Flux distortion device for a test machine

Abstract

The invention relates to a flow distortion device (100) configured to be mounted in a flow channel of a test machine, the device comprising a grid and a grid support (101), said grid support comprising an inner annular portion (102) and an outer annular portion (104) connected by reinforcing arms (106), said outer annular portion being coaxial with, and surrounding said inner annular portion, said reinforcing arms (106) extending radially and being distributed circumferentially around an axis of said inner and outer annular portions so as to form at least three intervals (108) between said reinforcing arms, in which every two adjacent intervals (108) have different angle values. Figure to be published with the abbreviation: [Fig. 3]

Description

Title of the invention: Flux distortion device for a testing machine Technical field of the invention

[0001] The invention relates to a flow distortion device, in particular for a testing machine, for example, an aero-acoustic testing machine. State of the prior art

[0002] In the context of aero-acoustic testing, it is known to install a flow distortion device in the upstream part of a flow vein, so as to be able to simulate different aerodynamic phenomena, such as the presence of an aircraft wing, the ground or the aircraft fairing near the engine.

[0003] [Fig. 1] illustrates a part of a test machine 1 of the prior art. This comprises a vein 2 of axis X whose dimensions are reduced compared to the real dimensions of a turbomachine, for example of a ratio 4. The vein 2 is delimited by an external casing 3, a machine 4 comprising a rotating shaft 5 being mounted in the vein. This shaft is integral with a disc 6 carrying blades 7, simulating for example a fan rotor.

[0004] Upstream of the disc 6 and the blades 7 is mounted a flow distortion device 8. The latter is thus mounted in an area simulating an air intake sleeve of a turbomachine. The device 8, better visible in [Fig. 2], comprises a grid 9 extending in a radial plane, and a reinforcement 10 located downstream of the grid 9.

[0005] The grid 9 is for example formed from a mesh of braided or welded wires, the diameter of the wires, the shape and the dimensions of the mesh being a function of the aerodynamic phenomenon to be simulated.

[0006] The reinforcement 10 comprises a radially internal annular part 11 and a radially external annular part 12, connected by rectilinear arms 13 extending between the internal 11 and external 12 annular parts. The arms 13 each extend in the radial direction.

[0007] The reinforcement 10 makes it possible to hold the grid 9 in position in order to prevent it from being torn off under the effect of the stresses which may be applied during operation. The external annular part 12 of the reinforcement 10 is fixed using flanges to the external casing 3.

[0008] In operation, the reinforcement 10 vibrates according to natural modes of several orders, some of the natural modes falling within the frequency range corresponding to normal operation of the testing machine. These vibrations can cause the grid to break if it enters into resonance. Furthermore, in order to take into account the vibrations of the reinforcement, it must be instrumented using sensors, which increases the complexity of machine 1 and calculations, and requires dynamic monitoring during testing.

[0009] In operation, the blades 7 encounter at each revolution the succession of wakes from the reinforcing arms, thus undergoing a variation in the aerodynamic stress at a frequency linked to the number of arms and the rotation speed of the wheel 6. The specific vibration modes of these blades 7 can be stressed at different speeds.

[0010] In order to avoid the aforementioned drawbacks, it is necessary to reduce the impact of the vibrations of the reinforcement, by modifying its geometry so that the natural modes are located outside the frequency range corresponding to normal operation.

[0011] One solution for this is to increase the thickness or width of the arms or the internal annular part. However, this significantly reduces the air inlet section, which disrupts the test to be carried out. Furthermore, the reinforcement is a mechanically welded structure and it is difficult to precisely modify the dimensions of such a structure.

[0012] The invention aims in particular to provide a simple, effective and economical solution to the aforementioned problems. Summary of the invention

[0013] For this purpose, the invention proposes a flow distortion device configured to be mounted in a flow vein of a testing machine, the device comprising a grid and a grid support, said grid support comprising an inner annular portion and an outer annular portion connected by reinforcing arms, said outer annular portion being coaxial with and surrounding said inner annular portion, said reinforcing arms extending radially and being distributed circumferentially around an axis of said inner and outer annular portions so as to form at least three intervals between said reinforcing arms, in which each two adjacent intervals have different angle values.

[0014] Thus, the blades of the moving impeller encounter the successive wakes of the reinforcement arms at irregular intervals over one revolution of the moving impeller and the probability of requesting a multiple mode of the engine speed is lower.

[0015] For example, the grid may include a large mesh attached to the reinforcing arm by welding and a fine mesh attached by twisted wires to the reinforcing or large mesh arms.

[0016] The reinforcing arms may be distributed circumferentially around the axis of revolution of the inner and outer annular parts.

[0017] A gap may extend in the plane of the flux distortion device and may be included between two adjacent reinforcement arms.

[0018] According to one embodiment, the angle values ​​of two adjacent intervals may have a variation of 8% to 20% relative to each other.

[0019] For example, the number of reinforcement arms can be between 3 and 12.

[0020] Each interval can have an angle between 20° and 80°.

[0021] At most two intervals can be formed by the reinforcing arms having the same angle value.

[0022] The outer annular portion may comprise fastening means configured to cooperate with fastening means of the testing machine.

[0023] The diameter of the internal annular part may be between 5% and 20% of the maximum diameter of the vein. The internal diameter of the external annular part may be equal to the diameter of the vein, for example the vein tested upstream of a bladed wheel of the test machine to avoid steps. This vein diameter may be between 250 mm for small-scale test machines or small engines and more than 3400 mm for high-power engine tests with a high dilution ratio.

[0024] Each reinforcement arm can obstruct less than 4.5% of the radial section of the vein.

[0025] Each reinforcement arm can be straight

[0026] A testing machine is also proposed comprising an air flow vein in which is located at least one bladed wheel rotating along an axis of the vein, in which it comprises a flow distortion device as mentioned above, located upstream of the bladed wheel, in the direction of flow of the air flow. Brief description of the figures

[0027] [Fig-1] represents a schematic half-sectional view of a testing machine of the art prior,

[0028] [Fig.2] represents a perspective view of an example of a flow distortion device of the prior art,

[0029] [Fig.3] represents a front view of a flow distortion device according to the invention,

[0030] [Fig.4] represents, on the right, the stresses produced by the distortion device of [Fig.2] and undergone on the blades of the testing machine over one revolution of the blades and represents, on the left, the stresses produced by the distortion device of [Fig.3] and undergone on the blades of the testing machine over one revolution of the blades. Detailed description of the invention

[0031] With reference to [Fig. 3], a flux distortion device 100 is proposed to reduce the risks of stressing a multiple mode of the regime of a test machine for example the test machine 1 of [Fig. 1]. The flux distortion device 100 comprises a grid support 101 comprising an inner annular portion 102 surrounded by an outer annular portion 104. The inner and outer annular portions are coaxial and connected by reinforcing arms 106. The reinforcing arms 106 extend radially and are distributed circumferentially around the axis of revolution of the annular portions. Each reinforcing arm 106 is rectilinear.

[0032] Each two adjacent reinforcing arms 106 define an interval 108 bordered radially on the outside by the external annular part 104 and radially on the inside by the internal annular part 102 and circumferentially by said two reinforcing arms 106.

[0033] The inner annular portion 102 and the outer annular portion 104 are made of steel. The reinforcing arms 106 are made of metal, for example steel.

[0034] A mesh grid is arranged in the plane of the flow distortion device on the grid support 101. A grid may be fixed to the outer annular portion 104 and / or to the reinforcing arms 106, for example by welding or by twisted wires. Said grid is for example formed from a mesh of wires braided or welded together, the diameter of the wires, the shape and the dimensions of the mesh being a function of the aerodynamic phenomenon to be simulated.

[0035] The axis of revolution of the annular parts coincides with the longitudinal axis of the testing machine, when the flow distortion device 100 is mounted in the testing machine 1.

[0036] To avoid stressing the natural modes of the test machine, in particular the natural modes of the blades 7, each two consecutive intervals 108 have different angle values. In particular, between each two consecutive intervals 108 having a variation in the angle value of 8% to 20% is provided with respect to each other.

[0037] For example, two intervals 108A and 108B have the same angle value 35°. At most, two intervals have the same angle value.

[0038] The external annular part 108 is provided with orifices 110 capable of receiving screws for fixing the external annular part 101 to the casing 3 of the testing machine 1.

[0039] The diameter of the internal annular part 102 is for example between 60 and 75 mm and the diameter of the external annular part 104 is between 450 and 550 mm.

[0040] Each reinforcing arm 106 is sized to obstruct less than 4.5% of the radial section of the air flow vein 2. The presence of the reinforcing arm 106 in the air flow vein 2 therefore has a low impact on the tests to be carried out.

[0041] In Figure 4a, curve 202 represents the stresses produced by the flow distortion device 8, according to the prior art of [Fig.2], over one revolution of the bladed disc 7. The stresses of curve 202 are regularly distributed over one revolution and are more likely to stress a harmonic of the blades 7.

[0042] In Figure 4b, curve 204 represents the stresses produced by the flow distortion device 100 of [Fig. 3], over one revolution of the bladed disc 7. The stresses of curve 204 are irregular, that is to say, the peaks of the stresses are spaced by unequal distances. This makes it possible to significantly reduce the risks of exciting the blades 7 according to a natural mode in a simple and inexpensive manner.

Claims

Claims

1. A flow distortion device (100) configured to be mounted in a flow duct (2) of a testing machine, the device comprising a grid and a grid support (101), said grid support comprising an inner annular portion (102) and an outer annular portion (104) connected by reinforcing arms (106), said outer annular portion being coaxial with and surrounding said inner annular portion, said reinforcing arms (106) extending radially and being distributed circumferentially around an axis of said inner and outer annular portions so as to form at least three gaps (108) between said reinforcing arms, wherein each two adjacent gaps (108) have different angle values.

2. The device (100) of claim 1, wherein the angle values ​​of two adjacent intervals (108) have a variation of 8% to 20% relative to each other.

3. Device (100) according to claim 1 or 2, wherein the number of reinforcing arms (106) is between 3 and 12.

4. Device (100) according to one of the preceding claims, in which each interval (108) has an angle between 20° and 80°.

5. Device (100) according to one of the preceding claims, wherein at most two intervals (108) formed by the reinforcing arms (106) have the same angle value.

6. Device (100) according to one of the preceding claims, wherein the external annular part (108) comprises fixing means configured to cooperate with fixing means of the testing machine (1).

7. Device (100) according to one of the preceding claims, in which the diameter of the internal annular part (102) is between 5% and 20% of the maximum diameter of the vein (2), the internal diameter of the external annular part (104) is equal to the diameter of the vein (2).

8. Device (100) according to one of the preceding claims, in which each reinforcing arm (106) obstructs less than 4.5% of the radial section of the vein (2).

9. Testing machine (1) comprising an air flow vein (2) in which is located at least one bladed wheel (7) movable in rotation along an axis of the vein, which machine comprises a device for flow distortion (100) according to one of claims 1 to 7, located upstream of the movable impeller, in the direction of flow of the air flow.

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