TURBOMACHINE FLOW PATH HAVING CIRCUMFERENTIALLY VARYING OUTER PERIPHERY

Description

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to turbomachines, and more particularly to an annular flow path of a turbomachine.

BACKGROUND OF THE INVENTION

[0002] A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.

[0003] Gas turbine engines include flow paths with a plurality of airfoils, both nonrotating stator vanes and rotating rotor blades, typically arranged in an axially alternating configuration. Such flow paths are defined between radially-inward and radially-outward endwalls, or periphery, that guide air flow within the turbomachine. The interaction between the air flow progressing through such a flow path and the plurality of airfoils may result in the formation of a non-uniform pressure field within the flow path. Rotor blade airfoils that are moving through this non-uniform pressure field may experience the non-uniform pressure field in a time-varying manner which may result in the generation of time-varying stresses within the airfoil. The magnitude of these stresses may be of considerable concern if they compromise the structural integrity of the rotor blades due to material failure.

[0004] EP 2484871 A2 discloses a prior art turbomachine as set forth in the preamble of claim 1.

[0005] US 2007/258818 A1 discloses a prior art airfoil array with an endwall depression and components of the array.

[0006] GB 2 408 546 A discloses prior art compressor casing treatment slots.

SUMMARY

[0007] From one aspect, there is provided a turbomachine as recited in claim 1.

[0008] There is also provided a method of reducing vibratory stress on a plurality of radially extending rotor blades as recited in claim 8.

[0009] Features of embodiments of the invention are set forth in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is a schematic cross-section of a gas turbine engine having an annular flow path.

Figure 2 is an enlarged schematic cross section of the gas turbine engine of Figure 1.

Figure 3 schematically illustrates the annular flow path according to the claimed invention having a circumferentially varying outer periphery, and having a single recess axially along a centerline axis of the turbomachine.

Figures 4 and 4a schematically illustrate perspective views of the flow path of Figure 3 along line Y-Y of Figure 2 according to the claimed invention.

Figure 5 schematically illustrates an example flow path having a circumferentially varying outer periphery, and having more than a single recess axially along the centerline axis of the turbomachine.

Figure 6a illustrates a topological view of another example flow path having a circumferentially varying outer periphery, and having more than a single recess axially along the centerline axis of the turbomachine.

Figure 6b illustrates a topological view of an interior of the example flow path of Figure 6a from a vantage point shown on the turbomachine centerline axis of Figure 3 aft of a turbomachine stator vane looking upstream.

Figure 7 schematically illustrates an example flow path having a circumferentially varying outer periphery that extends axially upstream of the trailing-edge of a stator vane.

Figure 8 schematically illustrates an example flow path portion having a circumferentially varying outer periphery and a circumferentially varying inner periphery.

Figure 9 schematically illustrates a ratio of an outer periphery recess amplitude to a stator vane axial chord length.

[0011] The embodiments, examples and alternatives of the preceding paragraphs, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

DETAILED DESCRIPTION

[0012] Figure 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section 22 drives air along a bypass flow path B in a bypass duct defined within a nacelle 15, while the compressor section 24 drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

[0013] The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis X relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

[0014] The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis X which is collinear with their longitudinal axes.

[0015] The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.

[0016] The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6:1), with an example embodiment being greater than about ten (10:1), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five (5:1). In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five (5:1). Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.

[0017] A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition -- typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. "Low fan pressure ratio" is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane ("FEGV") system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (518.7 °R)]^0.5. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about 1150 ft / second (350.5 meters/second).

[0018] Core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed with the fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46 along annular flow path 61. The turbines 54, 46 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion.

[0019] With reference to Figure 2, an inner wall 60 and an outer wall 62 at least partially define the annular flow path 61. The flow path 61 extends across a transition duct region of the engine 20, from rotor blades 64 (corresponding to high pressure turbine 54) through passages formed by a plurality of stator vanes 66 (corresponding to airfoils 59 of mid-turbine frame 57) to rotor blades 68 (corresponding to low pressure turbine 46). The rotor blades 68 rotate about the centerline axis X. Although only one stator vane 66 is shown, it is understood that the stator vane 66 is one of a plurality of radially extending stator vanes. Also, although only one rotor blade 68 is shown, it is understood that the rotor blade 68 is one of a plurality of radially extending rotor blades that rotates about the axis X. The annular flow path 57 has an outer radius R_outer and an inner radius R_inner with respect to the axis X. As will be described below with reference to Figures 3-9, at least a portion of a platform wing section 70 of the annular flow path 61 has a circumferentially varying outer periphery. It should be understood that this circumferentially varying outer periphery can be used along other portions of the annular flow path.

[0020] With reference to Figure 3, according to the invention a platform wing section 70a of annular flow path 61a extends between a trailing edge 74 of stator vanes 66 and a leading edge 76 of rotor blades 68. A portion 72a of the platform wing section 70a has a circumferentially varying outer periphery featuring a series of alternating recesses 81 circumferentially around the portion 72a. The circumferentially varying outer periphery of portion 72a includes one recess axially along the axis X such that the recess 81 does not axially overlap the adjacent vane 66 or blade 68.

[0021] With reference to Figures 4 and 4a (which illustrate perspective views of the flow path 61a along line Y-Y of Figure 2), the outer periphery of the portion 72a is defined by a circumferentially repeating pattern 100 which is non-axisymmetric with respect to turbomachine axis X, unlike the circumferentially adjacent conventional outer periphery 102 that is axisymmetric with respect to the axis X. The pattern 100 does not include structure that is proud of the conventional outer periphery 102 - only recessed - to provide recesses 81 that circumferentially alternate with axisymmetric surfaces. The surface geometry may be smoothed at the transition between these features.

[0022] As illustrated in Figure 4, the pattern 100 is defined to repeat once with each circumferential vane pitch P₁, P₂, etc. of vanes 66a, 66b. If the vanes 66a, 66b are constructed separately and are later assembled to abut each other, the pattern 100 that repeats with each vane pitch P₁, P₂, etc. avoids abrupt changes in the outer periphery of the flow path 57a. Of course, this is only an example pattern, and it is understood that other patterns would be possible. For example, the pattern 100 may instead repeat with multiples of vanes (e.g., repeat every 2 vanes, repeat every 3 vanes, etc.).

[0023] With reference to Figure 5, in one non-limiting embodiment a portion 72b of platform wing section 70b of annular flow path 61b having a circumferentially varying outer periphery may include a multiple of axially offset recesses 81 along axis X. In one example the outer periphery may be defined to have recess sets that are axially and circumferentially offset from each other.

[0024] Referring to Figure 6a, in one non-limiting embodiment, a topological view is shown of an exterior of annular flow path 61a having a circumferentially varying outer periphery featuring a plurality of recess sets 110. Each set 110 of recesses includes two indentations 112, 114 that are axially offset from each other and are circumferentially offset and out of phase with each other. The recess sets 110 are part of topologically raised areas, shown by outer boundary, which is axisymmetric surface 115. An area 116 between the sets 110 of indentations 112, 114 may include lowered areas having lowered peaks (see, e.g., Fig. 5).

[0025] Figure 6b shows another non-limiting embodiment of a topological view of an interior of the flow path 61c from the perspective shown in Figure 3 on the turbomachine centerline axis X aft of the stator vane 66, looking upstream. As shown, a plurality of lowered recess sets 140 is located between the topologically axisymmetric surface 115 of Figure 6a. The lowered recess sets 140 each include two indentations142, 144 that are circumferentially offset and out of phase with each other. In one example the topologically lowered areas correspond to the area 116 of Figure 6a.

[0026] With reference to Figure 7, in one non-limiting embodiment, a flow path section 72d of a platform wing section 70d having a circumferentially varying outer periphery may extend beyond the trailing edge 74 of the stator vane 66 to include a flow path portion 120 that terminates at a location 122 forward of the trailing edge 74. In the non-limiting embodiment of Figure 7, the location 122 is located at an intermediate location between the trailing edge 74 and leading edge 75 of the stator vane 66.

[0027] With reference to Figure 8, in one non-limiting embodiment, a flow path portion 72e of platform wing section 70e of annular flow path 61e may include a circumferentially varying outer periphery and a circumferentially varying inner periphery, such that both the inner and outer periphery of the flow path portion 72e vary circumferentially about the annular flow path 61e. Although the inner periphery of flow path portion 72e is shown as only including a single peak recess 81 axially along axis X, it is understood that the inner periphery could include multiple recesses such as the outer periphery of portion 72b of Figure 5.

[0028] With reference to Figure 9, the magnitude of the annular flow path outer periphery circumferential variations may be quantified in relation to stator vane axial chord length. As shown in Figure 9, portion 72f of annular flow path 57f has a recess to axisymmetric surface amplitude of A. In the non-limiting embodiment of Figure 9, a ratio of A to an axial chord length C_x of the stator vane 66 is greater than or equal to 0.005. Of course, this is only an example, and other ratios would be possible. In one example this same ratio applies to the circumferentially varying inner periphery (Fig. 8).

[0029] The circumferentially varying outer periphery (and the optional circumferentially varying inner periphery) of the flow path portion 72 reduces vibratory stresses on the rotor blades 68 while the rotor blades 68 are rotating. In one example the circumferentially varying periphery can achieve a vibratory stress reduction on the order of 10-20% for the rotor blades 68. Computer simulations may optionally be performed to optimize the flow path 72 in order to determine optimal flow path dimensions.

[0030] Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.

Claims

1. A turbomachine (20), comprising an annular flow path section (57,61) between a plurality of radially extending stator vanes (66) and a plurality of radially extending rotor blades (68), wherein the annular flow path section corresponds to a platform wing (70a-e) of the stator vane (66) extending between the trailing edge of a plurality of radially extending stator vanes (66) and the leading edge of a plurality of radially extending rotor blades (68), characterised in that at least a first annular portion (72a) of the annular flow path section (70a) has a circumferentially varying outer periphery (102) including a repeating pattern (100) of recesses (81) circumferentially alternating with axisymmetric surfaces, the pattern (100) not including any structure that is proud of the axisymmetric surfaces.

2. The turbomachine as recited in claim 1 wherein the pattern (100) repeats at least once with each circumferential vane pitch.

3. The turbomachine as recited in any preceding claim, wherein the outer periphery (102) of the first portion (72a) defines a plurality recess sets (110; 140), each recess set (110; 140) including two indentations (112, 114; 142, 144) that are axially and circumferentially offset from each other.

4. The turbomachine as recited in any preceding claim, wherein the radially extending stator vanes (66) are airfoil vanes of a gas turbine engine (20), and the radially extending rotor blades (68) are rotor blades of the gas turbine engine (20).

5. The turbomachine as recited in claim 4 wherein the radially extending rotor blades (68) correspond to a low pressure turbine (46) of the gas turbine engine (20), and the annular flow path (70) extends from a high pressure turbine (54) fore of the stator vanes (66) around the plurality of stator vanes (66) to the low pressure turbine (46).

6. The turbomachine as recited in any preceding claim, wherein the first portion (72a) of the flow path section (70a) also has a circumferentially varying inner periphery.

7. The turbomachine as recited in any preceding claim, wherein a second portion (72d) of the flow path extends from the first portion (70d) beyond a trailing edge (74) of the plurality of stator vanes (66) to a location intermediate the trailing edge (74) and a leading edge (75) of the plurality of stator vanes (66), the second portion (72d) also having a circumferentially varying outer periphery, the circumferentially varying outer periphery of the first portion (70d) being continuous with the circumferentially varying outer periphery of the second portion (72d).

8. A method of reducing vibratory stress on a plurality of radially extending rotor blades (68), comprising:

providing an annular flow path section (57,61) between a plurality of radially extending stator vanes (66) and a plurality of radially extending rotor blades wherein the annular flow path section corresponds to a platform wing (70a-e) extending between the trailing edge of a plurality of radially extending stator vanes (66) and the leading edge of a plurality of radially extending rotor blades (68),

characterized by providing a first annular portion (72a-e) of the flow path section (70a-e) to have a circumferentially varying outer periphery including a repeating pattern of recesses (81) circumferentially alternating with axisymmetric surfaces, the pattern not including any structure that is proud of the axisymmetric surfaces.

9. The method of claim 8, wherein the first portion (72a-e) of the flow path is defined such that the outer periphery (102) of the first portion (72a-e) forms a plurality recess sets (110; 140), each recess set (110; 140) including two indentations that are axially and circumferentially offset from each other.

10. The method of claim 8 or 9, 2. including providing the first portion (72a-e) of the flow path section (70a-e) to have a circumferentially varying inner periphery.

Ansprüche

1. Turbomaschine (20), die einen ringförmigen Flusspfadabschnitt (57, 61) zwischen einer Vielzahl von sich radial erstreckenden Statorschaufeln (66) und einer Vielzahl von sich radial erstreckenden Rotorschaufeln (68) umfasst, wobei der ringförmige Flusspfadabschnitt einem Plattformflügel (70a-e) der Statorschaufel (66) entspricht, der sich zwischen der Hinterkante einer Vielzahl von sich radial erstreckenden Statorschaufeln (66) und der Vorderkante einer Vielzahl von sich radial erstreckenden Rotorschaufeln (68) erstreckt, dadurch gekennzeichnet, dass mindestens ein erster ringförmiger Teil (72a) des ringförmigen Flusspfadabschnitts (70a) einen sich in Umfangsrichtung verändernden Außenumfang (102) aufweist, der ein sich wiederholendes Muster (100) von Aussparungen (81) beinhaltet, die sich in Umfangsrichtung mit achsensymmetrischen Oberflächen abwechseln, wobei das Muster (100) keine Struktur beinhaltet, die von den achsensymmetrischen Oberflächen absteht.

2. Turbomaschine nach Anspruch 1, wobei sich das Muster (100) bei jeder Schaufelteilung in Umfangsrichtung mindestens einmal wiederholt.

3. Turbomaschine nach einem der vorhergehenden Ansprüche, wobei der Außenumfang (102) des ersten Teils (72a) eine Vielzahl von Aussparungssätzen (110; 140) definiert, wobei jeder Aussparungssatz (110; 140) zwei Vertiefungen (112, 114; 142, 144) beinhaltet, die axial und in Umfangsrichtung zueinander versetzt sind.

4. Turbomaschine nach einem der vorhergehenden Ansprüche, wobei die sich radial erstreckenden Statorschaufeln (66) Tragflächenschaufeln eines Gasturbinentriebwerks (20) sind und die sich radial erstreckenden Rotorschaufeln (68) Rotorschaufeln des Gasturbinentriebwerks (20) sind.

5. Turbomaschine nach Anspruch 4, wobei die sich radial erstreckenden Rotorschaufeln (68) einer Niederdruckturbine (46) des Gasturbinentriebwerks (20) entsprechen und sich der ringförmige Flusspfad (70) von einer Hochdruckturbine (54) vor den Statorschaufeln (66) um die Vielzahl von Statorschaufeln (66) herum zu der Niederdruckturbine (46) erstreckt.

6. Turbomaschine nach einem der vorhergehenden Ansprüche, wobei der erste Teil (72a) des Flusspfadabschnitts (70a) auch einen in Umfangsrichtung variierenden Innenumfang aufweist.

7. Turbomaschine nach einem der vorhergehenden Ansprüche, wobei sich ein zweiter Teil (72d) des Flusspfades von dem ersten Teil (70d) über eine Hinterkante (74) der Vielzahl von Statorschaufeln (66) hinaus zu einer Stelle zwischen der Hinterkante (74) und einer Vorderkante (75) der Vielzahl von Statorschaufeln (66) erstreckt, der zweite Teil (72d) ebenfalls einen sich in Umfangsrichtung variierenden Außenumfang aufweist, wobei der sich in Umfangsrichtung variierende Außenumfang des ersten Teils (70d) kontinuierlich mit dem sich in Umfangsrichtung variierenden Außenumfang des zweiten Teils (72d) ist.

8. Verfahren zum Verringern der schwingenden Beanspruchung einer Vielzahl von sich radial erstreckenden Rotorschaufeln (68), umfassend:

Bereitstellen eines ringförmigen Flusspfadabschnitts (57, 61) zwischen einer Vielzahl von sich radial erstreckenden Statorschaufeln (66) und einer Vielzahl von sich radial erstreckenden Rotorschaufeln, wobei der ringförmige Flusspfadabschnitt einem Plattformflügel (70a-e) entspricht, der sich zwischen der Hinterkante einer Vielzahl von sich radial erstreckenden Statorschaufeln (66) und der Vorderkante einer Vielzahl von sich radial erstreckenden Rotorschaufeln (68) erstreckt,

gekennzeichnet durch Bereitstellen, dass ein erster ringförmiger Teil (72a-e) des Flusspfadabschnitts (70a-e) einen sich in Umfangsrichtung variierenden Außenumfang aufweist, der ein sich wiederholendes Muster von Aussparungen (81) beinhaltet, die sich in Umfangsrichtung mit achsensymmetrischen Oberflächen abwechseln, wobei das Muster keine Struktur beinhaltet, die von den achsensymmetrischen Oberflächen absteht.

9. Verfahren nach Anspruch 8, wobei der erste Teil (72a-e) des Flusspfades so definiert ist, dass der Außenumfang (102) des ersten Teils (72a-e) eine Vielzahl von Aussparungssätzen (110; 140) bildet, wobei jeder Aussparungssatz (110; 140) zwei Vertiefungen beinhaltet, die axial und in Umfangsrichtung gegeneinander versetzt sind.

10. Verfahren nach Anspruch 8 oder 9, beinhaltend Bereitstellen, dass der erste Teil (72a-e) des Flusspfadabschnitts (70a-e) einen in Umfangsrichtung variierenden Innenumfang aufweist.

Revendications

1. Turbomachine (20), comprenant une section de trajectoire d'écoulement annulaire (57, 61) entre une pluralité d'aubes de stator s'étendant radialement (66) et une pluralité d'aubes de rotor s'étendant radialement (68), dans laquelle la section de trajectoire d'écoulement annulaire correspond à une aile de plate-forme (70a-e) de l'aube de stator (66) s'étendant entre le bord de fuite d'une pluralité d'aubes de stator s'étendant radialement (66) et le bord d'attaque d'une pluralité d'aubes de rotor s'étendant radialement (68), caractérisé en ce que au moins une première portion annulaire (72a) de la section de la trajectoire d'écoulement annulaire (70a) a une périphérie extérieure variant circonférentiellement (102) comportant un motif répétitif (100) d'évidements (81) alternant circonférentiellement avec des surfaces axisymétriques, le motif (100) n'incluant aucune structure dépassant des surfaces axisymétriques.

2. Turbomachine selon la revendication 1, dans laquelle le motif (100) se répète au moins une fois à chaque pas circonférentiel d'aube.

3. Turbomachine selon une quelconque revendication précédente, dans laquelle la périphérie extérieure (102) de la première portion (72a) définit une pluralité d'ensembles d'évidements (110 ; 140), chaque ensemble d'évidements (110 ; 140) comportant deux échancrures (112, 114 ; 142, 144) qui sont décalées axialement et circonférentiellement l'une de l'autre.

4. Turbomachine selon une quelconque revendication précédente, dans laquelle les aubes de stator s'étendant radialement (66) sont des aubes aérodynamiques d'un moteur à turbine à gaz (20), et les aubes de rotor s'étendant radialement (68) sont des aubes de rotor du moteur à turbine à gaz (20).

5. Turbomachine selon la revendication 4, dans laquelle les aubes de rotor s'étendant radialement (68) correspondent à une turbine basse pression (46) du moteur à turbine à gaz (20), et la trajectoire d'écoulement annulaire (70) s'étend depuis une turbine haute pression (54) en avant des aubes de stator (66) autour de la pluralité d'aubes de stator (66) vers la turbine basse pression (46).

6. Turbomachine selon une quelconque revendication précédente, dans laquelle la première portion (72a) de la section de trajectoire d'écoulement (70a) a également une périphérie interne variant circonférentiellement.

7. Turbomachine selon l'une quelconque des revendications précédentes, dans laquelle une seconde portion (72d) de la trajectoire d'écoulement s'étend depuis la première portion (70d) au-delà d'un bord de fuite (74) de la pluralité d'aubes de stator (66) jusqu'à un emplacement entre le bord de fuite (74) et un bord d'attaque (75) de la pluralité d'aubes de stator (66), la seconde portion (72d) ayant également une périphérie externe variable circonférentiellement, la périphérie externe variable circonférentiellement de la première portion (70d) étant continue avec la périphérie extérieure variant circonférentiellement de la seconde portion (72d).

8. Procédé de réduction des contraintes vibratoires sur une pluralité d'aubes de rotor s'étendant radialement (68), comprenant :

la fourniture d'une section de trajectoire d'écoulement annulaire (57, 61) entre une pluralité d'aubes de stator s'étendant radialement (66) et une pluralité d'aubes de rotor s'étendant radialement, la section de trajet d'écoulement annulaire correspondant à une aile de plate-forme (70a-e) s'étendant entre le bord de fuite d'une pluralité d'aubes de stator s'étendant radialement (66) et le bord d'attaque d'une pluralité d'aubes de rotor s'étendant radialement (68),

caractérisé par la fourniture d'une première portion annulaire (72a-e) de la section de trajectoire d'écoulement (70a-e) pour avoir une périphérie extérieure variant circonférentiellement comportant un motif répétitif d'évidements (81) alternant circonférentiellement avec des surfaces axisymétriques, le motif n'incluant aucune structure dépassant des surfaces axisymétriques.

9. Procédé selon la revendication 8, dans lequel la première portion (72a-e) de la trajectoire d'écoulement est définie de sorte que la périphérie extérieure (102) de la première portion (72a-e) forme une pluralité d'ensembles d'évidements (110 ; 140), chaque ensemble d'évidements (110 ; 140) comportant deux échancrures décalées axialement et circonférentiellement l'une de l'autre.

10. Procédé selon la revendication 8 ou 9, comportant la fourniture de la première portion (72a-e) de la section de trajectoire d'écoulement (70a-e) pour qu'elle ait une périphérie interne variant circonférentiellement.

Drawing