Fan nozzle of adjustable section

An adjustable section nozzle having a ring of deformable panels arranged close to its trailing edge is disclosed. Each panel has a dual-strip type structure made up of two materials presenting different coefficients of expansion, together with controlled heater devices that are thermally coupled to the set of panels.

The invention relates to a bypass turbojet, and more particularly relates to an improvement to a fan nozzle that enables the outlet section of said nozzle to be adapted as a function of operating conditions.

BACKGROUND OF THE INVENTION

It is known that the performance of a turbojet can be improved and/or that its noise level can be reduced by varying the flowsection for air from the fan as a function of flying conditions. Thus, compared with the section that is normally appropriate for cruising conditions, improved performance can be obtained during takeoff or landing by reducing said section. For this purpose, it is known to place a ring of flaps close to the trailing edge of the nozzle, the flaps being movable and being controlled so as to retract towards the axis of the turbojet, thereby reducing the flowsection for the air flowing through the fan. The flaps are generally actuated by actuators, thereby adding considerably to the weight of the mechanism.

Document US 2006/0101803 describes a nozzle in which the trailing edge is provided with deformable panels known as “chevrons” that include inner tendons of shape memory alloy and of curvature that is determined by temperature. The curvature imposed by the tendons (which depends on their temperature) is transmitted to the panels. The electrical control means are simpler and lighter in weight, but the structure of such a panel remains complex.

OBJECT AND SUMMARY OF THE INVENTION

The invention seeks to provide another type of deformable panel.

More particularly, the invention provides an adjustable-section fan nozzle having a ring of deformable panels arranged close to its trailing edge, wherein each panel is of dual-strip type structure being made of two materials presenting different coefficients of expansion, and wherein controlled heater means are thermally coupled to the set of panels.

More precisely, it is possible to use a lamellar structure made up of two materials presenting different coefficients of expansion in association with an electrical heater device.

In a presently-preferred embodiment, each panel comprises an inner strip of thermally-insulating material and at least one outer strip of metal. The two strips are assembled one against the other so that the difference in elongation (parallel to the axis of the nozzle) of the two strips, under the effect of a rise in temperature, causes the panel to curve in a direction tending to reduce the flowsection at the outlet from the nozzle.

The thermally-insulating material may be a composite material, e.g. based on carbon.

In one possible embodiment, the panels may be heated by a set of electrical resistances. These resistances are distributed over the surfaces of the metal strips (with dielectric insulation being interposed) and they are in thermal contact therewith. Thus, the panels are controlled simultaneously by injecting electric current into the array of resistances.

In one possible embodiment, each panel is substantially trapezoidal in shape. Thus, the panels curving under the effect of a temperature rise take up a configuration in which they are practically edge to edge, without overlap.

Advantageously, the panels are mounted in the thickness of an annular space defined in the wall of the nozzle so they do not disturb the flow of the stream of air under cruising conditions. More particularly, the panels may be situated in continuity with the inner aerodynamic surface of the nozzle when the controlled heater means are not in operation.

The invention also provides a bypass turbojet fitted with a fan nozzle as defined above.

MORE DETAILED DESCRIPTION

FIG. 1shows the rear portion of the nacelle11of a bypass turbojet, and in particular it shows the structure of the annular nozzle12of the fan. The nozzle presents a trailing edge14having deformable panels16arranged in a ring in the vicinity of the edge thereof. The outer wall of the fan nozzle is made up of two annular casings18and19that join at the rear, forming an annular cavity21(seeFIG. 3) in which the deformable panels16are housed.

According to an important characteristic of the invention, each panel16presents a structure of the dual-strip type, being made up of two materials having two different coefficients of expansion. For each panel16, there can be seen an inner strip25of thermally-insulating material having a low coefficient of expansion and at least one outer metal strip26. The strip25may be made of a composite material, e.g. a material based on carbon. The strips are assembled one against the other by adhesive and/or by riveting. Adhesive could be replaced by conventional carbon/metal brazing. More precisely, each panel advantageously includes a plurality of metal strips26associated with a common strip of thermally-insulating material. The metal strips26are disposed side by side at small circumferential spacing, the strip25of thermally-insulating material acting as a common support for them. As shown inFIG. 2, the metal strips are specifically riveted to the strip of thermally-insulating material having a low coefficient of expansion. In this way, the expansion of the metal strip has no effect in the circumferential direction. In contrast, in the axial direction, the expansion of the metal strip, which is greater than the expansion of the strip of thermally-insulating material, causes the panel to become curved and to penetrate into the flowsection by moving out from the annular cavity21. The panels are disposed continuously with the internal aerodynamic surface when the control heater means are not activated, as shown inFIG. 3.

Each panel is substantially trapezoidal in shape. Thus, when the panels retract so as to engage into the flowsection for the air stream from the fan, they “reconstitute” a shroud of said nozzle by becoming practically edge to edge, but without overlap or abutment.

In addition, the control heater means are thermally coupled to the set of panels. More particularly in this example, the heater means comprise electrical resistances30that are distributed over the (outside) surfaces of the metal strips26and they are in thermal contact therewith, via a thin layer of dielectric insulation. These electrical resistances may be in the form of resistive deposits, in the form of adhesively-bonded resistive electric wires, etc.

As shown inFIG. 4, the electrical resistances30associated with each panel or even with each metal strip are electrically connected in parallel and connected to a power supply32. In addition, each panel carries a movement sensor34enabling the bending of the panels to be evaluated. The signals issued by the sensors are used in a servo-control loop36to determine the amount of electric current that is injected into the resistances in order to obtain the desired amount of bending for the panels.

As shown inFIG. 3, each composite strip25presents a stub35of predetermined thickness. Together these stubs form an annular spacer defining the spacing between the inner casing19and the outer casing18of the wall of the nozzle. It should be observed that the outer aerodynamic streamlines of the nozzle are not modified. When the panels are retracted inside the annular cavity21they do not disturb the continuity of the internal aerodynamic streamlines.

An additional insulating layer37may be provided that covers the outsides of the panels16so as to limit outward heat losses and consequently reduce the amount of electricity consumed by the system for controlling the resistances.