gradient ΔT _{M is} defined. It is a measure of temperature differences and thus also of the voltage load on the outer wall 4. By setting the thickness 8 of the metal wall 3 according to the invention, it is achieved that at least at predetermined locations on the outer wall 4, predetermined temperature Threshold values T _M and / or predetermined temperature gradients ΔT _M between the outer side 11 of the metal wall 3 and the inner side 12 of the metal wall 3, that is to say predetermined locations of the outer wall 4, are not exceeded. This ensures that the outer wall 4 of the turbine blade 1 is not excessively loaded, the ceramic protective layer 15 adheres better to the metal wall 3, no oxidation occurs and thus a permanent use of the turbine blade 1 is possible. For a target blade lifespan of at least 25,000 equivalent operating hours or approximately 1000 normal load cycles for current blade materials or operational load spectra, the predetermined temperature threshold value T _M is approximately 930 ° C to 950 ° C and the predetermined temperature gradient ΔT _M at approximately 200 to 220 ° C or at approximately 260 to 290 ° C above the metal wall thickness 8.

3 shows a plan view of the foot region 26 of a turbine blade in accordance with FIG. 1. The foot region 26 has an inlet 27 and an outlet 28 for the cooling fluid 6. The position of the airfoil area 7 relative to the foot area 26 of the turbine blade 1 is indicated schematically. The cooling fluid 6 flows through the turbine blade 1 in central cooling chambers 21 with impingement cooling elements 22 and convectively in front cooling chambers 31 in the leading edge region 32. On the rear edge 36 of the turbine blade 1 there is provided an additional cooling 56, which is preferably a separate, closed steam cooling.

4 shows a side view with a flow diagram of the cooling fluid 6. After the inlet 27 of the cooling fluid 6 m, the foot region 26 of the turbine blade 1, the cooling fluid 6 flows in a branched cooling fluid partial flow 47 through the rear edge region 36 of the turbine blade 1. Another branched cooling fluid partial flow 48 flows through a front cooling chamber 31 in the leading edge area 32. After leaving the airfoil area 7, the cooling fluid 6 flows through the head area 25 of the turbine blade 1. Thereupon, it first flows through the the front cooling chamber 31 located on the suction side 45 and, after a diversion, the adjacent front cooling chamber 31 lying on the pressure side up to the outlet 28 in the foot region 26.

Another cooling fluid partial flow 49, branched off from the supplied cooling fluid 6, flows through a first central cooling chamber 21 which has an impact cooling insert 22. After passing through the head region 25, the cooling fluid 6 flows serially through the second cooling chamber 21, which also has an impact cooling insert 22, in the opposite direction to the first. After reaching the root region 26 of the turbine blade 1, the various streams are brought together and released from the turbine blade 1 through the outlet 28. The cooling fluid 6 is also used to flow through the airfoil region 7 and the head region 25 and the foot region 26. Only a single closed circuit for the cooling fluid 6 is necessary, which simplifies handling and reduces the manufacturing costs.

The head area 25 and the foot area 26 are simple

Welded or soldered connections 24 are attached to the airfoil area 7 of the turbine blade 1 or closed with end plates 17. This simple type of attachment is possible due to the simple construction of the cavity 5. To support the cooling effect of the cooling fluid 6, baffle insert 22 can be accommodated in the head 25 and foot region 26, which is not shown.

5 shows, in an enlarged section, schematically ribs 16 which are used to reinforce the thinned areas of the outer wall 4. The ribs 16 from FIG. 1 are viewed in the transverse direction, so that only ribs 16 are visible transversely to the flow direction of the cooling fluid 6. Cross rib openings 19 of predetermined dimensions and spacings are provided along a rib 16, as shown in FIGS. 1 and 7. They serve for the cross exchange and the additional swirling of the cooling fluid 6, as a result of which the cooling effect of the cooling fluid 6 is improved. For example, the height 42 of the cross rib openings 19 and their distance 52 from the head 50 of the rib 16, see, can be varied. 6, as well as the spacing 43 of the rib cross openings 19. When the rib field is matched to the requirements due to the set thickness 34 of the outer wall 4, the dimensions, spacings and spatial arrangements mentioned above can be changed within certain limits. The limits are determined on the one hand by the fact that good cooling must be obtained, and on the other hand there should be sufficient stability of the outer wall 4 which is locally formed with a small thickness in accordance with the heat transfer numbers. For the latter, it is necessary to arrange the fins 16 closer, on the other hand they must not be too narrow, so that the cooling fluid 6 is not only flowed over them and may not be swirled. The

The height 41 of the ribs 16 is approximately one to two times the outer wall thickness 34. The load-bearing width 38 of the ribs 16 is approximately four times the thickness 34 of the outer wall 4. In the areas of the leading edge 32 there are preferably no ribs or conventional ones Turbulators as well as in the rear edge area 36.

FIG. 6 shows an exemplary arrangement of cross rib openings 19. They have an elongated oval shape. They effect a transverse exchange and swirling of the cooling fluids 6 flowing past, but they are arranged so spaced that they do not impair the stability of the ribs 16, which serve to stabilize the thin outer wall regions 14.

7 shows a section through an airfoil area 7 of a medium-pressure-steam-cooled turbine guide vane 1 with a varying outer wall thickness 34. The cavity 5 surrounded by the outer wall 4 has six cooling chambers 21, two front cooling chambers 31 in the area of the leading edge 32 and a rear cooling chamber 53 in the rear edge area 36 The six central cooling chambers 21 are separated from one another by inner walls 20. separates. The central cooling chambers 21 have approximately the same flow cross sections. According to a flow diagram shown in FIG. 3, the cow vapor 6 flows through them in series. The wall thickness 8 of the metal wall 3 varies over the circumference from approximately 1 to 2.2 mm, according to the same principle as already described for the low-pressure steam-cooled turbine guide vane, ie to compensate for the heat transfer numbers W _ex , W _ιnt that change over the cross section of the airfoil 7. The transitions between areas 14 of different wall thicknesses 8 are each continuous, corresponding to areas 10, that is to say continuous, preferably linear or interpolated by means of other functions.

The turbine blade 1 has rib fields on the entire inside 13 of the outer wall 4, with the exception of the trailing edge region 36, which serve to support the thinned outer wall 4. The medium pressure steam is almost twice as large as the low pressure steam (approximately 30 bar compared to approximately 15 bar). Thus, the internal pressure load on the outer wall 4 is significantly stronger and additional rib fields are added. Advantageous here, however, that the medium pressure steam ensured an improved heat removal and thus more favorable internal heat transition figures W _ιnt. The ribs 16 in turn have predetermined distances and dimensions and are equipped with cross-flow openings 19. The ribs 16 lie essentially transversely to the flow direction 18, which is parallel to the radial axis of the airfoil 7.

The cooling mass flow can be added or omitted

Current resistances 51, which are only indicated schematically in FIG. 4, are set such that a desired cooling current and an internal heat transfer or heat transfer number W _ιnt occurs, which is adapted to the varying wall thickness 34 of the outer wall 4. 8 shows a plan view of a foot region 26 of a medium-pressure-steam-cooled turbine blade from FIG. 7 with an inlet 27 and an outlet 28 for the cooling fluid 6.

FIG. 9 shows a longitudinal section of a medium-pressure-steam-cooled turbine blade according to FIG. 7 with a foot region 26, an airfoil 7 and a head region 25 and a flow diagram of the medium-pressure cow steam. The cooling medium 6 flows through the central cooling chambers 21 in series and the front 31 and the rear cooling chambers partially parallel. The foot region 26 and the head region 25 are welded or soldered to the airfoil region 7. They are cooled by a closed circuit with the same cooling fluid 6 as the airfoil area 7. This reduces the amount of coolant required and simplifies the construction of the cavity 5 or the interior of the head and foot area 26.

10 shows a schematic drawing of the coolant flow through a medium-pressure-steam-cooled turbine blade from FIG. 7. Different flow resistors 51 can be placed in different cooling chambers 21 in the inlet area 27, so that the partial mass flows of the cooling fluid 6 can be adjusted. An increased mass flow causes an increased cooling effect, but also increased pressure losses.

11 shows a schematic drawing of a medium-pressure steam-cooled turbine guide vane. The cavity 5 has five partial cooling chambers 21, the front region 32 two front cooling chambers 31 and the rear region 36 a rear cooling chamber 53. The central cooling chambers 21 have approximately the same flow cross sections, the wall thickness 8 of the outer wall 4 is almost constant. Due to the sufficient stiffening by the inner walls 20, no ribs 16 are necessary.

FIG. 12 shows a flow diagram of the turbine blade from FIG. 11.

Claims

claims

1. A turbine blade (1), in particular a gas turbine blade, which has an outer wall (4) against which a hot action fluid (2) flows, which surrounds a possibly multi-part cavity (5) through which a cooling fluid (6) flows, the outer wall ( 4) over the circumference of the airfoil area (7) of the turbine blade (1) is of different thickness, characterized in that the thickness (34) of the outer wall (4) at least over a partial circumference of the airfoil area (7) in accordance with the course of the external heat transfer number (W _ex ) on the outside (9) of the outside wall (4) and the course of the internal heat transfer number (W _ιnt ) on the inside (13) of the outside wall (4) so that predetermined temperature threshold values (T _M ) on the outside wall (4 ) and / or predetermined temperature gradients (ΔT _M ) over the outer wall (4) between predetermined locations of the outer wall (4) are not exceeded.

2. Turbine blade according to claim 1, characterized in that the outer wall (4) is constructed in multiple layers and on the outside of the outer wall (4) has a thin ceramic protective layer (15) and inside a metal wall (3) and that the temperature gradient (ΔT _M ) is decisive , which lies between the outside (11) and the inside (12) of the metal wall (3).

3. Turbine blade according to one of claims 1 to 3, characterized in that the temperature threshold (T _M ) on the entire outer wall (4) and / or predetermined temperature gradients (ΔT _M ) over the entire outer wall (4) are not exceeded.

4. Turbine blade according to one of claims 1 to 4, characterized in that the temperature threshold value (T _M ) and the temperature gradient (ΔT _M ) correspond to critical, material and voltage-dependent values.

5. Turbine blade according to claim 3 or 4 d a d u r c h g e k e n n e e c h n e t that the outer wall is one layer and consists of metal.

6. Turbine blade according to one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that in the cavity (5) em field of ribs (16) is provided where there is an outer wall region (14) of smaller thickness (34).

7. Turbine blade according to claim 6, characterized in that the ribs (16) of the field in accordance with the thickness (34) of the outer wall (4), the temperature threshold (T _M ) and / or the temperature gradient (ΔT _M ) and that of Mises-Ver - DC voltage have predetermined dimensions, distances and spatial arrangements.

8. Turbine blade according to claim 6 or 7, d a d u r c h g e k e n n z e i c h n e t that the field of the ribs (16) extends at least in sections transversely to the flow (18) of the cooling fluid (6).

9. Turbine blade according to one of claims 6 to 8, d a d u r c h g e k e n n z e i c h n e t that the ribs (16) have transverse openings (19).

10. Turbine blade according to one of claims 1 to 9, d a d u r c h g e k e n n z e i c h n e t that the

Cavity (5) from the pressure side (46) to the suction side (45) in the longitudinal direction of the turbine blade (1) from the inner walls (20) is pulled through, the inner walls (20) being connected to the pressure-side or suction-side outer wall (4) with a continuous course to the continuous course of the thickness (34) of the outer wall (4).

11. Turbine blade according to one of claims 1 to 10, d a d u r c h g e k e n n z e i c h n e t that the cavity (5) is provided with an aluminizing layer (54).

12. Turbine blade according to one of claims 1 to 11, d a d u r c h g e k e n n z e i c h n e t that the cooling fluid (6) is guided in a closed circuit through the turbine blade (1).

13. Turbine blade according to one of claims 1 to 12, d a d u r c h g e k e n n z e i c h n e t that the inlet (27) and the outlet (28) of the cooling fluid (6) are arranged in the foot region (26).

14. Turbine blade according to one of claims 1 to 13, d a d u r c h g e k e n n z e i c h n e t that the head (25) and foot region (26) of the turbine blade (1) is simultaneously cooled with the cooling fluid (6) of the airfoil region (7).

15. Turbine blade according to one of claims 1 to 14, so that the turbine blade (1) is a moving blade and the wall thicknesses (30) of the inner walls (20) in the cavity (5) vary locally in accordance with a local heat transfer coefficient.

16. Turbine blade according to one of claims 1 to 15, characterized in that in the central region (55) of the airfoil region (7) of inner «inner walls (20) formed central cooling chambers (21) are provided, through which cooling fluid (6) flows in series ,

17. Turbine blade according to one of claims 1 to 15, so that the central cooling chambers (21) formed in the middle region (55) of the airfoil region (7) by inner walls (20) and through which the cooling fluid (6) flows in parallel are provided.

18. Turbine blade according to claim 16 or 17, characterized in that at least one of the central cooling chambers (21) has an impact cooling insert (22) with outward directed impact cooling bores (23) which are spaced from the inside (13) of the outer wall (4) arranged and through which the cooling fluid (6) flows.

19. Turbine blade according to claim 18, characterized in that the baffle insert (22) from on the inside (13) of the outer wall (4) and / or from on the inner wall (20) and / or from spacers (44) attached to ribs (16) ) is held.

20. Turbine blade according to one of claims 1 to 19, d a d u r c h g e k e n n z e i c h n e t that on the rear edge (36) of the turbine blade (1) there is an additional cooling (56).

21. Turbine blade according to claim 20, so that the additional cooling (56) is a separate, closed steam cooling.

22. Turbine blade according to claim 20, characterized in that the additional cooling (56) is air cooling with a free outlet.

23. Turbine blade according to one of claims 1 to 22, d a d u r c h g e k e n n z e i c h n e t that the cooling fluid (6) is steam.

24. Turbine blade according to claim 23, that the steam is a low-pressure steam.

25. Turbine blade according to claim 23 that the steam is a medium pressure steam.

26. Turbine blade according to one of claims 1 to 25, so that the outer contour of the turbine blade (1) corresponds to the shape of an aerodynamically predetermined shape and that the thickness (34) of the outer wall (4) varies towards the cavity (5).

27. A method for producing a turbine blade, in particular a gas turbine blade, with an outer wall (4) which has a different thickness along a cross section through the blade area (7) of the turbine blade (1), and with the further features of one of claims 1 to 26, wherein the method comprises a casting method, in which a casting mold is used, which contains a casting core, for producing a turbine blade according to the features of one of claims 1 to 26, characterized in that the casting mold is arranged so that the profile profile of the outer contour of the Cast iron core corresponds to the difference between an aerodynamically predetermined profile profile of a turbine airfoil (7) and a function which, depending on the profile of the external heat transfer coefficient (W _ex ) on the outside (9) of the outer wall (4) of the turbine blade (1) and the course of the internal heat transfer coefficient (W _int ) on the inside (13) of the outside and (4) the turbine blade (1) runs continuously such that predetermined temperature threshold values (T _M ) and / or predetermined temperature gradients (ΔT _M ) are not exceeded at least at predetermined points on the outer wall (4).