Fixed housing of a turbomachine with unequally spaced arms

Abstract

The present invention relates to a fixed turbomachine housing (100) comprising: - a hub (102) centered on an axis (XX') of the housing (100); - a ferrule (103) coaxial with the hub (102) and extending radially around the hub (102); and - fixedly mounted arms (104) between the hub (102) and the ferrule (103), the arms (104) being arranged around the axis (XX'), the circumferentially adjacent arms (104) being separated at the hub (102) by a respective angular distance that varies periodically with respect to an equipartition angular distance of the arms (104) such that the arms (104) are not equidistant around the axis (XX'), preferably, each angular distance between the circumferentially adjacent arms (104) corresponding to a component of a Fourier series decomposition of a periodic signal. Figure for the abbreviation: Fig. 4

Description

Title of the invention: Fixed housing for a turbomachine with unequally distributed arms FIELD OF INVENTION

[0001] The present application relates generally to the field of turbomachinery, and more particularly to turbomachinery assemblies comprising a moving wheel mounted upstream or downstream of a fixed casing capable of generating a resonance on a natural mode of the moving wheel. STATE OF THE ART

[0002] A turbomachine has a longitudinal axis around which it extends and typically comprises, from upstream to downstream in the direction of gas flow, a fan, a compression section which may include a low-pressure compressor and a high-pressure compressor separated by an intermediate casing, a combustion chamber, a turbine section which may include a high-pressure turbine and a low-pressure turbine separated by an inter-turbine casing, and an exhaust casing extending downstream of the turbine section. The exhaust casing helps to define the primary fluid stream (or primary gas flow) passing through the turbomachine and ensures, by means of bearing supports, concentricity between the rotor and stator sections of the turbomachine.

[0003] The exhaust housing conventionally comprises a hub, centered on the axis of the turbomachine, an outer ferrule, coaxial with the hub, and a set of arms distributed around the axis of the turbomachine which connect the hub and the outer ferrule.

[0004] However, the presence of the exhaust casing downstream of the turbine section generates dynamic stresses on the portion of the turbine section located upstream of the exhaust casing through a pressure rise phenomenon. These dynamic stresses give rise to resonance, which can generate more or less significant vibrational stresses on the blades of the rotating wheel.

[0005] To reduce these constraints, it is possible to increase the distance between the exhaust housing and the turbine section. However, this implies increasing the length and mass of the engine, and therefore higher fuel consumption.

[0006] It is also possible to modify the number of arms or blades in the turbine section. However, this modification can affect the length of the exhaust casing or the mass of the moving blades, also resulting in increased fuel consumption. Manufacturing and cost constraints are also present. Description of the invention

[0007] One object of the invention is therefore to remedy the problems of generating stresses on a moving wheel located upstream or downstream of a fixed casing, which is simple to implement, of moderate cost and which does not increase fuel consumption.

[0008] To this end, according to a first aspect of the invention, a fixed turbine housing comprising: - a hub centered on an axis of the casing; - a coaxial ferrule with the hub and extending radially around the hub; and - fixedly mounted arms between the hub and the ferrule, the arms being arranged around the axis, the circumferentially adjacent arms being separated at the hub by a respective angular distance which varies periodically with respect to an equipartition angular distance of the arms so that the arms are not equidistributed around the axis, preferably, each angular distance between the circumferentially adjacent arms corresponding to a component of a Fourier series decomposition of a periodic signal.

[0009] The casing according to the invention may also have at least one of the following characteristics:

[0010] - the arms have different geometries,

[0011] - the arms have different thicknesses,

[0012] - each angular distance of the arms of a first geometry or of a first thickness corresponds to a Fourier series decomposition of a first periodic signal, and each angular distance of the arms of a second geometry or a second thickness corresponds to a Fourier series decomposition of a second periodic signal.

[0013] - the respective angular distance between the circumferentially adjacent arms includes a constant component corresponding to an angular equipartition distance of the arms and a variable component that varies periodically, the variable component remaining less than 25% of the constant component, and

[0014] - the respective angular distance between the circumferentially adjacent arms varies periodically between 50% of the equipartition angular distance of the arms and 150% of the equipartition angular distance of the arms.

[0015] It can be predicted that each angular distance separating two circumferentially adjacent arms in a trigonometric direction is parameterized by the following equation: 360 / X + A*cos(B*i*360 / X) in which: A and B are distribution parameters;

[0016] A is at most equal to 0.25*360 / X and B is at most equal to X / 2; X is the total number of arms in the housing; and i corresponds to the i-th arm.

[0017] It can be envisaged that said housing comprises one of the following housings: a rectifier configured to extend downstream of a moving stage of a compressor; a distributor configured to extend upstream of a moving stage of a turbine; an interturbine housing configured to extend between a high-pressure turbine and a low-pressure turbine; an exhaust housing configured to extend downstream of a low-pressure turbine.

[0018] The invention also provides for a turbomachine assembly comprising a movable wheel, around an axis and a fixed casing according to the invention, said casing being coaxial with the movable wheel and extending upstream or downstream of the movable wheel.

[0019] The invention also provides for a turbomachine comprising an assembly according to the invention, the moving wheel being driven in rotation by a drive shaft. DESCRIPTION OF THE FIGURES

[0020] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0021] Fig. 1 schematically illustrates a half-section of an example of an aircraft turbomachine according to an embodiment of the invention;

[0022] [Fig.2] is a simplified view of an example of a turbomachine which may include a fixed casing according to an embodiment of the invention;

[0023] the [Fig.3] is a fixed turbomachine housing according to an embodiment of the invention;

[0024] [Fig.4] illustrates in solid lines the fixed housing of [Fig.3] and in dashed lines a conventional fixed housing comprising the same number of arms as the housing of [Fig.3];

[0025] [Fig.5] illustrates in solid lines a fixed housing according to another embodiment of the invention and the conventional fixed housing of [Fig.4];

[0026] [Fig.6] illustrates a fixed housing according to another embodiment of the invention;

[0027] Figure 7 schematically illustrates, in unfolded form, the position of the arms of a fixed housing according to an embodiment of the invention and the conventional fixed housing of [Fig.4], with superimposed a graph showing a periodic curve representing the variation of the pitch between an arm of the fixed housing and an adjacent arm of the conventional fixed housing;

[0028] [Fig. 8a] is a graph schematically representing the evolution of the excitation frequency generated by a housing with equally spaced arms on a moving wheel (upstream or downstream of a conventional fixed casing) as a function of its rotational speed, the natural frequency of each natural mode of the blades of the moving wheel and the vibratory resonances of these blades;

[0029] [Fig.8b] is a graph representing a frequency spectrum of the excitation generated by the arms of a twelve-arm housing equally distributed on a blade of a moving wheel (upstream or downstream of a conventional fixed housing);

[0030] [Fig.9a] is a graph schematically representing the evolution of the frequency of each excitation generated by a housing with twelve non-equidistributed arms on a moving wheel (upstream or downstream of a fixed housing according to an embodiment of the invention) as a function of its rotation speed, the natural frequency of each natural mode of the blades of the moving wheel and the vibratory resonances of these blades in the case of a housing with non-equidistributed arms;

[0031] [Fig.9b] is a graph representing a frequency spectrum of the excitation generated by the arms of the housing with non-equally distributed arms on a blade of a moving wheel (upstream or downstream of a fixed housing according to an embodiment of the invention);

[0032] [Fig. 10] is a graph representing the attenuation of the intensity of the vibrations of the blades for different distributions of the arms of a fixed casing according to an embodiment of the invention;

[0033] [Fig. 1 1] is a graph representing a frequency spectrum of the excitation generated by the arms of another housing with non-equally distributed arms on a blade of a moving wheel (upstream or downstream of a fixed housing according to another embodiment of the invention); and

[0034] [Fig. 12] is a graph representing the attenuation of the intensity of the vibrations of the blades for different distributions of the arms of a fixed housing and several quantities of arms according to an embodiment of the invention.

[0035] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0036] A turbomachine 1 has a principal direction extending along a longitudinal axis XX', and typically comprises, from upstream to downstream in the direction of gas flow, a fan section 2, a primary casing comprising a compression section which may include a low-pressure compressor 4 and a high-pressure compressor 5 separated by an intermediate casing 42, a combustion chamber 6, a turbine section which may include a high-pressure turbine 7 and a low-pressure turbine 8 separated by an inter-turbine casing 81 and an exhaust casing 82 located downstream of the low-pressure turbine 8. The airflow entering the turbomachine 1 is divided into a primary flow configured to pass through the primary casing and a secondary flow which bypasses the primary casing and is compressed by blower 2.

[0037] The blower section comprises a fan 2 and an outer guide vane 40. Each compression section comprises a plurality of stages, each including a fan 41, 43 and a stator portion 40. Each turbine section comprises a plurality of stages, each including a fan 51, 52 and a stator portion 50. Finally, the intermediate casing 42, the inter-turbine casing 81, and the exhaust casing 82 each comprise a set of arms 104 fixed relative to the turbomachine 1.

[0038] The turbomachine 1 comprises at least two drive shafts, typically a high-pressure shaft 31 and a low-pressure shaft 30.

[0039] The low-pressure shaft 30 is connected to the low-pressure turbine 8 and is configured to drive the low-pressure compressor 4 and the blower 2 either directly via the low-pressure turbine 8 or through a reduction mechanism that may include a planetary or star-type epicyclic gearbox. The low-pressure shaft 30 is guided in rotation by the interposition of rolling elements such as ball bearings 33 or roller bearings 32, of which an outer ring of each bearing 32, 33 is mounted on the intermediate housing 42, the low-pressure shaft 30, or the exhaust housing 82, and an inner ring on the low-pressure shaft 30.

[0040] The high-pressure shaft 31 is connected to the high-pressure turbine 7 and is configured to drive the high-pressure compressor 5. The high-pressure shaft 31 is guided in rotation by the interposition of rolling elements of the type ball bearings 33 or roller bearings 32, of which an outer ring of each bearing 32, 33 is mounted on the intermediate housing 42 and the inter-turbine housing 81 and an inner ring on the high-pressure shaft 31.

[0041] In the present application, upstream and downstream are defined with respect to the normal direction of gas flow in the turbomachine 1. Thus, the axis XX' of the turbomachine 1 corresponds to the axis of rotation of its rotor parts. Furthermore, an element is considered fixed (or stator) when it is fixedly mounted on a structural housing of the turbomachine such that this element is fixed with respect to the aircraft pylon, when the turbomachine is mounted in such an aircraft.

[0042] The turbomachine 1 includes in particular a fixed housing 100 having: - a hub 102 centered on the XX' axis of the casing; - a ferrule 103 coaxial with the hub 102 and extending radially around the hub 102; and - arms 104 mounted fixed between the hub 102 and the ferrule 103.

[0043] In what follows, the invention will be described more particularly in the case where the fixed housing 100 is an exhaust housing 82. This is not, however, limiting, the invention applying to any fixed housing 100 of the turbomachine 1 exciting a bladed rotating wheel, either upstream or downstream. Furthermore, the arms 104 of the housing 100 may have an aerodynamic or non-aerodynamic shape. Thus, the fixed housing 100 may correspond, in particular, to an intermediate housing 42, an exhaust housing 82 of the turbomachine 1, an inter-turbine housing 81, a rectifier 40, or a distributor 50.

[0044] The arms 104 are arranged around the axis XX' and are mutually separated at the hub 102 by a respective angular distance.

[0045] The angular distance can separate adjacent, circumferentially adjacent, or immediately circumferentially adjacent arms 104.

[0046] In order to reduce the stresses on the axially adjacent moving blade wheel 52 (i.e. the moving wheel 52 of the low-pressure turbine 8 in the case of the exhaust casing 82), the arms 104 are not equidistant around the axis XX'. For this purpose, the angular distance can in particular be decomposed into a Fourier series, each component of the Fourier series representing an angular position of an arm 104.

[0047] For example, as illustrated in [Fig.7], the angular distance 25 varies periodically around the axis XX' along the circumference of the housing 100 compared to a configuration with equally spaced arms 204 in the case of a conventional fixed housing 200.

[0048] The arms 104 may also have different geometries and / or thicknesses. The geometry of an arm 104 is defined by all the dimensions of the arm 104 that are useful for the aerodynamic performance of the turbomachine 1, such as the curvature of the upper and lower surfaces or the chord at the toe or tip of the arm 104. The thickness of an arm is defined by the distance between two faces of the arm 104 that connect the leading edge and the trailing edge. For example, in [Fig. 6], a housing 300 comprises two distinct arm geometries 304, 306, where the arms 304 of one given geometry may alternate with the arms 306 of another given geometry. Alternatively, the arms of each given geometry may be grouped together and extend side by side adjacently. According to yet another variant, the arms 304 of a given geometry can be randomly alternated with the arms 306 of the other given geometry.Thus, the angular distances of the arms 304 of a first geometry correspond to a Fourier series decomposition of a first periodic signal and the angular distances of the arms 306 of a second geometry correspond to a Fourier series decomposition of a second periodic signal.

[0049] The Applicant has indeed observed that, in the case of excitation of the blades of the rotating wheel 52 synchronous with its rotational speed, all the energy is concentrated on a single harmonic corresponding to the arms of the housing 200, with the equipartition of the arms 204 of the conventional fixed housings 200, all the energy is concentrated on a single harmonic corresponding to the arms of the housing. Varying the angular distance A generally sinusoidal pattern leads to a distribution of the excitation energy over a wider frequency spectrum.

[0050] Indeed, the blades of the moving wheel 52 exhibit different natural modes that can generate different stresses when excited. For example, as illustrated in [Fig. 8a], the excitation energy 14 generated when the rotational speed of the moving wheel 52 reaches a value corresponding to the third natural mode MP3 of the moving blades is greater than that corresponding to the first natural mode MPI. The overall sinusoidal distribution of the arms 104 therefore makes it possible to distribute this excitation energy over a wider frequency range.

[0051] By way of comparison, in the case of a 200 housing with twelve equally distributed arms 204, the energy is concentrated solely on the harmonics 12 and its multiples (see the frequency spectrum of [Fig.8b]) and therefore has a greater amplitude.

[0052] Thus, the non-equal distribution proposed in this application makes it possible to spread the energy over several harmonics and to reduce the energy carried by each of these harmonics. Therefore, for each natural mode of the moving blades 52, the resonance is attenuated. Indeed, as illustrated by the example in [Fig. 9b], the energy carried primarily by the 12th harmonic is reduced compared to the equally distributed housing 200 ([Fig. 8b]) and is distributed among the neighboring harmonics.

[0053] On the other hand, there are more resonances than in the evenly distributed case. Indeed, as illustrated by the example in [Fig.9a], each natural mode exhibits resonances for several harmonics placed at widely separated turbine 8 rotational speeds.

[0054] It will be noted that, in the case of the inter-turbine casing 81, the arms 104 excite the moving wheels 51, 52 extending upstream and downstream, i.e. the wheel of the high-pressure turbine 7 and the moving wheel of the low-pressure turbine 8. In the case of a rectifier 40 or a distributor 50, the arms 104 excite the moving wheels 41, 43, 51, 52 extending upstream and downstream.

[0055] The position of the arms 104 of the housing 200 can be defined with respect to the presumed position of the arms 204 in a housing whose arms are equally distributed and having the same number X of arms 204. We will denote p the angular distance between two arms 204 of the equally distributed housing 200. Thus, Each arm 104 of the housing 100 is then distant from the immediately adjacent arm 204 by at most 25% of the angular distance p.

[0056] According to another embodiment, the distance between two adjacent non-equidistributed arms 104 varies between 50% of the angular distance p and 150% of the angular distance p.

[0057] Each angular distance, in a trigonometric direction, can be parameterized by the following equation:

[0058] 360 / X + A*cos(B*i*360 / X)

[0059] in which:

[0060] A and B are distribution parameters;

[0061] X is a total number of arms 104 in the housing 100; and

[0062] i corresponds to the i-th arm 104.

[0063] The parameter A, corresponding to an amplitude in the equation, influences the distribution of energy between the different harmonics. The parameter B, corresponding to the frequency, modifies the shape of the spectrum.

[0064] The optimal values ​​of parameters A and B can be obtained by a parametric study. For this purpose, for a given set of parameters A and B, a Fourier series decomposition of an excitation is calculated in order to determine the amplitude of the component corresponding to a given value of the number of arms for a housing with equal-distributed arms 200. Then, a frequency and amplitude sweep of the expression is performed for the given value of the number of arms in order to estimate the attenuation of the amplitude.

[0065] For example, as illustrated in [Fig. 10], the attenuation can correspond to the ratio between the value of the amplitude for the equally spaced arm housing 200 and the value of the amplitude obtained for each frequency and amplitude pair of the expression.

[0066] The optimal values ​​of parameters A and B represent a maximum reduction of stresses caused by vibrations. Indeed, in the case of a twelve-arm housing 104, the graph in [Fig. 10] shows that the attenuation is maximum for a sinusoid with B=6 and an amplitude A around 7.5°. Moreover, the distribution of the arms 104 according to this parameterization makes it possible to generate few harmonics, as illustrated in the example in [Fig. 11], thus limiting the range of turbine 8 rotational speeds that can cause high-amplitude resonance and the number of resonances of the moving blades 52.

[0067] Thus, from these results, it is possible to deduce a generalized expression of A and B allowing to reach a maximum attenuation for any number of arms 104 by repeating the parametric study for several numbers of arms.

[0068] For example, according to the parametric study for several numbers of arms illustrated in [Fig. 12], the parameter A can be at most equal to 0.25 * 360 / X. Indeed, for twelve arms 104, the value of the parameter A is exactly 7.5°.

[0069] The parameter B can be at most equal to X / 2 Indeed, for twelve arms 104, the parameter B representing the frequency of the distribution sinusoid of the arms 104 will be equal to 6, which will result in a synchronous excitation in 6N (where N represents the rotation speed of the shaft 30) generated by the arms 104 on the moving blades 52 (see [Fig. 11]) and will correspond to the maximum attenuation.

[0070] The list below gives the angular position of each arm 404 in an optimal configuration of a housing 400 composed of twelve arms 404:

[0071] 0°; 45°; 60°; 105°; 120°; 165°; 180°; 225°; 240°; 285°; 300°; 345°

[0072] However, according to [Fig. 9a], the use of unequally distributed arms 104 is likely to generate excitations on harmonics causing other natural modes of the moving blades 52 to resonate, potentially inducing mechanical stresses on the moving blades 52. In this case, another set of parameters can be selected to distribute the arms 104 differently and thus obtain excitations generating resonances of the natural modes of the moving blades 52 that are more acceptable from the point of view of blade deformation. The same applies to the amplitude value, which may impose manufacturing or assembly constraints in the turbomachine 1 or aerodynamic performance constraints.

[0073] Thus, in one embodiment of the invention, the housing 100 comprises twelve arms 104 spaced apart by a distance corresponding to the sum of a regular pitch separating the arms 204 of an evenly spaced housing 200 and a sinusoidal distance of amplitude 4° and frequency corresponding to a 6th harmonic with respect to a housing 200 with evenly spaced arms 204. The list below gives, on the first line, the regular pitch separating each arm 204 of the evenly spaced housing 200 and, on the second line, the angular position of each arm 104 of the housing 100:

[0074] 0°; 30°; 60°; 90°; 120°; 150°; 180°; 210°; 240°; 270°; 300°; 330°,

[0075] - 4° ; 34° ; 56° ; 94° ; 116° ; 154° ; 176° ; 214° ; 236° ; 274° ; 296° ; 334°.

[0076] This configuration makes it possible to attenuate the mechanical excitation without unduly penalizing the aerodynamic performance of the turbomachine 1.

[0077] Figure 5 illustrates the housing 400 according to an embodiment of the invention for which the mechanical attenuation is maximal, as well as the initial housing 200 in several views allowing them to be distinguished, and Figures 3 and 4 illustrate the housing 100 according to an aerodynamically acceptable embodiment of the invention and the initial housing 200 (in dashed lines).

Claims

Demands

1. Fixed turbomachine housing (100) comprising: - a hub (102) centered on an axis (XX') of the housing (100); - a ferrule (103) coaxial with the hub (102) and extending radially around the hub (102); and - arms (104) mounted fixed between the hub (102) and the ferrule (103), the arms (104) being arranged around the axis (XX'), the circumferentially adjacent arms (104) being separated at the hub (102) by a respective angular distance which varies periodically with respect to an equipartition angular distance of the arms (104) so ​​that the arms (104) are not equidistributed around the axis (XX'), preferably, each angular distance between the circumferentially adjacent arms (104) corresponding to a component of a Fourier series decomposition of a periodic signal.

2. Carter (100) according to claim 1, wherein the arms (104) have different geometries.

3. Carter (100) according to any one of claims 1 to 2, wherein the arms (104) have different thicknesses.

4. Carter (100) according to any one of claims 2 to 3, wherein each angular distance of the arms (304) of a first geometry or thickness corresponds to a Fourier series decomposition of a first periodic signal and each angular distance of the arms (306) of a second geometry or thickness corresponds to a Fourier series decomposition of a second periodic signal.

5. 5. Carter (100) according to any one of claims 1 to 4 wherein the respective angular distance between the circumferentially adjacent arms (104) comprises a constant component which corresponds to an equipartition angular distance of the arms (104) and a variable component which varies periodically, the variable component remaining less than 25% of the constant component.

6. 6. Carter (100) according to any one of claims 1 to 5 wherein the respective angular distance between the circumferentially adjacent arms (104) varies periodically between 50% of the equipartition angular distance of the arms (104) and 150% of the equipartition angular distance of the arms (104).

7. 7. Carter (100) according to any one of claims 1 to 6, wherein each angular distance separating two arms (104) circumferentially adjacent in a trigonometric direction is parameterized by the following equation: 360 / X + A*cos(B*i*360 / X) in which: A and B are distribution parameters; A is at most equal to 0.25*360 / X and B is at most equal to X / 2; X is a total number of arms (104) in the housing (100); and i corresponds to the i-th arm (104).

8. 8. Housing (100) according to any one of claims 1 to 7, said housing comprising one of the following housings: a rectifier (40) configured to extend downstream of a moving stage of a compressor (4, 5); a distributor (50) configured to extend upstream of a moving stage of a turbine (7, 8); an inter-turbine housing (81) configured to extend between a high-pressure turbine (7) and a low-pressure turbine (8); an exhaust housing (82) configured to extend downstream of a low-pressure turbine (8).

9. Turbomachine assembly (1) comprising a wheel (41, 43, 51, 52), about an axis (XX') and a fixed casing (100) according to any one of claims 1 to 8, said casing (100) being coaxial with the wheel and extending upstream or downstream of the wheel (41, 43, 51, 52).

10. OTurbomachine (1) comprising an assembly according to the preceding claim, the moving wheel (41, 43, 51, 52) being driven in rotation by a drive shaft (30, 31).

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