Inlet guide vane turbojet

Abstract

Turbojet (1) having a longitudinal axis (1), the turbojet (1) comprising a fairing (2) surrounding a fan (3) and a plurality of inlet guide vanes (5) arranged upstream of said fan (3) along the longitudinal axis (A). The fan (3) comprises a plurality of fan blades (7), each fan blade (7) comprising an upstream leading edge (17), comprising a first radially internal end (B) and a second radially external end (T), the two ends being separated from each other radially by a height (Hs) of a fan blade (7). The inlet guide vanes (5) project radially inward from the shroud (2), each inlet guide vane (5) having a radial length (Hg) greater than or equal to 20% of the fan blade height (Hs) (7). Figure to be published with the abbreviation: 1

Description

Title of the invention: Turbojet engine with inlet guide vanes Technical field of the invention

[0001] The invention relates to a turbojet engine comprising a fan and inlet guide vanes, for example a bypass turbojet engine.

[0002] The invention also relates to an aircraft equipped with such a turbojet. State of the prior art

[0003] In most bypass turbojets, a fan is placed upstream of a low-pressure compressor. The fan comprises blades regularly distributed around a longitudinal axis of the turbojet, rotating at high speed around this longitudinal axis.

[0004] The air inlet of a turbojet is the part located upstream of the fan. Its role is to capture the air in the best conditions and to guide it towards said fan and said low pressure compressor in a regular manner, in order to improve its aerodynamic behavior.

[0005] For this purpose, it is known to place inlet guide vanes upstream of the fan capable of regulating the flow of air through this part of the turbojet.

[0006] Such turbojets are described in more detail in documents US 2018 / 0363676 Al, US 2018 / 0363675 Al and US 2018 / 03635554 AL

[0007] The inlet guide vanes make it possible to accelerate the rotation of the fan and therefore of the low pressure shaft which it drives, thus improving the efficiency of the low pressure system and allowing a reduction in the mass of the turbojet.

[0008] Fan blades are very sensitive to impacts from external projectiles, given their large size and high rotation speed.

[0009] A recurring problem for aircraft equipped with turbojet engines is the swallowing of birds by the turbojet engine, which damages the fan blades. The damage inflicted can result in a reduction in the thrust provided by the turbojet engine, and requires regular inspection and replacement of damaged blades.

[0010] For the swallowing resistance test, birds are classified into small, medium and large sizes. Of particular interest here are swallowings of medium-sized birds, which cause significant damage and are relatively common in comparison.

[0011] The use of projectile resistant fan blades often involves a significant mass for the fan and reduces the performance of the low pressure system.

[0012] It is therefore desirable to improve the protection of the fan against projectiles swallowed by the turbojet, in particular medium-sized birds, without significantly increasing the mass of the turbojet and without deteriorating its performance and efficiency. Presentation of the invention

[0013] The invention aims to overcome these drawbacks. To this end, the subject of the invention is a turbojet engine having a longitudinal axis, the turbojet engine comprising a fairing surrounding a fan and a plurality of inlet guide vanes arranged upstream of said fan along the longitudinal axis, the fan comprising a plurality of fan blades, each fan blade comprising an upstream leading edge, comprising a first radially inner end and a second radially outer end, the two ends being separated from each other radially by a fan blade height,

[0014] characterized in that the inlet guide vanes project radially inwardly from the fairing, each guide vane having a radial length greater than or equal to 20% of the fan blade height.

[0015] Such a turbojet engine provides improved protection for the fan blades against projectiles swallowed by the turbojet engine, particularly medium-sized birds, and therefore improves their durability.

[0016] The length of the inlet guide vanes makes it possible to protect the part of the fan blades most sensitive to impacts, which extends between 85% and 100% of the height of the fan blade. However, the inlet guide vanes can still extend over a radial length, for example up to 40% and even up to 50% of the fan blade height.

[0017] Such improved protection makes it possible to use fan blades of reduced mass, in particular in their radially external part, which improves the aerodynamic performance of the fan, makes it possible to reduce the thickness of the fairing, and thus reduces the total mass of the turbojet.

[0018] The turbojet engine may comprise a number of inlet guide vanes greater than or equal to a fan radius, measured in meters, radially separating the tip of the fan blades from the longitudinal axis, divided by 0.0125.

[0019] Such a minimal number of inlet guide vanes greatly improves the chances of intercepting a medium-sized bird swallowed by the turbojet by at least one of the inlet guide vanes.

[0020] The turbojet engine may comprise a number of inlet guide vanes less than or equal to a radius of the fan, measured in meters, radially separating a tip of the fan blades from the longitudinal axis, divided by 0.0075.

[0021] Such a maximum number of inlet guide vanes makes it possible to maintain satisfactory aerodynamic operation upstream of the fan.

[0022] For each inlet guide vane, a pitch angle, formed with the longitudinal axis by a straight line connecting an upstream end and a downstream end of a section of the inlet guide vane, in a plane parallel to the longitudinal axis, may be greater than or equal to 5°.

[0023] Such a minimum value of the pitch angle of the inlet guide vane allows sufficient damping of a projectile swallowed by the turbojet, in particular a medium-sized bird, to sufficiently reduce damage to the downstream fan blades.

[0024] Said wedging angle may be less than or equal to 25°.

[0025] Such a maximum value of the pitch angle makes it possible to maintain optimal aerodynamic operation of the inlet guide vanes.

[0026] For each inlet guide vane, an angle of attack, formed with the longitudinal axis by a straight line connecting an upstream end of a section of the guide vane, in a plane parallel to the longitudinal axis, and a point of a center line of the inlet guide vane extending from a leading edge to a trailing edge, separated from the upstream end by a length equal to 10% of a total length of the length of said center line in said plane parallel to the longitudinal axis, may be less than or equal to 10°.

[0027] Such a maximum value of the angle of attack makes it possible to maintain satisfactory aerodynamic operation of the inlet guide vanes, in particular for high values ​​of the pitch angle.

[0028] Each inlet guide vane may have a radial length of between 20% and 50% of the fan blade height.

[0029] The invention also relates to an aircraft comprising a turbojet engine according to one of the preceding claims. Brief description of the figures

[0030] [Fig-1] [Fig. 1] is a partial sectional view of a turbojet engine comprising a fan and inlet guide vanes,

[0031] [Fig.2] [Fig.2] is a front view of the inlet guide vanes of the turbojet engine of [Fig.l],

[0032] [Fig.3] [Fig.3] is a sectional view in an orthoradial plane of a blade of input guidance of figures 1 and 2, and

[0033] [Fig.4] [Fig.4] is another view in an orthoradial plane of the guide vane input of [Fig.3]. Detailed description of the invention

[0034] [Fig.l] is a partial sectional view of an upstream part of a turbojet 1, comprising a fairing 2 surrounding a fan 3 and inlet guide vanes 5.

[0035] The turbojet engine 1 has a generally substantially cylindrical shape, and extends around a longitudinal axis A oriented from an upstream side to a downstream side, relative to the flow of air in the turbojet engine 1 in operation.

[0036] In all that follows, the terms “axial”, “radial”, “orthoradial” and “circumferential” are understood relative to the longitudinal axis A.

[0037] The fairing 2 has a substantially tubular shape around the axis A.

[0038] The fan 3 comprises a disc 6 and fan blades 7 regularly distributed around the longitudinal axis A.

[0039] Each fan blade 7 comprises a root 11, a platform 13 and a blade 15. The fan blades 7 are fixed to the disc 6 by their respective root 11, which is engaged in a cavity of the disc 6.

[0040] Each fan blade 7 defines a tip 16 radially away from the longitudinal axis A and in the vicinity of the fairing 2.

[0041] The blade 15 of each fan blade 3 defines a leading edge 17 extending upstream relative to the longitudinal axis A, from the platform 13 to the apex 16, and a trailing edge 19 extending downstream relative to the longitudinal axis A, from the platform 13 to the apex 16.

[0042] A height Hs of the fan blades 7 is defined as the height of the leading edge 17 measured radially, that is to say separating in the radial direction only a first radially internal end B and a second radially external end T of the leading edge 17.

[0043] The height Hs is representative of a height of the blade 15 in the radial direction, that is to say a height of the blade exposed to the impacts of projectiles swallowed by the turbojet 1.

[0044] Each inlet guide vane 5 projects radially inwardly from the fairing 2 to a tip 21.

[0045] A height Hg of the inlet guide vanes 5 is measured as the radial distance separating the fairing 2 from the tip 21 of the inlet guide vane 5.

[0046] The height Hg of the inlet guide vanes 5 is greater than or equal to 20% of the height Hs of the fan vanes 7, which makes it possible to protect the most vulnerable part of the fan vanes 7 against projectiles.

[0047] As shown in [Fig.2], the number of inlet guide vanes 5 must be sufficient to maximize the chances that a medium-sized bird-type projectile 23 will be intercepted by at least one of said inlet guide vanes 5.

[0048] The projectile 23 is for example a gelatin cylinder of the type used to simulate medium-sized bird strikes.

[0049] A spacing E separating, in a circumferential direction, the tops 21 of two neighboring inlet guide vanes 5, must for this purpose be less than or equal to the diameter of the projectile 23.

[0050] For inlet guide vanes 5 with a height Hg equal to 20% of the height Hs of the fan vanes 7, this condition can result in a minimum number of inlet guide vanes 5 as a function of a radius R of the fan 3.

[0051] The radius R of the fan 3 is defined as the distance measured radially separating the longitudinal axis A from the tip 16 of the fan blades 7. The radius R of the fan 3 is substantially equal to an internal radius of the fairing 2, measured radially between the fairing 2 and the longitudinal axis A at the level of the inlet guide blades 5.

[0052] The minimum number of inlet guide vanes 5 is then equal to the radius R of the fan 3, measured in meters, divided by 0.0125.

[0053] In order to maintain a satisfactory flow of the air flow through the inlet of the turbojet 1, the number of guide and inlet blades 5 must be less than or equal to the radius R of the fan 3, expressed in meters, divided by 0.0075.

[0054] [Fig. 3] is a sectional view of one of the inlet guide vanes 5 in an orthoradial plane P, parallel to the longitudinal axis A (see [Fig. 1]).

[0055] A setting angle a of the inlet guide vane 5 may be chosen to be greater than or equal to 5°, in order to increase the interaction between said inlet guide vane 5 and a projectile 23, and thus reduce the velocity of the projectile more effectively.

[0056] The setting angle a is defined as the angle between the direction of the longitudinal axis A and a straight line C, called the chord of the inlet guide vane 5, extending between a point Pb located at the intersection of the leading edge 17 and the orthoradial plane P, and a point P2, located at the intersection of the trailing edge 19 and the orthoradial plane P.

[0057] In order to maintain satisfactory operation of the inlet guide vanes 5, the setting angle α can be kept less than or equal to 25°.

[0058] [Fig.4] is a sectional view of one of the inlet guide vanes 5 in the orthoradial plane P, similarly to [Fig.3].

[0059] A skeleton S of the inlet guide vane 5 is defined as the center line of the inlet guide vane 5 extending from point Pi to point P2, i.e. the equidistant line of the two opposite faces of the inlet guide vane 5.

[0060] A point P3 is defined as the point of the skeleton S located at a distance, measured along the skeleton S, equal to 10% of the length of the skeleton S measured in the orthoradial plane P.

[0061] An angle of attack [3i is defined as the angle between the direction of the longitudinal axis A and a straight line D passing through the points Pi and P3.

[0062] In order to maintain satisfactory aerodynamic operation of the inlet guide vanes 5, in particular for high values ​​of the pitch angle a, the attack angle [3i can be chosen to be less than or equal to 10°.

[0063] The described characteristics of the turbojet engine 1 thus allow effective protection of the fan blades 7 and improve their service life. This also makes it possible to reduce the mass of the fan blades 7, which do not require as high a mechanical strength as for turbojet engines of the state of the art. Thus, the mass of the fan is reduced, as well as that of the fairing 2, which does not need to be as strong as previously, and the mechanical imbalance of the low-pressure compressor system as a whole is reduced.

Claims

Claims

1. A turbojet engine (1) having a longitudinal axis (1), the turbojet engine (1) comprising a shroud (2) surrounding a fan (3) and a plurality of inlet guide vanes (5) arranged upstream of said fan (3) along the longitudinal axis (A), the fan (3) comprising a plurality of fan blades (7), each fan blade (7) comprising an upstream leading edge (17), comprising a first radially inner end (B) and a second radially outer end (T), the two ends being separated from each other radially by a fan blade height (Hs) (7), characterized in that the inlet guide vanes (5) extend radially inwardly from the shroud (2), each inlet guide vane (5) having a radial length (Hg) greater than or equal to 20% of the height (Hs) of the fan blade (7),wherein the turbojet (1) comprises a number of inlet guide vanes (5) greater than or equal to a radius (R) of the fan (3), measured in meters, radially separating a tip (16) of the fan blades (7) from the longitudinal axis (A), divided by 0.0125.,

2. Turbojet (1) according to the preceding claim, comprising a number of inlet guide vanes (5) less than or equal to a radius (R) of the fan (3), measured in meters, radially separating a tip (16) of the fan blades (7) from the longitudinal axis (A), divided by 0.0075.

3. Turbojet (1) according to one of the preceding claims, in which, for each inlet guide vane (5), a pitch angle (a), formed with the longitudinal axis (A) by a chord (C) connecting an upstream end (Pi) and a downstream end (P2) of a section of the inlet guide vane (5), in a plane (P) parallel to the longitudinal axis (A), is greater than or equal to 5°.

4. Turbojet (1) according to the preceding claim, in which said pitch angle (a) is less than or equal to 25°.

5. Turbojet (1) according to one of the preceding claims, in which, for each inlet guide vane (5), an angle of attack (|3i), formed with the longitudinal axis (A) by a straight line (D) connecting an upstream end (Pi) of a section of the inlet guide vane (5), in a plane (P) parallel to the longitudinal axis (A), and a point (P3) of a center line (S) of the inlet guide vane (5) extending from a leading edge (17) to a trailing edge (19), separated from the upstream end (PI) by a length equal to 10% of a total length of the length of said center line (S) in said plane (P) parallel to the longitudinal axis (A), is less than or equal to 10°.

6. Turbojet (1) according to one of the preceding claims, in which each inlet guide vane (5) has a radial length (Hg) of between 20% and 50% of the height (Hs) of the fan vane (7).

7. Aircraft comprising a turbojet (1) according to one of the preceding claims.

Images