Masking wheel for a moving wheel of a turbojet compressor

Abstract

The invention relates to a bladed wheel (1) for masking a moving wheel of a turbojet engine, comprising blades (2), each blade (2) comprising an intrados wall (Pi) and an extrados wall (Pe) joined at a leading edge (3) and at a trailing edge (4), and in which each blade (2): – has an intrados wall (Pi) and an extrados wall (Pe) each comprising a concave zone (CCi) and a convex zone (CVi) spaced from the leading edge (3) and the trailing edge (4) and spaced from each other; – these concave zones (CCi, CCe) and these convex zones (CVe, CVi) each extend over the majority of the height of the blade (2); – The concave zone (CCi) of the intrados wall (Pi) is opposite the convex zone (CVe) of the extrados wall (Pe); – The concave zone (CCe) of the extrados wall (Pe) is opposite the convex zone (CVi) of the intrados wall (Pi). Figure 4

Description

Title of the invention: Masking wheel for a moving wheel of a turbojet compressor Technical field

[0001] The invention relates to a turbojet type engine equipped with means reducing its radar and / or noise signature. STATE OF THE PRIOR ART

[0002] A radar is an electromagnetic wave transmitter comprising a receiver for detecting whether part of the waves it emits are or are not reflected by an object or obstacle present in the region of emission of these waves.

[0003] In the case of a so-called stealth aircraft, the external elements of this aircraft are treated to limit the reflection of electromagnetic waves, so as to make it as weakly detectable by radar as possible.

[0004] When this aircraft is equipped with a turbojet type propulsion system, the air is admitted into an inlet sleeve to first pass through a low pressure compressor comprising a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0005] The rotating elements of this turbojet engine constitute in themselves a source of detection, because they reflect radar waves, and thereby contribute to making the aircraft detectable.

[0006] One possibility for limiting radar detection of the low-pressure compressor is to bend the inlet sleeve, so that the incident radar waves are deflected by reflection on the inclined walls of the sleeve during their progression therein. These waves thus have an oblique incidence on the rotor elements of the engine, so that they are diffused by them to be weakly reflected towards the inlet of the sleeve.

[0007] In practice, this solution remains insufficient, and the level of radar detection of the low pressure compressor of a turbojet is still too high.

[0008] In this context, the object of the invention is to provide a solution making it possible to reduce the level of radar detection of the rotor elements of a low-pressure turbojet compressor. Statement of the invention

[0009] To this end, the invention relates to a bladed wheel for masking a turbojet engine wheel, comprising blades, each blade comprising a lower surface wall and an upper surface wall joined at a leading edge and at from a trailing edge and extending along a span axis from a foot to a vertex, and in which:

[0010] - the intrados wall comprises an upstream portion extending from the leading edge to a convex area of ​​this intrados wall, a central portion extending from the convex area to a concave area of ​​this intrados wall, and a downstream portion extending from the concave area to the trailing edge;

[0011] - the extrados wall comprises an upstream portion extending from the leading edge to a concave area of ​​this extrados wall, a central portion extending from the concave area to a convex area of ​​this extrados wall, and a downstream portion extending from the convex area to the trailing edge;

[0012] - these concave zones and these convex zones each extend over the majority of the height of the blade along its span axis;

[0013] - the concave zone of the intrados wall is opposite the convex zone of the extrados wall, and the concave area of ​​the extrados wall is opposite the convex area of ​​the intrados wall.

[0014] With this arrangement, incoming magnetic waves passing through the wheel are deflected to have an oblique incidence on the low pressure compressor wheel so as to be weakly reflected by it.

[0015] The invention also relates to a bladed wheel thus defined, in which each blade is a variable-pitch blade pivotally mounted around an axis located at its leading edge.

[0016] The invention also relates to a bladed wheel thus defined, in which each blade comprises a downstream portion extending from the trailing edge to the convex and concave zones respectively of its extrados and intrados walls, and in which each downstream portion is a variable-pitch flap pivotally mounted between the convex and concave zones respectively of its extrados and intrados walls.

[0017] The invention also relates to a bladed wheel thus defined, in which the blades are covered with a coating absorbing electromagnetic radiation.

[0018] The invention also relates to a turbocharger comprising a low pressure compressor including a moving wheel upstream of which is arranged an inlet guide wheel upstream of which is mounted a bladed wheel thus defined.

[0019] The invention also relates to a turbocharger comprising a low pressure compressor including a moving wheel upstream of which is arranged a bladed wheel thus defined. Brief description of the drawings

[0020] [Fig-1] is a schematic perspective view of a portion of the masking wheel according to the invention;

[0021] [Fig.2] is a schematic representation showing two consecutive blades according to the invention in top view;

[0022] [Fig.3] is a sectional view along an orthoradial plane of a blade according to the invention;

[0023] [Fig.4] is a perspective representation of a blade according to the invention;

[0024] [Fig.5] is a schematic representation showing two masking blades consecutive variable timing in accordance with a variant of the invention;

[0025] [Fig.6] is a schematic representation in longitudinal section of an architecture propulsion system comprising an angled inlet sleeve opening into a turbojet;

[0026] [Fig.7] is a schematic view in longitudinal section of an inlet portion of turbojet engine equipped with a masking wheel according to the invention arranged upstream of an inlet guide wheel itself upstream of the low pressure compressor;

[0027] [Fig.8] is a schematic longitudinal sectional view of an inlet portion of a engine equipped with a masking wheel according to the invention arranged directly upstream of the low pressure compressor;

[0028] [Fig.9] is a schematic representation showing two masking blades consecutive each having a downstream flap with variable timing according to another variant of the invention.

[0029] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0030] The idea behind the invention is to provide between the air inlet and the low pressure compressor, a wheel carrying fixed blades arranged to geometrically mask the compressor rotor located downstream of them.

[0031] As shown schematically in [Fig.l] this masking wheel 1 carries fixed masking blades 2 regularly distributed along its circumference, and whose shapes are arranged to delimit between them inter-blade channels in the form of chicanes to offer angles of reflection to the electromagnetic radiation which passes through it in order to deflect them.

[0032] As visible in [Fig.2], each blade 2 extends between a leading edge 3 and a trailing edge 4 both oriented parallel to a span axis of the blade which is an axis extending radially relative to a longitudinal axis AX of the engine when the blade is mounted. This blade 2 comprises an upstream axial portion 6 extended by a central oblique portion 7 itself extended by an axial downstream portion 8. The upstream marked by AM, and the downstream marked by AV in the figures are defined relative to the direction of circulation of the air flow in the engine, that is to say along the longitudinal direction AX of the turbojet, in accordance with the usual conventions.

[0033] The upstream axial portion 6 extends in the longitudinal direction, that is to say approximately in a plane containing the longitudinal axis AX of the engine, to within approximately 10° of inclination. The central portion has an orientation oblique, which means that it is inclined relative to the axis AX. The downstream portion 8 is offset relative to the upstream portion around the axis AX, while extending approximately longitudinally, that is to say that this downstream portion extends along another plane passing through the longitudinal axis AX, to within approximately 10° of inclination.

[0034] The upstream, central, and downstream portions are symbolically represented by flat walls in Figures 1, 2, 5, and 9, to simplify understanding. In practice, each blade 2 has a curved shape that can be broken down into upstream, central, and downstream portions based on their functionalities with respect to fluid flow and electromagnetic deflection.

[0035] An example of a blade 2 according to the invention having a curved shape is shown in Figures 3 and 4. This blade 2 comprises a curved extrados wall Pe and an intrados wall Pi, each connecting its leading edge 3 to its trailing edge 4 while being laterally spaced from each other, and each extending from a root Pd to a tip Sm. The root Pd corresponds to the part by which this blade is connected or fixed to an internal shroud of the wheel 1, and its tip Sm corresponds to the part by which it is fixed to an external casing of this wheel 1.

[0036] The extrados wall Pe comprises, from the leading edge 3 to the trailing edge 4, an upstream axial portion 6e followed by a concave zone CCe followed by an inclined central portion 7e followed by a convex zone CVe followed by a downstream axial portion 8e ending at the trailing edge. These zones and these portions extend over the majority of the height of the blade, that is to say its length from its root Pd to its tip Sm measured along the span axis EV of this blade.

[0037] The intrados wall Pi comprises, from the leading edge 3 to the trailing edge 4, an axial upstream portion 6i followed by a convex zone CVi followed by an inclined central portion 7i followed by a concave zone CCi followed by an axial downstream portion 8i terminated by the trailing edge 4. These zones and these portions extend over the majority of the height of the blade measured along its span axis EV.

[0038] Each central portion 7e and 7i extends between a convex zone and a concave zone, so that the two central portions 7e and 7i each comprise an inversion of curvature.

[0039] As illustrated in [Fig.2], two consecutive masking blades 2 delimit between them an inter-blade fluid passage channel which constitutes a chicane between the two oblique central portions 7 inclined relative to the axis AX.

[0040] Generally speaking, this channel can be characterized by its masking coefficient and by its relative pitch which are representative of its geometry.

[0041] This channel thus has a pitch noted P which is the distance separating two consecutive blades 2 in top view, that is to say along the circumference of the wheel 1, and which corresponds approximately to the ratio of the perimeter of the wheel to its number of blades. This channel also has an apparent width L, corresponding to the smallest apparent distance between two consecutive blades when the wheel is seen from the front, i.e. along the axis AX.

[0042] The masking coefficient of the channel or of the wheel 1, namely the ratio L / P, thus corresponds to the proportion of blades of the compressor wheel located downstream of the masking wheel 1, which is visible through the blades of this wheel 1. In other words, for a radar located in the axis AX, facing the wheel 1, the proportion of emitted waves that can be reflected by the compressor blades is at most L / P. The effective masking coefficient is all the lower as the orientation of the radar is inclined relative to the axis AX.

[0043] The relative pitch of the inter-blade channel corresponds to the ratio of the pitch P to the chord length noted C of the oblique portion 7, namely P / C, and it mainly conditions the aerodynamics of the channel.

[0044] The central oblique portion 7 of the blade 2 is the one which ensures the masking: it is its inclination and its length which condition the coefficient L / P, that is to say the proportion of incident electromagnetic waves which are deflected by being reflected by this central oblique portion 7 when they pass through the wheel 1.

[0045] The upstream axial portion 6 is dedicated to straightening the incoming flow which may be disturbed in particular by its path in the bent inlet sleeve. Guiding this flow in the upstream axial portion of the channel makes it possible to straighten it and obtain a flow limiting the increase in entropy (limitation of losses by friction and shear), in order to avoid a drop in the air flow passing through the engine. These upstream axial portions thus provide the system with robustness with respect to flow distortions of the incoming air flow.

[0046] The upstream axial portion 6 is all the longer as the incident flow is likely to be disturbed: in the case of undisturbed flow, this upstream axial portion 6 could have a very short length, or even zero to be non-existent.

[0047] The downstream axial portion 8 is dedicated to straightening the flow at the outlet of the central oblique portion: the passage of the flow through the central oblique portion causes a gyration of this flow. The reduction of this gyration (flow straightening or untwisting) by the downstream axial portion 8 makes it possible to ensure optimal supply of the compression stages to be crossed. In practice, the gyration of the flow corresponds to a flow whose streamlines have helical shapes around the axis AX, as opposed to rectilinear streamlines parallel to the axis AX in the case of a straightened flow.

[0048] The downstream axial portion 8 is thus all the longer as the flow must be straightened to supply the compressor, so that this length can be very short or even zero in the case where the compressor presents a high robustness with respect to flow twisting.

[0049] Furthermore, the masking blades according to the invention can be provided with variable pitch, to adjust the degree of masking to the flight conditions. In this case, as shown in [Fig. 5], each blade 2 is mounted on the wheel 1 so as to be able to pivot around a radial axis coinciding with its leading edge 3, in order to modify its pitch angle. In addition, the wheel 1 is then equipped with control means, not shown, which control the pitch of the blades 2.

[0050] Thus, and as illustrated schematically in [Fig.5], a modification of the pitch angle of the blades 2 makes it possible, for example, to temporarily increase the apparent width L of the inter-blade channels, to promote the efficiency of the engine at the expense of stealth.

[0051] The masking wheel 1 is advantageously arranged upstream of a first mobile compressor wheel in a propulsion system architecture such as shown in [Fig.6], that is to say comprising an angled inlet sleeve 9 connected to a turbojet engine 11 comprising a compressor 12, to supply this turbojet engine 11 with air.

[0052] As can be seen in more detail in [Fig.7], the low-pressure compressor 12 comprises a first bladed moving wheel 13 upstream of which is arranged a known inlet guide wheel 14. This inlet guide wheel comprises axial fixed blades to stabilize the fluid flow having passed through the inlet sleeve 9 before it passes through the first moving wheel 13.

[0053] The masking wheel 1 according to the invention is installed upstream of this steering wheel 14 in the inlet sleeve, to reduce the reflection on the first moving wheel 13 of the electromagnetic radiation having penetrated into the inlet sleeve 9.

[0054] In this context, the masking wheel according to the invention comprises an external casing located at the inlet of the turbojet and to which the blades are connected by their tips Sm, and an internal shroud 16 to which the blades are connected by their roots Pd.

[0055] According to another arrangement shown in [Fig.8], the masking wheel according to the invention is located immediately upstream of the first moving wheel 13 of the compressor, so as to jointly ensure the functions of masking wheel and inlet steering wheel for the compressor.

[0056] With this other arrangement, the pressure losses introduced by the masking wheel are reduced by the fact that it replaces the existing guide wheel: the flow passing through the engine is entirely stabilized by the masking wheel before reaching the first moving wheel of the compressor: it is then the downstream axial portions 8 of the masking blades which ensure the function of the inlet guide wheel.

[0057] In this other arrangement, the blades 2 are advantageously in two parts: a first fixed part comprising the upstream portion 6 and the central portion 7, and a second part with variable pitch comprising the downstream portion 8.

[0058] The second part thus constitutes a variable-setting flap, capable of pivoting around its upstream edge which extends at the level of the concave zone CCi of the intrados wall Pi and the convex zone CVe of the extrados wall Pe.

[0059] The flap setting angle is then controlled to be adjusted according to the engine operating conditions so as to best adjust the flow straightening before admission into the compressor.

[0060] Generally speaking, the blades are sized to optimize the masking coefficient in order to reduce the radar signature, while maintaining sufficient compressor performance. This sizing consists mainly of determining the angle of inclination of the central oblique portion, and the chord length C of this oblique portion, i.e. the masking coefficient and the relative pitch. In practice, it appears that the optimal operating compromises can be obtained for an inclination of the oblique portion significantly less than 30° and a relative pitch less than 0.6.

[0061] In order to increase stealth, the blades 2 can advantageously be covered with a coating which partially absorbs incident electromagnetic radiation.

[0062] Furthermore, the invention has been described in the context of reducing the radar signature of a turbojet, but it also applies to reducing the noise emissions of such a turbojet. In the latter case, the invention applies in particular to an engine integrated into an aircraft tail, also called a buried engine.

Claims

Claims

1. Bladed wheel (1) for masking a turbojet engine wheel, comprising blades (2), each blade (2) comprising a lower surface wall (Pi) and an upper surface wall (Pe) joined at a leading edge (3) and at a trailing edge (4) and extending along a span axis (EV) from a root (Pd) to a tip (Sm), and in which: - the lower surface wall (Pi) comprises an upstream portion (6i) extending from the leading edge (3) to a convex zone (CVi) of this lower surface wall (Pi), a central portion (7i) extending from the convex zone (CVi) to a concave zone (CCi) of this lower surface wall (Pi), and a downstream portion (8i) extending from the concave zone (CCi) at the trailing edge (4);- the extrados wall (Pe) comprises an upstream portion (6e) extending from the leading edge (3) to a concave zone (CCe) of this extrados wall (Pe), a central portion (7e) extending from the concave zone (CCe) to a convex zone (CVe) of this extrados wall (Pe), and a downstream portion (8e) extending from the convex zone (CVe) to the trailing edge (4); - these concave zones (CCi, CCe) and these convex zones (CVe, CVi) each extend over the majority of the height of the blade (2) along its span axis (EV); - the concave zone (CCi) of the intrados wall (Pi) is opposite the convex zone (CVe) of the extrados wall (Pe), and the concave zone (CCe) of the extrados wall (Pe) is opposite the convex zone (CVi) of the intrados wall (Pi) and in which each blade (2) is a variable-pitch blade pivotally mounted around an axis located at its leading edge (3).;

2. Bladed wheel (1) according to claim 1, in which each blade (2) comprises a downstream portion (8) extending from the trailing edge (4) to the convex and concave zones (CVe, CCi) respectively of its extrados (Pe) and intrados (Pi) walls, and in which each downstream portion (8) is a variable-pitch flap pivotally mounted between the convex and concave zones (CVe, CCi) respectively of its extrados (Pe) and intrados (Pi) walls.

3. A bladed wheel according to one of the preceding claims, wherein the blades (2) are covered with a coating which absorbs electromagnetic radiation.

4. Turbojet comprising a low pressure compressor (12) including a moving wheel (13) upstream (AM) of which is arranged an inlet guide wheel (14) upstream (AM) of which is mounted a masking bladed wheel (1) according to claim 1.

5. A turbojet engine comprising a low pressure compressor (12) including a moving wheel (13) upstream of which is arranged a masking bladed wheel (1) according to claim 1.

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