FR2971553A1 - Method for reducing noise of propulsion jet reactor of aircraft, involves ejecting shear flows at trailing edge of nacelles of reactor with ejection velocity in range between velocities of flows at inner and outer sides of nacelles - Google Patents

Abstract

The method involves ejecting shear flows (51, 52) at a trailing edge of nacelles (41, 42) of a propulsion reactor (10) with ejection velocity of gas in range between velocity of gas flow at inner sides (411, 421) of the nacelles and the velocity of gas flow at outer sides (412, 422) of the nacelles. A velocity field in the flow of the shear flows is taken as constant and oriented in a direction of average speed of stream flows on the inner sides and the outer sides of the nacelles.

Description

Method for reducing the acoustic signature of a propulsion reactor and reduced acoustic signature reactor

The present invention belongs to the field of aircraft propulsion. More particularly, the invention relates to a jet propulsion engine or reactor for which the thrust produced is obtained by the ejection of gases whose speed is greater than the rate of advance in the air.

Reactor propulsion, in particular by turbojet engine, is well known for the propulsion of aircraft and especially civil transport aircraft. One of the disadvantages of this type of propulsion is related to the noise, especially at low altitude, which is generated by the reactors and which affects the environment of the airports. In a conventional reactor, the sources of noise are diverse, mainly the forward fan noises radiated by the reactor air inlet and the backward jet noises radiated by the jet nozzles. reactor, and the relative importance of each of the sources depends on the flight conditions of the aircraft: speed, altitude, attitude and engine speed.

To reduce the noise of the reactors many efforts have been made. The generation of turbofan engines by increasing the average accelerated gas flow at the expense of the ejection speed made it possible to significantly reduce the noise of these reactors given the influence of the ejection speed on the engine. noise that evolves as the power eight of the said speed. The acoustic treatment of the reactor walls, in particular the air inlets and certain parts of the nozzles, has also made it possible to reduce the sound signature of the reactors.

However, it still appears necessary to reduce the noise level generated by aircraft propulsion reactors, which proves all the more difficult as the level currently reached is already relatively low technically.

The accelerated gas ejection velocity is a major source of noise originating from the large pressure field variations prevailing in the aerodynamic flow at the interface between the different aerodynamic flows circulating outside the reactor and in the different zones of the reactor, the primary flow and the secondary flow on a conventional double flow reactor. It has been proposed to act on the average accelerated gas ejection speed by favoring the mixing, at the nozzle outlets, of the gases of the different flows of different speeds so as to decrease the average speed of the flow having the greatest This principle can be applied either between the primary flow and the secondary flow of the reactor, or between the secondary reactor flow and the external aerodynamic flow. Various forms of nozzles have thus been devised to facilitate this mixing, in particular the nozzles having a sawtooth or chevron trailing edge, as in US Pat. No. 6,360,528, and the nozzles whose skirt folds so as to increase the contact surfaces between two streams and to facilitate the mixing of flows as in US Pat. No. 5,884,472. This type of solution is applied for example between the primary flow and the secondary flow of a double-flow reactor in order to act. on the primary flow with the highest ejection speed.

However, these solutions, besides the fact that they may be unfavorable to the propulsive efficiency of the reactor and may be penalizing in weight, have the disadvantage of reducing the average speed of a portion of the jet flow to be generated by the reactor. mixing two streams a significant level of noise turbulence destroys some of the benefits of decreasing the average speed of ejection of the fastest flow.

The present invention provides a method and a device which acts without seeking to mix the reactor streams but by the interposition between two adjacent reactor streams of intermediate shear flow whose intermediate velocities between the flow velocities provide a controlled rate transition in the flow with a minimal generation of turbulence. According to the method of reducing the jet noise of a propulsion reactor, at least one shear flow is ejected at at least a portion of a trailing edge of a nacelle of the reactor with an ejection speed , a gas ejected shear flow, intermediate between the speed of the reactor flow on the inner side of the nacelle and a flow rate of the reactor or the external flow on the outside of the nacelle. By thus reducing the flow gradients in the flow between the different flows of the reactor, the jet noise is reduced. Advantageously, the field of velocities in the flow of a shear flow is substantially constant and oriented in the mean direction of the velocities in the flows of the reactor flows on the inner and outer sides of the nacelle. To further increase the jet noise reduction effect, two or more shear flows are ejected simultaneously at the same part of the same trailing edge of a nacelle, so as to form behind the edge of the nacelle. leakage, according to the direction of the aerodynamic flow, of the layers stacked between the reactor flow on the inner side of the nacelle and the flow of the reactor on the outside of the nacelle, and this with different ejection speeds and such said ejection velocities are always increasing from the reactor flow on the side, outside or inside, of the nacelle having the lowest speed and the flow of the reactor, on the inside or outside, of the nacelle having the largest speed. The method is applicable depending on the engine architectures considered one or more trailing edges of nacelles of a reactor which may include a core nacelle and one or more fan nacelles. Thus the nacelle can be a nacelle core of a reactor gas generator whose flow on the inner side is a primary flow of the reactor ejected by the gas generator and whose flow on the outer side is a secondary flow of the reactor, for example a flow of the fan, or an aerodynamic flow external to the reactor. The nacelle can also be a fan nacelle of a fan whose flow on the inner side is a secondary flow of the fan and whose flow on the outer side is another secondary flow of the reactor or an aerodynamic flow external to the reactor. Finally, mainly for reasons of economy, the flow or the shear flows, or a part of the shear flows, are interrupted under flight conditions for which a reduction in acoustic power of the jet is not desired and are activated. in flight conditions for which a reduction of the acoustic power of the jet is sought. In the propulsion reactor of the invention, at least one flow is ejected at the rear of the reactor at a nozzle outlet, the reactor comprising at least one nacelle whose nacelle structure separates two flows of the reactor between a inner side and an outer side of the nacelle and has a trailing edge at the nozzle outlet. Furthermore, in the reactor of the invention, in order to carry out the process of the invention and to produce the advantages thereof: the trailing edge is provided with a continuous trailing edge opening on all or substantial part of said trailing edge; the reactor comprises means for dispensing a compressed gas at the opening, the geometric characteristics of said opening on the one hand and flow and pressure characteristics of the gas on the other hand being chosen to eject at said edge; leakage a shear flow having uniform flow characteristics; - An ejection rate, characteristic of the flow of the shear flow, being between the flow rates of the reactor on the inner and outer sides of the nacelle. In an improved embodiment for improving the aerodynamic transition conditions between adjacent flows of the reactor, all or a substantial part of the trailing edge of at least one nacelle comprises at least two openings arranged parallel to the trailing edge and parallel to each other. so as to eject two independent shear flows in the part of the nacelle trailing edge concerned. When the reactor is a reactor comprising at least two separate streams, a primary stream and a secondary stream, comprising a gas generator provided with a core nacelle and generating the primary stream, comprising a fan provided with a fan nacelle and generating the secondary stream, the nacelle core and or the nacelle fan are provided with at least one annular trailing edge opening on at least a substantial part of the perimeter of the trailing edge of said nacelle core and or said nacelle fan.

In order to limit the impacts on the design and construction of the nacelles, preferably one or more nacelle trailing edge openings are limited according to the perimeter defined by the trailing edge so as to correspond to at least about one quarter of said perimeter. The invention is also directed to an aircraft propelled by at least one reactor according to the invention, such an aircraft obtaining many operational advantages of the noise reduction obtained such as for example being able to take off from terrain having reduced noise requirements. , at least during certain time slots, or practicing a taxation of noisy planes.

The description of a turbocharger according to the invention is made with reference to the figures which show the invention in a schematic and nonlimiting manner: FIG. 1: according to a partial section, a double-flow reactor with a high dilution ratio; Figures 2: in perspective from the rear a detail of a double flow reactor at the outlet nozzles and illustrates the different flows;

FIG. 1 shows in partial section a turbojet engine 10 having a conventional architecture of a double-flow reactor with a high dilution ratio similar to the reactor models used on most current civil transport aircraft.

Such a reactor 10 comprises in particular a gas generator 11, or core, the detail of which is not shown in FIG. 1, which is traversed by a primary flow 31 ejected at the rear of the reactor at an outlet of primary nozzle 21, in an area close to an axis 15 of the reactor which corresponds to the axis of rotation of the rotating parts of the reactor. The reactor 10 also comprises a fan 12, or fan, which is rotated by the gas generator 11 so as to create a secondary flow 32 which is ejected at a secondary nozzle outlet 22. In ordinary operation of the reactor 10, for example in the propelled phase of an aircraft and in particular at takeoff, uphill or cruising, the speed of the flow in the primary flow 31 is greater than the flow velocity in the secondary flow 32 which is itself greater than the speed of the external flow 33 outside the reactor, corresponding to the speed of movement of the aircraft, and therefore the reactor, relative to the ambient air.

Although the flow velocities are susceptible to significant variations from one reactor model to another as well as the operating speed and the displacement velocity for the same reactor, it can be considered as an example that, for a double-flow reactor with a high dilution ratio of an aircraft and operating at a speed close to the maximum allowed speed, take-off speed or climb rate, the ejection speed of the primary flow 31 is of the order of 400m / s and the speed of the secondary flow 32 is of the order of 200m / s, values to be compared to a flight speed of the order of 100m / s corresponding to the speed of the external flow 33. To ensure internal aerodynamic operation and correct external reactor, the functional elements, not shown, of the reactor are enveloped by nacelle structures, in the case shown a core nacelle 41 around the gas generator 11 and a nacelle fan 42 around the blower 12. The reactor 10 further comprises at the trailing edges of nacelle structures 41, 42 openings 43, 44 through which are maintained shear flows 51, 52, ie ejected gas flow rates backwards, the gas being in its most convenient form of air.

In practice, and depending on the desired results, the trailing edge of the nacelle structure 41 of the gas generator is provided with a core trailing edge opening 43 and or the trailing edge of the nacelle structure 42 of the blower 12 is provided with a fan trailing edge opening 44.

Such core or fan trailing edge openings are openings along the trailing edge at the periphery of the nozzle concerned, annular in the illustrated case. The opening 43, 44 on a trailing edge is substantially continuous or must behave aerodynamically as a continuous opening, that is to say that in terms of shear flow 51, 52 generated aerodynamic characteristics, in particular the flow and the velocity field in the flow of this shear flow is homogeneous, and this even if, for reasons of manufacture of the nacelles, the trailing edge opening is made in several segments.

By homogeneous it should be understood that the characteristics of a shear flow are relatively constant in flow and speed, in the vector sense of the term, all along the annular opening, although in this case it is not required extreme accuracy of the values of these parameters for which deviations of the order of 10 or 20% or more is of sufficient accuracy to achieve the desired result. Unrepresented means, which may consist of compressed gas generators or sampling on compression stages of the reactor itself, produces a compressed gas, a priori air, which is fed to the annular openings 43, 44 to be dispensed with controlled pressure and flow so that for each trailing edge core and or fan a shear flow is ejected to the rear of the trailing edge of the corresponding nacelle, 41, respectively 42. As illustrated in FIG. 2, a shear flow 51, 52 is at the separation of two characteristic flows of the reactor 10 during its operation. Thus the shear flow 51 from the trailing edge of the core nacelle 41 is ejected between the primary flow 31 ejected by the gas generator 11 and the secondary flow 32 ejected by the fan 12. Thus the shear flow 52 from the edge leakage of the nacelle fan 42 is ejected between the secondary flow 12 ejected by the fan 12 and the external flow 33 of the air around the reactor.

In addition, the parameters: geometry and section of the trailing edge openings 43, 44, pressure and flow rate of compressed gas supplied to said trailing edge openings, are chosen so that for each trailing edge opening 43, 44, the rate of air ejection is between the flow velocities on each side of the trailing edge considered.

To combat the creation of turbulence, and maintain a shear flow with characteristics as stable and constant as possible, advantageously the openings 43, 44 are in the form of an open slot between an inner side 411, 421 and a side external 412, 422 of the nacelle 41, 42 considered whose lips of said slot are maintained in spacing by junction elements in the form of aerodynamic profiles evenly distributed along the opening, said elements in the form of aerodynamic profiles stabilizing the direction in which the shear flow is oriented when ejected backward. According to the device of the invention, the ejection of a shear flow between two adjacent flows of the reactor of different speeds in the zone where these two different flow velocities are found tangents allows, by the choice of a speed of intermediate ejection for the shear flow to decrease relative tangential velocity differences in the flow at the interfaces between different flows, reactor flow and shear flow.

By thus reducing the differences in speeds at the interfaces, the turbulence in the flow is also reduced with a beneficial effect on the jet noise.

Insofar as the advantages provided by the device of the invention are not necessary during operation of the reactor, preferably the device is placed in a stopped mode in which shear flow is no longer produced, or in a standby mode in which the shear flow is reduced, when the noise reduction is not sought. For example for a plane taking off and climbing at low altitude, in a situation where the ground acoustic trace is critical, the device will be in operation and above a certain altitude or cruising the device will be advantageously stopped or put Standby.

The invention is capable of variants within the reach of those skilled in the art without departing from the principles described in the detailed mode above. In particular, the invention can be implemented in the case of a reactor having only one flow, the primary flow, or in the case of a gas generator operating a propeller, such a gas generator being similar to a reactor, or in the case of reactor having more than two streams. In particular, it is possible, on a reactor comprising several trailing edges of nacelles, to generate a shear flow only at a single trailing edge of nacelle corresponding to the separation of only one of the reactor streams with another stream. Such a choice is for example motivated by reasons of simplicity of the device, simplicity necessarily having an impact on the costs of implementation and maintenance, on the mass ..., and in this case it will be preferred to implement the device between the flow having the highest ejection speed and the flow that is close to it. It is also possible to implement an improved device in which two or more openings are concentrically arranged at the same nacelle trailing edge so as to eject, at different speeds, as many shear flows between the two flows. located on each side of the nacelle. In this case the velocities of each shear flow will be chosen so that the velocities in the flow evolve as smoothly as possible between the velocities of the two flows located on each side of the fan or core pod considered, creating a regular gradient of the field. speeds to limit turbulence in the flow. It is also possible that only a portion, at least a quarter of the perimeter of the nozzle, of the trailing edge of a nacelle is provided with the device. Thus, it is preferentially treated an area of the nacelle to avoid noise radiation in a preferred direction, for example in the direction of the ground during the takeoff and initial climb phases of an aircraft when the engines develop the maximum thrust. Although illustrated for a reactor provided with a conventional nacelle substantially of revolution, the invention can be implemented for nacelles whose nozzles have outlet sections that are not substantially circular, for example nacelles having rectangular outlet sections, not shown, for which the choice of nacelle trailing edge parts implementing the method advantageously corresponds to one or more entire sides of the rectangular section trailing edge.

The invention also relates to a method in which at least one shear flow 51, 52 of a gas, a priori air, is ejected towards the rear at all or part of a trailing edge of a nacelle, core 41 or fan 42, of a propulsion reactor 10 between two streams 31, 32, respectively 32, 33, having different speeds in the region of the trailing edge where these two different flow rates are found tangent, and such that the speed of ejection of the shear flow 51, 52 is an intermediate speed between the speeds of the two flows located on each side of the nacelle 41, respectively 42, whose trailing edge is considered. The shear flow 51, 52 is ejected so as to form a flow which is uniformly interposed between the reactor flows and has flow characteristics and a substantially constant velocity field oriented in the mean direction of the velocities of the flows of the reactor. reactor. The speed of ejection of the shear flow 51, 52 is for example the average speed between the speeds of the two streams 31, 32, respectively 32, 33, 30 between which the shear flow is ejected. In a general form of application of the method, two or more shear flows are ejected at the same nacelle trailing edge with different speeds intermediate between the speed of the flow on the inner side of the nacelle considered and the speed of the flow from the outside of the nacelle considered, the shear flow ejection velocities being increased from the flow, outside or inside, of the reactor having the lowest speed towards the flow, inside or outside, of the reactor having the velocity higher. The two or more shear flows thus ejected form a stack of shear flows which is inserted between the two flows of the reactor and ensures a gradual and controlled transition of the velocities in the aerodynamic flow.

Advantageously, the process is carried out on a reactor in the only periods of use of the reactor during which noise reduction is desired.

The method of the invention and the device of the invention implementing the method thus make it possible to reduce the noise level of a reactor for the part generated by the jets at the outlet of the nozzles and thus contribute to the overall improvement of the reduction of the noise of the reactors, in particular the jet engines.

Claims (9)

CLAIMS1 - Process for reducing the jet noise of a propulsion reactor (10) in which at least one shear flow (51, 52) is ejected at at least part of a trailing edge of a nacelle (41, 42) of the reactor (10) with an ejection velocity, a gas of said ejected shear flow intermediate between a speed of a reactor flow on an inner side (411, 421) of the nacelle and a speed of a reactor flow or an external flow (33) on an outer side (412, 422) of the nacelle. 2 - Process according to claim 1 wherein a field of velocities in the flow of the at least one shear flow (51, 52) is substantially constant and oriented in the mean direction of the flow velocities of the reactor streams on the sides inside and outside the basket. 3 - Process according to claim 2 wherein at least two shear streams are ejected simultaneously at the same part of the same trailing edge of a nacelle (41, 42), so as to form behind the edge leakage of the layers stacked between the flow on the inner side (411, 421) of the nacelle and the flow on the outer side (412, 422) of the nacelle, and with different ejection speeds and such that said speeds of ejection are always increasing from the flow on the outer or inner side of the nacelle having the lowest speed and the flow on the inner or outer side of the nacelle having the highest speed. 4 - Process according to one of claims 1 to 3 wherein the nacelle is a nacelle core (41) of a gas generator (11) of the reactor whose flow on the inner side (411) is a primary flow (31). ) ejected by the gas generator and whose flow on the outer side (412) is a secondary flow (32) of the reactor or an external aerodynamic flow (33) to the reactor, and or wherein the nacelle is a fan nacelle (42). ) a fan (12) whose flow on the inner side (521) is a secondary flow (31) of the fan and whose flow on the outer side (422) is another secondary flow of the reactor or an aerodynamic flow external (33) to the reactor. 5 - Method according to one of the preceding claims wherein the flow or shear flows are interrupted in flight conditions for which a reduction of acoustic power of the jet is not sought and are activated in flight conditions for which a reduction of the acoustic power of the jet is sought. 6 - Propulsion reactor (10) in which at least one flow (31, 32) of the reactor is ejected at the rear of the reactor at a nozzle outlet (21, 22), said reactor comprising at least one nacelle (41, 42), which at least one nacelle comprises a nacelle structure separating two flows between an inner side (411, 421) and an outer side (412, 422) of the nacelle and having a trailing edge at the nozzle outlet (21, 22) characterized in that: - the trailing edge is provided with a continuous trailing edge opening (43, 44) on all or a substantial portion of said trailing edge; the reactor comprises means for dispensing a compressed gas at the opening (43, 44), the geometric characteristics of said opening on the one hand and flow and pressure characteristics of the gas on the other hand being selected for ejecting at said trailing edge a shear flow (51, 52) having homogeneous flow characteristics; - An ejection speed, characteristic of the flow of the shear flow (51, 52), being between the flow rates on the inner (411, 421) and outer (412, 422) sides of the nacelle. 7 - .Reactor according to claim 6 wherein all or a substantial part of the trailing edge of at least one nacelle (41, 42) comprises at least two openings arranged parallel to the trailing edge and parallel to each other so as to eject two streams in the part of the nacelle trailing edge concerned. 8 - reactor according to claim 6 or claim 7 wherein the reactor is a reactor comprising at least two separate streams, a primary stream (31) and a secondary stream (32), comprising a gas generator (11) provided with a nacelle core (41) and generating the primary flow, comprising a fan (12) provided with a fan nacelle (42) and generating the secondary flux, and wherein the nacelle core (41) and or the nacelle fan (42) are provided with at least one annular trailing edge opening (43, 44) on at least a substantial part of the perimeter of the trailing edge of said nacelle core and or said nacelle fan. 9 - Reactor according to one of claims 6 to 8 wherein at least one trailing edge opening (43, 44) is limited along the perimeter defined by said trailing edge so as to correspond to at least about one quarter of said perimeter . - Aircraft propelled by at least one reactor according to one of claims 6 to 9.