Wavy tilting of platforms at the gaps between rotor and stator in a turbomachine compressor

Description

Domaine technique

[0001] The invention relates to the field of turbomachines, more particularly jet engines for aircraft. Technique antérieure

[0002] In a turbomachine, the annular fluid stream passing through the machine is delimited, in the compressor and the turbine, by an outer guide surface, generally formed by the casing of the machine, and an inner guide surface formed by the annular platforms of rows of rotor and stator blades succeeding one another in alternation.

[0003] One of the key parameters in the performance and operability of turbomachinery compressors and turbines is the correct alignment of the inner annular platforms of the fixed and moving parts to ensure optimal aerodynamic guidance of the fluid stream.

[0004] However, the passage for the fluid stream is dotted with irregularities formed mainly by the blades and the air gaps between the annular platforms of rows of rotor and stator blades, disturbing the flow.

[0005] Also, the manufacturing and assembly tolerances of these different parts reconstituting this internal surface guiding the fluid vein mean that projections, unfavorable from an aerodynamic point of view, can appear. The projections forming an upward step, in the direction of fluid flow, are significantly more unfavorable, from an aerodynamic point of view, than the projections forming a downward step.

[0006] The usual rules of the state of the art of design are based on these geometric considerations to achieve this good alignment of internal guide surface, essentially by tilting the platforms and / or by providing a rounding at the upstream edges of the platforms, so as to form descending steps in the most unfavorable configurations within the manufacturing and assembly tolerances. This approach, however, has limitations, essentially in that it is limited to geometric considerations, and is therefore subject to improvement in order to optimize the flow of the fluid vein.

[0007] Patent document US 2008 / 0310961 A1 discloses a set of compression stage(s) of a turbomachine, according to the preamble of claim 1, and a method for dimensioning at least one annular platform of a row of stator blades and / or a row of rotor blades of a set of compression stage(s) of a turbomachine, according to the preamble of claim 7.

[0008] Document US6524070B1 discloses a fan with platforms whose outer surface is hollowed between two blades for the purpose of reducing circumferential stresses in the platforms. Exposé de l'invention

[0009] The invention aims to overcome at least one of the drawbacks of the aforementioned prior art. More particularly, the invention aims to improve the flow of the fluid stream within a compressor, in particular along the inner guide surface.

[0010] The subject of the invention is a set of compression stage(s) of a turbomachine, according to claim 1.

[0011] Depending on manufacturing tolerances, the nominal profile may be aligned with the upstream annular platform while remaining parallel to a theoretical and perfect profile of the fluid vein, in particular aligned with the downstream edge when said upstream annular platform also has an inclined longitudinal profile.

[0012] The annular platform(s) may be segmented. Their circumference corresponds to their envelope around the main axis.

[0013] According to an advantageous embodiment of the invention, the inclination of the external longitudinal profile of the or each of the annular platforms, relative to the nominal profile of the fluid vein, contributes to a lowering of a radial distance I Ri and / or I Si , respectively, of an upstream edge of said external longitudinal profile, relative to said nominal profile of the fluid vein.

[0014] According to an advantageous embodiment of the invention, the maximum and minimum values ​​of radial distance I Ri and / or I Si of lowering of the upstream edge of the external longitudinal profile of the or each of the annular platforms, relative to the nominal profile of the fluid vein, have a difference A of between 0.05 and 0.15 mm.

[0015] According to an advantageous embodiment of the invention, the lowering of the upstream edge of the external longitudinal profile of the or each of the annular platforms relative to the nominal profile of the fluid vein is achieved not only by the inclination, but also by a rounding of the upstream edge of said external longitudinal profile.

[0016] According to an advantageous embodiment of the invention, the rounding of the upstream edge of the external longitudinal profile of the annular platform(s) has a radius of curvature R Ri or R Si , respectively, greater than 5mm and / or less than 15mm. According to an advantageous embodiment of the invention, the rounding of the upstream edge of the external longitudinal profile of the or each of the annular platforms extends over a distance greater than 20% and / or less than 30% of the total extent of said external longitudinal profile.

[0017] According to an advantageous embodiment of the invention, the inclination of the external longitudinal profile of the or each of the annular platforms, relative to the nominal profile of the fluid stream, oscillates along the circumference of at least one stator annular platform and at least one rotor annular platform, the minimum inclination of the external longitudinal profile of the at least one rotor annular platform being greater than the minimum inclination of the external longitudinal profile of the at least one stator annular platform, respectively.

[0018] Advantageously, the minimum inclination of the external longitudinal profile of the at least one annular rotor platform is greater than 150% of the minimum inclination of the external longitudinal profile of the at least one annular stator platform. The invention also relates to a method for dimensioning at least one annular platform of a row of stator blades and / or a row of rotor blades of a set of compression stage(s) of a turbomachine, according to claim 7.

[0019] The measures of the invention are interesting in that they make it possible to optimize the aerodynamic flow of the fluid stream, taking into account particularities of the flow precisely in the different air gaps, these particularities being able to change from air gap to air gap. They also make it possible to optimize the aerodynamic flow of the fluid stream under the most unfavorable conditions of manufacturing and assembly tolerances. Brève description des dessins

[0020] [ Fig 1 ] is a longitudinal sectional view of a turbomachine; [ Fig 2 ] is a detail view, in longitudinal section, of an air gap between a row of stator blades and a row of rotor blades; [ Fig 3 ] is a schematic representation of tilting of the inner guide surface of the fluid vein, taking into account manufacturing tolerances; [ Fig 4 ] is a schematic representation of the velocity vectors of the fluid stream in the air gaps between the rows of stator and rotor blades; [ Fig 5 ] is a schematic representation in longitudinal section of a row of stator blades, illustrating air recirculation in the rotating joint with the rotor; [ Fig 6 ] is a schematic representation of inclinations and roundings of platforms forming the inner guiding surface of the fluid vein; [ Fig 7 ] is a detailed geometric representation of the inclination and roundness of the upper longitudinal profile of an annular platform of a row of stator or rotor blades; [ Fig 8 ] is a schematic representation of cyclic variations in the tilting of the platform of a row of stator or rotor blades, in accordance with the invention. Description détaillée

[0021] In the following description, the terms "inner" and "outer" refer to the radial direction relative to the main axis of the turbomachine. The term "inner" expresses a position closer to the axis in question than the term "outer" and vice versa.

[0022] There figure 1 is a longitudinal sectional view of an axial turbomachine forming a jet engine for an aircraft. The turbomachine 2 is housed inside an external nacelle 4 via guide vanes 6 and holding arms (not shown). The latter provide a rigid attachment between the nacelle 4 and the casing 8 of the turbomachine 2. The latter essentially comprises, from upstream to downstream along the main axis X of the machine, a fan 10, more commonly referred to by the English expression “turbofan”, a low-pressure compressor 12, a high-pressure compressor 14, a combustion chamber 16, a high-pressure turbine 18 and a low-pressure turbine 20. The air flow F entering the nacelle 4, upstream of the turbomachine 2, is divided into two air flows F.1 and F.2 after the fan 10, namely into a primary flow F.1 forming an annular fluid stream circulating inside the turbomachine 2, and a secondary flow F.2 also forming an annular fluid vein concentric with the primary flow F.1, delimited by the casing 8 of the turbomachine 2 and the internal wall of the nacelle 4. The primary flows F.1 and secondary flows F.2 join at the outlet of the turbomachine 2. This turbomachine architecture is in itself well known to those skilled in the art and does not require further explanation.

[0023] The low-pressure 12 and high-pressure 14 compressors consist of alternating moving parts and fixed parts, more particularly alternating rows of rotor blades and rows of stator blades. The rotor, or moving, blades are mounted on a rotor of the turbomachine while the stator, or fixed, blades are mounted on the casing 8 of the turbomachine. For this purpose, the inner fluid flow guide surface of the primary flow F.1 is formed by alternating moving and fixed annular platforms forming air gaps.

[0024] The figure 2 schematically illustrates an air gap E between a row 22 of stator blades 22.1, commonly referred to as the stator row 22, and a row 26 of rotor blades 26.1, commonly referred to as the rotor row or wheel 26. The stator row 22 comprises an internal shroud 22.2 forming an annular platform with an external longitudinal profile 22.3. The inner shell 22.2 supports on an inner face rotating sealing means 22.4 with wipers 24.1 formed on the rotor 24. The rotor row 26 comprises the rotor blades 26.1 supported by the rotor 24. The latter in this case comprises an annular protrusion 24.2 forming or supporting the inner platform 26.2 having an external longitudinal profile 26.3 generally aligned with the external longitudinal profile 22.3 of the platform 22.2 of the stator row 22. The air gap E is formed by the mechanical axial clearance between the adjacent edges of the platforms 22.3 and 26.3, in this case between the downstream edge of platform 22.2 and the upstream edge of platform 26.2.

[0025] There figure 3 schematically illustrates the influence of manufacturing and assembly tolerances on the alignment between these adjacent platforms. Platform 22.2 of stator row 22 of the figure 2 , with its upper longitudinal profile 22.3, is illustrated schematically. The nominal profile N of the platform of the rotor row 26 is shown in broken line (center line). This profile is perfectly aligned with that of the upstream stator row. The extreme positions of this theoretical profile are shown in dotted line, corresponding to the tolerances +T and -T. It can then be seen that in the case of the upper tolerance +T, the profile forms a rising step, which is particularly unfavorable from an aerodynamic point of view. Indeed, the aerodynamic losses of a projecting rising step are twice as great as the aerodynamic losses of a descending step of the same amplitude. Also, the aerodynamic losses of a rising step with a rounding or a chamfer are greatly reduced compared to the aerodynamic losses of a rising and projecting step (i.e. without rounding or chamfer).In accordance with the invention, it may then be provided to incline the profile 26.3 inwards and upstream relative to the nominal profile N and optionally to provide a rounding or a chamfer, 26.3.2, at its upstream edge 26.3.1, so that at the maximum of the manufacturing and assembly tolerances, in this case +T, the profile 26.3 does not form an upward step. The inclination of the profile inwards and upstream consists, from a nominal profile, in lowering the upstream edge relative to the downstream edge. It is however understood that the profile is not necessarily rectilinear.

[0026] What has just been described in relation to the figure 2 and more particularly the figure 3 also applies to the upper longitudinal profile of the platform of a stator row arranged directly downstream of a rotor row.

[0027] There figure 4 is a schematic representation of the velocity vectors of the fluid stream in the air gaps between rows of stator and rotor blades, illustrating the absolute and relative velocities (i.e. in a frame of reference rotating with the rotor). At the figure 4 two alternations of stator blade rows and rotor blade rows are shown, in this case a stator row 22, followed by a rotor row 26, followed by a stator row 22, followed by a rotor row 26. For reasons of clarity in the description of the invention, the stator rows all have the same reference sign 22, it being understood, however, that these rows are not identical but may have common characteristics relating to the present invention. The same applies to the rotor rows having the reference sign 26.

[0028] To the figure 4 , we can observe the absolute speed vector V 1 of the air flow at the outlet of the first stator row 22. This vector is oriented essentially along the chord of the upstream blade profile; it has an inclination α 1 relative to the axial direction, more precisely the direction located in an axial plane and tangent to the upper longitudinal profile of the annular platform 22. This direction corresponds to the axial direction if the fluid stream is perfectly cylindrical, which is not necessarily the case. If we take the point of view of the rotor row 26 directly downstream, where the platform rotates at a speed U, the fluid flow is along the speed vector W 1 . This relative speed vector W 1 of the air flow entering the rotor row 26 corresponds to the vector V 1 from which the vector U 1 has been subtracted and has an inclination β 1 relative to the axial direction, which is opposite to the angle α 1 and is significantly greater.The physical displacement of the air flow in the air gap E (substantially exaggerated at the . figure 4 ) from the stator row 22 to the rotor row 26 corresponds to the vector V 1 , that is to say in a fixed reference frame, while this same flow has a speed vector W 1 relative to the blades of the rotor row 26, substantially different from V 1 .

[0029] Still referring to the figure 4 , the air flow leaving the rotor row 26 mentioned above (the one on the left) has a relative speed vector with respect to said row, W 2 , essentially oriented along the chord of the profile of the blades of the row in question, and forming an angle β 2 with respect to the axial direction. If we add to it the speed vector U 2 of the rotor row 26 corresponding to U and U 1 , we obtain the absolute speed vector V 2 of the air flow, forming an angle α 2 with the axial direction, in this case opposite to the angle β 2 . However, it is the rotor row 26 which distributes the fluid in the air gap E and it is therefore appropriate to consider the speed vector W 2 of the fluid in a relative frame of reference, fixed with the rotor row in question, to determine the distance traveled by the fluid in the air gap E.

[0030] Still in reference to the figure 4 , the air flow leaving the second stator row 22 (on the right) located directly in front of the rotor row 26 mentioned above, has an absolute speed vector V 3 forming an angle α 3 with the axis of the turbomachine, similarly to the vector V 1 and the angle α 1 at the outlet of the first stator row 22. The relative speed of the fluid with respect to the rotor row 26 located directly downstream is represented by the vector W 3 . Similar to what was detailed above in relation to the first stator row 22 (on the left in the figure), it is appropriate to consider the absolute speed vector V 3 to determine the distance traveled by the fluid in the air gap E.

[0031] In summary, the flow of fluid in an air gap E between a fixed part 22 and a mobile part 26 of the turbomachine is not necessarily axial but inclined according to the angles α 1 , β 2 and α 3 mentioned above in relation to the figure 4 These angles are potentially important and significantly influence the distance traveled by the fluid in the air gap.

[0032] However, a fluid flow not guided by a wall, which is precisely the case in the air gap, will tend not to follow the direction of the tangent of the downstream edge of the upstream platform. The flow will tend to penetrate the air gap, in a radial direction towards the axis of the turbomachine. Consequently, the greater the path of the flow in the air gap, the more the flow will be deflected radially in the air gap and therefore the greater the need for inclination of the upper longitudinal profile of the annular platform and / or rounding or chamfering of the upstream edge.

[0033] At the exit of the fixed part 22, the absolute speed vector should be considered and at the exit of the moving part 26, the relative speed vector should be considered, i.e. in a frame of reference rotating with the moving part. For air gaps with greater inclinations and therefore longer paths, the upper longitudinal profile of the platform downstream of the air gap should be inclined more in order to minimize the risk of upward movement.

[0034] It is understood that the angles of inclination of the fluid flow in the air gaps are not constant over the entire speed and load range of the turbomachine. It is therefore appropriate to consider one or more specific operating points of the turbomachine such as for example one or more critical operating points for the specific consumption of the turbomachine and / or the operability of the turbomachine compressor.

[0035] There figure 5 illustrates another phenomenon influencing the flow of fluid in the air gap at the outlet of the fixed part, namely the leakage flow circulating under the platform of the stator row 22. Indeed, the sealing between a row of stator blades 22 and the rotor 24 is not perfect in that a certain leakage flow takes place between the wiper(s) 24.1 of the rotor 24 and the rotating sealing means 22.4 on an inner face of the platform 22.2. This flow depends essentially on the pressure difference between the upstream and downstream of the row of stator blades 22 and the clearance δ at the rotating sealing means. This flow enters the downstream air gap, crosses the cavity of the rotor 24 and opens into the upstream air gap essentially perpendicular to the fluid stream and thus modifies the orientation of the flow in a longitudinal plane passing through the axis of the turbomachine, and this in an opposite manner upstream and downstream.

[0036] Upstream, the leakage flow leaving the cavity adds to the flow of the fluid vein and deflects it upwards. This deflection angle γ can be calculated by adding the fluid momentum P before this leakage flow and the momentum of the leakage flow P f . Momentum is a vector quantity equal, for a fluid flow, to the velocity vector multiplied by the mass flow rate. The corrected momentum of the fluid after the leakage flow rate, P c , is then equal to P+Pr. From this relationship, we can deduce the angle γ.

[0037] Similarly, downstream, the leakage flow entering the cavity adds to the flow of the fluid vein and deflects it downwards by an angle γ', which to a first approximation is equal to the angle γ. The angle γ' can also be obtained by adding the respective momentum quantities P' And P f ′ to obtain the corrected fluid momentum after the leakage flow rate P c '. This calculation method is an example, it being understood that other methods, particularly computer simulation, can be used.

[0038] The fluid flow at the outlet of a stator row 22 therefore has an azimuthal inclination directed inwards, requiring a greater inclination of the rotor platform directly downstream to be provided, compared with a stator platform.

[0039] There figure 6 illustrates the external longitudinal profiles 22.3 and 26.3 of the platforms 22.2 and 26.2 of successive stator and rotor rows, these profiles being corrected so as to optimize the fluid flow, taking into account, on the one hand, the manufacturing and assembly tolerances and, on the other hand, the phenomena described above in relation to the figures 4 et 5 . These profiles 22.3 and 26.3 are the theoretical profiles and have an upstream edge lowering I Si and I Ri (i being a positive integer corresponding to the number of a stator or rotor row) obtained at least in part by an inclination of the profiles upstream and inwards with respect to the nominal profiles N. These lowerings I Si and I Ri express a radial lowering distance of the upstream edge 22.3.1 and 26.3.1 with respect to the nominal profile N. These lowerings are obtained at least in part by a rotation of the external longitudinal profiles 22.3 and 26.3 by an angle α Si and α Ri around the downstream edge 22.3.3 and 26.3.3. They can further be increased by the formation of roundings 22.3.2 and 26.3.2, in this case arcs of circles with radius of curvature R Si and R Ri (i being a positive integer corresponding to the number of a stator or rotor row) at the upstream edges 22.3.1 and 26.3.1 of the external longitudinal profiles 22.3 and 26.3.In light of what has been detailed in relation to the . figure 2 , manufacturing and assembly tolerances have the effect, in practice, that the actual profiles, i.e. on turbomachines produced and assembled on the basis of these theoretical profiles, will deviate from the theoretical profiles within the tolerances in question, the most unfavorable case being when the actual profile is at the maximum of the tolerances towards the outside so as to form an upward step. The reductions illustrated in figure 6 are therefore dimensioned to minimize aerodynamic losses under these adverse conditions within the limits of manufacturing and assembly tolerances as well as the particularities of the flow in the fluid stream as illustrated in relation to the figure 5 .

[0040] We observe at the figure 6 that the outer longitudinal profiles 26.3 of the rotor row platforms 26.2 have a greater upstream edge lowering I R1 and I R2 than the upstream edge lowering I S1 and I S2 of the outer longitudinal profiles 22.3 of the stator row platforms 22.2, essentially due to the fact that the flux in the air gaps directly upstream of the rotor rows are deflected inwards (azimuthal angle γ' at the figure 5 ) and, similarly, the flux in the air gaps directly upstream of the stator rows are deflected outwards (azimuthal angle γ at the figure 5 ). The inclinations of the flow due to the orientations of the blades, as mentioned in relation to the figure 4 (namely the angles α 1 , β 2 and α 3 ) can influence this tendency by intensifying or decreasing it. Indeed, with reference to the figure 4 described above, it can be observed that the angle β 2 is greater than the angles α 1 and α 3 (in absolute value, i.e. without consideration of the positive or negative sign of the angle with respect to the main axis), which means that, for air gaps of the same size, the path of the flux leaving the rotor row 26 is greater than the path of the flux leaving the stator rows 22. In this case, the lowering of the upstream edge of the outer profile of the platform of the stator row 22 directly downstream of this rotor row 26 in question will be increased. The inclination angles α 1 , β 2 and α 3 illustrated in figure 4 are however illustrative in that they can take other values, in particular the angles of inclination of the flow at the outlet of certain rotor rows can be greater than the angles of inclination of the flow at the outlet of certain rotor rows.

[0041] There figure 7 is a detailed and profile representation of an upper longitudinal surface of a stator or rotor annular platform. The figure represents, on the left, the downstream edge of a rotor annular platform 26.2 or stator 22.2; and, on the right, the upper longitudinal surface 22.3 or 26.3 of an adjacent stator 22.2 or rotor 26.2 platform. The nominal profile N, already mentioned in figures 3 And 6, is represented in dotted lines taking into account a manufacturing and / or assembly tolerance +T having the effect of mounting the upper longitudinal surface 22.3 or 26.3 relative to the upper longitudinal surface of the rotor row 26.2 or stator row 22.2 located directly upstream. It can be observed that the upper longitudinal surface 22.3 or 26.3 comprises a first portion, in this case the main one, corresponding to a rotation of the nominal profile N around the downstream edge 22.3.3 or 26.3.3 by an angle α Si or α Ri , and a second portion corresponding to the rounding 22.3.2 or 26.3.2, in this case an arc of a circle with a radius R Si or R Ri . The first portion is advantageously tangent to the second portion. The rounding 22.3.2 or 26.3.2 extends, following the main direction of the fluid vein, over a distance L 1 corresponding to a fraction of the total length L of the upper longitudinal surface 22.3 or 26.3, said fraction being able to be between 20 and 30%. The main portion of the upper longitudinal surface 22.3 or 26.3, for its part, extends over a length L 2 corresponding to the remainder of the total length L of the upper longitudinal surface 22.3 or 26.3. It can be observed that the upstream edge lowering I Si or I Ri is the sum of two partial lowerings, namely a partial lowering I 1 resulting from the inclination of the profile relative to the nominal profile N and a partial lowering I 2 resulting from the rounding 22.3.2 or 26.3.2. Each of these partial lowerings I 1 and I 2 corresponds to a fraction of the upstream edge lowering I Si or I Ri , advantageously between 40 and 60%, where I 1 +I 2 = I Si or I Ri .

[0042] There figure 8 is a representation of a stator row segment 22 or rotor row segment 26 of the turbomachine, in accordance with the invention. With reference to what has been described in relation to the figure 6 , the upper longitudinal profile 22.3 or 26.3 of the platform 22.2 or 26.2 of the stator row 22 or rotor row 26 is inclined upstream and inwards. At the figure 8 , the upstream and inward inclination of the upper longitudinal profile 22.3 or 26.3 of the platform 22.2 or 26.2 oscillates cyclically along the circumference of the platform, between a maximum inclination value at the blades 22.1 or 26.1 and a minimum inclination value between the blades in question. This contributes to a cyclic variation of the upstream edge lowering IR or IS, of amplitude A and period S, which makes it possible to take into account the azimuthal heterogeneity of injection and sampling of the leakage flow in the air gaps in front of the stator and rotor rows, due to the presence of the blades. Indeed, the obstruction generated by the blades directly downstream of an air gap generates a flow blocking effect favoring a flow entering the air gap, precisely in front of the blades. Outside of these areas, the flow tends to flow upwards in the vein compared to the average flow.It is therefore advantageous to further inclinate the upper longitudinal profile of the platforms in the areas subject to this blocking effect, namely in front of the blades. This then results in an oscillating inclination, preferably cyclically, along the platform in its circumferential direction. This applies to both rotor and stator rows, although the blocking phenomena may differ from one row to another, depending in particular on the orientation and size of the blades.

[0043] It should be noted that the oscillating and cyclic tilting detailed above can be implemented independently of manufacturing tolerances and the influence of leakage recirculation under the stator annular platforms, as detailed in relation to the figure 5 , because the phenomenon of azimuthal heterogeneity of injection and sampling of the leakage flow in front of the stator and rotor annular platforms is a phenomenon which is not directly linked to the problem of rising step between two adjacent annular platforms resulting from manufacturing and assembly tolerances, nor to the influence of leakage recirculation. This means that the minimum inclination value, between the blades, can be zero. Conversely, this minimum inclination value between the blades of a rotor annular platform 26.2 can be non-zero and greater than the minimum inclination value, zero or non-zero, between the blades of a stator annular platform 22.2, so as, in addition, on the one hand, to avoid rising step due to manufacturing and assembly tolerances and, on the other hand, to compensate for the effect of leakage recirculation at the stator level.

[0044] The alignment of the oscillating profile of the inclination with the blades can be adjusted according to the effective direction of flow in the fluid vein in the air gap directly upstream of the blades concerned. Indeed, with reference to the discussion in relation to the figure 4 , the flow velocity in the air gap is in principle not axial (more precisely the direction is located in an axial plane and tangent to the upper longitudinal profile of the annular platform) but rather inclined essentially along the profile of the blades which receive the flow. According to the invention, the points or zones of maximum inclination of the oscillating inclination profile are aligned with the leading edges of the blades along the profile of said blades, namely along the chord lines of said blades. The same applies to the zones of minimum inclination which are aligned with the spaces between each pair of adjacent blades.

[0045] The oscillation amplitude A of the upstream edge lowering of the upper longitudinal profile 22.3 or 26.3 of the platform 22.2 or 26.2 of the stator row 22 or rotor row 26, as illustrated in figure 8 can be greater than 0.05mm and / or less than 0.15mm. The pitch S of the oscillation is advantageously equal to a pitch of blades, i.e. the number of blades / 2πr, where r is the internal radius of the fluidic vein.

[0046] It is understood, however, that these values ​​may vary and potentially deviate from the above-mentioned ranges. They depend on a number of parameters such as the size of the turbomachine, manufacturing and assembly tolerances, air gap distance and flow conditions in the fluid stream (in particular the speed).

Claims

1. Set of compression stage(s) of a turbomachine (2), forming an annular fluid passage (F.1) and comprising at least one alternating row of stator (22) and rotor (26) blades, with annular platforms (22.2, 26.2) inside the fluid vein (F.1) and delimiting said vein; at least one annular stator platform (22.2) and / or at least one annular rotor platform (26.2) having an outer longitudinal profile (22.3, 26.3) inclined inwards and upstream with respect to to a nominal profile (N) of the fluid stream (F.1) passing through a downstream edge of said annular platform and parallel to a theoretical and perfect profile of the fluid stream; wherein the inclination of the outer longitudinal profile (22.3, 26.3) of the or each of the annular platforms (22.2, 26.2), relative to the nominal profile (N) of the fluid stream (F.1), oscillates along the circumference of said annular platform(s) (22.2, 26.2), between a maximum value opposite the blades (26.1, 22.1) of said annular platform (22.2, 26.2) following a chord line of said blades and a minimum value between each pair of adjacent blades of said annular platform (22.2, 26.2) characterized in that the inclination of the outer longitudinal profile (22.3, 26.3) of the or each annular platform (22.2, 26.2) relative to the nominal profile (N) of the fluid stream (F.1) is achieved by pivoting said outer longitudinal profile (22.3, 26.3) about the downstream edge (22.3.3, 26.3.3) of said outer longitudinal profile (22.3, 26.3).

2. Set of compression stage(s) according to claim 1, characterized in that the inclination of the outer longitudinal profile (22.3, 26.3) of the or each of the annular platforms (22.2, 26.2), with respect to the nominal profile (N) of the fluid stream (F.1) contributes to lowering a radial distance IRi and / or ISi, respectively, of an upstream edge (22.3.1, 26.3.1) of said outer longitudinal profile (22.3, 26.3), with respect to said nominal profile (N) of the fluid stream (F.1).

3. Set of compression stage(s) according to claim 2, characterized in that the maximum and minimum values of radial distance IRi and / or ISi of upstream edge lowering of the outer longitudinal profile (26.3) of the or each of the platforms annular (22.2, 26.2), compared to the nominal profile (N) of the fluid stream (F.1), has a difference A of between 0.05 and 0.15mm.

4. Set of compression stage(s) according to one of claims 1 to 3, characterized in that the upstream edge lowering of the outer longitudinal profile (22.3, 26.3) of the or each of the annular platforms (22.2, 26.2) with respect to to the nominal profile (N) of the fluid stream (F.1) by not only by inclination, but also by a rounding (22.3.2, 26.3.2 ) of the upstream edge (22.3.1, 26.3.1) of said outer longitudinal profile (22.3, 26.3).

5. Set of compression stage(s) according to Claim 4, characterized in that the rounding (22.3.2, 26.3.2) of the upstream edge (22.3.1, 26.3.1) of the outer longitudinal profile (22.3, 26.3) of the annular platform or platforms (22.2, 26.2) has a radius of curvature RRi or RSi, respectively, greater than 5mm and less than 15mm6. Set of compression stage(s) according to one of claims 4 and 5, characterized in that the rounding (22.3.2, 26.3.2) of the upstream edge (22.3.1, 26.3.1) of the longitudinal profile exterior (22.3, 26.3) of the or each of the annular platforms (22.2, 26.2) extends over a distance greater than 20% and less than 30% of the total extent of said outer longitudinal profile (22.3, 26.3) .

7. Method for dimensioning at least one annular platform (22.2, 26.2) of a row of stator blades (22) and / or of a row of rotor blades (26) of a set of stages compression of a turbomachine (2), said rows of blades being alternately and forming air gaps (E), the method comprising, for the or each of the annular platforms (22.2, 26.2), determining as a function of the air gap (E) directly upstream, an inclination of an outer longitudinal profile (22.3, 26.3) of said annular platform inwards and upstream with respect to a nominal profile (N) of the fluid vein (F.1) passing through a downstream edge of said annular platform and parallel to a theoretical and perfect profile of the fluid stream; wherein the inclination of the or each of the annular platforms (22.2, 26.2) oscillates along the circumference of the said annular platform (22.2, 26.2), between a maximum value in front of the blades (26.1, 22.1) of said annular platform (22.2, 26.2) following a chord line of said vanes and a minimum value between each pair of adjacent blades of said annular platform (22.2, 26.2); characterized in that the inclination of the outer longitudinal profile (22.3, 26.3) of the or each annular platform (22.2, 26.2) relative to the nominal profile (N) of the fluid stream (F.1) is achieved by pivoting said outer longitudinal profile (22.3, 26.3) about the downstream edge (22.3.3, 26.3.3) of said outer longitudinal profile (22.3, 26.3).