IT201600084015A1 - SHOVEL FOR A TURBOMACCHINA, TURBOMACCHINA INCLUDING THE SHAFT, METHOD TO REALIZE THIS SHELF AND METHOD FOR DESINTING THE SHAFT - Google Patents

Description

"SHOVEL FOR A TURBOMACHINE, TURBOMACHINE INCLUDING SAID BLADE, METHOD FOR MAKING SAID BLADE AND METHOD FOR DESINTONI ZZARE SAID BLADE"

The present invention relates to a blade for a turbomachine, to a turbomachine comprising said blade, to a method for making said blade and to a method for detuning said blade.

In particular, the present invention relates to a blade for a turbomachinery, such as for example a compressor, a gas turbine, a steam turbine, etc.

Turbomachinery blades can run into various vibratory phenomena. One of these phenomena is generally referred to in the industry as "flutter".

The "flutter" is a self-excited aeroelastic vibration of a non-linear and non-stationary nature which arises from the interaction between aerodynamic, elastic and inertial forces and which is established in structures in relative motion with respect to a fluid in particular conditions.

The "flutter" is mainly related to the variation of the aerodynamic forces consequent to the different orientation that the parts of the structures, due to their own oscillations, assume with respect to the direction of the fluid flow. The "flutter", therefore, can only be induced by non-conservative and non-stationary forces.

The control of the phenomenon of "flutter" in turbomachinery is of fundamental importance since the vibrations associated with it can lead to structural failures and / or catastrophic breakages of components of compressors and turbines, in particular of the blades.

Within the "flutter" phenomenon it is possible to distinguish three types:

• only bending fluctuations;

• only torsional oscillations;

• combined torsion and flexion oscillations.

The most frequent type is the combined type of torsion and bending (called classic "flutter"), which is reached when the frequencies of the vertical and torsional oscillations, which change as the speed of the structure with respect to the fluid increases, become equal to each other and with appropriately out of phase periods.

In the field of turbomachinery, the classic "flutter" occurs above all in conditions close to the normal operating line, in general for small angles of incidence of the flow on the blade.

Solutions are known which provide for modifying the existing blades so as to detune the blades, that is, so as to vary the frequency of vibration of the blades themselves.

A known technique for detuning a blade provides for removing a part of the material along the aerodynamic profile in correspondence with the apex and the trailing edge. In particular, this technique provides for the elimination of a portion of a tetrahedral shape. This removal, the amount of which must be calculated in advance, has the effect of modifying the natural frequency of the blade.

However, this solution reduces the performance of the blade as it reduces the aerodynamic surface.

Another known solution provides for creating recesses along the aerodynamic profile of the blade and possibly coupling to each recess an element made of a material different from the material of which the blade is made. An example of this technique is described in document EP 1640562. This technique, however, is very laborious because the recess must be correctly worked, furthermore the step of coupling the element to the recess requires careful welding and a consequent accurate removal of the scraps. processing in order not to alter the aerodynamic profile.

Furthermore, this technique compromises any surface coatings obtained through preventive treatments (for example, in the case of a gas turbine, the thermal insulation treatments determine the so-called Thermal Barrier Coating).

The restoration of the coating causes an increase in costs and, moreover, there is the risk that the restoration operations will not be able to obtain the desired coating.

A further technique described in document US2014 / 0050590A1 consists in making a blade having increases in thickness in different points (for example on the lower wall of the blade, on the upper wall of the blade, etc.), or decreases in thickness / volume. These actions lead to an increase and / or decrease in the mass of the blade and / or its spatial redistribution. This solution, however, requires further work on the part of the aerodynamic designers, who must modify and / or redesign and recalculate the performance of one or more aerodynamic profiles with an evident increase in production times and costs.

It is therefore an object of the present invention to provide a blade which is capable of reducing the phenomenon of "flutter" and keeping its aerodynamic characteristics unchanged and which, at the same time, is easy and economical to manufacture.

In accordance with these purposes, the present invention relates to a blade for a turbomachine according to claim 1.

It is also an object of the present invention to provide a turbomachine in which the phenomenon of the flutter of the blades is reduced and which, at the same time, is efficient and easy and inexpensive to manufacture.

In accordance with these purposes, the present invention relates to a turbomachine according to claim 8.

It is a further object of the present invention to provide a method for making a blade for a turbomachine which is simple and economical and capable of providing a blade in which the "flutter" phenomenon is reduced.

In accordance with these purposes, the present invention relates to a method for making a blade for a turbomachine according to claim 11.

Finally, a further object of the present invention is to provide a method for detuning a blade for a turbomachine which is simple and capable of maintaining the aerodynamic characteristics of the blade itself unaltered.

In accordance with these purposes, the present invention relates to a method for detuning a blade for a turbomachine according to claim 12.

Further characteristics and advantages of the present invention will appear clear from the following description of a non-limiting example of its implementation, with reference to the figures of the annexed drawings, in which:

Figure 1 is a schematic perspective view, with parts in section and parts removed for clarity, of a blade for a turbomachine according to the present invention in a first operating configuration;

Figure 2 is a schematic perspective view, with parts in section and parts removed for clarity, of a blade for a turbomachine according to the present invention in a second operating configuration;

Figure 3 is a schematic perspective view, with parts in section and parts removed for clarity, of the blade for a turbomachine according to the present invention according to a second embodiment;

Figure 4 is a schematic perspective view of a portion of a turbomachine according to the present invention.

In Figure 1, the reference number 1 indicates a rotor blade for a turbomachine 2 (Figure 4).

In the non-limiting example described and illustrated here, the rotor blade 1 described and illustrated here is a blade of a gas turbine 2 (a portion of which is visible in figure 4) of a plant for the production of electricity (not illustrated ).

It is understood that the blade according to the present invention can be a blade of any turbomachine, such as for example a compressor, a steam turbine, etc.

The blade 1 is provided with a main body 3, normally defined in the jargon as "airfoil" and with a root 4 coupled to the main body 3.

The main body 3 extends along a longitudinal axis A and is provided with a base face 5 (not completely visible in figure 1), with a top face 6 also called "apex", arranged opposite to the base face 5 along the longitudinal axis A, and of an external face 7, which extends between the base face 5 and the top face 6 and defines the aerodynamic profile of the blade 1. The main body 3 is shaped so as to define along the external face 7 a leading edge 10, commonly called "leading edge", a trailing edge 11, commonly called "trailing edge", a concave face 12 called belly (commonly called "pressure side") and a convex face 13 called back (commonly called "suction side").

The root 4 is coupled to the main body 3 along the base face 5.

In the non-limiting example described and illustrated here, the main body 3 and the root 4 are made in one piece.

Preferably, the main body 3 is a solid body in which at least one blind hole 15 is made along the top face 6. The blind hole 15 extends inside the main body 3 without reaching the outer face 7.

In other words, the blind hole 15 does not affect the external face 7 and therefore does not modify the aerodynamic profile of the blade 1.

In the non-limiting example described and illustrated here, the blind holes 15 are four and extend inside the main body 3 parallel to the axis A. It is understood that the blind holes 15 can also extend transversely to the axis A.

In the non-limiting example described and illustrated here, the blind holes 15 have different depths.

Preferably, the blind holes 15 have a cylindrical shape.

The number of blind holes 15 and the dimensions of the blind holes 15 (mainly diameter and depth) are determined a priori. Preferably, the number of blind holes 15 and the dimensions of the blind holes 15 are calculated by means of a finite element simulation (FEM) by imposing mechanical and thermal constraints. Basically, the number of blind holes 15 and the dimensions of the blind holes 15 are calculated by simulating the mechanical and vibratory of the blade 1.

The removal of material, in fact, modifies the vibratory behavior of the blade 1. The calculation of the number and dimensions of the blind holes 15 is then carried out in order to change the natural oscillation frequency of the blade 1 and to modify the spatial position of the center of gravity of the blade 1 itself.

Each blind hole 15 has a variable content, where by content we mean air and / or one or more masses of one or more different materials.

In other words, the blind holes 15 can be selectively filled with masses of materials 17 as illustrated in Figure 2.

The content of the blind holes 15 is modified to detune the blade 1. In other words, the content of the blind holes 15 is modified to obtain a controlled variation of the natural oscillation frequencies of the blade 1 and of its modal shapes.

Generally, the calculation relating to the masses of materials 17 to be introduced into one or more blind holes 15 is again carried out by means of finite element simulation (FEM).

The simulation envisages analyzing the mechanical and vibratory behavior of the blade and calculating the masses of materials to be introduced in order to further change the natural oscillation frequency of the blade 1 and to modify the spatial position of the center of gravity of the blade 1 itself.

The masses of materials 17 are generally made up of materials having a different density from the material of which the main body 3 is made.

Masses of materials 17 with a higher density than that of the material with which the main body 3 is made can be used, such as, to cite a non-limiting example, tungsten and / or its alloys and / or copper and / or its alloys ).

Masses of materials 17 with a reduced density with respect to that of the material with which the main body 3 is made, such as, for example, Titanium and / or its alloys, can also be used.

In the non-limiting example described here and illustrated in Figure 2, the end blind holes 15 (i.e. arranged in proximity to the leading edge 10 and the trailing edge 11) are filled with a copper alloy, while the central blind holes 15 they are filled with a tungsten alloy.

A further variant not illustrated in the attached figures provides that masses of different materials can be placed inside the same blind hole.

The masses of materials 17 can be inserted with an interference fit.

A variant not illustrated provides for further blocking the masses of materials 17 by welding in the upper part of the holes.

A further variant not illustrated provides for the adoption of Seeger rings or threaded members (eg grains) screwed to a respective upper portion of the blind hole 15 suitably threaded.

Figure 3 illustrates a blade 100 according to a variant in which the blind holes 115 and the relative masses of material 117 are made in the casting phase. In this case, the masses of materials 117 are made of one or more materials having a higher melting point than the melting point of the material of which the main body 103 is made. Preferably, the melting point of the material of which they are made the masses of material 117 exceeds by at least about 1000 ° C the melting point of the material with which the main body 103 is made.

In detail, the method of manufacturing the blade 100 provides for inserting the product in high-melting or refractory alloy (eg tungsten) into the mold of the blade 100; the latter, even in the melting phase, remains solid and "trapped" in the spindle of the blade. Any processing scraps, consisting of tungsten parts (eg rods protruding from the top face 106 of the blade 100) can be removed later.

Spherical masses of material 117 can be inserted into the main body 103. This allows you to concentrate the greatest amount of mass in the least volume.

As already described for the blade 1, the calculation relating to the masses of material 117 to be incorporated in the main body 103 is carried out by means of finite element simulation (FEM).

The detuning method described for blade 1 is applicable for blade 100.

In the case not illustrated in the attached figures in which the blade is provided with a so-called canopy ("shroud") coupled to the top of the blade, the blind holes are made on the top wall of the canopy and / or on the canopy wall exposed to the flow. Normally, canopy blades are steam turbine blades.

Figure 4 illustrates a portion of a turbomachine 2, in which a rotor ring 20 rotatable around a respective axis of rotation B is visible.

The rotor ring 20 is coupled to a circle of blades 21, which follow one after the other along a circumferential direction and are arranged radially with respect to the axis B.

At least one blade of the circle of blades 21 is a blade 1 or a blade 100 of the type described above.

Basically, at least one blade of the circle of blades 21 is provided with at least one blind hole 15, 115 made along the top wall 5, 105 of the blade 1, 100.

In the non-limiting example described and illustrated here, the circle of rotor blades 21 comprises first blades alternating with second blades; the first blades being blades 1 or blades 100 of the type described above.

In this way, the flutter phenomenon is reduced over the entire circle of blades 21.

Advantageously, the blade manufacturing method and the blade detuning method can also be implemented on existing blades, without requiring any aerodynamic modification.

According to the present invention, in fact, the blind holes 15 115 do not affect the external face 7107 of the blade 1 100 and therefore do not modify the aerodynamic profile.

In this way there is no loss of power in the turbomachinery because the blade surface remains intact and unchanged from an aerodynamic point of view.

Thanks to the present invention it is possible to obtain a controlled variation of the natural oscillation frequencies of the blade 1 and of its modal shapes in a simple and fast way and without having to face further redesign costs.

Furthermore, the masses of materials 17 can be made starting from existing products and used in other fields. For example, it is possible to use the infusible electrodes used in suitably cut TIG welding processes.

Finally, it is evident that modifications and variations can be made to the blade, the turbomachine, the blade manufacturing method and the blade detuning method without departing from the scope of the attached claims.

Claims (14)

CLAIMS 1. Rotor blade for a turbomachinery (2) comprising a main body (3; 103) extending along a longitudinal axis (A) and provided with a base face (5; 105), a top face (6; 106) , arranged opposite to the base face (5; 105) along the longitudinal axis (A), and of an external face (7; 107) which extends between the base face (5; 105) and the top (6; 106) and defines the aerodynamic profile of the blade (1; 100); the main body (3; 103) being provided with at least one blind hole (15; 115), which is made along the top face (6; 106) and extends inside the main body (3; 103). 2. Shovel according to claim 1, wherein the blind hole (15; 115) is at least partially engaged by at least one mass of materials (17; 117) made of at least one first material. Blade according to claim 2, wherein the first material is different from the material of which the blade (1; 100) is made. The blade according to claim 2 or 3, wherein the first material has a density different from the density of the material of which the blade (1; 100) is made. 5. Shovel according to any one of the preceding claims, wherein the blind hole (15) is substantially cylindrical in shape. 6. Shovel according to any one of the preceding claims, comprising a plurality of blind holes (15; 115), which are made along the top face (5; 105) and extend inside the main body (3; 103) . Shovel according to claim 6, wherein the holes of the plurality of holes (15; 115) have different depths. 8. Turbomachine comprising at least one rotor ring (20) rotating around a longitudinal axis (B) and a circle of rotor blades (21) coupled to the rotor ring (20) so as to extend radially with respect to the longitudinal axis (B) ; the rotor blades being arranged next to each other in a circumferential direction; at least one first blade (1; 100) of the circle of rotor blades (21) being of the type claimed in any one of the preceding claims. 9. Turbomachine according to claim 8, wherein the circle of rotor blades (21) comprises first blades alternating with second blades; the first blades (1; 100) being of the type claimed in any one of claims 1 to 8. 10. Turbomachine according to claim 8 or 9 selected from the group comprising: gas turbine, compressor, steam turbine. 11. Method of manufacturing a rotor blade (1) of a turbomachine comprising the steps of: • calculate by means of finite element simulation the number and dimensional characteristics of the blind holes (15) to be made; • make the blind holes (15) along a top face (4) of the main body (2) of the blade (1) according to what was determined in the calculation phase. Method of detuning a rotor blade (1; 100) of a turbomachinery (2) of the type claimed in any one of claims 1 to 7 comprising the step of selectively varying the content of the at least one blind hole (15; 115 ). Method according to claim 12, wherein the content of the at least one blind hole is air and / or at least a mass of materials (17; 117). Method according to claim 13, wherein the mass of material (17; 117) is made of at least a first material other than the material of which the blade (1; 100) is made.