Retaining housing of a blower with a truncated spherical section

Abstract

An assembly comprising: - a fan rotating about an axis, comprising a disk and blades extending radially from the disk, each blade pivotally mounted on the disk about a mounting axis and having a chord of a given length; and - a casing extending about the axis, the casing comprising a first part, one of whose inner face is substantially cylindrical of revolution and having a first radius, and a second part extending opposite a tip of the blades; the second part extending axially from the first part to the mounting axis and having a second radius greater than the first radius, a distance along the axis between the first part and a projection onto the axis of a leading edge at the tip of a fan blade being at most 110% of the chord length. Figure for the abbreviation: Fig. 1

Description

Title of the invention: Retention casing of a fan having a truncated spherical part FIELD OF THE INVENTION

[0001] The present application relates generally to the field of turbomachines, and more particularly to fan casings. STATE OF THE ART

[0002] A turbomachine has a main direction extending along a longitudinal axis, and typically comprises, from upstream to downstream in the direction of gas flow, a fan and a primary body comprising a compression section which may comprise a low-pressure compressor, a high-pressure compressor, a combustion chamber, and a turbine section which may comprise a high-pressure turbine and a low-pressure turbine. In the case of a shrouded turbomachine, the fan is housed in a retention casing and comprises a nacelle defining an aerodynamic envelope of the engine. The air flow entering the turbomachine is divided into a primary flow configured to pass through the primary body and a secondary flow which bypasses the primary body and passes through a bypass duct delimited by the fan casing.

[0003] Reducing polluting emissions linked to air transport involves in particular improving the performance of the low pressure part of the turbomachine by reducing the flow speed of the airflow passing through the fan.

[0004] In order to maintain the incoming air flow, and therefore the thrust force, one solution is to increase the diameter of the blower and the section of the bypass duct.

[0005] However, this change in scale results in a gain in mass compromising the performance of the turbomachine. The solutions currently being considered include:

[0006] - to modify the nacelle in order to remove the elements whose role is to guide the flow upstream and downstream of the blower as well as those which ensure the reverse function (reverse operation), and

[0007] - the integration of a variable timing system into the blower, in order to allow the pi fan blades, which allows to maintain the advantages linked to flow guidance as well as the reverse function previously possible thanks to the nacelle and guaranteeing the performance of the turbomachine for all its flight conditions.

[0008] However, the use of variable timing makes it difficult to manage the steps as well as the clearances at the head and foot of the blower and the constraints linked to the assembly / disassembly of the blades. The risks of self-engagement of the fan due to clearances at the blade tip can also cause damage to the fan and the fan casing. Statement of the invention

[0009] An aim of the invention is to remedy the problems of mounting and dismounting variable-pitch fan blades as well as the phenomenon of self-engagement when the head of these blades comes into contact with the fan casing.

[0010] For this purpose, according to a first aspect of the invention, a turbomachine assembly is proposed comprising: - a fan rotatable about an axis, the fan comprising a fan disk and a plurality of blades extending radially from the disk, each blade being pivotally mounted on the fan disk about a respective pitch axis and having a chord having a length; and - a fan casing extending around the axis, the fan casing comprising a first part of which an internal face is substantially cylindrical of revolution and having a first radius, and a second part which extends opposite a tip of the fan blades; the second part extending axially from the first part to the pitch axis and having a second maximum radius greater than the first radius, a distance along the axis between the first part and a projection on the axis of a leading edge of a blade of the fan at the blade tip being at most equal to 110% of the length of the chord.

[0011] A stopping point between the first part and the second part is therefore configured so as to allow the assembly / disassembly of the fan blade, facilitating the maintenance of the variable-pitch blades.

[0012] It can be provided that the length of the chord is measured at the level of one foot of the blade.

[0013] It may also be provided that an internal face of the second part of the fan casing is curved so as to form a truncated spherical surface.

[0014] It is also possible to provide that the head of each blade also has a curved edge.

[0015] The geometry of each blade head is therefore adapted to the shape of the casing of fan is also curved. This reduces the risk of contact between the blade and the casing.

[0016] It can be provided that the first radius is greater than a sum of a height of the blade and a distance measured in a radial direction to the axis between the axis and a bottom of a footprint of the disk configured to receive a blade root.

[0017] It can also be provided that the first radius is greater than the radius of the blower.

[0018] Thus, the maintenance operations of the blades are facilitated. Indeed, the blade can be dismantled and then can slide along the first part of the casing in order to be able to remove it.

[0019] It may be provided that the blade further has a chord at the tip, the distance along the axis between the first part and the projection on the axis of a leading edge of the fan blade at the blade tip being at most equal to 30% of a length of the chord, where the chord is measured at the blade tip.

[0020] Thus, a second stopping point between the first part and the second part of the casing is configured in order to avoid the risks of self-engagement of the fan linked to the clearances at the blade head which can, in addition, cause damage to the fan and the fan casing.

[0021] It can be provided that the first radius is equal to the square root of the difference of the squares of the second maximum radius of an internal face of the second part and 30% of the length of the chord at the head.

[0022] Thus, it is possible to express the radial position of this stopping point as a function of reference data of the assembly.

[0023] It can be provided that a turbomachine comprises an assembly according to the invention and a motor body configured to drive the fan in rotation around the axis.

[0024] It is also possible to provide an aircraft comprising the turbomachine fixed to the aircraft by means of a pylon. DESCRIPTION OF FIGURES

[0025] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0026] [Fig.l] schematically illustrates a half-section of an aircraft turbomachine;

[0027] [Fig.2] is a simplified view of an exemplary embodiment of a fan blade;

[0028] [Fig. 3] illustrates a partial view of a turbomachine according to an embodiment of the invention on which a blade, a fan disk and a fan casing are visible;

[0029] [Fig.4] illustrates a detail of [Fig.3] at the fan disc;

[0030] [Fig.5] shows an embodiment of the invention of the casing with its blower whose parameters are necessary for the description of this mode; and

[0031] [Fig.6] shows another embodiment of the invention of the casing with its blower, the parameters of which are necessary for the description of this embodiment.

[0032] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0033] A turbomachine 1, illustrated in [Fig.l], has a main direction extending along a longitudinal axis X, and typically comprises, from upstream to downstream in the direction of gas flow, a fan 2 and a primary body 3 comprising a compression section which may comprise a low-pressure compressor 4, a high-pressure compressor 5, a combustion chamber 6, and a turbine section which may comprise a high-pressure turbine 7 and a low-pressure turbine 8. The fan is housed in a retention casing 9 and comprises a nacelle 10 defining an aerodynamic envelope of the turbomachine 1. The air flow entering the turbomachine 1 is divided into a primary flow configured to pass through the primary body 3 and a secondary flow which bypasses the primary body 3 and passes through a bypass duct delimited radially on the outside by the fan casing 9.

[0034] The turbomachine 1 can for example be fixed to an aircraft by means of a pylon.

[0035] In the present application, upstream and downstream are defined relative to the normal flow direction of the gas in the fan 2. Thus, the X axis of the fan 2 corresponds to its axis of rotation. The axial direction corresponds to the direction of the X axis and a radial direction is a direction perpendicular to this axis and passing through it. Furthermore, the circumferential direction corresponds to a direction perpendicular to the X axis and not passing through it. Unless otherwise specified, internal (respectively, interior) and external (respectively, exterior), respectively, are used with reference to a radial direction such that the internal part or face of an element is closer to the X axis than the external part or face of the same element.

[0036] The fan 2 is rotatable about the axis X and comprises a fan disc 20 and a plurality of blades 22 extending radially from the disc 20, each blade 22 being pivotally mounted on the fan disc 20 about a respective pitch axis Y and having a chord having a length C.

[0037] The turbomachine further comprises a fan casing 9 extending around the axis X, the fan casing 9 comprising a first part 91 of which an internal face is substantially cylindrical of revolution and has a first radius R2, and a second part 92 which extends opposite a head 25 of the blades 22 of the fan 2.

[0038] In addition, the second part 92 extends axially from the first part 91 to the setting axis Y and has a second maximum radius R3 greater than the first radius R2, a distance Li along the axis X between the first part 91 and a projection XBa on the axis X of a leading edge 27 at the tip of the blade 25 of a blade 22 of blower 2 being at most equal to 110% of the length C of the chord.

[0039] In one embodiment, Xi is 110% of the chord length C.

[0040] In this way, the assembly and disassembly of the blades 22 of the fan 2 with timing variable is facilitated. In addition, this configuration makes it possible to remedy the self-engagement phenomena during contact of the head 25 of these blades 22 with the fan casing 2.

[0041] Fan blade 22

[0042] A fan blade 22 comprises a root 23 configured to be fixed on the disk 20 of the fan 2 and an aerodynamic profile blade 24 capable of extending in an air flow. The blade 22 has a blade head 25 extending facing the fan casing 9 opposite the root 23 as well as a leading edge 27 and a trailing edge 28. The leading edge 27, corresponding to the front part of an aerodynamic profile 24 which faces the air flow in normal operation of the engine and which divides the air flow into a lower surface flow and an upper surface flow, is configured to extend opposite the flow of gases entering the fan 2. The trailing edge 28 corresponds to the rear part of the aerodynamic profile 24, where the lower and upper surface flows meet.The aerodynamic profile blade 24 also has a dimension h along the setting axis Y, between a radially lower face of the root 23 of the blade and the blade head 25.

[0043] It is recalled here that the chord C corresponds to the straight line segment connecting the leading edge 27 and the trailing edge 28. The length of the chord C can therefore vary along the aerodynamic profile blade 24 from the root 23 to the head 25.

[0044] Where appropriate, the radially external edge 26 of the head 25 of the blade 22 of the fan 2 has a generally curved shape, for example substantially spherical between the leading edge 27 and the trailing edge 28.

[0045] Blower 2

[0046] The root of the blade 22 is axially engaged in indentations 21 of the fan disk 20. The bottom of each indentation 29 extends at a distance Ri from the axis X along the setting axis Y. The distance Ri is therefore measured in a direction radial to the axis X between the axis X and the bottom of the indentation of the disk 29 configured to receive the blade root 23.

[0047] The blades 22 of the fan 2 are variable-pitch, that is to say that it is possible to pivot the blades 22 around the Y axis in order to change their angle of incidence. The Y-pitch axis extends radially relative to the X axis. If necessary, the Y-pitch axis may be slightly inclined upstream or downstream of the fan 2 or even tangentially, the upstream and downstream being defined in the direction of flow of the gases in the turbomachine 1.

[0048] Variable timing has the advantage of allowing “reverse” operation of the fan 2 and to adapt the angle of incidence of the fan blades 22 according to the flight phases of the turbomachine 1.

[0049] A shim 30 is interposed between each blade root 23 and the bottom of the corresponding cavity 29 (see for example [Fig. 4]) for the purpose of maintaining and preventing premature wear of the blade root 23. Examples of mounting / dismounting blades on a fan disk are for example described in document FR3034130 in the name of the Applicant. The radially external face of the shim is configured to come into contact with the blade root 23 while its radially internal face is configured to come into contact with the bottom of the corresponding cavity 29. Each shim 30 has a thickness d, which corresponds to its dimension along the setting axis Y.

[0050] Fan housing 9

[0051] As indicated above, the fan casing comprises a first part 91 and a second part 92, the second part 92 extending axially from the first part 91 to the pitch axis Y and having a second maximum radius R3 greater than the first radius R2, a distance Li along the axis X between the first part 91 and a projection XBa on the axis X of a leading edge 27 at the blade tip 25 of a blade 22 of the fan 2 being at most equal to 110% of the length of the chord C. It will be noted here that, the blades 22 being identical and distributed symmetrically around the axis, the distance Li can be measured from any blade 22 of the fan 2.

[0052] Preferably, the chord is taken here at the root of the blade 23 and measures a length Ci. The internal face of the second part 92 therefore comprises a recess. In one embodiment, the recess is curved so as to form a truncated spherical surface. This configuration of the fan casing 9 makes it possible to define when to stop the recess upstream of the fan 2 in order to allow assembly / disassembly of the blade 22 and to facilitate maintenance of the turbomachine 1 with a fan 2 comprising variable-pitch blades 22.

[0053] For example, in [Fig.5], the stop of the recess is marked by the point Di whose projection on the X axis is marked by the point XL

[0054] In one embodiment, the first radius R2 of the first part 91 of the fan casing 2 is strictly greater than the sum of the height h of the blade 22 and the radius Rb. Preferably, the first radius R2 is strictly greater than this sum at any point of the first part 91 of the fan casing 9.

[0055] Furthermore, the difference between the second radius R3 and the first radius R2 is greater than the thickness d of the shim 30. Preferably, the chord C is measured at the blade root 23.

[0056] Stopping the recess upstream of the fan 2 also makes it possible to protect against self-engagement phenomena. This phenomenon occurs during contact between the head of the blade 25 and the fan casing 9. Depending on the shape of the casing and the blade, once contact has appeared, the blade 22 deforms, amplifying the contact and penetrating more and more into the casing 9 until it ruins contact areas of the parts.

[0057] In order to avoid this phenomenon, it is also possible to provide for stopping the curved shape 92 earlier upstream. In particular, the distance L2 along the axis X between the first part 91 and the projection XBa on the axis X of the leading edge 27 at the blade tip 25 of a blade 22 of the fan 2 is at most equal to 30% of the length of the chord (the chord being taken here at the blade tip 25 and having a length Co). Thus, from this position, the recess of the fan casing 9 stops. The radius of the fan casing 9 is then constant and greater than or equal to the first radius R2. In the example of [Fig.6], it stops to remain at a radius equal to R2.

[0058] For example, in [Fig.6], the stop of the curved shape is identified by point D2 whose projection on the X axis is identified by point X2

[0059] The first radius R2 is an unknown to be determined as a function of the second maximum radius R3 taken as a reference at the level of a maximum depth of the recess of the fan casing 9, as illustrated by way of example in [Fig.3].

[0060] In this case, the first radius R2 is equal to the square root of the difference of the squares of a radius R3 of an internal face of the second part 92 and 30% of the length Co of the chord Co (taken at the blade head 25): r2=^-(o.3-c o ) 2

[0061] The fan 2 can comprise between 8 and 16 blades.

[0062] Where appropriate, the turbomachine 1 further comprises a reduction mechanism, for example a planetary or star epicyclic gear train, interposed between the shaft of the low pressure turbine 8 and the fan 2 in order to decouple the speed of the low pressure turbine 8 from that of the fan 2 and thus improve their respective efficiency.

[0063] The compression ratio of the blower 2 is preferably between 1.1 and 1.5, for example between 1.1 and 1.25.

[0064] In addition, the hub ratio of the fan 2, which corresponds to the ratio between the internal radius and the external radius of the aerodynamic vein, where the internal radius corresponds to the distance between the axis X of the fan 2 and the surface of the platform which radially delimits the flow vein inside, at the level of the leading edge 27 of the blade 22 of the fan 2, and the external radius corresponds to the distance between the axis X of the fan 2 and the fan casing 9, at the same level of the blade 22 (i.e. at the level of the leading edge 27 of the blade 22, at the intersection with the platform) is between 0.2 and 0.4 in order to guarantee good efficiency of the turbomachine 1.

Claims

Claims

1. A turbomachine assembly (1) comprising: - a fan (2) rotatable about an axis (X), the fan (2) comprising a fan disc (20) and a plurality of blades (22) extending radially from the disc (20), each blade (22) being pivotally mounted on the fan disc (20) about a respective pitch axis (Y) and having a chord having a length (C);and - a fan casing (9) extending around the axis (X), the fan casing (9) comprising a first part (91) of which an internal face is substantially cylindrical of revolution and having a first radius (R2), and a second part (92) which extends opposite a tip of the blades (22) of the fan (2), the first radius (R2) being greater than a sum of a height (h) of the blade (22) and a distance (RJ measured in a direction radial to the axis (X) between the axis (X) and a bottom of a cavity of the disk (29) configured to receive a blade root (23);the second part (92) extending axially from the first part (91) to the setting axis (Y) and having a second maximum radius (R 3) greater than the first radius (R2), a distance (Li) along the axis (X) between the first part (91) and a projection (XBA) on the axis (X) of a leading edge (27) at the blade tip (25) of a blade (22) of the fan (2) being at most equal to 110% of the length (C) of the chord.;

2. An assembly according to claim 1, wherein the length of the chord (Ci) is measured at a foot of the blade (23).

3. An assembly according to either of claims 1 and 2, wherein an inner face of the second portion (92) of the fan casing (9) is curved so as to form a truncated spherical surface.

4. An assembly according to claim 3, wherein the head of each blade (25) has a curved edge (26).

5. 5. Assembly according to one of claims 1 to 4, in which the first radius (R2) is greater than the radius of the fan (2).

6. 6. Assembly according to one of claims 1 to 5, in which the blade (22) further has a chord at the head (25), the distance (L2) along the axis (X) between the first part (91) and the projection (XBA) on the axis (X) of a leading edge (27) at the blade head (25) of the blade (22) of the fan (2) being at most equal to 30% of a length (Co) of the chord, where the chord (Co) is measured at the blade tip (25).

7. Assembly according to one of claims 1 to 6, in which the first radius (R2) is equal to the square root of the difference of the squares of the second maximum radius (R3) of an internal face of the second part (92) and 30% of the length of the chord at the head (Co).

8. 8. Turbomachine (1) comprising an assembly according to one of claims 1 to 7 and an engine body configured to drive the fan (2) in rotation around the axis (X).

9. 9. Aircraft comprising at least one turbomachine (1) according to claim 8 fixed to the aircraft by means of a pylon.

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