Technical Field

The object of the invention is a turbine blade, in particular a blade for use in turbine engines and gas turbines.

Background of the Invention

Since the beginning of the existence of turbojet engines, fatigue failure to the blades caused by vibrations was the main challenge in operating the engine. This problem has not yet been fully solved, since high cycle fatigue (HCF) is the main cause of failures of turbine engines. In the case of rotor blades, their vibrations lead to cyclic oscillations, which result in cyclic stresses and deformations under the difficult conditions of high centrifugal forces, high temperature and pressure. Such combination of medium stresses and an amplitude of stresses in the blades of rotor machines often leads to instability of operation of these devices and their malfunctions, in particular under the conditions of resonance.

Blade vibration amplitudes are usually reduced by the use of bandages, shelves or friction dampers below the root. Each of these solutions entails reduction in the performance of the machine, including disruption in the flow of gas, an increase in the load of the centrifugal force, and introduction of the risk of accelerated creep in the material of the element. Therefore, there is a search for solutions which would increase the damping of vibrations, in particular under the conditions of resonance, which would have minimal negative impact on the performance of the machine.

The patent application EP0926312A2 discloses a blade comprising a metal airfoil with first and second opposite sides extending radially between the root and the tip of the airfoil, and axially between a leading edge and a trailing edge. The airfoil further includes pockets disposed in the first side, having elastomeric fillers bonded therein. A panel is bonded to the filler along the pocket for allowing differential movement therebetween for damping the vibrations of the blade. Various kinds of vibrations are damped depending on the used elastomeric material. The filler may take any form such as an elastomeric-like rubber or fluorosilicone molded and cured to bond in the pockets, the filler having lower density than the metal of which the airfoil is made. The use of the filler provides internal damping of the vibrations, which reduces the amplitude of vibrations of the airfoil during operation.

The patent description EP3018292B1 in turn discloses a turbine blade comprising a surface, a recess within the surface, and a damping inlay within the recess, wherein the damping inlay comprises a chamber and a damping material disposed within the chamber. The damping material can, e.g., have the form of powder. The structural feature of the pockets with non-fused powder is the introduction of two main damping mechanisms. The first one is a change in the properties of the material between the solid area and the powder area— the wave propagates along various media causing changes in the propagation speed of the wave, and causing multiple reflections of the wave. The second damping mechanism is the dissipation of friction between the particles of powder. Unfortunately, the dissipation of energy in powder caused by relative movements between the particles is the most effective in areas close to the walls of the pockets, and drops in the centre of the pocket.

Therefore, it is desirable to develop such a technical solution which would allow for improving the dissipation of energy in the entire volume of powder in the pockets, and therefore increase the efficiency of damping the vibrations.

The Essence of the Invention

The object of the invention is a turbine blade, in particular the blade of a turbine engine or a gas turbine, comprising a locking portion and an airfoil with a uniform structure, in which there is at least one pocket filled with powder. The essence of the invention is in that in the at least one pocket there is at least one pin connected to the airfoil and at least one bar connected to the airfoil and/or at least one bar connected to the pin.

The introduction of a pocket and/or pockets filled with powder, in which there are the pin and the bars, into the volume of the blade allows for transferring the energy of vibrations into the entire volume of powder, making the damping of vibrations more effective. As a result, during vibrations of the blade, a considerable increase in the dissipation of energy in the powder is achieved, and therefore better damping of vibrations. The use of the described configuration significantly reduces the amplitudes of vibrations, primarily under the conditions of resonance, thus considerably reducing the risk of failure.

Preferably, both ends of the at least one bar are connected to the airfoil. Bilateral connection of the bars to the airfoil allows for damping vibrations with a higher frequency. The connection of only one end of the bar to the airfoil or to the pin in turn allows for damping vibrations with lower frequencies.

It is preferable when at least one bar in the pocket connects the pin to the wall of the pocket. Such arrangement of the bars improves the transfer of the energy of vibrations into the powder. At the same time, it allows for damping vibrations with an even higher frequency than in the case of bilateral connection of the bar to the airfoil. It is desirable for the bars to be arranged substantially parallel with respect to each other, due to which the entire volume of powder is activated to absorb the energy of vibrations. This avoids the existence of locations in which there is no absorption of the energy of vibrations.

Preferably, the bars placed in the pockets have a openwork structure. The openwork structure of the bars will increase the intensity of engagement between the powder and the bars, thus increasing the efficiency of damping.

It is preferable for the pins placed in the pockets to have various dimensions. A pin with specific dimensions is characterized by a given frequency of damping vibrations, which is characteristic of it. The use of various dimensions of the pins in the pockets results in damping a broad spectrum of resonance frequencies and forms of vibrations (intentional dephasing of vibrations).

It is particularly preferable when the turbine blade according to the invention comprises a plurality of pockets distributed in the entire volume of the airfoil, which allows for achieving a maximum damping effect.

The distribution of pockets in the plan of a matrix is in turn preferable from the point of view of static strength of the turbine blade due to its orientation parallel to the centrifugal force acting on the blade.

Due to the technology of production, it is preferable when the pocket is filled with the material of which the airfoil is made, in pulverized form. This allows for achieving closed pockets, due to which the powder does not pour between the pockets, which could lead to is concentration in some pockets, leaving other pockets not filled.

Preferably, the airfoil, the pin, and the bars form a monolithic element, which has a preferable effect on the efficiency of transferring the energy of vibrations into the volume of the powder— the wave propagates in a solid medium much better than in powder.

It is recommended for the turbine blade according to the invention to be made using the additive manufacturing technique, most preferably the Laser Powder Bed Fusion (LPBF) technique.

Preferably, the turbine blade is made of an alloy based on nickel, cobalt or tungsten (in military applications). When used in compressors, the turbine blade is in turn made of an alloy based on aluminum or magnesium. The turbine blade may also be made of steel. Advantages of the Invention

The solution according to the invention allows for transferring the energy of vibrations into the entire volume of powder, making the damping of vibrations more effective. As a result, during vibrations of the turbine blade, a considerable increase in the dissipation of energy is achieved in the powder, and therefore so is better damping of vibrations.

The solution according to the invention allows for considerable reduction in the amplitude of vibrations, primarily under the conditions of resonance, thus considerably reducing the risk of failure.

The proposed solution according to the invention, which comprises pockets with powder comprising pins and bars, provides excellent improvement in damping compared to solid parts, almost by two orders of magnitude.

The solution according to the invention allows for reducing the mass of the turbine blade. When using the solution according to the invention, it is possible to reduce the mass compared to the structure of a solid blade, at the same time improving the damping of vibrations.

Moreover, the solution according to the invention also allows for fine-tuning the frequencies of the damped vibrations without changing the airfoil blade profile.

The manufacturing of the blade using the Laser Powder Bed Fusion (LPBF) technique in turn allows for shortening the manufacturing time of the blade (a smaller volume of the element has to be fused, reducing the time of manufacturing).

Description of the Drawings

The object of the invention is shown in embodiments in the drawing, in which:

Fig. 1 presents schematically the turbine blade according to the invention, with visible pockets arranged in the airfoil volume of the turbine blade; for clarity of the figure, the powder is not visible;

Fig. 2 presents schematically a sample pocket of the turbine blade according to the invention in one of the embodiments; for clarity of the figure, the powder is not visible;

Fig. 3 presents schematically a sample pocket of the turbine blade according to the invention in one of the embodiments; for clarity of the figure, the powder is not visible; Fig. 4 presents various views of fragments of the turbine blade according to the invention, in a longitudinal section across a pocket, upon cutting the element and pouring out the powder;

Fig. 5 presents a cut turbine blade according to the invention;

Detailed Description of the Invention— an Embodiment of the Invention

As presented in Fig. 1, the turbine blade 1, in particular the blade of a turbine engine or a gas turbine, comprises a locking portion 2 and an airfoil 3 with a uniform structure.

In the structure of the airfoil 3 there are a plurality of pockets 4, arranged in the plan of a matrix, filled with non-fused powder of the material of which the turbine blade 1 is made. In this embodiment, the matrix comprises four columns and ten rows. The number of pockets in other embodiments of the invention may vary, and their number, size, and position depend on the needs specified for a given turbine blade. The distribution of pockets 4 in the plan of a matrix is preferable from the point of view of static strength of the blade. In the presented embodiment, the pockets 4 are distributed in the entire volume of the airfoil 3, which has preferable impact on maximizing the damping effect.

In the pockets 4, there are pins 5 connected to the airfoil 3. In the pockets 4, there are also bars 6 connected to the airfoil 3, and bars 6 connected to the pin 5. Sample views of the pockets 4 are presented in Figs. 2 and 3. The bars 6 can also have an openwork structure.

The pins 5 placed in the pockets 4 have various dimensions. A pin with specific dimensions is characterized by a given frequency of damping vibrations, which is characteristic of it. The use of various dimensions of pins in the pockets results in damping a broad spectrum of resonance frequencies and forms of vibrations (intentional dephasing of vibrations).

Some of the pockets comprise bars 6, some of which have both ends connected to the airfoil 3, which enables damping vibrations with a higher frequency. The remaining part of the bars 6 connect the pin 5 to the wall of the pocket 4, improving the transfer of energy into the powder.

Another part of the pockets 4 in turn comprises bars 6, whose only one end is connected to the airfoil 3 or to the pin 5, which allows for damping vibrations of lower frequencies. The number and arrangement of the bars 6 in the pockets depend on the dimensions of the pockets.

The bars 6 are arranged substantially parallel with respect to each other, due to which the entire volume of the powder is 'activated', which means that its entire volume actively participates in the damping of vibrations. This prevents the existence of the so-called 'ineffective spaces', which do not participate in damping the vibrations. The number and arrangement of the bars 6 (rows/columns) depend on the size of the pocket. However, they are supposed to enable uniform transfer of wave energy to the volume of the non-fused powder.

The turbine blade 1 may be made of an alloy based on nickel, cobalt or tungsten (in the case of military applications). When used in compressors, the turbine blade may in turn be made of an alloy based on aluminum or magnesium. The turbine blade may also be made of steel, for example 316L, Stl2T, 17- 4PH, St T17/13W, and 15-5PH steel.

The turbine blade 1 is formed using the additive manufacturing technique, and more precisely the Laser Powder Bed Fusion (LPBF) technique. The LPBF technology (Laser Powder Bed Fusion) is based on applying thin layers of metal powder, which powder is subsequently melted by means of a laser beam in accordance with the geometry of the manufactured element. Using the LPBF process, a turbine blade with unique inner geometry is manufactured, within which pockets 4 with pins 5 and bars 6 are formed, which pockets 4 are filled with non-fused powder. During the manufacturing of the blade, the powder present in the location of the pocket 4 being formed does not undergo melting. As a result, the airfoil 3, the pins 5, and the bars 6 form a monolithic element, and the nonfused powder remaining in the formed pockets ensures the damping of vibrations.

In the volume of the turbine blade 1 there are pockets 4 in which there are the pin 5 and the bars 6, surrounded by non-fused powder. During vibrations of the turbine blade 1, the energy is dissipated by friction between the powder particles. The bars 6 and the pin 5 present in the pockets 4 cause transfer of the energy of vibrations into the entire volume of the powder, making the damping of vibrations more effective than in solutions known from prior art. The solution proposed in the present invention considerably reduces the amplitudes of vibrations, primarily under the conditions of resonance, thus considerably reducing the risk of malfunctions.

List of references

1— turbine blade

2— locking portion

3— blade airfoil

4— pockets

5— pin

6— bars