The invention relates to a vane for use in a fluid flow of a turbine engine according to the preamble of claim 1. The in ^¬ vention relates further to a turbine engine according to the preamble of claim 13.

Gas turbines have a compressor assembly, a combustor assembly and a turbine assembly. The compressor compresses normally ambient air, which is then channeled into the combustor, where it is mixed with a fuel. The fuel and compressed air mixture is ignited, creating a working gas that may reach high temperatures, up to 1300°C to 1600°C, for example. This working gas then passes through the turbine assembly. In some gas turbines C02 is the main component of the working medium. In that case pure oxygen is added as is fuel in the combus- tion chamber to burn and heat up the C02 gas. The turbine as ^¬ sembly has a rotating shaft holding a plurality of rows of rotating wheels. The turbine assembly can have a plurality of stationary wheels attached to a casing of the turbine. Each rotating wheel is preceded by a stationary wheel to direct the working gas at an optimum angle against the vanes of the rotating wheels. Expansion of the working gas through the turbine assembly results in a transfer of energy from the working gas to the rotating wheels, causing rotation of the shaft .

Each vane of a wheel may have an outer platform connected to a radially outer end of the vane body for attachment to the turbine casing, and an inner platform connected to the inner end of the vane body. The outer platforms for a given row of vanes are mounted adjacent to each other as segments in a circular array, defining an outer shroud ring. The inner platforms are likewise mounted adjacent to each other in a circular array, defining an inner shroud ring. These outer and inner shroud rings define a flow channel between them to channel the working gas.

The vane body may include passages for a cooling fluid, such as air. However, the surfaces of the vane assemblies exposed to the working gas are subjected to high operational tempera ^¬ tures and thermal stresses. This can cause cracks in the vane body and platforms. Typically, each vane body and at least one platform are formed together as a unitary structure, so damage to a platform may require replacement of an entire vane assembly, even when the vane body is still in a service ^¬ able condition.

Each vane of a turbine engine, like a gas or steam turbine engine, has areas of excessive stress in the aerofoil leading edge area due to a mechanical loading of the vane in the downstream direction. Such vanes have an internal cooling and therefore and because of thermal stress reasons the vane body of the vanes has a limit on the maximum wall thickness.

The aerodynamic design of the vane body has been changed in the past to give a larger volume of material at the leading edge whilst maintaining the maximum wall thickness. Therefore the aerodynamic performance is degraded in order to reduce the stress levels to an acceptance limit.

To improve the strength of the vane body several constructive features are known. The US 5,484,258 discloses a guide vane with a double outer wall. The outer wall of the vane body has a one-pieced integrally formed double wall construction in ^¬ cluding an inner wall spaced apart from an outer wall with mechanically and thermally tying elements in the form of con ^¬ tinuous tying ribs which are integrally formed with and dis ^¬ posed between the inner and outer walls. The ribs space apart the inner and outer walls and respectively such that the walls are essentially parallel to each other. Such a double outer wall is structurally very complicated and expensive to manufacture . A web-like structure in the inside of a vane body is known from US 5,660,524. The vane body has a first outer wall and a second outer wall together defining an airfoil shape includ- ing a leading edge, a trailing edge, a pressure side along the first outer wall, a suction side along the second outer wall, a blade tip and a blade root. Between the two outer walls are a couple of monolithic inner walls arranged. These monolithic inner walls have a web-like structure to

strengthen the vane body or the outer walls of the vane body, respectively. The web-like inner structure makes the cooling of the vane body complicated and expensive. Further, the web ^¬ like inner structure increases the weight of the vane and therefore decreases the aerodynamic performance of the vane.

A similar web-like structure is known from US 2,974,926. The turbine blade comprises an outer shell and a center strut- root-fin assembly. The center strut-root-fin assembly comprises a root, which is preferably of a conventional fir tree type. The root extends downwardly from a root platform and is embedded in the core of a turbine motor. The center strut- root-fin assembly further comprises a strut to which fins are attached. The strut is secured to the root platform. The strut extends from the root platform upwardly. In the assem- bled position of the turbine blade the outer shell of the turbine blade is slipped over the strut-root-fin assembly. The outer shell is spot welded at various places along the blade height to the fins of the strut-root-fin assembly and at various places around a shell platform to a root platform ledge. The spot welds between the fins of the strut-root-fin assembly and the outer shell are arranged at the suction side and at the pressure side of the turbine blade. To enable to slip the outer shell over the strut-root-fin assembly there are tolerances between the outer shell and the strut-root-fin assembly. Welding the fins to the suction side and the pres ^¬ sure side of the outer shell is complicated and cost effec ^¬ tive . US 2009/0047136 Al discloses a stator with an airfoil, an outer diameter shroud and an inner diameter shroud. The airfoil comprises a thin-walled structure that forms a hollow cavity leading edge, pressure side, suction side and trailing edge. The airfoil further comprises interior cooling features including cooling channels, cooling holes, gill holes, peanut cavities, an impingement rib, nozzles, a divider, partitions, trip strips, an outer diameter end cap and an inner diameter end cap. Cooling air enters the cooling holes at the leading edge of the airfoil to flow into the peanut cavity between the leading edge and the impingement rib or into to cooling channels behind the impingement rib. The impingement rib is spaced apart from the leading edge and runs partially paral ^¬ lel to the leading edge of the airfoil.

Therefore it is an object of the invention to provide a vane for use in a fluid flow of a turbine engine which enables to reduce the stresses induced into the vane to an acceptable level without adverse effects on the cooling of the vane body and the aerodynamic performance of the vane. Further, a tur ^¬ bine engine should be provided, which can be manufactured easy and cost-effective and which can resist high stresses, like thermal stresses. The problem of the invention is solved by a vane for use in a fluid flow of a turbine engine with the features according to claim 1 and by a turbine engine with the features according to claim 13. Advantages, features, details, aspects and ef ^¬ fects of the invention arise from the dependent claims, the description and the figures. Features and details which are described in connection with the vane count as well for the turbine engine, and vice versa.

According to a first aspect of the present invention the problem is solved by a vane for use in a fluid flow of a tur ^¬ bine engine comprising a thin-walled radially extending aero ^¬ dynamic vane body having axially spaced leading and trailing edges, the wall of said vane body comprising an outer shell and an inner shell, the wall of said vane body defining an interior cavity therein for flowing a cooling medium, and an radially outer platform, whereby a radially extending load strut is arranged at the inner shell of the wall of the lead- ing edge of the vane body. The outer shell corresponds to the outer surface of the vane wall and the inner shell corre ^¬ sponds to the inner surface of the vane wall. Preferred is the vane a guide vane of a guide wheel of a turbine engine. Further, the vane can be also a vane of a rotating wheel of a turbine engine. The vane of a rotating wheel is also known as blade. The load strut is added to the inside of the vane leading edge. Therefore the leading edge is stiffened and the bending load can reacted onto a wider portion of the outer platform of the vane. The load strut reduces the stresses, in particular the thermal stresses, induced into the vane to an acceptable level without adverse effect on the cooling of the aerofoil and the aerodynamic performance of the vane. The in ^¬ terior cavity of the vane body is not or only marginal ef ^¬ fected by the load strut, because the load strut extends par- allel to the leading edge of the vane. The load strut pro ^¬ trudes advantageously only a little bit into the interior cavity of the vane body, so that the flow of the cooling me ^¬ dium, especially the flow of a fluid medium, through the interior cavity of the body vane is not effected in a negative way. Advantageously the load strut has a rectangular cross- section form. The load strut itself has an elongated form. The load strut protrudes at the inner shell of the wall of the leading edge of the vane body. The load strut increases in contrast to the double wall or the web-like structure ac- cording to the aforementioned prior art the weight of the vane only marginal.

According to a preferred development of the vane, the outer platform of the vane covers the end of the vane body, whereby the load strut is arranged at the outer platform. The outer platform is extended to cover the end of the load strut.

Therefore the leading edge can be better stiffened and the bending load is reacted onto a wider portion of the outer platform. The load strut expands the leading edge of the vane body and therefore increases the contact to the covering outer platform. The combination of the leading edge and the load strut has an umbrella-like cross-section form. This al- lows that the bending load is reacted to a greater surface of the covering outer platform of the vane.

According to a preferred development of the invention, a vane can be provide, whereby the wall of the vane body and the load strut are integrally formed and are produced in one op ^¬ eration in a common mold. That means the load strut and the leading edge and the vane body, respectively, are advanta ^¬ geously made out of one-piece. Preferred is a vane whereby the load strut and the vane body are monolithic manufactured. The outer platform which covers the tip of the vane can be welded to the front end of the leading edge and the load strut .

Alternatively a vane is preferred, whereby the wall of the vane body, the outer platform and the load strut are inte ^¬ grally formed and are produced in one operation in a common mold. Such a structure stiffens the transition region between the front end of the vane body at the leading edge and the load strut to the outer platform. A monolithic manufacture of the wall of the vane body, the load strut and the outer plat ^¬ form enables that stresses induced into the vane at the lead ^¬ ing edge can be reduced to an acceptable level.

According to a preferred development of the invention the load strut of the vane is arranged at the inner shell of the wall of the entire leading edge of the vane body. The load strut extends radially between the vane tip and a vane root. The load strut can extend over the full length of the vane body that means between the inner and outer platform. Alter- natively, the load strut can extend only along a part of the length of the load strut. The load strut can extend from the middle of the vane body to the outer platform, for example. In another even more preferred embodiment of vane, the vane is characterized in that the end of the load strut which is averted to the outer platform is arranged at a protrusion at the inner shell of the wall. That means the load strut is added to the inside of that part of the vane leading edge which is arranged next to the outer platform. Therefore, ac ^¬ cording to a very preferred development of the invention the protrusion is arranged at the inner shell of the wall in the central area of the vane body. Such an arrangement of the load strut stiffens the vane leading edge at the vane tip. The protrusion at the inner shell of the wall can be shaped in different ways. The protrusion can be built by a weld seam. Advantageously the protrusion is like a salient bolt or the like.

According to another preferred development of the invention the protrusion at the inner shell of the wall of the vane body has a U-shaped, a ring-shaped or ringlike form. The U- shaped, ring-shaped or ringlike protrusion is advantageously manufactured in one-piece with the wall of the vane body. The U-shaped, ring-shaped or ringlike protrusion is preferred ar ^¬ ranged at the inside of the wall from the suction side, over the leading edge to the pressure side of the vane. Thereby the leading edge of the vane can be stiffened and the

stresses in that part of the leading edge can be forwarded into the body of the vane. Such a protrusion makes the entire vane body more rigid without effecting the cooling of the vane negatively and without effecting to the aerodynamic per ^¬ formance of the vane negatively.

The ring-shaped or ringlike protrusion can be closed like a complete ring. Such a protrusion is arranged along the entire wall and the inner shell of the wall, respectively. Preferred is a protrusion with a U-shaped form.

As mentioned before, a vane is preferred, whereby the protru ^¬ sion and the wall of the vane body are integrally formed and are fabricated in one operation in a common mold. Alterna- tively, the load strut can be welded to the protrusion, to the wall of the vane body and to the outer platform.

According to a further preferred embodiment of the vane, the vane can comprise an inner platform at the root end of the vane. The inner platform and the wall of the vane body are advantageously integrally formed and are fabricated in one operation in a common mold. The vane can consist of metal, ceramics or fiber composite.

Preferred is the vane a guide vane of a guide wheel of a tur ^¬ bine engine. The vane will be preferably non-rotating. Fur ^¬ ther, the vane can possibly be also a vane of a rotating wheel of a turbine engine, i.e. a blade. The turbine engine is advantageously a gas turbine engine, possibly also a steam turbine engine.

According to a second aspect of the present invention the problem is solved by a turbine engine comprising at least one rotating wheel with a plurality of rotating vanes and at least one guide wheel with a plurality of guide vanes, whereby the rotating vanes and/or the guide vanes are built like the vane according to the first aspect of the invention. Such a turbine engine can be manufactured easy and cost- effective and can resist high stresses, in particular high thermal stresses, because of the stress-resistant vanes of the guide and/or rotating wheels. The turbine engine is ad ^¬ vantageously a gas turbine engine or a steam turbine engine.

The foregoing, and other features and advantages of the pre ^¬ sent invention, will become more apparent in the light of the following description and the accompanying drawings, where: Figure 1 shows schematic in a longitudinal-section a vane for use in a fluid flow of a turbine engine, which is being built according to the construction principle of the invention, Figure 2 shows schematic in a cross- section a vane for use in a fluid flow of a turbine engine, which is being built ac ^¬ cording to the construction principle of the invention.

Elements with the same function and mode of operation are provided in the fig. 1 to 2 with the same references.

Fig. 1 shows schematic in a longitudinal-section one possible embodiment of a vane 1 for use in a fluid flow of a turbine engine, which is being built according to the construction principle of the invention. The vane 1 comprises a thin- walled radially extending aerodynamic vane body 2 having axi- ally spaced a leading edge 3 and a trailing edge 4. The vane body 2 has a wall 5 comprising an outer shell 6 and an inner shell 7. The wall 5 of said vane body 2 defining an interior cavity 8 therein for flowing a cooling medium. The vane 1 further comprises an outer platform 9 and an inner platform. A radially extending load strut 10 is arranged at the inner shell 7 of the wall 5 of the leading edge 3 of the vane body 2.

The load strut 10 is added to the inside of the vane leading edge 3. The load strut 10 stiffens the leading edge 3 and the bending load can be transferred onto a wider portion of the outer platform 9 of the vane 1. The load strut 10 reduces the stresses induced into the vane 1 to an acceptable level with ^¬ out adverse effects on the cooling of the vane body 2 and the aerodynamic performance of the vane. The interior of the vane body 2 is not or only marginal effected by the load strut 10, because the load strut 10 extends parallel to the leading edge 3 of the vane 1.

The load strut 10 protrudes only a little bit into the inte- rior cavity 8 of the vane body 2, so that the flow of the cooling medium, especially the flow of a fluid medium, through the interior cavity 8 of the body vane 2 is not ef ^¬ fected in a negative way. The load strut has a rectangular cross-section and a longish form. The load strut 10 protrudes at the inner shell 7 of the wall 5 of the leading edge 3 of the vane body 2. The outer platform 9 of the vane covers the end of the vane body 2, whereby the load strut 10 is arranged at the outer platform 9. The outer platform 9 is extended in such a way that it covers the end of the load strut 10, as well. There ^¬ fore the leading edge 3 can be better stiffened and the bend- ing load is reacted onto a wider portion of the outer plat ^¬ form 9.

The wall 5 of the vane body 2, the inner platform 13, the outer platform 9, the load strut 10 and the protrusion 11 are integrally formed and are fabricated in one operation in a common mold. The load strut 10 stiffens the transition region 14 between the wall 5 of the vane body 2 at the leading edge 3 and the load strut 10 to the outer platform 9. The load strut 10 expands the leading edge 3 of the vane body 2 and therefore increases the contact to the covering outer plat ^¬ form 9.

The load strut 10 is arranged from the central area 12 of the vane body 2 to outer platform 9. Therefore the protrusion 11 which holds the load strut 10 is arranged in the central area 12 of the vane body 2. The load strut 10 has the form of a part of a ring or better is U-shaped and is arranged at the inner shell 7 of the wall 5 of the vane body 2. The combination of the leading edge 3 and the load strut 10 has an umbrella-like cross-section form, as illustrated in fig. 2. The combination of the wall 5 of the leading edge 3 and the load strut 10 allows that the bending load of the vane 1, especially of the leading edge 3, is transferred to a greater surface of the covering outer platform 9 of the vane 1. The load strut 10 extends to the interior cavity 8 of the vane 1 without effecting the cooling of the vane 1 nega ^¬ tively. Such a vane 1 enables that the leading edge is stiff- ened and the bending load is reacted onto a wider portion of the outer platform 9. The stresses induced into the vane 1 are reduced to an acceptable level without adverse effect on the cooling of the vane body 2 or the airfoil, respectively, or the aerodynamic performance of the vane 1. The front rail 18 of the vane 1 is fixed to a mounting arrangement.