FR3025564B1 - VARIABLE-TIMING AUB SYSTEM FOR A TURBOMACHINE - Google Patents

Abstract

Variable-pitch blade system (14) for a turbomachine, comprising a first annular row of variable pitch vanes extending substantially over a first circumference (U1), characterized in that it comprises a second annular row of variable-pitch blades (14) extending substantially over a second circumference (U2) different from said first circumference, said second row being located directly downstream of said first row.

Description

Variable valve blade system for a turbomachine

TECHNICAL AREA

The present invention relates to a variable-pitch blade system for a turbomachine.

STATE OF THE ART

A system of this type comprises an annular row of variable-pitch stator vanes (also called VSVs) which are carried by an outer annular casing, generally a compressor of the turbomachine. Each blade comprises a blade which is connected at its radially outer end by a platen with a substantially circular contour to a substantially radial cylindrical pivot which defines the axis of rotation of the blade and which is guided in rotation in a corresponding orifice of the outer casing . The radially inner end of the blade of each blade generally comprises a second cylindrical pivot extending along the axis of rotation of the blade and guided in rotation in an orifice of an inner ring of the compressor. The radially outer end of the outer pivot of each vane is connected by a connecting rod to a control ring rotated around the outer casing by cylinder actuating means or the like. The rotation of the control ring is transmitted by the rods to the outer pivots of the blades and rotates about their axes.

The angular setting of the stator vanes in a turbomachine is intended to adapt the geometry of the compressor to its operating point and in particular to optimize the efficiency and the pumping margin of this turbomachine and to reduce its fuel consumption in the various flight configurations. .

Each of these blades is movable in rotation about its axis between a first "open" or "full opening" position in which each blade extends substantially parallel to the longitudinal axis of the turbomachine, and a second "Close" or "quasi-closing" position in which the blades are inclined relative to the axis of the turbomachine and thus reduce the air passage section through the blade grid.

As part of the increase in dilution rates to improve the performance of turbomachinery, and especially for turboprops, engine architectures lead to increasingly small pressure compressors for which control of the games becomes increasingly difficult. . The control of games in variable pitch blade systems is therefore an important issue.

For an overall aerodynamic load of the order of 0.4 (given by the formula AH / (n.u2), where ΔΗ is the enthalpy between the inlet and the outlet of a turbomachine, where n is the number of stages rotor, and u their rotational driving speed), it is necessary to decrease the relative pitch (given by the formula S / C, C being the blade string and S being the inter-blade pitch) between the blades until to a value of about 0.5 so as to sufficiently guide the flow of air.

However, to reach this relative step value, the blades of the blades which must remain at a distance from each other not to come into contact, can cover only about 50% of the blade rope. A downstream portion of the blade of each blade is thus not covered by the plate and is found in "cantilever" vis-à-vis the plate. A radial clearance is required between the radially outer end or end of this "cantilevered" portion and the outer casing, to allow the blades to pivot without risk of blockage in the operating range of the compressor. We find the same difficulty between the foot or the radially inner end of the blade and the inner shell, where the presence of a game in the cantilever is necessary to ensure the free rotation of the blade. However, this results in compression efficiency losses, which are all the greater as the compressor is small because the games can not be fully scaled.

The present invention provides a simple, effective and economical solution to this problem.

DESCRIPTION OF THE INVENTION The invention proposes a variable-pitch blade system for a turbomachine, comprising a first annular row of variable-pitch vanes extending substantially over a first circumference, characterized in that it comprises a second an annular row of variable pitch vanes extending substantially over a second circumference different from said first circumference, said second row being located directly downstream of said first row. The invention thus proposes, within the same stage or the same grid, to ensure the deflection of the air by means of two blades in tandem rather than a single blade. In the prior art, a compression stage comprises an annular array of variable pitch vanes and a movable rotor wheel. The annular rows of variable-pitch vanes of two consecutive compression stages are separated from each other by a moving wheel. The present invention differs from this prior art in particular in that two annular rows of blades variable pitch are adjacent, without a movable wheel is interposed between these rows. In other words, according to the invention, a compression stage would comprise two (or a pair of) annular rows of variable pitch vanes and a movable wheel which would be arranged upstream or downstream of rows of variable pitch vanes. Thus, the number of rows of variable-pitch vanes of this stage would be twice that of moving wheel.

This invention solves the above technical problem. Indeed, because of the use of two separate rows of blades, the aforementioned radial clearances can be reduced or even eliminated by significantly reducing or even removing the above parts cantilever blades.

The present invention may comprise one or more of the following characteristics, taken separately from each other or in combination with each other: each vane of each row has at at least one of its radially outer and inner ends a substantially contoured plate circular, - each blade of each row comprises a blade having a leading edge and a trailing edge, the blade of each blade comprises at least one of an upstream portion comprising said leading edge and a downstream portion comprising said trailing edge, which is cantilever vis-à-vis the plate of the dawn- the system is configured so that the blades of the rows can be wedged so that each blade of the second row extends in the extension of a blade of the first row and the leading edge of the blade of the second row is separated by a relatively small clearance of the trailing edge of the blade of the first row, - each blade of each row has at at least one of its radially outer and inner ends a pivot defining an axis of rotation of the blade, - the blades of the second row are arranged substantially staggered relative to to the blades of the first row, and - the second row is substantially nested in the first row, - a pitch between the blades of the first row is substantially equal to the corresponding pitch between the blades of the second row, - a rope of the blades of the first row is substantially equal to a corresponding chord of the blades of the second row, - a chord of the blades of the first row is substantially less than one pitch between the blades of the first row, - a chord of the blades of the second row is substantially less than one step between the blades of the second row.

The present invention also relates to a turbomachine, characterized in that it comprises at least one system as described above.

DESCRIPTION OF THE FIGURES The invention will be better understood and other details, characteristics and advantages of the invention will emerge more clearly on reading the following description given by way of nonlimiting example and with reference to the appended drawings in which: FIG. 1 is a partial schematic half-view in axial section of turbomachine variable valve blade stages according to the prior art; FIG. 2 is a partial schematic view from above of a turbomachine variable valve blade system according to the prior art; and FIG. 3 is a partial schematic view from above of a turbine engine variable-pitch blade system according to the invention.

DETAILED DESCRIPTION

FIG. 1 diagrammatically shows, in axial section, a portion of a high-pressure compressor 10 of a turbomachine, such as an aircraft turboprop, having a plurality of compression stages, each stage comprising an annular row of moving blades 12 carried by the rotor (not shown) of the turbomachine and an annular row of fixed vanes 14 forming rectifiers carried by a casing 16 of the stator of the turbomachine. The angular orientation of the blades 14 is adjustable to optimize the gas flow in the compressor 10, the blades 14 being commonly called variable-pitch vanes.

Each blade 14 comprises a blade 18 and a radially outer cylindrical pivot 20, connected by a plate 22 extending perpendicularly to the axis 24 of the blade in a housing 26 corresponding to the housing 16. The plate 22 of each blade 14 has a substantially circular contour and thus substantially forms a disk. The radially inner surface 28 of the plate 22 is aligned with the inner wall 30 of the housing so as not to oppose the gas flow.

The cylindrical pivot 20 of each vane 14 extends inside a radial cylindrical chimney 32 of the casing 16 and its radially outer end is connected by a connecting rod 34 to a control ring 36 which surrounds the casing 16 and which is associated with actuating means (not shown) for rotating it in one direction or the other around the longitudinal axis of the housing 16 to drive the vanes 14 of an annular row in rotation about their axes 24 .

The vanes 14 are movable in rotation about their axes 24 between a closed or quasi-closed position and an open or fully open position.

In the closed position, the blades 18 of the blades are inclined relative to the longitudinal axis of the turbomachine and define between them a minimum section of air passage in the vein. The blades 14 are brought into this position when the turbomachine is at low speed or at idle, the flow of air flowing in the compressor then having a minimum value.

In the open position, the blades 18 of the vanes extend substantially parallel to the axis of the turbomachine so that the outlet angle of the vanes corresponds to optimum operation of the compressor for a flow rate close to the maximum flow rate . The blades 14 are brought into this position when the turbomachine is at full throttle, the flow of air flowing in the compressor then having a value close to the maximum value.

In the prior art, the variable-pitch system of each stage comprises a single annular row of blades 14, as can be seen in FIG.

As explained in the foregoing and shown in Figure 2, it is sought to reduce the relative pitch (given by the formula S / C, C being the rope of the blades 14 and S being the inter-blade pitch) between the blades 14 until to a value of about 0.5 so as to sufficiently guide the flow of air. However, to reach this value, the plates 22 of the blades 14 cover only about 50% of the blade string 14. A downstream portion 38 of the profile 18 of each blade 14 is not covered by the plate 22 and is found in "cantilever" vis-à-vis the plate 22. A radial clearance R (Figure 1) is required between the top or the radially outer end of this portion 38 cantilever and the outer casing 16, to allow the blades 14 to rotate without risk of blockage in the operating range of the compressor. However, this results in compression efficiency losses, which are all the greater as the compressor is small because the games can not be fully scaled. The invention overcomes this problem by adding another annular row of variable valve blades within the aforementioned system, that is to say within a compression stage of the prior art.

FIG. 3 represents an embodiment of the invention in which the elements described in the foregoing are referenced by the same figures.

It is noted that the first row of blades 14 variable pitch, left in the drawing, extends substantially on a first circumference U1 which passes substantially through the pivots 20 of the blades 14. The second row of blades 14 wedging variable, right in the drawing, extends substantially on a second circumference U2 which passes substantially through the pivots 20 of the blades 14. The circumferences U1, U2 are coaxial and at an axial distance from one another. In other words, although the rows of blades 14 can be nested one in the other, in the axial direction, these rows are not confused. The rows of blades 14 are therefore adjacent, the second row being here located directly downstream of the first row.

The plates 22 of the blades are similar to those of the prior art. On the other hand, each blade 14 of the prior art is here replaced by two successive blades 14 which can thus have an individual rope C2, C3 weaker than that C of the prior art. The strings C2, C3 of the vanes 14 of FIG. 2 are substantially equal to and lower than the chord C of FIG. 1. Each chord is measured between the leading edge and the trailing edge of the blades of the blades of a row. . We denote C1, the chord of the complete system of FIG. 2, namely the chord of the two rows of blades 14, measured between the leading edge of a blade of the first row and the trailing edge of the dawn of the second row, which is arranged directly downstream of the blade of the first row with respect to the air flow. The rope C1 therefore integrates the clearance between the trailing edge of the first-stage dawn and the leading edge of the second-stage dawn. The rope C1 is substantially equal to the rope C.

S1 and S2 are further noted the inter-blade pitch within the first and second rows, respectively. These steps S1, S2 are substantially equal to each other and to the pitch S. Moreover, for each row, the rope C2, C3 of the blades is smaller than the pitch S1, S2 between the blades of the row.

As can be seen in FIG. 3, the blade 18 of each blade 14 of each row can comprise an upstream part comprising the leading edge and / or a downstream part comprising the trailing edge, which is cantilevered to platinum 22 of dawn. However, compared with the prior art, it is noted that the platinum covers more than 80% or even 90% of the rope C1, C2 of the blades 14.

As explained above, each blade 14 of each row is rotatable about the axis defined by its pivot 20. As seen in Figure 3, the system according to the invention is configured so that the blades 14 rows may be wedged so that each blade of the second row extends in line with a blade of the first row and the leading edge of the blade of the second row is separated by a relatively weak of the trailing edge of the dawn of the first row (this game being the aforementioned one integrated in the calculation of the rope C1). It is better understood in this position why the rows of blades can be likened to a single row of tandem variable pitch blades.

In the example shown, the blades 14 of the second row are arranged substantially staggered with respect to the blades 14 of the first row. On the other hand, as indicated above, the second row is substantially nested in the first row.

The blades 14 of the two rows can be oriented by means of a single control ring 36 similar to those used in the prior art. The radially outer end of the pivot 20 of each blade 14 of each row is then connected by a rod to a control ring 36, which surrounds the housing 16 and which is associated with actuating means (not shown) allowing the rotate in one direction or the other. The control ring 36 is schematically represented by dashed lines. Three different positions of the ring 36 are shown here. The ring 36 can indeed extend upstream of the rows, between the rows, or downstream of the rows. When the ring 36 is upstream or downstream, a rotation of the ring 36 will cause the blades 14 to rotate about their axes in the same direction. On the contrary, when the ring 36 is between the rows, a rotation of the ring 36 will cause a rotation of the blades of the first row in the opposite direction of the direction of rotation of the blades of the second row.

As explained in the foregoing, the invention makes it possible to improve the sealing of the blades with variable pitch. It also reduces the stresses between the blade and the plate because each plate maintains a blade much lighter and undergoing much less aerodynamic efforts than in the single-row configuration of blades. It therefore reduces the connection radius and thickness of the profiles in the foot and at the top of the blades which has the effect of improving aerodynamic performance. In addition, partial regime, the closing law of the blades can be different for the first row and the second row. If we close less the second row than the first row, we can greatly reduce the blockage losses while maintaining the same exit angle and thus improve the partial regime yield and pumping margin. This performance is increased especially as the blades in tandem have better performance in terms of resistance to incidence. However, the blades undergo very strong partial-regime effects. The result is very positive from an aerodynamic point of view.

Claims (10)

A variable-pitch vane system (14) for a turbomachine, having a first annular row of variable-pitch vanes extending substantially over a first circumference (U1) and a second annular row of vanes (14). independent variable timing and extending substantially over a second circumference (U2) different from said first circumference, said second row being located directly downstream of said first row, each blade (14) of each row having at least at its radially outer end a pivot (20) defining an axis of rotation of the blade, characterized in that said radially outer end of each blade (14) of each row is connected to said pivot by a plate (22) with a substantially circular contour, and in that each platen covers more than 80% of the rope (C2, C3) of the corresponding blade, 2. System according to claim 1, wherein each plate (22) covers more than 90% of the rope (C2, C3) of the corresponding blade. 3. System according to claim 1 or 2, wherein each blade (14) of each row comprises a blade (18) having a leading edge and a trailing edge. 4. The system of claim 3, wherein the pay (18) of each blade (14) comprises at least one of an upstream portion having said leading edge and a downstream portion comprising said trailing edge, which is in cantilevered vis-à-vis the plate (22) of the dawn, 5. System according to claim 3 or 4, wherein it is configured so that the blades (14) rows can be wedged so that each blade of the second row extends in the extension of a blade of the first row and that the leading edge of the blade of the second row is separated by a relatively small clearance of the trailing edge of the blade of the first row. 6. System according to claim 5, wherein the sum of the strings (C2, C3) of a blade of the first row and the blade of the second row, which extends in the extension of the dawn of the first row, is smaller than the rope (C1) measured between the leading edge of the dawn of the first row and the trailing edge of the dawn of the second row, which extends in the extension of the dawn of the first row. 7. System according to one of the preceding claims, wherein the blades (14) of the second row are arranged substantially staggered relative to the blades of the first row. 8. System according to one of the preceding claims, wherein the second row is substantially nested in the first row. 9. System according to one of the preceding claims, wherein: - a pitch (S1) between the blades (14) of the first row is substantially equal to the pitch (S2) corresponding between the blades of the second row, and / or - a rope (C2) of the blades of the first row is substantially equal to a corresponding rope (C3) of the blades of the second row, and / or ~ a rope (C2) of the blades of the first row is substantially smaller than a pitch (S1 ) between the blades of the first row and / or, - a rope (C3) of the blades of the second row is substantially less than a pitch (S2) between your blades of the second row. 10. Turbomachine, characterized in that it comprises at least one system according to one of the preceding claims.