BE1023825B1 - TEST BENCH FOR AXIAL TURBOMACHINE WITH HORIZONTAL WIND TURBINE - Google Patents

Abstract

The invention relates to a test stand for an axial turbomachine, in particular for an airplane turbojet engine, comprising: a vertical inlet channel, a vertical outlet channel interconnected by a passage containing the turbomachine; at least one energy recovery wind turbine (14) driven by the turbomachine; the wind turbine comprising an axis of rotation (42) and several blades (30), each blade (30) comprising aerodynamic profiles (34) with ropes (40). At least one blade (30) comprises a rope (40) inclined at an angle α with respect to the axis of rotation (42) of the wind turbine, said angle α being between 64 ° and 81 ° and allows a recovery of without significantly disturbing the test conditions. The invention also relates to a method for recovering energy from such a test bench.

Description

TEST BENCH FOR AXIAL TURBOMACHINE WITH HORIZONTAL WIND TURBINE

Technical Field The invention relates to a test stand for a turbomachine. More particularly, the invention relates to a turbomachine test stand configured for energy recovery generated during a test.

Patent document WO 2012/171105 A1 discloses a test bench for a turbomachine comprising an energy recovery system. The system recovers the kinetic energy of a mixture of combustion gases and air moving in the test stand and converts this kinetic energy into electricity by means of a wind turbine. The turbomachine is located in a test chamber and the wind turbine is located in a tube downstream of the test chamber. The tube is commonly called "collector tube" in that it collects the combustion gases leaving the turbomachine. The high velocity of the combustion gases in the tube makes it possible to draw a minimum of ambient air around the turbomachine so as to satisfy the test conditions required in terms of the minimum air flow in the test chamber. The collector tube acts as a kind of pump of the gas mixture with a view to its expulsion, it also avoids localized inversions of the flow downstream of the turbomachine. The collecting tube may in particular be configured to absorb the sound waves downstream of the turbomachine. The wind turbine comprises blades with variable pitch to adapt to the different flow rates of the gas mixture reached depending on the size of the turbomachines tested; it is connected to an alternator / generator to convert the mechanical energy of the air flow (kinetic energy) into electricity. This teaching is interesting in that the wind turbine positioned in the collector tube receives a substantially laminar gas mixture flow. In addition, the tube limits the size of the wind turbine. However, the teaching is limited to turbine engine tests for which the speed and pressure of the exhaust gases, modified by the presence of the wind turbine in the tube, always guarantee the minimum ambient air suction of the chamber. necessary test for the test. Furthermore, the position of the wind turbine in the tube receiving a gas mixture of high temperature combustion products imposes operating constraints on the wind turbine which increases the cost. Moreover, the presence of a wind turbine disrupts flow flow through the test bench; so that the test conditions are disturbed. The operating mode of the turbomachine is influenced, and the measurements collected during the tests no longer correspond to the actual operating conditions. As a result, the test results are distorted.

TECHNICAL PROBLEM The invention aims to propose a turbomachine test bench solution that overcomes at least one disadvantage of the state of the art. More particularly, the invention aims to limit the influence of energy recovery during a turbomachine test on a test bench. The invention also aims to provide a robust and reliable bench solution.

TECHNICAL SOLUTION The subject of the invention is a test bench for a turbomachine capable of driving a flow of air, in particular for a turbojet engine, the test bench comprising: an inlet; output; a passage connecting the inlet to the outlet, and intended to receive the turbomachine during a test; at least one turbine for energy recovery from the air flow of the turbomachine, the wind turbine comprising an axis of rotation and several blades, each blade comprising aerodynamic profiles with ropes; remarkable in that at least one blade comprises a rope inclined at an angle with respect to the axis of rotation, said angle a being between 50 ° and 85 °.

According to an advantageous embodiment of the invention, at least one or for each blade, the majority or all of the ropes are inclined relative to the axis of rotation of an angle α between 64 ° and 81 °.

According to an advantageous embodiment of the invention, the angle a is commonly called wedging angle.

According to an advantageous embodiment of the invention, for at least one or for each blade, the angle a is between 75 ° and 85 ° at the blade head and / or for at least one or for each blade, the angle a is between 60 ° and 70 ° at the bottom of the blade.

According to an advantageous embodiment of the invention, at least one or each blade is designed so as to compensate, at least partially, the deformation of the blade due to the pressure difference, the gravity, and the centrifugal force, possibly a projection of water droplets, or any combinations thereof.

According to an advantageous embodiment of the invention, at least one or each blade has a leading edge and / or a trailing edge in the form of a hyperbola.

According to an advantageous embodiment of the invention, at least one or each blade has a generally straight leading edge, said edge being wrapped in a cylinder of radius less than or equal to 30 cm, or 20 cm or 10 cm.

According to an advantageous embodiment of the invention, the axis of rotation of the wind turbine is vertical, and possibly perpendicular to the axis of rotation of the turbomachine.

According to an advantageous embodiment of the invention, the wind turbine is capable of producing an electrical power of between 0.5 MW and 5MW, the test bench optionally comprising a device for projecting water droplets between the inlet and the outlet. exit.

According to an advantageous embodiment of the invention, the length of at least one or each blade is between 150 cm and 600 cm, or between 200 cm and 500 cm, or between 250 cm and 400 cm.

According to an advantageous embodiment of the invention, at least one or each blade has a blade root profile whose length is greater than twice the length at the blade head, and / or at least one or each blade has a profile in foot of blade whose thickness is greater than twice the thickness at the top of the blade.

According to an advantageous embodiment of the invention, the wind turbine comprises a hub to which the blades are fixed, the diameter of the hub is greater than or equal to 10%, or 25%, or the majority of the length of each blade.

According to an advantageous embodiment of the invention, the wind turbine extends over most of the width of the passage, for example over the majority of the width of the tunnel and / or the chamber, and / or the chimney.

According to an advantageous embodiment of the invention, the blade is fixed to the rotor by a dovetail-type fastener and / or via a fastening platform.

According to an advantageous embodiment of the invention, the compensation is from 10% to 50%, possibly 15% to 20% of the axial and / or radial deformation.

According to an advantageous embodiment of the invention, at least one or each blade comprises decreasing string lengths, possibly monotonically or continuously, from the rotor towards the outside of the wind turbine.

According to an advantageous embodiment of the invention, at least one or each blade comprises a decreasing thickness variation, possibly monotonically or continuously, of the rotor towards the outside of the wind turbine.

According to an advantageous embodiment of the invention, the turbojet engine is an airplane turbojet engine.

According to an advantageous embodiment of the invention, the wind turbine is a first wind turbine, the test bench further comprising a second wind turbine, at least one or each wind turbine comprises a vertical axis of rotation.

According to an advantageous embodiment of the invention, the passage comprises a corridor intended to accommodate the turbomachine, the corridor possibly being straight, the wind turbine being at a distance from said corridor.

According to an advantageous embodiment of the invention, the rotor comprises a hub with a plurality of grooves extending axially on its periphery and spaced circumferentially.

According to an advantageous embodiment of the invention, the blade root is fixed in a groove of the rotor by locking means, preferably by means of fixing screws and washers.

According to an advantageous embodiment of the invention, the test rig comprises at least one device for projecting water droplets upstream of the wind turbine or one of the wind turbines.

According to an advantageous embodiment of the invention, the or at least one of the projection devices is disposed directly upstream of the corresponding wind turbine, preferably at a distance of less than 3m, more preferably less than 1m, from said wind turbine.

According to an advantageous embodiment of the invention, the section of the inlet and / or outlet, at the height of the wind turbine along its axis of rotation, is between 2 m 2 and 200 m 2, preferably between 40 m 2 and 70 m 2.

According to an advantageous embodiment of the invention, the test bench comprises a bent portion connecting the vertical chimney to the chamber, said elbow comprising deflectors for guiding the flow of air from a vertical direction to a horizontal direction, the at least one of the wind turbines being disposed at the entrance of said elbow.

According to an advantageous embodiment of the invention, the or at least one of the wind turbines comprises systems for converting mechanical energy into electrical energy.

According to an advantageous embodiment of the invention, the wind turbine comprises from six to twenty blades, or from eight to fifteen blades, or from nine to twelve blades, possibly ten blades.

According to an advantageous embodiment of the invention, the inlet and / or outlet are each formed by a chimney, the chimneys being connected by the passage, the wind turbine being arranged in a chimney.

According to an advantageous embodiment of the invention, the blade is made of composite material, possibly with carbon fibers and / or organic matrix.

According to an advantageous embodiment of the invention, for at least one or for each blade, the angle difference α between the blade root and the blade head is between 20 ° and 30 °.

According to an advantageous embodiment of the invention, for at least one or each blade, one or each profile, has a rope whose length is between ten and fifteen times the thickness of said profile. The subject of the invention is also a method for recovering energy in a test bench for a turbomachine, in particular for an airplane turbojet engine, the wind turbine comprising blades with aerodynamic profiles having ropes, the method comprising the following steps a) installation of a turbomachine in the test stand; b) operating test of the turbomachine by driving a flow of air; c) energy recovery from the airflow; remarkable in that at least one blade comprises a rope inclined at an angle with respect to the axis of rotation of the wind turbine, said angle a being between 50 0 and 85 °, the bench possibly being in conformity with the 'invention.

Process according to claim 12, characterized in that during step c) recovery, the pressure difference between the upstream and the downstream of the wind turbine is between 10 Pa and 1000 Pa, or between 50 Pa and 500 Pa or between 80 Pa and 150 Pa.

Process according to one of Claims 12 to 13, characterized in that during step c) recovery, the speed of the air flow passing through the wind turbine is between 10 m / s and 100 m / s, or between 20 and m / s and 50 m / s, or between 25 m / s and 35 m / s.

Method according to one of claims 12 to 14, characterized in that during step c) recovery, the test bench recovers less than 10%, or 6% or 3% or 1% of the maximum power of the turbomachine.

According to an advantageous embodiment of the invention, the turbomachine; in particular the turbojet engine; is capable of exerting a thrust of at least 50 kN, or at least 200 kN, or at least 500 kN.

According to an advantageous embodiment of the invention, during step (b) test, the turbomachine generates a flow with a mass flow rate of air in the passage between 0.1kg / s and 3000kg / s, preferably between 200kg / s and 1200kg / s.

According to an advantageous embodiment of the invention, the speed of rotation of the or at least one of the wind turbines is between 50tr / min and 1000tr / min, preferably between 100tr / min and 500tr / min.

According to an advantageous embodiment of the invention, the wind turbine is placed upstream of the turbomachine and is configured so as to be able to operate with a pressure difference of 100 Pa. The invention also relates to the use of a rotor of wind turbine for recovering energy, the rotor having an axis of rotation and having a series of blades, each blade showing aerodynamic profiles with chordal axes; characterized in that at least one or each chord axis is inclined with respect to the axis of rotation by an angle of between 60 ° to 85 °.

Technical advantages

The measurements of the invention are interesting in that the test bench for axial turbomachine is able to recover in electricity the kinetic energy of the air flow generated in the bench by the testing of various models of turbomachines, without disturbing nor damage the device. Indeed, the wind turbine positioned in a vertical channel at the entrance or exit of the test stand is detached from the areas around the turbomachine, especially downstream and at the periphery, areas in which the air displacement velocities are high and their modification critical to the quality of the conditions of the test. In addition, the air velocity in the vertical channels is relatively lower than that in the areas around the turbomachine. The wind turbines, configured to rotate in such air velocity conditions, are able to generate a suitable electrical power while avoiding disturbance and / or damage to the device due to the particular inclination of the blades with respect to the axis of rotation of the rotor. Moreover, the air flow is substantially laminar in the vertical channels, which is favorable to the efficiency of the energy recovery.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will be better understood from the description and the drawings, in which: FIG. 1 represents a test bench according to the invention in which a turbomachine is mounted; axial. - Figure 2 sketches an axial view of a blade according to the invention. - Figure 3 is a representation of a cross section of a blade of a wind turbine according to the invention. FIG. 4 illustrates a diagram of the energy recovery method on a test bench according to the invention.

Description of an embodiment

In the following description, the axial term refers to the direction along the axis of rotation of the wind turbine. The term radial refers to the direction perpendicular to the axis of rotation of the wind turbine. Each length is measured according to the principal direction of the corresponding entity.

FIG. 1 is a simplified representation of a test stand 2 of the engine 4, more particularly a test stand 2 for an axial turbomachine 4. The turbomachine 4 can be used to propel an aircraft (not shown).

The turbomachine is in this case an airplane turbojet engine. The turbojet engine 4 is capable of producing a thrust of 100 kN, or even exceeding 550 kN depending on the model. Its installation at test stand 2 is carried out in various circumstances. The turbojet engine 4 can pass to the test bench as part of a new development or for quality control after manufacture, or following maintenance. During its operation the turbomachine propels a breath. When in test stand 2, the surrounding air is also driven by the breath. The air flow 14, because of its mass and its speed, represents a substantial kinetic energy. Part of this kinetic energy is intended, in the context of the invention, to be recovered. For the testing of such turbojet engines 4, the test bench 2 is configured to generate an air mass flow rate of between 0.1 kg / s and 3000 kg / s, preferably between 200 kg / s and 1200 kg / s.

The test bench 2 forms an infrastructure, a construction. It comprises an inlet vertical chimney 8 and an outlet vertical chimney 10. They are interconnected by a passage 6. The two vertical chimneys (8; 10) allow vertical air intake and exhaust, in elevation by relative to the passage 6. The passage 6, as the vertical chimneys (8; 10) are crossed by the air flow 14.

The passage 6 may comprise an elongated corridor 12. Its length may be greater than 10 m, or 30 m; or 50 m. The length of the passage 12 allows the flow in a straight line of the air flow 14; or air circulation 14; by limiting the whirlpools. In order to limit the resistance to flow, in particular at the inlet of the turbojet engine 4, the passage 12 may have a passage cross section greater than or equal to 20 m 2, preferably greater than or equal to 50 m 2. The passage section, or free section, can be measured in a test chamber 16 of the turbojet engine 4, at the level of the bell which is mounted at the inlet of the turbojet engine 4. The passage section can be observable over at least a quarter of the length of the corridor 12, preferably on the majority. The turbojet engine 4 is mounted in the test chamber 16, possibly by means of a fixing arm 18. The arm 18 can extend vertically from the ceiling of the corridor 12, in the manner of a column or a post. The arm 18 makes it possible to mount the turbojet engine 4 with an offset and to center the latter in the middle of the corridor 12. The centering is vertical and horizontal.

The test bench 2 comprises a wind turbine 22 located in the inlet 8. The wind turbine 22 is inside the inlet chimney 8 which forms a sleeve around it. The wind turbine 22 makes it possible to convert into mechanical or electrical energy a part of the kinetic energy of the air flow 14 inherent in the test of the turbojet engine 4. It can be observed that the wind turbine 22 has a vertical axis of rotation 42. . The wind turbine 22 may be located in a bent portion 20 of the test bench 2, portion connecting the inlet chimney 8 to the corridor 12. Alternatively, the wind turbine 22 is at a distance from the corridor. That is, it is surrounded only by the inlet chimney 8. The wind turbine 22 comprises a series of blades 30, also called vanes. These blades 30 are distributed around the central hub 31 of the rotor of the wind turbine 22. During the rotation of the blades 30 about their axis of rotation 42, they move in a plane perpendicular to the axis of rotation 42. They scan a disk. They can sweep the majority of the passing section of the passage 6, or the inlet chimney 8. Each section can be measured in a plane perpendicular to the axis of rotation 42, at the blades 30. The wind turbine 22 comprises in addition, conversion systems (not shown) of mechanical energy into electrical energy. These may include a control (not shown) determining the electrical power to be converted. The conversion system can be housed in the hub, or be axially offset. The system may include a rotating electrical machine, such as an alternator. The wind turbine 22 is configured to recover an electric power of between 0.5MW and 10MW. At the junction 20 between the inlet chimney 8 and the passage 12, the bench 2 is equipped with a series of deflectors 28. They make it possible to return the air coming down from the inlet chimney 8 in a horizontal direction. They extend horizontally, and cross the entire corridor 12 along its width. They have curved profiles.

In the embodiment presented here, the vertical chimneys (8; 10) comprise noise reduction devices, in this case acoustic baffles 24. The wind turbine 22 can be located between the acoustic baffles 24 and the baffles 28. The inlet chimney 8 comprises in this case several rows of acoustic baffles 24. At the entrance to the passageway 12, the bank 2 optionally has a gate 38 for intercepting debris capable of disturbing the test and damaging the turbojet engine. 4.

Optionally, the test stand 2 comprises, a device 32 for projecting water droplets, disposed directly upstream of the wind turbine 22; preferably at a distance of less than 1m, more preferably less than 0.5m, from said wind turbine 22. This projection device 32 is configured to increase the density of the air flow 14, and thus increase the potentially recoverable energy. The density of the air flow 14 can be increased by 10%. The water is favorably projected in the form of a mist of water which mixes with the air flow 14, the projection being carried out on a portion greater than 50%, preferably greater than 80%, of the cross section of the vertical channel. entry 8.

The flow of water projected into the inlet chimney 8 is adjusted so that the relative humidity of the air downstream of the projection device 32 may be greater than 95%, preferably greater than 99.9%. The water projection device 32 is intended to produce a water flow rate of up to 150 kg / s, preferably a water flow rate of between 2 kg / s and 40 kg / s. This measurement is interesting in that the increase in the density of the air mass moving in the test bench increases its kinetic energy. Increasing the kinetic energy of the air stream 14 is advantageous for energy recovery, its high relative humidity is also favorable to the efficiency of the turbojet engine.

In an alternative embodiment (not shown) the test bench according to the invention may comprise several wind turbines in the vertical input channel and / or in the vertical outlet channel. The axes of rotation could be horizontal.

The term "wind turbine" is a commonly used term for a wind turbine, or wind turbine, to convert mechanical energy into electrical energy. The "wind turbine" can also be understood as a fan for generating an air flow, in this case by transforming electrical energy into mechanical energy.

Figure 2 shows a plan view of a wind turbine blade. The blade 30 may correspond to one of the wind turbine blades 30 shown in connection with FIG. 1. Although reference is made to a single blade 30, the following description may be applied to each wind turbine blade.

The blade 30 has a leading edge 36 and a trailing edge 38. The leading edge 36 is generally straight. It deviates less than 25 cm, preferably less than 10 cm from an average straight line. For its part, the trailing edge 38 generally forms a hyperbola, or a concave curve.

The blade 30 has a succession of aerodynamic profiles 34. These aerodynamic profiles 34 move along the blade 30. In particular, their lengths decrease from the inside to the outside; away from the axis of rotation 42. The thicknesses of the profiles 34 follow the same progression. The profile 34 at the bottom 44 of the blade 30 is longer and thicker than at the blade head 30. The head 46 and the foot 44 of the blade 30 form its radially opposite ends. The free face of the blade head 46 is flat. The length of the blades 30 is measured from the hub to which they are attached. The length of the blades 30 is understood as their free length.

For at least one or for each blade 30, the centers of gravity of the profiles 34 describe a curve along the blade 30. This curve can be configured to compensate, at least partially, the deformation of the blade 30 due to the pressure difference, the gravity, and the centrifugal force, or possibly the projection of water droplets, or any combinations thereof. The compensation can correct a minority part of the axial and / or radial deformation, possibly by 15%.

Figure 3 is a representation of an aerodynamic profile 34 of a blade 30 of the wind turbine according to the invention. The profile 34 may be a section made perpendicularly to the main elongation of the blade 30. The blade 30 corresponds to a wind turbine blade presented in relation with FIGS. 1 to 2.

The profile 34 of the blade 30 comprises a leading edge 36 and a trailing edge 38 interconnected by a rope 40, as well as by a lower surface 48 and an extrados surface 50. It is observed that the rope 40 is inclined relative to the axis of rotation 42 of the rotor. The arrow represents the angle of inclination of the rope 40 relative to the axis of rotation 42, which according to the invention is inclined at an angle α between 50 ° and 85 °. By convention, the angle a would be equal to 0 ° in case of parallelism between the rope 40 and the axis of rotation 42 of the wind turbine. The angle has gradually decreased along the blade 30, from its head; or free end; at his foot, end tied to the hub. The angle may be between 64 ° and 81 °. This measurement is interesting in that the adjustment of the inclination of the blades 30 of the wind turbine allows to establish an optimal energy recovery, possibly of the order of 10%, while limiting the impact on the flow of energy. The angle α varies along the blade 30. The angle has increased towards the blade head 30. The increase can be monotonous or continuous from the blade root 30 to the blade head. The angle at the top of the blade can be at least 10 °, or 15 ° or 20 °, or 25 ° higher than the angle a at the bottom of the blade.

The plane 52 according to which the blade 30 is moving is represented. This plane 52 is perpendicular to the axis of rotation 42. Because of the deformations of the blade, for example due to gravity, the plane 52 may be substantially conical; keeping the axis of rotation 42 as a central axis.

The blade can be made of a composite material. This material comprises a matrix and a fibrous reinforcement intermingled. The matrix can be organic. The fibers may be carbon, glass. This embodiment promotes the reduction of the mass, and therefore the moment of inertia.

Figure 4 outlines a method of energy recovery in a test bench. The test bench may correspond to that detailed in FIG. 1. The method may comprise the following steps: a) installation 100 of a turbomachine in the test bench; b) operating test 102 of the turbomachine which drives a flow of air in or through the test bench; c) energy recovery 104 from the air flow, d) projecting 106 water droplets into the test stand; optional.

The steps b) test 102 and c) energy recovery 104 can be performed simultaneously. Step b) operating test 102, may include phases during which the turbomachine operates without any measurement being performed, and phases where measurements are made under the test. The measurements may be measurements of the thrust or the power of the turbomachine. The measurements may be measurements of vibration, pressure, and / or temperature. Step c) energy recovery 104 can be performed during both types of phases, or only in the absence of measurement. Step c) energy recovery 104 may be intermittent. It can therefore be carried out between measurement phases on the turbomachine. It can also be synchronized with step d) splashing water droplets. This optional step is also performed discontinuously.

Claims (15)

claims 1. Test stand (2) for a turbomachine (4) capable of driving an air flow (14), in particular for a turbojet engine, the test rig comprising: - an inlet (8); an outlet (10); - a passage (6) connecting the inlet (8) to the outlet (10), and for receiving the turbomachine (4) during a test; at least one turbine (22) for energy recovery from the air flow (14) of the turbomachine (4), the wind turbine (22) comprising an axis of rotation (42) and several blades (30), each blade (30) comprising aerodynamic profiles (34) with ropes (40); characterized in that at least one blade (30) comprises a rope (40) inclined at an angle α relative to the axis of rotation (42), said angle a being between 50 ° and 85 °. 2. Bench (2) according to claim 1, characterized in that for at least one or for each blade (30), the majority or all of the ropes (40) are inclined relative to the axis of rotation (42) an angle between 64 ° and 81 °. 3. Bench (2) according to one of claims 1 to 2, characterized in that for at least one or for each blade (30), the angle a is between 75 ° and 85 ° at the head (46) of blade and / or for at least one or for each blade (30), the angle a is between 60 ° and 70 ° in foot (44) blade. 4. Bench (2) according to one of claims 1 to 3, characterized in that at least one or each blade (30) is designed to compensate, at least partially, the deformation of the blade (30) in because of the pressure difference, the gravity, and the centrifugal force, possibly a projection of water droplets, or any combinations thereof. 5. Bench (2) according to one of claims 1 to 4, characterized in that at least one or each blade (30) has a leading edge (36) and / or a trailing edge (38) in form of hyperbole. 6. Bench (2) according to one of claims 1 to 5, characterized in that at least one or each blade (30) has a leading edge (36) generally straight, said edge being wrapped in a cylinder of radius less than or equal to 30 cm, or 20 cm or 10 cm. 7. Bench (2) according to one of claims 1 to 6, characterized in that the axis of rotation (42) of the wind turbine (22) is vertical, and possibly perpendicular to the axis of rotation (42) of the turbomachine (4). 8. Bench (2) according to one of claims 1 to 7, characterized in that the wind turbine (22) is capable of producing an electrical power of between 0.5 MW and 5MW, the test bench (2) optionally comprising a device (32) for projecting water droplets between the inlet (8) and the outlet (10). 9. Bench (2) according to one of claims 1 to 8, characterized in that the length of at least one or each blade (30) is between 150 cm and 600 cm, or between 200 cm and 500 cm , or between 250 cm and 400 cm. 10. Bench (2) according to one of claims 1 to 9, characterized in that at least one or each blade (30) has a profile (34) at the foot (44) of the blade whose length is greater than twice the length at the head (46) of blade, and / or at least one or each blade (30) has a profile (34) at the bottom (44) of blade whose thickness is greater than twice the thickness at the top (46) blade. 11. Bench (2) according to one of claims 1 to 10, characterized in that the wind turbine (22) comprises a hub (31) to which the blades (30) are fixed, the diameter of the hub (31) is greater or equal to 10%, or 25%, or the majority of the length of each blade (30). 12. A method of energy recovery in a test stand (2) for a turbomachine (4), in particular for an airplane turbojet, the wind turbine (22) comprising blades (30) with aerodynamic profiles (34) having ropes (40), the method comprising the following steps: a) installing (100) a turbomachine (4) in the test stand (2); b) operating test (102) of the turbomachine (4) by driving an air flow (14); c) recovering (104) energy from the air stream (14); characterized in that at least one blade (30) comprises a rope (40) inclined at an angle α relative to the axis of rotation (42) of the wind turbine (22), said angle a being between 50 ° and 85 °, the bench being optionally according to any one of claims 1 to 11. 13. The method of claim 12, characterized in that during step c) recovery (104), the pressure difference between the upstream and downstream of the wind turbine (22) is between 10 Pa and 1000 Pa or between 50 Pa and 500 Pa, or between 80 Pa and 150 Pa. 14. Method according to one of claims 12 to 13, characterized in that during step c) recovery (104), the speed of the air flow (14) passing through the wind turbine (22) is between 10 m / s and 100 m / s, or between 20 m / s and 50 m / s, or between 25 m / s and 35 m / s. 15. Method according to one of claims 12 to 14, characterized in that during step c) recovery (104), the test bench (2) recovers less than 10%, or 6% or 3% or 1% of the maximum power of the turbomachine (4).