AIRCRAFT TURBOMACHINE COMPRISING BLADE PITCH CONTROL BY LOCAL PRESSURE MEASUREMENTS

Abstract

A computer (10) such as a FADEC includes a module (11) for correcting the pitch of fixed or rotating blades of an aircraft turbomachine in order to reduce their noise emissions, by acting on actuators (9) that rotate the blade mounting axes. This module primarily uses measurements taken by pressure sensors (14) installed on or near the blades, which detect, in particular, the possibility of noise occurring due to flow separation at the blade surface. (See Figure 7 for abbreviations)

Description

Title of the invention: AIRCRAFT TURBOMACHINE COMPRISING BLADE PITCH CONTROL BY LOCAL PRESSURE MEASUREMENTS

[0001] The invention relates to an aircraft turbomachine equipped with blade pitch control by local pressure measurements.

[0002] Developments in aircraft turbomachinery research suggest the future use of devices with high bypass ratios and large diameters, in order to increase propulsive efficiency and reduce fuel consumption and pollutant emissions. Some of these turbomachines will not be enclosed, meaning they will have wheels with blades directly exposed to the outside air. Others will include several bladed wheels arranged in succession along the turbomachine, for example, with two propellers having different, even counter-rotating, rotational speeds, or a single propeller combined with a stator wheel belonging to the turbomachine's stator and therefore composed of fixed blades. Larger numbers of propellers or stators are also being considered.

[0003] It is further envisaged that the blades may have variable pitch, that is to say, a variable angle of incidence relative to the axis of the turbomachine, in order in particular to improve efficiency according to the phases of flight or the characteristics of the airflow around the blades. This implies that the blades are mounted on axes all oriented in the radial direction of the turbomachine, and pivoting by means of actuators. The blades of each wheel may optionally have different pitch values ​​that can be independently adjusted from one another.

[0004] A marked disadvantage of turbomachinery, especially unfaired turbomachinery, is their noise level, which is also limited by regulations. The noise emitted results from the inherent noise of the blades, produced mainly by the passage of the boundary layer that develops on the blades at the trailing edge of the blades, and from interaction noise between the blade wheels when there are several, produced mainly by the tip vortices of the blades of one wheel, which impact the wheel with following blades.

[0005] There are possibilities for reducing the acoustic emissions of turbomachinery by modifying the design of the blades and surrounding surfaces of the turbomachine, for example by coating them with layers that absorb acoustic vibrations. However, these methods have limitations. They are less suitable for unshod blades, for which the surrounding surfaces are...

[0006] The noise levels emitted vary considerably depending on the circumstances and flight parameters, in particular the turbomachine speed and the characteristics of the flow along them and through the paddle wheels.

[0007] The primary object of the invention is to provide a device capable of reducing the noise emitted by wheels with blades, in particular unfaired, according to the circumstances and parameters of the flight.

[0008] A general definition of the invention is an aircraft turbomachine comprising: a wheel with blades distributed around a hub, the blades having variable pitch by being mounted on the hub by axes pivoting around directions radiating around the hub; actuators for adjusting the blade pitch; a computer controlling the actuators according to operating parameters of the turbomachine; characterized in that it comprises pressure sensors mounted on blade surfaces and / or turbomachine surfaces adjacent to the blades, said surfaces being exposed to external air flows around the turbomachine, and a computer module, informed by said sensors, estimating corrections to the blade pitch which would attenuate acoustic noise produced by the blades and contributing to controlling the actuators according to said pitch corrections.

[0009] Noise reduction is achieved by actively adjusting the blade pitch based on ambient pressure measurements taken either on the blades themselves or in their vicinity. The pressure can be static or unsteady. The pitch corrections can be independent for each blade. Pressure sensors may or may not be present on all blades, or only on some of them. The pitch corrections can be determined based on preliminary tests and according to flight conditions, flow parameters, aircraft speed or turbomachine speed, and the relative need to reduce this noise compared to other constraints.

[0010] It should be emphasized that pressure measurements on or near the blades make it easier to determine the pitch corrections suitable for reducing acoustic emissions than, for example, direct measurements of this acoustic emission, which have many sources; an important cause of noise is the appearance of turbulence on the surface of the blades, which is easy to correlate with measured pressure parameters.

[0011] A successful implementation of the invention will often depend on the correct positioning of the sensors. According to preferred characteristics, these can be placed on the blades at heights between 40% and 95% (or, even more preferably, between 40% and 80%), with a height of 0% corresponding to an inner radius of the blades, and a height of 100% to an outer radius; at chord positions between 0% and 50% (even more preferably, between 5% and 20%), with a chord position of 0% corresponding to a leading edge of the blades, and a position of 100% corresponding to an outer radius; corresponding to a trailing edge; and to the extrados of the blades.

[0012] Even more preferably, the computer module is favorably arranged to impose (or at least submit to the actuator control modules) the pitch corrections based on an estimate of the appearance of airflow separations on the blade surfaces, at the measurement location or elsewhere, particularly downstream of the sensors on the blade, towards the trailing edge.

[0013] The module can be further informed by other sensors to complement the pressure measurements: such sensors can be acoustic or aeromechanical sensors, which respectively measure the noise emitted and the forces exerted either in the blades or by the blades on other parts of the turbomachine.

[0014] The device of the invention is advantageously integrated into a FADEC computer, to which the aforementioned module will then belong.

[0015] Preferred applications of the invention will relate to turbomachines whose wheel with blades will be unfaired, or to turbomachines which will include a second wheel with blades having aerodynamic interactions (at the origin of interaction noise) and in relative rotation with said wheel with blades.

[0016] Another aspect of the invention is a method for adjusting the pitch of variable-pitch blades of an aircraft turbomachine, the blades being mounted on a hub by axes pivoting about directions radiating around the hub; characterized in that it comprises pressure measurements of an atmosphere adjacent to the blades; computer estimations of blade pitch corrections that attenuate an acoustic noise produced by the blades; and controls for blade pivoting actuators to apply said corrections.

[0017] In some principal embodiments, the turbomachine comprises two blade wheels which follow one another in a longitudinal direction of the turbomachine, the variable pitch blades being present on at least one of said wheels; the wheels can then correspond to two counter-rotating propellers; or a first of the wheels is rotating about a longitudinal axis of the turbomachine, and a second of the wheels is fixed.

[0018] The invention will now be described in more detail in its various aspects, characteristics and advantages by means of the following figures, annexed by way of pure limitation and which detail preferred embodiments:

[0019] - [Fig.1] illustrates an unfaired turbomachine;

[0020] - [Fig.2] illustrates the variable timing of such a turbomachine;

[0021] - the [Fig.3], the flow characteristics around the blades and the effects of mo modifications to their calibration;

[0022] - the [Fig.4], the possible arrangement of the sensors;

[0023] - the [Fig.5], another arrangement, with a different connection to the computer;

[0024] - the [Fig.6] is a diagram of blades;

[0025] - the [Fig.7], a diagram of the computer; and

[0026] - [Fig.8] explains the timing control method.

[0027] The turbomachine of [Fig. 1] comprises an outer skin, or hub, 1 of the shape of The approximately ovoid shape is equipped with two wheels 2 and 3 with blades 4 opening directly to the outside. This embodiment relates to an unfaired turbomachine, lacking a nacelle enclosing the blades 4; however, the invention would also be beneficial to faired turbomachines. The blades 4 are shown here at the rear of the turbomachine, near a nozzle 5, but they could be at the front without affecting the invention, the invention also being applicable, for example, to an air intake fan. The wheels 2 and 3 with blades are shown on respective rotor rings 6 and 7, but they could also (or only one of them) belong to the stator of the turbomachine, the blades 4 then being fixed. In general, the term "hub" will refer to the part or parts, including the rotor or stator rings of the turbomachine, around which the blades 4 are distributed, as well as all the contents of the outer skin 1.

[0028] As mentioned, the invention will also be applicable to turbomachines comprising a single wheel with 4 blades, or a greater number of wheels.

[0029] Figure 2 shows that the blades 4 have variable pitch, meaning that the blades 4 pivot about radial axes R, radiating from a central longitudinal axis X of the turbomachine along which the wheels 2 and 3 are arranged successively. For this purpose, they are mounted on shafts 8 which are rotated about the respective radial axes R by respective actuators 9, attached to rings 6 and 7. The pitch angles of the individual blades 4 can all be identical in each of the wheels 2 and 3, or, conversely, all different.

[0030] The actuators 9 are controlled by a computer 10, and more specifically a FADEC computer (Figures 4 and 7; FADEC being an aeronautical abbreviation for "Full Automatic Digital Engine Control," designating a computer that automatically adjusts the operating parameters of the turbomachine, particularly during flight). The computer 10 comprises various modules 11, 12, and 13 for correcting the pitch of the blades 4, which are sensitive to sensors or other information (rotational speed, Mach number, temperature, etc.) on the operation of the turbomachine. Together, they contribute to the pitch of the blades 4. By processing the information they receive, they send pitch correction notifications to a control module 22, which synthesizes these notifications and acts on the actuators 9. This discussion will focus on module 11, which is specific to the invention.It receives measurements originating from pressure sensors 14, and possibly from acoustic sensors 15 and aeromechanical sensors 16. The pressure sensors 14 can be placed. on the blades 4 or in their vicinity, for example between them, on the rings 6 and 7, or on the outer skin 1, for example between the wheels 2 and 3. The important criterion is that they can measure a pressure representative of that exerted on the blades 4. Preferably, and in accordance with the representations in figures 3 to 6, the pressure sensors are placed on an extrados face 17 of the blades 4, at a height (along the radial axis R) between 40% and 95%, or better still between 40% and 80% (the height H being at 0% at the inner radius Ri of the blade 4, and 100% at the outer radius Re, which correspond respectively to the junction with the axis 8 and the outer edge 18); and their position on the chord 19 joining a leading edge 20 to a trailing edge 21 of the blade 4 considered is advantageously between 0% and 50% of the length of the chord 19 counted from the leading edge 20, and preferably around 10%, for example between 5% and 20%. The [Fig.[Fig. 4] indicates that the sensors 14 can transmit their measurements to the computer 10 by telemetry; [Fig. 5] shows that they can also do so by means of wires passing through the blades 4 or under the outer skin 1, which also houses said computer 10.

[0031] The acoustic sensors 15 that can also be used can be placed in the same locations as the pressure sensors 14. The aeromechanical sensors 16 can be placed either on the blades 4 or on other parts of the turbomachine; they can consist of strain gauges or existing sensors, such as torque measurement sensors on propellers; the forces measured can be internal, in particular present within the blades 4, or exerted between different parts of the turbomachine, in particular the hubs of the wheels 2 and 3, directly or indirectly by the blades 4.

[0032] The flow phenomena that the pressure sensors 14 allow us to understand through their measurements are described by means of [Fig. 3]. Air arrives at a blade 4 at an angle of attack V which makes an angle A with the direction of the chord 19 of the blade 4. As a result, a pressure P++ on an intrados face 23 is greater than a pressure P- - on the extrados 17. These pressures P++ and P- - vary on the intrados 23 and the extrados 17, with the pressure P- - normally decreasing towards the trailing edge 21. Flow separation may occur at a sufficient distance from the leading edge 20, giving rise to a turbulent zone 24 originating from significant acoustic emissions.

[0033] The lower portion of [Fig. 3] illustrates that reducing the angle of attack A to a smaller value A', with the angle of attack speed remaining unchanged V, results in the pressure on the lower surface 23 decreasing and becoming P+, while the pressure on the upper surface 17 increasing and becoming P-. The turbulent zone 24 is then likely to disappear. This explains why the blade pitch settings 4 have an effect on acoustic emissions.

[0034] This can be further explained by means of [Fig. 8]. The upper line Po indicates the total surrounding pressure, which is assumed to be uniform over a blade 4. The line Pi expresses the pressure distribution measured over a profile of the blade 4, more precisely at a constant height H on the upper surface 17, the value of which decreases constantly towards the trailing edge 21. This line, whose general evolution is known, is estimated by means of the measurement made by a sensor 14, possibly a single one located nearby. The difference AP between the lines Po and Pi corresponds to an unsteady pressure component that can be expressed by a local Mach number. If this number reaches a threshold, flow separation is to be expected. Decreasing the pitch angle to A' raises the line Pi to Pf, thus reducing the difference AP and the local Mach number at each point of the flow on the upper surface 17.

[0035] An analogous process could be applied by using measurements by sensors 14 placed on the intrados 23, which would then measure a pressure P2 equal to the surrounding pressure (still equal to Po) increased this time by an unsteady component AP* whose calculation would still allow to determine (indirectly) the Mach number at the extrados 17, and to determine the desirable pitch correction for the blade 4. Adaptations of the process to sensors 14 placed elsewhere would be feasible.

Claims

Demands

1. Aircraft turbomachine comprising a wheel (2, 3) with blades (4) distributed around a hub, the blades having variable pitch by being mounted on the hub by shafts (8) pivoting about directions (R) radiating around the hub; actuators (9) for adjusting the blade pitch; a computer (10) controlling the actuators according to operating parameters of the turbomachine; characterized in that it comprises pressure sensors (14) mounted on surfaces of the blades and / or surfaces of the turbomachine adjacent to the blades, said surfaces being exposed to external airflows around the turbomachine, and a module (11) of the computer, informed by said sensors, estimating corrections to the blade pitch that would attenuate acoustic noise emitted by the blades, and contributing to controlling the actuators (9) according to said pitch corrections.

2. Aircraft turbomachine according to claim 1, characterized in that the sensors (14) are placed on the blades at heights (H) between 40% and 95%, a height of 0% corresponding to an inner radius (Ri) of the blades, and a height of 100% to an outer radius (Re).

3. Aircraft turbomachine according to claim 1 or 2, characterized in that the sensors are placed on the blades, at chord positions between 0% and 50%, a chord position of 0% corresponding to a leading edge (20) of the blades, and a position of 100% corresponding to a trailing edge (21).

4. Aircraft turbomachine according to claim 1 or 2, characterized in that the sensors are placed on the blades, at chord positions between 5% and 20%.

5. Aircraft turbomachine according to any one of claims 2 to 4, characterized in that the sensors are placed on an extrados (17) of the blades.

6. Aircraft turbomachine according to any one of claims 1 to 5, characterized in that the computer module is arranged to submit pitch corrections based on an estimate (AP, AP*) of the occurrence of flow separations on the blade surfaces.

7. Aircraft turbomachine according to any one of claims 1 to 6, characterized in that the module (11) is also informed by acoustic (15) and / or aeromechanical (16) sensors, respectively measuring acoustic noise and forces exerted either on the blades or on other parts of the turbomachine.

8. Aircraft turbomachine according to any one of claims 1 to 7, characterized in that the computer (10) is a FADEC computer.

9. Turbomachine according to any one of claims 1 to 8, characterized in that the wheel (2, 3) is unshod.

10. Turbomachine according to any one of claims 1 to 9, characterized in that it comprises a second wheel with blades having aerodynamic interactions and in relative rotation with said wheel.

11. A method for adjusting the pitch of variable-pitch blades (4) of an aircraft turbomachine comprising pressure sensors (14) mounted on surfaces of the blades and / or surfaces of the turbomachine adjacent to the blades, the blades being mounted on a hub (1) by shafts (8) pivoting about directions (R) radiating around the hub; characterized in that it comprises pressure measurements of an atmosphere adjacent to the blades; computer (10) estimations of blade pitch corrections that attenuate acoustic noise produced by the blades; and controls for blade pivoting actuators (11) to apply said corrections.

12. Method according to claim 11, characterized in that the turbomachine comprises two wheels (2, 3) of blades which follow one another in a longitudinal direction of the turbomachine, the variable pitch blades (4) being present at least one of said wheels.

13. Method according to claim 12, characterized in that the wheels correspond to two counter-rotating helices.

14. Method according to claim 12, characterized in that a first of the wheels rotates about a longitudinal axis of the turbomachine, and a second of the wheels is fixed.

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