Undulating tilt of platforms at rotor-stator clearances in turbine engine compressors

Abstract

The invention relates to a compressor stage group of a turbomachine forming an annular fluid passage and comprising 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 inwardly and upstreamly (I Si / I Ri ) with respect to a nominal profile of the fluid flow, wherein the inclination (I Si / I Ri ) of the outer longitudinal profile (22.3, 26.3) of the or each annular platform (22.2, 26.3) with respect to the nominal profile of the fluid flow oscillates between a maximum value in front of the blades (26.1, 22.1) of the annular platform (22.2, 26.2) along the circumference of the one or more annular platforms (22.2, 26.2) and a minimum value between each pair of adjacent blades of the annular platform (22.2, 26.2).

Description

Technical Field

[0001] This invention relates to the field of turbines, and more particularly, to jet propulsion for aircraft. Background Technology

[0002] In a turbine, the annular fluid flow through the machine is defined in compressors and turbines by an outer guide surface typically formed by the machine housing and an inner guide surface formed by an annular platform of rotor and stator blade rows, which alternate with each other.

[0003] One of the key parameters for the performance and operability of turbine compressors and turbines is the proper alignment of the internal annular platforms of both fixed and moving components to ensure optimal aerodynamic guidance of fluid flow.

[0004] However, the channels used for fluid flow are irregularly distributed, and these irregularities are mainly formed by air gaps between the annular platforms of the blades and rotor and stator blade rows, which interfere with the flow.

[0005] Furthermore, the manufacturing and assembly tolerances of these different components that constitute the inner surface used to guide fluid flow mean that steps that are unfavorable from an aerodynamic point of view may occur. From an aerodynamic point of view, steps forming upward steps in the direction of fluid flow are more disadvantageous than steps forming downward steps.

[0006] The conventional design rules of existing technologies are based on these geometric considerations to achieve such good alignment of the internal guiding surface, essentially by tilting the platform and / or by providing rounding at the upstream edge of the platform to form a descending step within manufacturing and assembly tolerances with the most unfavorable construction. However, this approach has limitations, primarily in that it is constrained by geometric considerations and therefore requires improvements to optimize fluid flow. Summary of the Invention

[0007] The object of this invention is to overcome at least one of the aforementioned disadvantages of the prior art. More specifically, the invention aims to improve the flow of fluid within a compressor, particularly the flow along the inner guide surface.

[0008] The subject of this invention is a compression stage assembly of a turbine forming an annular channel for fluid flow and including at least one alternating row of stator and rotor blades, having an annular platform within the fluid pulse and defining the pulse; at least one annular stator platform and / or at least one annular rotor platform having an outer longitudinal profile inclined inward and upstream relative to the nominal profile of the fluid flow; characterized in that the inclination of the outer longitudinal profile of said or each annular platform relative to the nominal profile of the fluid flow oscillates along the circumference of said annular platform between a maximum value in front of the blades of said annular platform and a minimum value between each pair of adjacent blades of said annular platform.

[0009] The nominal profile of the fluid flow refers to a profile parallel to the theoretical and ideal profile of the fluid flow, aligned with the directly upstream and downstream platforms to ensure a perfect connection. More specifically, the nominal profile extends through the downstream edge of the annular platform, whose longitudinal profile is inclined. Depending on manufacturing tolerances, this nominal profile can be aligned with the upstream annular platform while remaining parallel to the theoretical and ideal profile of the fluid flow, particularly when the upstream annular platform also has an inclined longitudinal profile, and aligned with the downstream edge.

[0010] At least one toroidal platform can be segmented. Their perimeter corresponds to the envelope around the principal axis.

[0011] According to an advantageous embodiment of the invention, the inclination of the outer longitudinal profile of the or each annular platform relative to the nominal profile of the fluid flow is a radial distance I at the upstream edge of the outer longitudinal profile relative to the nominal profile of the fluid flow. Ri and / or I Si .

[0012] According to an advantageous mode of the invention, the radial distance I of the inclination of the outer longitudinal profile of the said or each annular platform relative to the nominal profile of the fluid flow. Ri and / or I Si The maximum and minimum values ​​have a difference A between 0.05 and 0.15 mm.

[0013] According to an advantageous embodiment of the invention, the inclination of the outer longitudinal profile of the or each annular platform relative to the nominal profile of the fluid flow is achieved by pivoting the outer longitudinal profile about the downstream edge of the outer longitudinal profile and / or by rounding the upstream edge of the outer longitudinal profile.

[0014] According to an advantageous embodiment of the invention, the rounded edges of the upstream edges of the outer longitudinal profile of the annular platform have radii of curvature R greater than 5 mm and / or less than 15 mm, respectively. Ri Or R Si .

[0015] According to an advantageous embodiment of the invention, the rounding of the upstream edge of the outer longitudinal profile of the or each annular platform extends over a distance greater than 20% and / or less than 30% of the total length of the outer longitudinal profile.

[0016] According to an advantageous embodiment of the invention, the inclination of the outer longitudinal profile of the or each annular platform relative to the nominal profile of the fluid flow oscillates along the circumference of at least one annular stator platform and at least one annular rotor platform, wherein the minimum inclination of the outer longitudinal profile of at least one annular rotor platform is greater than the minimum inclination of the outer longitudinal profile of at least one annular stator platform.

[0017] Advantageously, the minimum inclination of the outer longitudinal profile of at least one annular rotor platform is greater than 150% of the minimum inclination of the outer longitudinal profile of at least one annular stator platform.

[0018] According to an advantageous embodiment of the invention, the maximum value of the inclination of the outer longitudinal profile of the or each annular platform is opposite to the blade of the annular platform along the chord of the blade.

[0019] The present invention also relates to a method for determining the dimensions of at least one annular platform of a stator blade row and / or rotor blade row of a compressor stage of a turbine, the blade rows being alternately arranged and forming air gaps, the method comprising, for said or each annular platform, determining an inward and upstream tilt of the outer longitudinal profile of said annular platform relative to the nominal profile of a fluid flow, based on the air gap directly upstream; characterized in that the tilt of said or each annular platform oscillates along the circumference of said annular platform between a maximum value in front of the blades of said annular platform and a minimum value between each pair of adjacent blades of said annular platform.

[0020] According to an advantageous embodiment of the invention, at a nominal operating speed, the maximum value of the inclination of the outer longitudinal profile of the annular platform is aligned with the blades of the annular platform relative to the direction of fluid flow in the air gap directly upstream of the annular platform.

[0021] The features of this invention are of interest because they enable the optimization of the aerodynamic flow of fluids, precisely taking into account the specific characteristics of the flow in different air gaps, which can vary between the air gaps. They also enable the optimization of the aerodynamic flow of fluids under the most unfavorable manufacturing and assembly tolerance conditions. Attached Figure Description

[0022] Figure 1 This is a longitudinal cross-sectional view of the turbine;

[0023] Figure 2 It is a detailed longitudinal section view of the air gap between the stator blade row and the rotor blade row;

[0024] Figure 3 This is a schematic diagram showing the inclination of the inner surface used to guide fluid flow, taking into account manufacturing tolerances;

[0025] Figure 4 This is a schematic diagram of the velocity vector of the fluid flow in the air gap between the stator and rotor blade rows;

[0026] Figure 5 This is a schematic diagram of a longitudinal section of a row of stator blades, showing air reflow in a rotary joint with a rotor;

[0027] Figure 6 It is a schematic diagram of the inclination or slope of the inner surface used to guide fluid flow;

[0028] Figure 7 It is a detailed geometric representation of the inclination of the upper longitudinal profile of a row of stator or rotor blades on an annular platform.

[0029] Figure 8 This is a schematic diagram of the cyclical change in the platform tilt of a row of stator or rotor blades according to the present invention. Detailed Implementation

[0030] In the following description, the concepts of "inner" and "outer" refer to the radial direction relative to the turbine's main axis. Compared to the concept of "outer," the concept of "inner" expresses a closer position to the axis under discussion, and vice versa.

[0031] Figure 1 This is a longitudinal sectional view of an axial-flow turbine forming a jet propulsion system for an aircraft. The turbine 2 is housed within an external nacelle 4 via guide vanes 6 and retaining arms (not shown). The latter provides a rigid attachment between the nacelle 4 and the casing 8 of the turbine 2. The latter, running from upstream to downstream along the main axis X of the machine, essentially comprises a fan 10 (generally referred to as a "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 airflow F entering the nacelle 4 upstream of the turbine 2 splits into two airflows, F.1 and F.2, after the fan 10: a main flow F.1 forming an annular fluid flow circulating within the turbine engine 2, and a secondary flow F.2 forming an annular fluid flow concentric with the main flow F.1, defined by the casing 8 of the turbine engine 2 and the inner walls of the nacelle 4. The main flow F.1 and the secondary flow F.2 converge at the outlet of the turbine 2. This turbine architecture is well known to those skilled in the art and requires no further explanation.

[0032] The low-pressure compressor 12 and the high-pressure compressor 14 consist of alternating moving and stationary parts, more specifically, alternating rows of rotor blades and rows of stator blades. The rotor blades, or moving blades, are mounted on the rotor of the turbine engine, while the stator blades, or stationary blades, are mounted on the turbine engine housing 8. For this purpose, the inner surface used to guide the fluid flow of the main flow F.1 is formed by alternating moving and stationary annular platforms that create air gaps.

[0033] Figure 2The air gap E between the stator blades 22.1 row 22, commonly referred to as stator row 22, and the rotor blades 26.1 row 26, commonly referred to as row or rotor wheel 26, is schematically shown. The stator row 22 includes an inner shroud 22.2 forming an annular platform having an outer longitudinal profile 22.3. The inner shroud 22.2 supports a rotary seal 22.4 on its inner surface, which has a wiper 24.1 formed on the rotor 24. The rotor row 26 includes rotor blades 26.1 supported by the rotor 24. In this case, the latter includes a protruding ring 24.2 forming or supporting the inner platform 26.2, which has an outer longitudinal profile 26.3 substantially aligned with the outer longitudinal profile 22.3 of the platform 22.2 of the stator row 22. The air gap E is formed by a mechanical axial clearance between 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.

[0034] Figure 3 The diagram schematically illustrates the impact of manufacturing and assembly tolerances on the alignment between these adjacent platforms. Figure 2 The stator row 22 has a platform 22.2 and an upper longitudinal profile 22.3. The nominal profile N of the rotor row 26's platform is shown as a dashed line (center line). This profile is perfectly aligned with the profile of the upstream stator row. The extreme positions of this theoretical profile are indicated by dashed lines, corresponding to tolerances +T and -T. It is then observed that, at the upper tolerance limit +T, the profile forms a rising step, which is particularly disadvantageous from an aerodynamic point of view. In fact, the aerodynamic loss of a protruding rising step is twice as large as that of a descending step of the same magnitude. Furthermore, the aerodynamic loss of a rising step with rounded or chamfered edges is significantly reduced compared to the aerodynamic loss of rising and protruding steps (i.e., without rounding or chamfering). According to the invention, it can then be specified that profile 26.3 is inclined inward and upstream relative to the nominal profile N, and optionally a rounded or chamfered edge 26.3.2 is provided at its upstream edge 26.3.1, such that, at the maximum manufacturing and assembly tolerance (in this case +T), profile 26.3 does not form a rising step. Starting from the nominal profile, the inward and upstream slope of the profile is intended to lower the upstream edge relative to the downstream edge. However, it should be understood that the profile is not necessarily a straight line, and the slope discussed is not necessarily a rotation of the nominal profile. In fact, the shape of the profile (in this case, its curvature) can be modified to effectively lower the upstream edge.

[0035] about Figure 2 Especially Figure 3 The description just given also applies to the upper longitudinal profile of the platform of the stator bank directly downstream of the rotor bank.

[0036] Figure 4This is a schematic diagram of the fluid velocity vector in the air gap between the stator and rotor blade rows, showing both absolute and relative velocities (i.e., in a reference frame rotating with the rotor). Figure 4 The diagram illustrates two alternative configurations of a row of stator blades and a row of rotor blades, in this case, stator row 22 followed by rotor row 26, then stator row 22 again, and finally rotor row 26. For clarity of description, all stator rows are given the same reference numeral 22; however, it should be understood that these rows are not identical but may have common features relevant to the invention. The same applies to rotor rows with reference numeral 26.

[0037] exist Figure 4 In the diagram, the absolute velocity vector V1 of the airflow at the outlet of the first stator row 22 can be observed. This vector is oriented essentially along the chord of the upstream blade profile; it has an angle α1 relative to the axial direction, more precisely, this direction lies in the axial plane and is tangent to the upper longitudinal profile of the annular platform 22. This direction corresponds to the axial direction if the fluid flow is perfectly cylindrical, which is not necessarily the case. If viewed from the directly downstream rotor row 26, where the platform rotates at velocity U, the fluid flow follows the velocity vector W1. This relative velocity vector W1 of the airflow entering the rotor row 26 corresponds to vector V1, from which vector U1 has been subtracted, and has an angle β1 relative to the axial direction, which is opposite to and much larger than angle α1. The air gap E (in Figure 4 The physical displacement of the airflow from stator row 22 toward rotor row 26 in the (which is basically exaggerated) corresponds to vector V1, that is, in a fixed coordinate system, while the same flow has a velocity vector W1 relative to the blades of rotor row 26, which is basically different from V1.

[0038] Still refer to Figure 4 The airflow leaving the aforementioned rotor row 26 (the one on the left) has a relative velocity vector W2 relative to the row, which is oriented substantially along the chord of the airfoil blades of the row and forms an angle β2 relative to the axial direction. If the velocity vector U2 of the rotor row 26 corresponding to U and U1 is added to it, the absolute velocity vector V2 of the airflow is obtained, forming an angle α2 with respect to the axial direction, which is opposite to angle β2. However, since it is the rotor row 26 that distributes the fluid in the air gap E, it is necessary to consider the velocity vector W2 of the fluid in a relative coordinate system fixed to the rotor row in question to determine the distance the fluid travels in the air gap E.

[0039] Still refer to Figure 4The airflow exiting the second stator row 22 (on the right) directly in front of the aforementioned rotor row 26 has an absolute velocity vector V3, which forms an angle α3 with the turbine axis, similar to vector V1 and angle α1 at the output of the first stator row 22. The relative velocity of the fluid with respect to the rotor row 26 directly downstream is represented by vector W3. Similar to the detailed description above regarding the first stator row 22 (on the left side of the figure), the absolute velocity vector V3 should be considered to determine the distance the fluid travels in the air gap E.

[0040] In summary, the fluid flow in the air gap E between the stationary part 22 and the moving part 26 of the turbine is not necessarily axial, but rather actually follows the above-mentioned... Figure 4 The angles α1, β2, and α3 mentioned are tilt angles. These angles can be large and significantly affect the distance the fluid travels in the air gap.

[0041] However, fluid flow not guided by the wall (which is precisely the case in the air gap) will tend not to follow the tangential direction of the downstream edge of the upstream platform. This flow will tend to seep into the air gap in a radial direction toward the turbine axis. Therefore, the greater the path of this flow in the air gap, the more radially deflected it will be, and consequently, the greater the need for the inclination of the upper longitudinal profile of the annular platform and / or the rounding or chamfering of the upstream edge.

[0042] At the exit of the fixed section 22, the absolute velocity vector should be considered, while at the exit of the moving section 26, the relative velocity vector, that is, in a reference frame rotating with the moving section, should be considered. For air gaps with greater inclination and therefore longer routes, the upper longitudinal profile of the platform downstream of the air gap should be more inclined to minimize the risk of rising steps.

[0043] It should be understood that the angle of inclination of the fluid flow in the air gap is not constant throughout the turbine's speed and load range. Therefore, it is appropriate to consider one or more specific operating points of the turbine as, for example, one or more critical operating points for the turbine's specific consumption and / or the turbine's compressor operability.

[0044] Figure 5Another phenomenon affecting fluid flow in the air gap at the stationary section outlet is illustrated: leakage flow flowing beneath the platform of stator row 22. In reality, the seal between stator blade row 22 and rotor 24 is not perfect, as a certain leakage rate occurs between the wiper blades 24.1 of rotor 24 and the rotary seal 22.4 on the inner surface of the platform 22.2. This leakage rate depends primarily on the pressure difference between the upstream and downstream of stator blade row 22 and the clearance δ at the horizontal level of the rotary seal. This flow enters the downstream air gap, passes through the cavity of rotor 24, and is substantially perpendicular to the fluid flow towards the upstream air gap, thus altering the flow orientation in the longitudinal plane through the turbine axis, and this is reversed upstream and downstream.

[0045] Upstream, the leakage flow leaving the cavity is added to the fluid pulse and deflects it upwards. This deflection angle γ can be determined by the momentum P of the fluid before the leakage rate and the momentum P of the leakage rate. f The momentum is calculated by addition. Momentum is a vector quantity, and for fluid flow, it equals the velocity vector multiplied by the mass flow rate. The corrected momentum P of the fluid after leakage rate is calculated. c Then it equals P + P f Angle γ can be derived from this relationship.

[0046] Similarly, downstream, the leakage flow entering the cavity is added to the fluid flow and deflects it downwards by an angle γ', which is approximately equal to angle γ. Angle γ' can also be shifted by their respective displacements P' and P f The values ​​are added together to obtain the corrected fluid displacement P after the leakage rate. c This calculation method is an example and should be understood; other methods, especially computer simulation, can also be used.

[0047] Therefore, the fluid flow at the outlet of stator row 22 has an inward azimuth angle tilt, making it necessary to provide a larger rotor platform tilt directly downstream compared to the stator platform.

[0048] Figure 6 The external longitudinal profiles 22.3 and 26.3 of the continuous stator and rotor rows 22.2 and 26.2 are shown. These profiles have been corrected to optimize fluid flow, taking into account manufacturing tolerances and assembly, as well as the above-mentioned... Figure 4 and 5 The phenomena described. These contours 22.3 and 26.3 are theoretical contours and have an upstream and inward slope I relative to the nominal contour N. Si and I Ri (i is a positive integer corresponding to the number of rows of stator or rotor). These tilt angles I Si and I RiThis represents the radial reduction distance relative to the upstream edges 22.3.1 and 26.3.1 of the nominal profile N. These inclinations can be achieved by rotating the outer longitudinal profiles 22.3 and 26.3 by an angle α around the downstream edges 22.3.3 and 26.3.3. Si and α Ri They can also be obtained by rounding the upstream edges 22.3.1 and 26.3.1 of the outer longitudinal profiles 22.3 and 26.3.1, in which case the radius of curvature is R. Si and R Ri The arc (i is a positive integer corresponding to the number of rows of stator or rotor). According to... Figure 2 As already described in detail, manufacturing and assembly tolerances actually have the effect that the actual profile, meaning that turbines produced and assembled based on these theoretical profiles, will deviate from the theoretical profile within the tolerances in question. The worst-case scenario is when the actual profile is at its maximum tolerance facing outwards, thus creating an upward step. Therefore, Figure 6 The tilt angle dimensions shown are designed to minimize aerodynamic losses under these adverse conditions, within the constraints of manufacturing and assembly tolerances and the flow characteristics in the fluid flow, such as... Figure 5 As shown.

[0049] exist Figure 6 It was observed that the outer longitudinal profile 26.3 of the rotor row platform 26.2 has a greater inclination I than the outer longitudinal profile 22.3 of the stator row platform 22.2. S1 and I S2 Greater tilt I R1 and I R2 This is mainly due to the inward deflection of the flux in the air gap directly upstream of the rotor assembly. Figure 5 Similarly, the flux in the air gap directly upstream of the stator row is deflected outwards (as shown by the azimuth angle γ′). Figure 5 (The azimuth angle γ in the text). For example, regarding... Figure 4 The flow inclination (i.e., angles α1, β2, and α3) caused by the blade orientation can be influenced by increasing or decreasing this tendency. In fact, referring to the preceding description... Figure 4 It can be observed that angle β2 is greater than angles α1 and α3 (in absolute value, i.e., regardless of the sign of the angle relative to the main axis), which means that for the same air gap size, the flow path leaving rotor row 26 is greater than the flow path leaving stator row 22. In this case, the inclination at the upstream edge of the outer contour of the platform of stator row 22, which is directly downstream of the rotor row 26 under discussion, will increase. However, Figure 4The tilt angles α1, β2, and α3 shown are illustrative, as they can take other values, in particular the tilt angle of the flow at the outlet of some rotor rows can be greater than the tilt angle of the flow at the outlet of some rotor rows.

[0050] Figure 7 This is a detailed profile view of the inclination of the upper longitudinal surface of the annular stator or rotor platform. The figure shows the downstream edge of the annular rotor 26.2 or stator 22.2 platform on the left; and on the right is the upper longitudinal surface 22.3 or 26.3 of the adjacent stator 22.2 or rotor 26.2 platform. [The last sentence appears to be incomplete and possibly refers to a separate section.] Figure 3 and 6 The nominal profile N mentioned above is shown as a dashed line in the figure, taking into account the effect of manufacturing and / or assembly tolerance +T, which raises the upper longitudinal surface 22.3 or 26.3 relative to the upper longitudinal surface of the rotor 26.2 or stator 22.2 row located directly upstream. It can be observed that the upper longitudinal surface 22.3 or 26.3 includes a first portion, in this case the main portion, corresponding to the nominal profile N rotated by an angle α around the downstream edge 22.3.3 or 26.3.3. Si or α Ri And the second part corresponding to the rounded end 22.3.2 or 26.3.2, in this case having a radius of R. Si Or R Ri The arc. The first portion is advantageously tangent to the second portion. The rounding 22.3.2 or 26.3.2 extends along the main direction of fluid flow at a distance L1 corresponding to a portion of the total length L of the upper longitudinal surface 22.3 or 26.3, said portion may be between 20% and 30%. The main portion of the upper longitudinal surface 22.3 or 26.3 extends, in itself, along the length L2 of the remaining portion corresponding to the total length L of the upper longitudinal surface 22.3 or 26.3. It can be observed that the inclination I Si or I Ri It is the sum of two partial tilts: the partial tilt I1 produced by the rotation of the nominal profile N and the partial tilt I2 produced by the rounding 22.3.2 or 26.3.2. Each of these partial tilts I1 and I2 corresponds to tilt I... Si or I Ri A portion of it, advantageously between 40% and 60%, where I1 + I2 = I Si or I Ri .

[0051] Figure 8 This is a diagram of the stator 22 or rotor 26 segments of a turbine according to the present invention. See also: [Regarding...] Figure 6 As already described, the upper longitudinal profile 22.3 or 26.3 of the platform 22.2 or 26.2 of the stator 22 or rotor 26 rows slopes upstream and inward. Figure 8In the middle, the upward and inward inclination I of the upper longitudinal profile 22.3 or 26.3 of platform 22.2 or 26.2. Si or I Ri The platform oscillates cyclically between the maximum inclination at the blade level of 22.1 or 26.1 along its circumference and the minimum inclination between the blades in question. This cyclic variation of the inclination amplitude A and period S, due to the presence of dawn, allows for consideration of the azimuthal non-uniformity of the injection and withdrawal of the leakage flow in the air gap in front of the stator and rotor rows. In effect, the obstruction created by the blades directly downstream of the air gap produces a flow blocking effect, favoring flow into the air gap, just in front of the blades. Outside these regions, the flow exhibits a greater upward tendency in the pulse compared to the average flow. Therefore, it is advantageous to tilt the upper longitudinal profile of the platform more significantly in the regions affected by this blocking effect, i.e., in front of the blades. This then results in an oscillating tilt along the platform in its circumferential direction, preferably cyclically. The same applies to the rotor and stator rows; however, the blocking phenomenon may vary from row to row, depending on the blade orientation and size.

[0052] It should be noted that the oscillations and cyclic tilts described in detail above can be implemented independently of the effects of manufacturing tolerances and leakage recirculation under the toroidal stator platform, as per [reference to...]. Figure 5 In detail, the non-uniformity of the azimuth angle of the leakage flow injection and recovery in front of the annular stator and rotor platforms is not directly related to the upward running problems between two adjacent annular platforms caused by manufacturing tolerances and assembly, nor even to the effects of leakage reflow. This means that the minimum tilt angle value between the blades can be zero. Conversely, the tilt angle I between the blades of the annular rotor platform 26.2 is... Ri The minimum value can be non-zero and greater than the tilt angle I between the blades of the platform annular stator 22.2. Si The minimum value is zero or non-zero, thus avoiding upward movement due to manufacturing and assembly tolerances on the one hand, and compensating for the effects of leakage recirculation at the stator level on the other.

[0053] The tilted oscillation profile and blade alignment can be adjusted based on the effective flow direction of the fluid flow in the air gap directly upstream of the relevant blade. In fact, refer to... Figure 4 The discussion posits that the flow velocity in the air gap is not, in principle, axial (more precisely, located in the axial plane and tangent to the upper longitudinal profile of the annular platform), but rather inclined substantially along the profile of the receiving blade. The point or region of maximum inclination of the oscillating inclined profile can then be aligned with the leading edge of the blade along the blade profile, such as the chord of the blade. The same applies to the point or region of minimum inclination aligned with the space between each pair of adjacent blades.

[0054] like Figure 8 As shown, the oscillation amplitude A of the inclination of the upper longitudinal profile 22.3 or 26.3 of the stator row 22 or rotor 26 platform 22.2 or 26.2 can be greater than 0.05 mm and / or less than 0.15 mm. The oscillation pitch S is advantageously equal to the blade pitch, that is, the number of blades / 2πr, where r is the inner radius of the fluid flow.

[0055] However, it should be understood that these values ​​can vary and may deviate from the ranges described above. They depend on a number of parameters, such as, in particular, the turbine dimensions, manufacturing and assembly tolerances, the distance between air gaps, and the flow conditions in the fluid flow (especially the velocity).

Claims

1. A compression stage assembly of a turbine (2) forming an annular fluid passage (F.1) and including at least one alternating row of stator (22) and rotor (26) blades, annular platforms (22.2, 26.2) located within and defining the annular fluid passage (F.1); at least one annular stator platform (22.2) and / or at least one annular rotor platform (26.2) having an inward and upstream inclination (I) relative to the nominal profile (N) of the annular fluid passage (F.1). Si / I Ri The external longitudinal profiles (22.3, 26.3); Its features are, The inclination (I) of the external longitudinal profile (22.3, 26.3) of the annular platform (22.2, 26.2) relative to the nominal profile (N) of the annular fluid channel (F.1) is... Si / I Ri The value oscillates along the circumference of the annular platform (22.2, 26.2) between the maximum value relative to the blades (26.1, 22.1) of the annular platform (22.2, 26.2) and the minimum value between each pair of adjacent blades of the annular platform (22.2, 26.2).

2. The compression stage group according to claim 1, characterized in that, The inclinations of the outer longitudinal profiles (22.3, 26.3) of the annular platforms (22.2, 26.2) relative to the nominal profile (N) of the annular fluid channel (F.1) are respectively the radial distances I at the upstream edges (22.3.1, 26.3.1) of the outer longitudinal profiles (22.3, 26.3) relative to the nominal profile (N) of the annular fluid channel (F.1). Ri and / or I Si .

3. The compression stage group according to claim 2, characterized in that, The radial distance I of the inclination of the outer longitudinal profile (26.3) of the annular platform (22.2, 26.2) compared to the nominal profile (N) of the annular fluid channel (F.1). Ri and / or I Si The maximum and minimum values ​​have a difference A between 0.05 mm and 0.15 mm.

4. The compression stage group according to any one of claims 1 to 3, characterized in that, The inclination of the outer longitudinal profile (22.3, 26.3) of the annular platform (22.2, 26.2) relative to the nominal profile (N) of the annular fluid channel (F.1) is achieved by pivoting the outer longitudinal profile (22.3, 26.3) about the downstream edge (22.3.3, 26.3.3) of the outer longitudinal profile (22.3, 26.3) and / or by rounding the upstream edge (22.3.2, 26.3.2) of the outer longitudinal profile (22.3, 26.3).

5. The compression stage group according to claim 4, characterized in that, The rounded edges (22.3.1, 26.3.1) of the upstream edges (22.3.1, 26.3.2) of the outer longitudinal profiles (22.3, 26.3) of one or more annular platforms (22.2, 26.2) have radii of curvature R greater than 5 mm and less than 15 mm, respectively. Ri Or R Si .

6. The compression stage group according to claim 5, characterized in that, The rounded edges (22.3.1, 26.3.1) of the upstream edges (22.3.1, 26.3.2) of the outer longitudinal profiles (22.3, 26.2) of the annular platforms (22.2, 26.2) extend over a distance greater than 20% and less than 30% of the total length of the outer longitudinal profiles (22.3, 26.3).

7. The compression stage group according to claim 1, characterized in that, The inclination (I) of the external longitudinal profile (22.3, 26.3) of the annular platform (22.2, 26.2) relative to the nominal profile (N) of the annular fluid channel (F.1) is... Si / I Ri The minimum tilt (I) of the outer longitudinal profile (26.3) of at least one annular rotor platform (26.2) along the circumferential oscillation of at least one annular stator platform (22.2) and at least one annular stator platform (26.2) is as follows: Ri The minimum tilt (I) of the outer longitudinal profile (22.3) of at least one annular stator platform (22.2) is greater than that of the other two. Si ).

8. The compression stage group according to claim 1, characterized in that, The inclination (I) of the external longitudinal profile (22.3, 26.3) of the annular platform (22.2, 26.2) Si / I Ri The maximum value of ) is along the chord of the blade facing the blade (26.1, 22.1) of the annular platform (22.2, 26.2).

9. A method for determining the dimensions of at least one annular platform (22.2, 26.2) of a stator blade (22) row and / or rotor blade (26) row of a compression stage group of a turbine (2), the blade rows being alternately arranged and forming an air gap (E), the method comprising, for the annular platform (22.2, 26.2), determining, based on the air gap (E) directly upstream, an inward and upstream inclination (I) of the outer longitudinal profile (22.3, 26.3) of the annular platform relative to the nominal profile (N) of the annular fluid passage (F.1). Si / I Ri ); characterized in that, The inclination (I) of the ring platform (22.2, 26.2) Si / I Ri The value oscillates along the circumference of the annular platform (22.2, 26.2) between the maximum value in front of the blade (26.1, 22.1) of the annular platform (22.2, 26.2) and the minimum value between each pair of adjacent blades of the annular platform (22.2, 26.2).

10. The method according to claim 9, characterized in that, At the nominal operating speed, the orientation of the fluid flow in the air gap (E) directly upstream of the annular platform, and the inclination (I) of the outer longitudinal profile (22.3, 26.3) of the annular platform (22.2, 26.2). Si / I Ri The maximum value of ) is aligned with the blades (26.1, 22.1) of the annular platform (22.2, 26.2).

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