ULTRA-COMPACT DUAL-FLOW VARIABLE SECTION BLOWER NOZZLE

Abstract

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Description

Title of the invention: ULTRA COMPACT DOUBLE FLOW FAN NOZZLE WITH VARIABLE SECTION

[0001] The present invention relates to the field of aircraft gas turbine engines, in particular for high bypass ratio turbofans.

[0002] A double-flow turbofan can be defined generally as a gas turbomachine, driving at least one shrouded fan of a fan module.

[0003] The air entering the engine is then divided into two flows, a so-called "hot" flow entering the turbomachine, and a so-called "cold" flow passing through the fairing, the ratio between the volume of the cold and hot flows defining what is commonly called the "dilution ratio" of the engine.

[0004] The new generations of high bypass ratio turbofans also include a mechanical speed reducer coaxially connected between the output shaft of the turbomachine and the fan shaft. Usually, the speed reducer, or reducer, has the purpose of transforming the so-called fast rotation speed of the turbomachine shaft into a slower rotation speed for the shaft driving the fan, thus making it possible to optimize the rotation speed of the turbomachine while maintaining a suitable fan rotation speed. This also makes it possible to increase the propulsive efficiency and reduce the noise level of the engine.

[0005] In order to further improve the propulsive efficiency of high bypass turbofans, it is possible to use a low pressure ratio fan, having an "FPR" (Fan Pressure Ratio in English) of less than 1.4 or even lower. The FPR expresses the ratio between the pressure upstream and downstream of the fan.

[0006] It is known to those skilled in the art that such low FPR fans significantly improve propulsive efficiency and therefore allow for more fuel-efficient engines.

[0007] The fans allowing the lowest FPRs are open rotor, i.e. unducted fans, but these are however difficult to integrate on a commercial aircraft due to a larger fan diameter than a ducted fan, and the non-containment of the fan blades which can pose safety and certification problems.

[0008] Ducted fans allow for a smaller fan diameter but generally require a fairly high FPR, such as greater than 1.5 to maintain sufficient fan operating safety margin.

[0009] Indeed, for complex reasons known to those skilled in the art, a ducted fan does not have the same operating characteristics in cruise and on takeoff, with notably speed and altitude conditions which are very different. Since the engine can only be optimized for a single phase of flight, generally the cruise phase, the ducted fan can be subject to malfunctions during takeoff if its FPR is too low.

[0010] Solutions have been proposed in the prior art to attempt to have a low FPR fan while maintaining a sufficient operational safety margin.

[0011] The variable pitch fan naturally allows this problem to be overcome by adjusting the propeller pitch to the flight conditions. However, this technology is mechanically delicate and can cause unwanted reliability problems.

[0012] Another technology known to those skilled in the art is the variable area fan nozzle, also called a "VAFN". The principle of the VAFN is to vary the outlet section of the cold flow by means of movable flaps that open or close to allow more or less air to pass through.

[0013] This system makes it possible to adjust the pressure inside the fairing according to the flight conditions and therefore makes it possible to solve the previously described problem of safety margin encountered with a low FPR fan.

[0014] The systems imagined in the prior art, however, pose other problems which do not allow them to be considered on commercial aircraft, because current engines being exclusively equipped with single fans, the VAFN to operate correctly requires a fairly large variation in the surface area of ​​the nozzle, such as for example 20% variation between the closed and open VAFN. To achieve this level of variation, the VAFN system must be positioned at the downstream end of the fairing and on the periphery thereof. In addition to the technical over-complexity and the excess weight generated by such a VAFN, the aerodynamics of the fairing are significantly degraded, which is very detrimental to the propulsive efficiency of the engine.

[0015] It is known to those skilled in the art that a pair of counter-rotating fans, that is to say a fan composed of two fans rotating in opposite directions to each other, allows greater propulsion efficiency than a single fan rotating in one direction. Also, due to the current strong trend of research into an aircraft engine with very high propulsive efficiency, it is advantageous to be able to use such a pair.

[0016] In the same way as for a single fan, a low FPR counter-rotating fan gains in efficiency but is also less sensitive to malfunctions at takeoff than a single fan. As a result, such a fan can operate with a VAFN having a smaller variation in nozzle surface area, such as for example 10% variation between the closed and open VAFN, and therefore less heavy and not degrading the aerodynamics of the fairing.

[0017] Since the energy performance and reliability of commercial aircraft engines are in constant need of improvement, the objective of the invention is to propose a low variation rate VAFN device solving the aforementioned problems of prior art VAFNs arranged on the fairing of a dual-flow turbofan. DESCRIPTION OF THE FIGURES

[0018] In these drawings: - [Fig.l] is a general view in half longitudinal section of an example of a double-flow turbofan architecture with a counter-rotating fan incorporating the device according to the invention

[0019] - [Fig.2] is a front detail view according to [Fig.l], following a first position B1 of the device

[0020] - [Fig.3] is a front detail view according to [Fig.l], following a second position B2 of the device

[0021] - [Fig.4] is an isometric detail view according to [Fig.2]

[0022] - [Fig.5] is an isometric detail view according to [Fig.3]

[0023] - [Fig.6] is an exploded isometric view of the device according to an exemplary embodiment

[0024] To this end, the invention relates, in its most general sense, to a device for varying the section of the cold flow nozzle, not integrated or incorporated into the fairing of a high bypass ratio turbofan, faired, with longitudinal rotation axis X.

[0025] In [Fig.l] is shown the double-flow, ducted turbofan 10 with a reduced counter-rotating fan, which comprises from upstream to downstream, in the flow direction of the flows (A; B), a reducer 5 driving the fans S and S', and a turbomachine 2 comprising a low-pressure compressor 2a, a high-pressure compressor 2b, a combustion chamber 2c, a high-pressure turbine 2d, a low-pressure turbine 2e and an exhaust nozzle 2f. The high-pressure compressor 2b and the high-pressure turbine 2d are connected by a high-pressure shaft 3 (HP). The low-pressure compressor 2a and the low-pressure turbine 2e are connected by a low-pressure shaft 4 (LP). The axes of the high pressure shaft 3 (HP), the low pressure shaft 4 (LP) and the fan S;S' are substantially coincident with the axis of rotation X of the turbofan 10.

[0026] The reducer 5 is positioned in the front part of the turbofan 10 and is attached to a casing 8 which can be likened to an element of the stator of the turbofan 10. The casing 8 is attached to a fairing 11 by means of a plurality of profiled spokes 9.

[0027] As illustrated in the figures the air flow sucked in by the counter-rotating fan S;S' is, at its downstream end, divided into two flows A and B. An air flow A entering the turbomachine 2 and an air flow B, called “cold flow” circulating in the air stream formed by the outer walls 6 of the turbomachine 2 on the one hand and the inner wall 11a of the fairing 11.

[0028] In order to vary the surface area of ​​the nozzle at the outlet of the cold flow B, that is to say to vary the annular section 12 of said air stream, without modifying the geometry of the fairing 11, a device 6 according to the invention makes it possible, by a set of conical surfaces, to increase to a value B1 or to reduce to a value B2, said annular passage section 12 between said device 6 and a conical annular wall 11a, of axis X, of the fairing 11.

[0029] The device 6 is generally constituted by a circular wall 7, with an axis of revolution X, encircling the turbomachine 2 and attached to the fixed casing 8, longitudinally guiding a shaped wall 20, with an axis of revolution X, here called a “nozzle”, centered diametrically and sliding inside said wall 7. The nozzle 20 is furthermore driven in longitudinal translation along X, by at least one linear cylinder 25 or any other device allowing said translation of the nozzle 20.

[0030] The nozzle 20 is generally formed by a cylindrical wall 20a, extended by a conical wall 20b, of axis X.

[0031] According to the figures

[0032] In the nominal position, the at least one cylinder 25, attached by one end to the nozzle 20, is in the retracted position, with a rod length L1, thus moving the conical wall 20b of the nozzle 20 away from the conical wall 11a of the fairing, thus opening the nozzle of the cold air flow B, increasing the section 12.

[0033] In the reverse position, the at least one jack 25 is in the extended position, with a rod length L2, thus bringing the conical wall 20b of the nozzle 20 closer to the conical wall 11a of the fairing, thus closing the nozzle of the cold air flow B, reducing the section 12.

[0034] The translation of the nozzle 20 along the axis X allows a variation of the annular passage section 12 without modification of the geometry of the fairing 11, which therefore has the effect of being able to regulate the pressure in the air stream of the cold flow B, without degrading the aerodynamic performance of said fairing 11.

[0035] According to the figure

[0036] In a non-limiting example of embodiment, the shaped wall 20 is formed by a plurality of shaped plates 21 fitting together to form said nozzle 20. Said plates 21 can for example be made from casting or stamped plates, and have a tenon-mortise system 21a; 21b arranged on their adjacent edges in order to hold each other together once assembled together.

[0037] The cylindrical surface 20a of the nozzle 20 can be adjusted diametrically in order to be centered on a sliding surface 7a of the cylindrical wall 7.

[0038] A plurality of jacks 25, for example in number identical to the plurality of plates 21, can for example be attached to said plates 21 by the end of their movable rod 25a, via a hole made in the plate 21 and a fixing nut.

[0039] The at least one cylinder 25 may for example be an electric or hydraulic linear type actuator well known to those skilled in the art.

Claims

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