Grating for the formation of a reverse flow of an aircraft turbofan engine

A grating for the formation of a reverse flow of a turbofan engine and comprising fins of a first type having a curved profile whose rounding is oriented aft and whose center of curvature is forward relative to the fin of the first type, fins of a second type having a curved profile whose rounding is oriented aft and whose center of curvature is forward relative to the fin of the second type. In this grating, each fin of one of the two types is inserted between two fins of the other type moving from forward to aft and the cord of the fins of the second type is smaller than the cord of the fins of the first type.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the French patent application No. 1761914 filed on Dec. 11, 2017, the entire disclosures of which are incorporated herein by way of reference.

BACKGROUND OF THE INVENTION

The present invention relates to a grating for the formation of a reverse flow of a turbofan engine of an aircraft, a turbofan engine comprising at least one such grating, and an aircraft comprising at least one such turbofan engine.

An aircraft comprises a fuselage, on each side of which is fixed a wing. Under each wing, there is suspended at least one turbofan engine. Each turbofan engine is fixed under the wing via a pylon which is fixed between the structure of the wing and the structure of the turbofan engine.

The turbofan engine comprises an engine in the form of a core and a nacelle which is fixed around the engine to a fixed structure of the jet engine. Between the engine and the nacelle, the jet engine has a secondary jet in which there flows, from upstream to downstream, a secondary flow of gasses originating from a fan positioned upstream of the engine.

The nacelle comprises a cowl that is fixed relative to the fixed structure and, forward, a mobile cowl which moves translationally aft to free a window between the mobile cowl and the fixed cowl and which allows the passage of gasses between the secondary jet and the outside.

Initially, one or more blocker doors are displaced from an inactive position to an active position. In the inactive position, the blocker door is outside of the secondary jet and does not prevent the flow of the secondary flow. In the active position, the blocker door is across the secondary jet and directs the secondary flow from the secondary jet to the window and therefore to the outside.

The displacements of the mobile cowl and of the blocker doors are produced by a control system comprising, for example, thrusters and rods.

To best guide the flow outgoing through the window, gratings, also called “cascades,” are positioned across the window to enhance the efficiency of the reverser by more accurately controlling the direction of the diverted secondary flow.

These gratings take the form of profiled fins which divert the secondary flow. Each fin has a curved profile whose rounding is oriented aft and whose center of curvature is forward relative to the fin. While these fins allow a good deflection of the secondary flow forward, the air flow at the output of the grating tends to separate at the trailing edge of each fin, which tends to reduce the performance of the grating.

To ensure a better efficiency of these gratings, it is necessary to find fin forms which are more efficient from an aerodynamic point of view and from a weight point of view.

SUMMARY OF THE INVENTION

One object of the present invention is to propose a grating for the formation of a reverse flow of a turbofan engine of an aircraft.

To this end, a grating is proposed for the formation of a reverse flow of a turbofan engine having a forward end and an aft end, the grating comprising fins of a first type having a curved profile whose rounding is intended to be oriented aft and whose center of curvature is forward relative to the fin of the first type, the grating being characterized in that it comprises fins of a second type, in that each fin of one of the two types is inserted between two fins of the other type moving from forward to aft, in that each fin of the second type has a curved profile whose rounding is configured to be oriented aft and whose center of curvature is forward relative to the fin of the second type, and in that the cord of the fins of the second type is smaller than the cord of the fins of the first type.

Such a grating allows for a reduction of the weight while ensuring an efficient diversion.

Advantageously, the trailing edges of the fins of the first type and the trailing edges of the fins of the second type are in one and the same output plane.

Advantageously, the leading edges of the fins of the first type are in one and the same input plane parallel to the output plane, and in that the leading edge of each fin of the second type is in an intermediate plane between the input plane and the output plane and at a distance from each of them.

where “c” is the cord of the fins of the first type,

“c′” is the cord of the fins of the second type,

“s” is the distance between two consecutive fins of the first type,

“s′” is the distance between a fin of the first type and a consecutive fin of the second type,

“h” is the height of the fins of the first type,

“h′” is the height of the fins of the second type,

“θ1” is the input angle between the tangent to the curvature of the leading edge of the fins of the first type and the vertical axis,

“θ1′” is the input angle between the tangent to the curvature of the leading edge of the fins of the second type and the vertical axis,

“θ2” is the output angle between the tangent to the curvature of the trailing edge of the fins of the first type and the vertical axis,

“θ2′” is the output angle between the tangent to the curvature of the trailing edge of the fins of the second type and the vertical axis,

“st” is the offset angle of the fins of the first type, and

“st′” is the offset angle of the fins of the second type.

According to a particular embodiment, the heights of the fins of the second type vary from one fin of the second type to another fin of the second type.

According to a particular embodiment, the distance between a fin of the first type and the consecutive fin of the second type in the forward to aft direction, is different from the distance between another fin of the first type and the fin of the second type consecutive in the forward to aft direction to this other fin of the first type.

According to a particular embodiment, the input angles of the fins of the second type vary from one fin of the second type to another fin of the second type.

The invention also proposes a turbofan engine comprising at least one grating for the formation of a reverse flow according to one of the preceding variants.

The invention also proposes an aircraft comprising at least one turbofan engine according to the preceding variant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, the terms relating to a position are taken with reference to an aircraft in an advancing position as is represented inFIG. 1.

FIG. 1shows an aircraft10which comprises a fuselage12, on each side of which is fixed a wing14which bears at least one turbofan engine100according to the invention. The turbofan engine100is fixed under the wing14via a pylon16.

In the following description, and by convention, X will denote the longitudinal axis of the nacelle102and of the turbofan engine100which is overall parallel to the longitudinal axis X of the aircraft10, or roll axis, oriented positively in the direction of advance of the aircraft10, Y denotes the transverse axis or pitch axis of the aircraft which is horizontal when the aircraft is on the ground, and Z denotes the vertical axis or vertical height or yaw axis when the aircraft is on the ground, these three directions X, Y and Z being mutually orthogonal and forming an orthonormal reference frame whose origin is the center of gravity of the aircraft.

The turbofan engine100comprises a nacelle102which comprises, forward, a fixed cowl106and, rearward of the fixed cowl106relative to the longitudinal axis X, a mobile cowl108.

As is shown inFIGS. 2 and 3, the turbofan engine100comprises an engine20in the form of a core which is housed inside the nacelle102. The jet engine100has a jet202delimited between the nacelle102and the engine20and in which circulates a secondary flow208originating from an upstream fan.

The fixed cowl106is fixedly mounted on a fixed structure209of the nacelle102and constitutes an outer wall of the nacelle102.

The mobile cowl108is mounted to be translationally mobile on the fixed structure209in a direction of translation that is overall parallel to the longitudinal axis X. The translation is produced by any appropriate means such as, for example, runners, or by any actuation systems such as, for example, thrusters or motors.

In the embodiment of the invention presented here, the mobile cowl108comprises an inner wall207aand an outer wall207bwhich surrounds the inner wall207a.

The mobile cowl108is mobile between a position of closure (FIG. 2) in which the mobile cowl108is against the fixed cowl106and a position of opening (FIG. 3) in which the mobile cowl108is moved away from the fixed cowl106aft so as to open a window210open to the outside of the nacelle102and which opens a passage between the secondary jet202and the outside. In the position of closure, the fixed cowl106and the outer wall207bare extended to form the outer jacket of the nacelle102and to close the window210, and in the position of opening, the fixed cowl106and the outer wall207bare separated from one another.

At the same time, in the position of closure, the inner wall207acomes into contact with the fixed structure209and constitutes an outer wall of the secondary jet202, and, in the position of opening, the inner wall207ais moved away from the fixed structure209so as to open the passage between the secondary jet202and the window210.

The nacelle102comprises at least one blocker door104. In particular, there can be two blocker doors104positioned facing one another, or several, for example four, blocker doors104distributed regularly over the periphery of the nacelle102.

The thrust reversing system which is described here is described only by way of illustration and the invention can be applied to any type of thrust reverser for which cascades are used in order to increase the efficiency of the thrust forward of the nacelle.

Furthermore, here, the invention is more particularly described for a single blocker door104, but it applies in the same way for each blocker door104when there are several thereof.

In the embodiment of the invention presented here, the blocker door104is positioned between the inner wall207aand the outer wall207bin the position of closure.

The blocker door104is mounted to rotate freely about an axis of rotation50on the fixed structure of the nacelle102between an inactive position (FIG. 2) in which it is not in the jet202and an active position (FIG. 3) in which it at least partly blocks the jet202.

When the mobile cowl108is in the position of closure, the blocker door104is in the inactive position, and when the mobile cowl108is in the position of opening, the blocker door104is in the active position so as to divert at least a part of the secondary flow208to the outside of the nacelle102.

The displacement of the blocker door104is linked to the displacement of the mobile cowl108. The displacement of the blocker door104is controlled by any appropriate means, such as a system of rods, thrusters or motors.

Thus, in the position of opening of the mobile cowl108and in the active position of the blocker door104, the secondary flow208is diverted to the outside through the window210.

For each window210, the nacelle102is equipped with gratings250which allow the formation of a reverse gas flow of the jet engine100from the secondary gas flow208, also known as “cascades”, which are positioned across the window210to enhance the efficiency of the reverser by more accurately controlling the direction of a diverted secondary flow208and, in particular, by orienting the secondary flow into a direction forward of the nacelle102.FIG. 4shows the grating250on its own and in cross section.

The number of gratings250per window210varies according to the dimensions of the gratings250and of the window210. In the following description, the invention is more particularly described for a single grating250, but it applies in the same way for each grating250when there are several thereof.

The grating250takes the form of a frame having an upstream edge252and a downstream edge254parallel to the upstream edge252, and lateral edges253at right angles to the upstream252and downstream254edges. The grating250is fixed to the fixed structure of the nacelle102, for example by screws.

Inside the frame, the grating250has fins256of a first type and fins258of a second type, where each fin256,258of one of the two types is inserted between two fins258,256of the other type going along the longitudinal axis X, that is to say, from forward to aft of the jet engine100.

Each fin256of the first type has a curved profile whose rounding is oriented aft of the jet engine100and whose center of curvature is forward relative to the fin256of the first type. Each fin256of the first type therefore makes it possible to divert the secondary flow208forward.

Each fin258of the second type also has a curved profile whose rounding is oriented aft of the jet engine100and whose center of curvature is forward relative to the fin258of the second type, but whose chord is smaller than the chord of the fins256of the first type.

Thus, with respect to the secondary flow208entering into the grating250, each fin258of the second type has a drag which is lower than the drag of the fins256of the first type. Since the fins258of the second type are smaller than the fins256of the first type, they are less heavy, hence a weight saving, and they make it possible, by reducing the output surface of the secondary flow208, to create a convergent section and speed up the secondary flow208at the output of the grating250and thus reduce the separation of the air flow at the fins256of the first type.

The trailing edges of the fins256of the first type and the trailing edges of the fins258of the second type are aligned in a direction that is overall parallel to the longitudinal axis x. In other words, the trailing edges of all the fins256and258are all in one and the same output plane that is overall parallel to the longitudinal axis X. This output plane may be curved to follow the curvature of the nacelle, such as a surface of revolution about the longitudinal axis of the engine.

On the other hand, the leading edges of the fins256of the first type and the leading edges of the fins258of the second type are not aligned in a direction that is overall parallel to the longitudinal axis X. The leading edges of the fins256of the first type are all in one and the same input plane parallel to the output plane and the leading edge of each fin258of the second type is in an intermediate plane between the input plane and the output plane and at a distance from each of them. The input plane and the intermediate plane may also be curved in the same manner as the output plane to follow the curvature of the nacelle, such as a surface of revolution about the longitudinal axis of the engine, with all of the input, output and intermediate planes being concentric.

FIG. 5shows an enlargement of the grating250where:

“c” is the chord of the fins256of the first type,

“c′” is the chord of the fins258of the second type,

“s” is the distance between two consecutive fins256of the first type in the forward to aft direction,

“s′” is the distance between a fin256of the first type and a consecutive fin258of the second type in the forward to aft direction,

“h” is the height of the fins256of the first type,

“h′” is the height of the fins258of the second type,

“θ1” is the input angle between the tangent to the curvature of the leading edge of the fins256of the first type and the vertical axis,

“θ1′” is the input angle between the tangent to the curvature of the leading edge of the fins258of the second type and the vertical axis,

“θ2” is the output angle between the tangent to the curvature of the trailing edge of the fins256of the first type and the vertical axis,

“θ2′” is the output angle between the tangent to the curvature of the trailing edge of the fins258of the second type and the vertical axis,

“st” is the offset angle of the fins256of the first type, that is to say the angle between the chord and the vertical axis, and

“st′” is the offset angle of the fins258of the second type, that is to say the angle between the chord and the vertical axis.

The vertical axis is taken here with reference toFIGS. 2 to 6, but this axis is more generally a radial direction of the turbofan engine100. Furthermore, different thickness laws can be applied to the profile of the fins.

According to a particular embodiment, the fins256of the first type and the fins258of the second type are such that:

FIG. 6shows different variants which can be implemented independently of one another or in combination with one another.

According to a first variant, the heights of the fins258of the second type vary from one fin258of the second type to another fin258of the second type. These variations are represented by different heights h1′, h2′.

According to a second variant, the distance between a fin256of the first type and the consecutive fin258of the second type in the forward to aft direction, is different from the distance between another fin256of the first type and the fin258of the second type consecutive in the forward to aft direction to this other fin256of the first type. These variations are represented by different distances s1′, s2′.

According to a third variant, the input angles of the fins258of the second type vary from one fin258of the second type to another fin258of the second type. These variations are represented by different angles θ1′, θ2′.