VENTILATION OF THE STAGES OF A TURBINE

Abstract

VENTILATION OF STAGES OF A TURBINE One aspect of the invention relates to a moving wheel comprising: a disc comprising alternating teeth and cells formed on its outer periphery, blades of a first series and blades of a second series each comprising a blade root in a corresponding cell, each blade root comprising an internal base housed entirely in the cell, characterized in that the internal base of the blade root of the second series comprises a surplus of material compared to each internal base of each blade root of the first series, the surplus of material adding a surface area to the radial section of at least 1 mm2 more than on each radial section of an internal base of a blade root of the first series, each internal base of the blade root of the second series reducing by at least 1 mm2 one of the leakage sections delimited between this internal base and the surfaces of the disc delimiting the cell housing it,with respect to each leak section delimited between an internal base of a blade root of the first series and the walls of the disc forming the cell housing it. Figure to be published with the abstract: Figure 2,

Description

Title of the invention: VENTILATION OF THE STAGES OF A TURBINE TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the ventilation of the stages of a turbomachine turbine, in particular aircraft turbojets and turboprops. More particularly, it relates to the ventilation of the part located radially under stator blades. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] A turbomachine conventionally comprises a nacelle whose opening allows the admission of a determined flow of air towards the engine itself. Conventionally, the gases flow from upstream to downstream through the turbomachine. Generally, the turbomachine comprises one or more sections for compressing the air admitted into the engine (generally a low pressure section and a high pressure section). The air thus compressed is admitted into the combustion chamber and mixed with fuel before being burned there. The hot combustion gases resulting from this combustion are then expanded in different turbine stages. A first expansion is made in a high pressure stage immediately downstream of the combustion chamber and which receives the gases at the highest temperature. The gases are expanded again by being guided through the so-called low pressure turbine stages. Part of a section of a turbine of axis A is illustrated in [Fig.l], which can be low pressure or high pressure, conventionally comprises one or more stages (four of which are shown in [Fig.l]), each consisting of a row of fixed blades 3, also called a distributor, followed by a row of moving blades 6, which form a rotor with discs 8. The distributor diverts the flow of gas taken from the combustion chamber towards the moving blades 6 of the turbine at an appropriate angle and speed in order to drive these moving blades 6 and the turbine rotor in rotation. The rotor generally comprises an assembly of moving wheels each comprising a disc 8, four of which are shown in section in [Fig.l] and moving blades 6 mounted on the periphery of the disc 8. These discs 8 generally comprise a succession of teeth 81 and peripheral grooves in the shape of a cell 80, hereinafter called a cell 80.The moving blades 6 each comprise a blade root 2 placed and held in position in a corresponding cell 80, in particular thanks to the particular profile of the teeth 81 of the disc 8. [Fig.2] represents an axial view of an example of the shape of a part of the blade root 2 inserted in a cell 80 formed between two teeth 81, partially represented, of the disc 8.

[0003] The axial stop of the blade root 2 in the cell 80 of the disk 8 can be ensured by upstream and downstream flanges retained by a movable ring 4, a portion of which is shown in [Fig. 3] retaining the upstream flange of a movable blade 26 and the downstream flange of a preceding movable blade 6 while forming a seal with the fixed blade root. In this example, the disk 8 comprises on either side axially a fixing ring 84 each comprising a fixing zone fixed to the movable ring 4 and to a drive cone 15 by a bolt thus connecting the rotor to a turbine shaft 5 (partially shown).

[0004] A reduced ventilation circuit for each cell 80 per disc 8 and each blade root 2 has been designed to limit the effects due to the extreme thermal environment to which the rotor is subjected. The ventilation circuit directs a pressurized air flow F (of which a single flow is represented by black arrows in [Fig.l]) taken upstream of the turbine, typically at the level of one of the compressors, to introduce it into the rotor in order to cool its cells 80 and its blade roots 2, see the blades of its blades 26. For this purpose, the ring 4 comprises a plurality of lunules 40 and at least one leakage zone 85 is formed between the blade root 2 and the bottom of the cell 80 of the disc 8 allowing the cooling flow F to circulate inside them and to cool the blade root 2 more effectively.The cooling flow F thus circulates from an upstream cavity formed between the disc 8, the rotor shaft 5 and the drive cone 15 to an intermediate cavity formed between the ring 4 and the fixing crown 84 via the lunules 40 then into the leakage zone 85.

[0005] In the example shown in [Fig.2], the circuit further comprises two lateral leakage zones 84 formed in the cell 80 between two bearing zones between the teeth 81 and the blade root 2. In addition, the moving blade 6 may comprise a series of internal channels passing through its blade root 2 opening onto the leakage zone 85. The disc 8 may also have lunules as described in application FR3064667 to allow the air flow to enter between the flange and the leakage zone.

[0006] Current ventilation circuits are mainly calibrated (section creating the air flow) by the lunules 40 in the mobile rings and / or that in the disc 8.

[0007] However, for reasons of mass reduction and mechanical difficulty, the elimination of the movable rings while maintaining the blade roots in the cells is an important issue in improving the performance of the turbine and the engine. Thus, as shown for example in a schematic diagram of [Fig. 4], representing a radial section of a part of a turbine T of a turbomachine comprising two movable wheels RI, R2 connected to each other by a connecting ring 77 extending from a disc 7 of the movable wheel RI to another disc 7 of the movable wheel R2, a distributor D comprising fixed blades 3 between the movable blades 6 of the two wheels RI, R2 and an intermediate chamber Cl delimited between the two wheels mobile wheels RI, R2 and the distributor D. The removal of the mobile ring results in a cooling air circuit called cascade due to the air flow passing from intermediate chamber Cl to intermediate chamber formed between different successive mobile wheels RI, R2. Thus, the air circuit passes from intermediate chamber to intermediate chamber, by means of the leakage zones (as shown in [Fig.2]) between each blade root 2 and each cell of each disc 7 for each stage in series and no longer by the lunules of the fixing zone sized according to the leakage zones.

[0008] The flow of the cooling flow must be controlled and are dependent on the pressure losses which are a function of the manufacturing tolerances of the cells of the disc 7 and of the blade root 2 of each moving blade 6 which is approximately + or - 0.1 mm for the root. However, due to the large number of blades and the succession of moving wheels (stages), the sum of the manufacturing tolerances of the roots and the cells generates a gap between the minimum and maximum flow losses of the flow which is too large, preventing control of the air flow. Too low an air flow due to excessive pressure losses limits the cooling and therefore reduces the service life of the moving blades 6 and too strong an air flow reduces the performance and therefore the efficiency of the turbomachine.

[0009] The proposed invention aims in particular to provide a simple and effective solution to this problem. Summary of the invention

[0010] The invention offers a solution to the problems mentioned above, by making it possible to adapt the overall section of all the leakage zones between the blade root and the cell to allow cascade cooling.

[0011] One aspect of the invention relates to a mobile wheel comprising: • a disc comprises an alternation of teeth and alveoli formed on its external periphery, • blades of a first series and blades of a second series each comprising a blade root in a corresponding cell, each blade root comprising an internal base housed entirely in the cell, • characterized in that the internal base of the blade root of the second series comprises a surplus of material compared to each internal base of each blade root of the first series, the surplus of material adding a surface to the radial section of at least 1 mm2 more than on each radial section of an internal base of a blade root of the first series, each internal base of the blade root of the second series reducing by at least 1 mm2 one of the leakage sections delimited between this internal base and the surfaces of the disc delimiting the cell housing it, in relation to each trailing section delimited between an internal base of a blade root of the first series and the walls of the disc forming the cell housing it.

[0012] Thanks to the invention, the air flow passing through each moving wheel is controlled as a function of the desired leakage section sum by modifying only certain blades having a blade root base that is more voluminous than other blade roots.

[0013] Indeed, instead of the lunules produced to calibrate the air flow, the invention makes it possible to calibrate the air flow by means of certain blade roots. Indeed, it has been realized that, from the manufacturing tolerances, it is possible to calculate: • a minimum theoretical leakage section calculated in 1 cell = minimum cell section and maximum nominal blade root section = S minimum, • a maximum theoretical leak section calculated in 1 cell = Cell at maximum and blade root section at minimum = S maximum, • the variation in leakage section calculated in 1 Cell = S max - S min = VS leakage and therefore • a variation in the total leakage section calculated on the disc = S leakage x N alveolus = VS total leakage.

[0014] Thus by choosing an additional nominal section of at least 1mm2' in the base for each blade root of the second series corresponding according to the manufacturing tolerances to the difference in leakage section in a cell comprising a blade of the second series compared to that comprising a nominal blade root, it is possible to calculate the number of blades of the second series necessary for the moving wheel which is equal to VS total leakage / additional nominal section. Thus, the maximum quantity of blades of the second series that the moving wheel can receive corresponds to the case of the disc with cells having its maximum section and the other blade roots at the minimum. Thus, the operator can know the maximum number of blades of the second series to have to avoid having too much pressure loss in the moving wheel.

[0015] Thus, the invention makes it possible to control the air flow rate to cool the blades and the disk by determining the maximum additional surface area by blades of the second series to be inserted in place of the nominal blade to reduce the section in order to increase the efficiency of the turbomachine. Of course, the blades of the second series will be less cooled due to the smaller leakage section in the cell, and therefore can undergo more thermal stress at the blade roots. The invention therefore makes it possible to gain service life on the blades of the first series, also called normal, and / or increase the efficiency of the turbomachine, but requires either changing these blades of the second series more quickly or designing them with more complexity (therefore more expensive) to withstand higher temperatures for longer.

[0016] An example calculation is described in the detailed description.

[0017] Furthermore, in the case where each blade section of the first series is measured before insertion on the disk, it is then possible to optimize and choose the air circulation flow rate by selecting the number of blades of the second series according to the nominal total leakage section requirement in the turbomachine.

[0018] In addition to the characteristics which have just been mentioned in the preceding paragraph, the mobile wheel according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • According to one embodiment, the internal base of the blade root of each blade of the second series comprises an internal radial end surface facing a bottom surface of the disc delimiting the cell of each specific blade and different from each of the internal radial end surfaces of a blade of the first series. • According to one example, the blade root of each specific blade comprises an upstream radial face and a downstream radial face, a first and a second lateral face comprising at least one bearing surface connecting the downstream radial face to the upstream radial face, each running along the internal radial end surface, in which the internal radial end surface comprises an alternation of concave and convex portions from the first to the second lateral face. • According to another example of this embodiment, the blade root of each specific blade comprises an upstream radial face and a downstream radial face different from the upstream radial face and in that each blade root of each blade of the first series comprises an upstream radial face and a downstream radial face identical to the upstream radial face. • This embodiment, of which these two examples, makes it possible to visually identify the blades of the second series so that they can be easily replaced by another blade of the second series (if necessary). • According to one embodiment, the wheel includes a marking visible to the naked eye on each specific blade allowing them to be differentiated from the blades of the first series. This allows the blades of the second series to be visually identified even if the additional section, for example only 1mm2 additional, is difficult to recognize in order to be able to easily replace them with another blade of the second series (if necessary). • According to one embodiment, the disc comprises an engraving comprising a number of blades of the second maximum series or a number of maximum additional sections. This makes it possible to know the maximum number of blades of the second series of maximum additional sections in the case of dif various sizes of additional blade. • According to one embodiment, the disc comprises an engraving comprising an optimal number of blades of the second series or an optimal number of additional sections. This makes it possible to know the maximum number of blades of the second series of maximum additional sections in the case of different sizes of additional blade. • According to one embodiment, an internal base of a blade root of the second series comprises an excess thickness at the level of one of the two lateral faces facing a lateral surface of a tooth of the disc delimiting the cell. This makes it possible to reduce the leakage section cooling the zone of the blade root furthest from the bearing surfaces subjected to the greatest stresses.

[0019] Another aspect of the invention relates to a turbomachine comprising at least one moving wheel according to the preceding aspect of the invention with or without one or more characteristics of the examples and embodiment described previously.

[0020] Another aspect of the invention relates to a method for determining a number of blades of the second series on a moving wheel comprising a disc comprising teeth and a number N of cells, blades of the first series each having a blade root having an internal base housed in the cell, the internal base having a nominal section with a variation in tolerance for being mounted in a cell of the disc, comprising the steps: • measurement of at least one nominal cell section, • determination of an average value of the cell sections, • calculation of the variation in leakage section VS total, by calculating the difference between: • the maximum total leakage section STmaxi generated with blade roots of the first series having an entire internal base section with the minimum tolerance, and • the minimum total leakage section STmini generated with blade roots of the first series having an entire internal base section with the maximum tolerance, • calculating a quantity of second series blades to replace first series blades, each second series blade each comprising a larger internal base blade root section with a surface value added by a surplus of at least 1 mm2 compared to the average value of the nominal internal base blade root sections of the first series blades, by dividing the total leakage section variation VS calculated by the surface added by the surplus material of a second series blade.

[0021] Another aspect of the invention relates to a method for determining a number of blades of the second series on a moving wheel comprising a disc comprising teeth and a number N of cells formed between each tooth, a number N of blades of the first series each having a blade root having a nominal section with a variation in tolerance for being mounted in a cell of the disc, comprising the steps: • determination of an optimal total nominal leakage section value, • measurement of at least one nominal cell section, • calculating a value of all the cell sections by multiplying an average value of the cell sections from the at least one measured nominal cell section multiplied by the number N of cells, • measuring an internal base section of the blade root of a plurality of first series blades and deducing therefrom an average value of the internal base section of the blade root, • calculation of a total leakage section equal to subtracting the value of all the cell sections from the total section of the internal bases equal to the multiplication of the internal base sections of the blade root of each blade of the first series by the number N, • calculating a surplus leakage section value equal to the optimal total nominal leakage section value subtracted from the total leakage section value and • determining a number of blades of the second series to replace blades of the first series each comprising a larger internal base section of the blade root by a surface value added by a surplus of at least 1 mm2 compared to the average value of the nominal internal base sections of the blade root of the blades of the first series, by dividing the surplus value of the leakage section by the added surface value.

[0022] Another aspect of the invention relates to a method for assembling a disc comprising N cells and N blades, by inserting a number NX of normal blade roots into NX cells of a disc, characterized in that it further comprises a step of inserting a number X of blade roots of the second series into the X other cells of the disc and a step of marking a number X on a radial face of the disc.

[0023] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0024] The figures are presented for information purposes only and in no way limit the invention.

[0025] [Fig-1] represents a schematic diagram of a part of a section of an axis A turbine according to the prior art.

[0026] [Fig.2] represents a schematic diagram of an axial view of part of a foot of dawn in a cell.

[0027] [Fig.3] represents a schematic diagram of a part of a moving ring including lunules.

[0028] [Fig.4] represents a schematic diagram of a radial section of a part of a turbine representing a cascade of cooling air circulation.

[0029] [Fig.4'] represents a schematic diagram of a radial section of a part of a A-axis turbine comprising at least one moving wheel according to one embodiment of the invention.

[0030] [Fig.5] represents a schematic diagram of an axial view of an internal base of a blade foot of the second series in a cell of a moving wheel according to an example of the invention. DETAILED DESCRIPTION

[0031] The figures are presented for information purposes only and in no way limit the invention.

[0032] [Fig.4'] shows a schematic representation of a part of an axial section of two mobile wheels A1, A2 according to an example of the invention and a part of a distributor D of a turbine T', one of its fixed blades 3 of which is shown in the section.

[0033] Each of the two moving wheels A1, A2 is in this case according to the invention, but the turbine may comprise only one moving wheel according to the invention.

[0034] Each of the mobile wheels A1, A2 thus comprises a disc 7 which may be similar to that of [Fig.4], comprising an alternation of teeth 71 and cells 70 (referenced in [Fig.5] explained below) formed on its external periphery housing a blade root 1, 2 of a blade 6 of the first series or of the second series 9. Each blade root of the second series 1 or of the first series 2 has an internal base 17 (referenced in a [Fig.5] explained below) housed entirely in the corresponding cell 7 and an external base extending from the internal base 17 entirely outside the cell 7. In this example, each external base of each blade root of the second series 1 or of the first series 2 comprises on either side axially a platform 18, 28 which each extend axially towards a neighboring fixed blade 3 to radially cover each a platform 38 of the fixed blade 3.

[0035] [Fig. 5] represents an axial view of a cell 70 between two teeth 71 each represented partially of the disc 7 of one of the two mobile wheels A1, A2 housing the internal base 17 of a blade root 1 of a blade 9 of the second series. Each alveolus 70 is therefore delimited on the one hand circumferentially between a lateral surface 72 of a tooth 71 comprising a zone called a bearing surface, and another lateral surface 72 of a tooth 71 also comprising a zone called a bearing surface, and on the other hand radially a bottom surface 73 of the disc 7 and is open at its external radial end represented by a dotted line, delimited between the two external radial ends 720 of the lateral surfaces 72 of each of the two teeth 71. Thus each tooth 71 of the disc 7 comprises on either side a surface 72 each delimiting a different alveolus 70. Each alveolus 70 comprises two open axial ends. In [Fig.4]', it can be seen that the axial section is made on a blade 6 of the first series of the first wheel Al, comprising its blade root 2 in one of the cells 70 of the disc 7 of the wheel Al and on a blade 9 of the second series of the second wheel A2 comprising its blade root 1 of the second series in one of the cells 70 of the disc 7 of the second wheel A2.

[0036] Each blade root 1, 2 comprises an upstream radial face 14, 24 and a downstream radial face 15, 25 (the radial face 15 of the blade root 1 of the second series of which is visible in [Fig. 5]), a first and a second lateral face 12 (referenced on the blade root 1 of the second series of [Fig. 5]) each comprising at least one bearing surface, in this case two bearing surfaces, connecting the downstream radial face 15, 25 to the upstream radial face 14, 24. Each blade root 1, 2 further comprises an internal radial end surface 13 facing the bottom surface 73 delimiting the cell 70.

[0037] Each blade root 1 of blade 9 of the second series comprises an internal base 17 comprising a surplus of material compared to an internal base of a blade root 2 of blade 6 of the first series, thus adding a surface area to the radial section of at least 1mm2 more than each radial section of an internal base of a blade root 2 of the first series. Thus the internal base 10 has a larger section of at least 1mm2 more than the section of the internal base of each blade of the first series. In this case the surplus of material 10 adds a surface area (hereinafter called added surface area) of 4mm2, represented by hatching, more than each radial section of an internal base of a blade root 2 of a blade 6 of the first series mounted in another cell 70 of the disc 7.Each internal base 17 of blade root 1 of the second series thus reducing by at least 1mm2 one of the leakage sections delimited between this internal base 17 and the surfaces of the disc 72, 73 forming the cell 70 housing it, relative to each leakage section delimited between an internal base of a blade root 2 of the first series of blades 6 and the walls of the disc 7 forming the cell 70 housing it. In this example, the excess material 10 of the internal base 17 represented by hatching in [Fig.5], extending towards the bottom surface 73 delimiting the cell 70 over the entire axial length of the blade, thus modifying the internal radial surface 13, the upstream radial face 14 and the downstream radial face 15. Thus in this . for example, the bottom leakage zone 75 is limited by the excess material 10 relative to each of the leakage zones delimited between a blade root 2 of a moving blade 6 of the first series housed in another cell 70 of the disc 7.

[0038] In the example shown, the normal blade roots 2 comprise a flat surface facing the bottom surface 73 delimiting the cell 70 and the blade roots 1 of the second series comprise a corrugated internal radial end surface 13 facing the bottom surface 73 delimiting the cell 70. More precisely, the internal radial end surface 13 comprises an alternation of concave and convex parts from the first to the second lateral face 12. This difference in shape of the internal radial end surface 13 of the blade 9 of the second series compared to the same internal radial end surface of a blade 6 of the first series makes it possible to be visible from the upstream radial face 14, 24 or downstream 15, 25 to enable the operator to easily change a worn blade 9 of the second series, with another blade 9 of the second series or replace a worn blade 6 from the first series with another blade 6 from the first series.

[0039] Of course, the internal base 17 may have excess material elsewhere than its zone facing the bottom surface 73, for example on one of the lateral faces 12 at the level of a zone 11 between two bearing zones in contact with the lateral surface 72 of a tooth 71. In this other example not shown, at least one of the lateral leakage zones 74 formed between the zone 11 of the internal base 17 and a lateral surface 72 is then restricted relative to a lateral leakage zone formed by a tooth root 2 of the first series of blades 6.

[0040] According to another example, or optionally in addition, each blade 9 of the second series comprises a marking visible to the naked eye, preferably on the upstream radial face 14 or the downstream radial face 15 while each blade 6 of the first series is devoid of this marking. The marking may correspond to the quantity of surface in mm2 measured in a radial section, formed by the surplus material 10.

[0041] An air flow F is represented as in [Fig. 4] by arrows representing a cascade cooling air circulation, in which the air passes into an intermediate chamber Cl delimited axially between the two moving wheels A1, A2, and radially between on the one hand the platforms 18, 28 of each blade root 1, 2 of each of the wheels A1, A2 with the internal end of each fixed blade 3 comprising the platform 38 and on the other hand by the connecting ring 74 of the disc 7 of the first moving wheel A1 fixed to the disc 7 of the second moving wheel A2. It can thus be seen that the air circulation passes through the lateral and bottom leakage zones 74, 75 represented in [Fig. 5] in each cell 70, for each stage in series and no longer through the lunules of the movable ring fixing zone sized according to the leakage zones.

[0042] In this example, the two mobile wheels A1, A2 are therefore fixed to each other by having their blades 1 of the second series not axially aligned, that is to say angularly offset from each other. This makes it possible to have better homogeneity of the air flow in the cooling channel.

[0043] In this example, each disc 7 comprises one hundred and forty cells 70 and therefore each wheel A1, A2 comprises one hundred and forty blades 6, 9.

[0044] Each cell 70 of each disc 7 is machined by the same tool by rotation of the disc 7, thus by measuring only one or two or ten as a precaution, radial section of a cell 70, one can easily obtain the value or the average nominal radial section or the average. For example the nominal section is 50mm2 + or -0.1mm2.

[0045] In this example, the minimum desired leakage section is 2250mm2 to ensure sufficient air flow to cool the blades, but it is desired to avoid it exceeding 2550mm2 to avoid a loss of efficiency. In this example, the optimal leakage section must be 2400mm2 to have an optimal air flow between the cooling of the blades and not reduce efficiency losses. The internal base of the blade root 2 of each blade 6 of the first series therefore has a section here of 33mm2, (50-33) x 140 = 2380mm2.

[0046] However, each blade 6 includes manufacturing tolerances at the level of the internal base of the blade root 2. Thus, for example, each of the two lateral faces 12 has an average manufacturing tolerance of + or - 0.06 mm2 and the internal radial end surface 13 has a manufacturing tolerance, for example + or - 0.1 mm2. For example, the maximum surface area of ​​the section of the internal base of a blade root 2 is 33.3 mm2 and the minimum surface area of ​​the section of the internal base of a blade 2 is 32.7 mm2, i.e. a leakage variation of 0.6 mm2 between a blade 6 of the first series having an internal base having a maximum surface area and a blade 6 of the first series having an internal base having a minimum surface area.

[0047] The maximum leakage section Smaxi generated in one of these cells 70 having the maximum section according to the maximum tolerance with blade roots 2 having a section with the minimum tolerance is therefore 50.1 mm2 - 32.7 mm2 = 17.4 mm2

[0048] The minimum leakage section Smini generated in one of these cells 70 having the minimum section according to the minimum tolerance with blade roots having a section with the maximum tolerance is therefore 49.9mm2 - 33.3mm2 = 17.3 mm2.

[0049] However, since the tool for producing the cells 70 is the same for calculating the variation in total leakage section VS, the value of the nominal section of 50 can be taken to calculate the maximum total leakage section and the minimum total leakage section, i.e. the maximum leakage section of all the bottom zones 75. The same applies to calculating the value of the minimum leakage section. fund areas.

[0050] In this example, the maximum total leakage section STmaxi generated with blade roots 2 all having a section with the minimum tolerance is therefore equal to 50mm2 -32.7mm2 = 17.3 mm2x 140 = 2422mm

[0051] The minimum total leakage section STmini generated with blade roots 2 all having a section with the maximum tolerance is therefore equal to 50mm2 - 33.3mm2 = 16.7 mm2x 140 = 2338mm

[0052] In this example, the total leakage section variation VS is therefore equal to 2422-2338= 84mm.

[0053] The calculation can also be carried out more simply by calculating the quantity of blades 6 of the first series multiplied by the sum of the tolerance differences 0.3mm2 + 0.3 mm2 * by the number of blades, i.e. 0.6 mm2 x 140 = 84mm2

[0054] In this case, the maximum quantity of blades in the second series can be calculated by dividing the calculated total leakage section variation VS 84 mm2 by the blades in the second series having an added surface area of ​​4 mm: i.e. 21 blades in the second series.

[0055] Thus, by replacing between 1 and 21 blades of the first series with blades of the second series, the leakage section is reduced to between 4 and 84mm2, and it is possible to approach the optimal value to ensure a nominal section therefore between 2342 mm2 and 2502mm2.

[0056] In the case where several internal base radial sections of the blades 6 of the first series are measured, the operator can calculate the average or a median according to the maximum deviations between the samples, for example between the 40 and 50 measurements of internal base radial sections of the blades 6 of the first series, the average section varies by only 0.01 mm at most. For example, the average value of the measured internal base radial section is 32.9 mm2. Of course, the operator can also measure all the internal bases of the blades 6 of the first series to increase the probability of having the optimal total leakage section.

[0057] The operator can thus deduce the missing surface area to obtain the value of the optimal section 2400mm2 by dividing it by the average value, in this case 32.9mm2 or 72.95mm2 and thus deduce the optimal number of blades of the first series to be replaced by blades of the second series by dividing the missing surface area by the surface area added by the surplus material 10 or 72.95mm2 / 4mm2 = 18.23 or an optimal number of 18 blades of the second series.

[0058] The disc 7 can thus have an engraving comprising a maximum number of blades of the second series (for example in this case 84) or a maximum number of additional sections. The disc 7 can also comprise an engraving comprising an optimal number of blades 9 of the second series, (in this case 18) or an optimal number of additional sections. As these blades of the second series will have a less good cooling, their lifespan will be more limited and will therefore normally have to be replaced before a blade 6 of the first series. The marking makes it possible to indicate the number of blades 9 of the second series to be changed or checked.

[0059] Unless otherwise specified, the same element appearing in different figures has a single reference.

Claims

Claims

1. A movable wheel (A1, A2) comprising: - a disc (7) comprising alternating teeth (71) and cells (70) formed on its outer periphery, - blades of a first series (6) and blades (9) of a second series each comprising a blade root (2, 1) in a corresponding cell (70), each blade root (2, 1) comprising an internal base (17) housed entirely in the cell (70), - characterized in that the internal base (17) of the blade root (1) of the second series comprises a surplus of material compared to each internal base of each blade root (2) of the first series, the surplus of material adding a surface area to the radial section of at least 1mm2 more than on each radial section of an internal base of a blade root (2) of the first series, each internal base (17) of the blade root (1) of the second series reducing by at least 1mm2 one of the leakage sections delimited between this internal base (17) and the surfaces of the disc (72,73) delimiting the cell (7) housing it, with respect to each leak section delimited between an internal base of a blade root (2) of the first series and the walls of the disc (7) forming the cell (70) housing it.,

2. Movable wheel (Al, A2) according to the preceding claim, in which the internal base (17) of the blade root (1) of each blade (9) of the second series comprises an internal radial end surface (13) facing a bottom surface (73) of the disc (7) delimiting the cell (70) of each blade (9) of the second series is different from each of the internal radial end surfaces of a blade (6) of the first series.

3. Movable wheel (A1, A2) according to the preceding claim, in which the blade root (1) of each blade of the second series (9) comprises an upstream radial face (14) and a downstream radial face (15), a first and a second lateral face (12) comprising at least one bearing surface connecting the downstream radial face (15) to the upstream radial face (14), each running along the internal radial end surface (13), in which the surface internal radial end (13) comprises an alternation of concave and convex part of the first to the second lateral face (12).

4. Movable wheel (A1, A2) according to any one of the preceding claims, comprising a marking visible to the naked eye on each blade (9) of the second series making it possible to differentiate them from the blades (6) of the first series.

5. A movable wheel (Al, A2) according to any preceding claim, wherein the disc (7) comprises an engraving comprising a number of blades (9) of the second maximum series or a number of maximum additional section.

6. A moving wheel (Al, A2) according to any preceding claim, wherein the disc (7) comprises an engraving comprising an optimal number of blades (9) of the second series or an optimal number of additional sections.

7. Movable wheel (Al, A2) according to any one of the preceding claims, in which an internal base (17) of a blade root (1) of the second series comprises an excess thickness at the level of one of the two lateral faces (12) facing a lateral surface (72) of a tooth (71) of the disc (7) delimiting the cell (70).

8. Method for determining a number of blades (9) of the second series on a moving wheel (A1, A2) comprising a disc (7) comprising teeth (71) and a number N of cells (70), blades (6) of the first series each having a blade root (2) having an internal base housed in the cell (70), the internal base having a nominal section with a tolerance variation for being mounted in a cell (70) of the disc (7), comprising the steps of: - measuring at least one nominal cell section (70), - determining an average value of the cell sections (70), - calculating the total leakage section variation VS, by calculating the difference between: • the maximum total leakage section STmaxi generated with blade roots (2) of the first series having an entire internal base section with the minimum tolerance, and • the minimum total leakage section STmini generated with blade roots of dawn (2) of the first series having.

9. an entire internal base section with the maximum tolerance, - calculating a quantity of second series blades (9) to replace first series blades (6), each second series blade (9) each comprising an internal base section (17) of the blade root (1) greater by a surface value added by a surplus of at least 1mm2 compared to the average value of the nominal internal base sections of the blade root (2) of the first series blades (6), by dividing the total leakage section variation VS calculated by the surface added by the surplus material (10) of a second series blade (9). Method for determining a number of blades of the second series (9) on a moving wheel (A1, A2) comprising a disc (7) comprising teeth (71) and a number N of cells (70) formed between each tooth, a number N of blades (6) of the first series each having a blade root (2) having a nominal section with a variation in tolerance to be mounted in a cell (70) of the disc (7), comprising the steps: - determination of an optimal total nominal leakage section value, - measuring at least one nominal cell section (70), - calculation of a value of all the cell sections (70) by multiplying an average value of the cell sections (70) from the at least one nominal measured cell section (70) multiplied by the number N of cells (70), - measuring an internal base section of the blade root (2) of a plurality of blades (6) of the first series and deducing therefrom an average value of the internal base section of the blade root (2), - calculation of a total leakage section equal to subtracting the value of all the cell sections from the total section of the internal bases equal to the multiplication of the internal base sections of the blade root (2) of each blade (6) of the first series by the number N, - calculation of a surplus leakage section value equal to the optimal total nominal leakage area value subtracted from the total leakage area value and - determining a number of blades of the second series (9) to replace blades (1) of the first series each comprising an internal base section (17) of the blade root (1) greater by a surface value added by a surplus of at least 1mm2 compared to the average value of the nominal internal base sections of the blade root (2) of the blades (6) of the first series, by dividing the excess value of the leakage section by the added surface value.

10. Method of assembling a mobile wheel according to one of claims 1 to 7 comprising a disc comprising N cells and N blades, by inserting a number NX of normal blade roots into NX cells of a disc, characterized in that it further comprises a step of inserting a number X of blade roots of the second series into the X other cells of the disc and a step of marking a number X on a radial face of the disc.

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