FR3046196B1 - TURBINE MACHINE TURBINE DISPENSER - Google Patents

Abstract

The invention relates to a turbomachine turbine distributor comprising a plurality of circumferentially distributed vanes defining between them guide and fluid acceleration channels, characterized in that at least two successive channels comprise flow sections. which accelerate the fluid in an off-set manner, the offset between the accelerations in the channels being such that the indirect acoustic waves generated in said channels by the fluctuations of the temperature of the entropic-type fluid are out of phase and at least partially compensate for each other, or even cancel.

Description

GENERAL TECHNICAL FIELD AND PRIOR ART

The present invention relates to turbomachine turbine distributors.

More particularly, it relates to the reduction of noise emissions from turbomachinery and in particular from aircraft engines.

A non-negligible share of noise emissions from aeronautical engines comes from the combustion chamber (~ 20% takeoff on CFM engines, for example).

The combustion noise is generated mainly by two mechanisms.

On the one hand, the expansion of gases during unsteady combustion directly generates acoustic waves in the combustion chamber. These acoustic waves propagate at the speed of sound and flow through the high pressure and low pressure turbine to add to other sources of noise. This mechanism is called "live".

On the other hand, the combustion chamber generates temperature fluctuations which are convected by the flow downstream of the combustion chamber (entropic waves). These temperature fluctuations or entropic waves do not generate noise as long as they are convected at constant speed, and generate acoustic waves when they are accelerated in the turbine.

This indirect mechanism is illustrated in FIGS. 1a, 1b and 2a and 2b, in which the state of a temperature fluctuation (FIGS. 1a and 2a) is shown at two different times and propagates in a nozzle 1 with the fluid carried by it, and the state of the possible pressure fluctuation in the conduit 1 at these two times (Figures lb and 2b). The nozzle 1 has a narrowing 2 at the passage of which the fluid is accelerated. As long as the temperature fluctuation propagates to constant section (FIG. 1a), no pressure fluctuation is generated in the conduit (FIG. 1b). On the other hand, the passage of the narrowing 2 by the fluctuation of temperature (FIG. 2a) generates a fluctuation of pressure (FIG. 2b) and therefore an indirect combustion noise.

For a general presentation of these mechanisms, it will be advantageous to refer to the following articles:

Comparison of Direct and Indirect Combustion Noise Mechanisms in a Model Combustor, AIAA Journal, Vol. 47, No. 11 (2009), pp. 2709-2716, M. Leyko, F. Nicoud, and T. Poinsot.

"The Journal of Sound and Vibration," Volume 330, Issue 16, August 1, 2011, pp. 3944-3958, M. Leyko, Journal of Sound and Vibration, Vol.

S. Moreau, F. Nicoud, T. Poinsot.

It has been shown that indirect combustion noise can be up to 10 times higher than direct source noise.

A general object of the invention is therefore to propose a solution for reducing the noise of indirect origin.

It is known from US3572962A a compressor (stator) compressor in which a stator vane has zones (4,5,6) offset from one another in the circumferential direction, so that the air of the wake of a rotor blade impinges two zones (4 + 6, 5, or even 35, 36) of the same area at staggered instants so that the acoustic waves produced at the stator vane divide into two out of phase halves. The circumferential offset of the areas of the blade is dimensioned so that the phase shift of the acoustic waves produces a destructive interference of the fundamental frequency.

This document does not, however, focus on the problem of indirect noise due to entropic waves.

GENERAL PRESENTATION OF THE INVENTION

The invention proposes a solution for reducing the indirect noise generated by temperature fluctuations during fluid acceleration.

It proposes in particular a turbomachine turbine distributor comprising a plurality of circumferentially distributed vanes defining between them guide and fluid acceleration channels, characterized in that at least two successive channels comprise flow sections which accelerate the fluid in an off-set manner, the offset between the accelerations in the channels being such that the indirect acoustic waves generated in said channels by fluctuations in the temperature of the entropic-type fluid are out of phase and at least partially compensate, or even cancel each other out .

In one particular embodiment, it comprises a succession of several channels of different types which is repeated at the circumference of the dispenser, the law of the areas along a channel of a given type being distinct from that along a another type of channel, so that the fluid acceleration in a given type channel is shifted with respect to the fluid acceleration in a channel of another type. The number of channel types can be at least two.

The succession of channels of different types may be repeated depending on the frequency content at the outlet of the combustion chamber and the overall number of vanes of the distributor, in particular for each angular sector of the injector.

The blades can be fixed or orientable type.

In a further embodiment, at least one blade comprises an air injection orifice making it possible to dissymmetrize the average flow field in a channel.

The air injection can be controllable.

The invention also relates to an assembly comprising at least one combustion chamber sector, at least one injector and at least two channels of different types for a distributor of the aforementioned type.

It also relates to a turbomachine and in particular a turbine engine for an aircraft comprising a distributor according to the invention.

PRESENTATION OF FIGURES

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and should be read with reference to the appended figures in which:

• Figure la - already discussed - illustrates the state of a temperature fluctuation that propagates in a conduit before passing an acceleration narrowing;

• Figure lb - also already discussed - illustrates the state of the pressure fluctuation at the same time;

• Figures 2a and 2b - also already discussed - illustrate the state of the temperature fluctuation after passing the acceleration narrowing and the state of the pressure fluctuation at the same time;

FIG. 3a schematically illustrates an exemplary embodiment for a turbomachine distributor according to the invention;

FIG. 3b schematically illustrates the laws of the areas along the channels A and B of the distributor of FIG. 3a;

FIG. 3c illustrates the generation of acoustic waves in phase opposition at the output of said channels;

FIG. 4 illustrates a combustion chamber sector for a distributor-type turbine engine of the type illustrated in FIG. 3a;

• Figure 5 schematically illustrates another possible embodiment.

DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND REALIZATION

FIG. 3a shows three vanes Al, A2, A3 which belong to a vane E of a distributor D of a turbomachine turbine. The various blades of this blade E are distributed around the axis of the distributor D and together define a plurality of successive channels which are distributed around the axis of the turbine and in which the fluid is accelerated.

In the example illustrated in FIG. 3a, the blades A1, A2, A3 - and more generally the various vanes of the blading E - are of two types distributed alternately all around the distributor D, two successive blades around the distributor D having profiles respectively corresponding to one of the first type of blading, the other to the second. In this way, the law of the areas of two adjacent channels of the distributor is different, the channels distributed around the axis alternatively having a law of the areas of a first type (channel A) or a second type (channel B) .

More specifically, the profiles of the different types of blades and the law of the areas along the different types of channels are chosen so that the entropic waves, coming from fluctuations of the temperature of the fluid convected by the flow downstream of the chamber of combustion, are accelerated staggered in different types of channels, and so that the indirect acoustic waves that are generated in them are with components tending to compensate.

Thus, in the example illustrated in FIGS. 3a, 3b and 3c, the law of areas along a channel of type A and that along a channel of type B are such that for any pair of adjacent channels the zones of narrowing (and therefore those of the velocity accelerations for the fluid) in one channel are shifted with respect to the narrowing zones in an adjacent channel along the channels.

The realization of the two types of channels can be obtained by alternating two types of blades having different profiles.

As illustrated very schematically in Figure 3a, where only three successive blades are shown, the blades A1 and A3 have identical profiles of a first type. The blade A2 disposed between the blades A1 and A3 has a different profile of a second type, which implies that two adjacent channels have different shapes (profiles). These different shapes are shaped to create areas of narrowing suitably shifted from one channel to another.

It is understood that each blade A1 or A3 is disposed between the blade A2 and a blade (not shown) of profile identical to that of the blade A2, so as to achieve alternating channels of types A and B.

When the distributor D receives a plane entropic wave Ws (x), the channel A accelerates the fluid for example in advance with respect to the channel B. The indirect acoustic wave due to the entropic wave and generated at the moment of acceleration in the B-channel therefore arrives late compared to that of the A-channel.

The profiles of the various types of blades are chosen so that this delay allows for certain acoustic frequencies at least partial compensation, or even a cancellation, of indirect acoustic waves between them.

For this purpose, the shapes of their leading edges, as well as those of their intrados and extrados, are used to obtain profiles that are different from one type of blade to another.

For example, the delay is chosen to correspond to a half-period of the wave. The acoustic waves generated by the entropic waves being in phase opposition to the output of the distributor D, these acoustic waves are then canceled.

One or more offsets may be produced in the dispenser to attenuate one or more frequencies.

It should be noted that combinations using a number of channel types up to half of the total number of blades can be envisaged for this purpose in order to attenuate a maximum of frequencies.

The proposed solution is advantageously used in the case of a distributor at the outlet of the combustion chamber.

For example, in the case of a combustion chamber having eighteen injectors distributed in eighteen sectors, the temperature of the combustion chamber has a fluctuation which repeats substantially every ^{1/18 th} of circumference.

The distribution of the different types of channels allowing compensation or attenuation of the acoustic waves generated by the entropic fluctuations is repeated for each sector. Each sector has two or even three types of channels whose area laws are different and are chosen to allow this compensation or mitigation.

This is illustrated in FIG. 4, in which a combustion chamber sector S is shown which comprises an injector I. Two vanes of a distributor D are arranged at the outlet of this combustion chamber sector. These two blades define together, as well as with the vanes of the adjacent sectors with which said sector is intended to be associated, alternating channels of types A and B.

Moreover, the blades of the distributor D can be fixed vanes.

The blades can also be steered to adjust the flow.

The desired effect can also be achieved by an axial blade offset.

In another variant, or even in addition to embodiments of the type of that of Figure 3a, the offset between the entropic waves can be achieved by other means than by playing on the geometry of the blades.

For example, as shown in Figure 5, it can be provided for example at the leading edges of the blades of the air injection orifices Ol for blowing inwardly of the air channel from of interior ducts to blades. There is thus a controllable device allowing, by air injection, to dissymmetrize the average flow field, in order to cause the desired acceleration.

These air injection orifices Ol can themselves be controllable in flow and orientation to allow control of the phase shift performed.

Such a solution is particularly interesting because it makes it possible to deactivate the noise attenuation system during the phases that do not require it (cruise) and to keep a circumferentially uniform flow in order to preserve the life of the turbine.

As a further variant, it may be provided that a blade comprises a controllable flow geometry modification device which comprises at least one active electrical component of the NRP type (or "Nanosecond Repetitively Pulsed" according to the generally used English terminology). .

NRP techniques are conventionally known and used to obtain hydrodynamic effects and control flows.

We can advantageously refer to this effect to the book:

"Low Temperature Plasma Technology - Methods and Applications"

- Paul K. Chu - XienPei Lu - CRC Press - pages 139 and following.

The active electrical component (s) NRP of the blade (electrodes) locally generate nano-second electric discharges which locally deflect the flow by pushing it away from an area in which the discharges occur, this area being adjacent to a wall of a dawn. By locally repelling the flow, these electrical components act on the law of areas in the same way as if a bulge had been created on the shape of the dawn.

Claims (11)

A turbomachine turbine distributor comprising a plurality of circumferentially distributed vanes defining between them guide and fluid acceleration channels, characterized in that at least three successive channels have laws of different areas and comprise flow sections which accelerate the fluid in an offset manner, the offset between the accelerations in the channels being such that the indirect acoustic waves generated in said channels by fluctuations of the temperature of the entropic fluid are out of phase and at least partially compensate for each other , even cancel each other out. 2. turbomachine turbine distributor according to claim 1, characterized in that it comprises a succession of at least three channels of at least three different types which is repeated at the circumference of the distributor, the law of areas along the a channel of a given type being distinct from that along a channel of another type such that the fluid acceleration in a given channel is offset from the fluid acceleration in a channel of another type. 3. turbomachine turbine distributor according to claim 2, characterized in that the succession of three channels of different types is repeated for each angular sector of the injector. 4. Dispenser according to one of the preceding claims, characterized in that the blades are fixed. 5. Dispenser according to one of claims 1 to 3, characterized in that the blades are of orientable type. 6. Dispenser according to one of the preceding claims, characterized in that at least one blade comprises a controllable device for changing the geometry of the flow to dissymmetrize the average flow field in a channel. 7. Dispenser according to claim 6, characterized in that the controllable device comprises at least one injection port 5 of air. 8. Dispenser according to claim 6, characterized in that the controllable device comprises at least one active electrical component N RP type. 9. Assembly comprising at least one chamber sector of Combustion, at least one injector and at least three channels of at least three types for a dispenser according to claim 2, taken alone or in combination with one of claims 3 to 8. 10. Turbomachine, and in particular turbine engine for aircraft, 15 having a distributor according to one of claims 1 to 8.