centrifugal compressor with double-impeller rotor, and diffuser

Abstract

Turbomachine assembly 10) comprising a centrifugal compressor (11) with a rotor (50) having two impellers arranged in a back-to-back configuration, and a diffuser (12) arranged radially opposite the outlet (13) of the rotor (50) with two impellers, wherein the diffuser (12) comprises means (14) for separating the air exiting the centrifugal compressor (11) arranged such that a first airflow exiting a first impeller (15) feeds a first annular duct (16) of the diffuser (12) and a second airflow exiting a second impeller (17) feeds a second annular duct (18) of the diffuser (12). Abstract figure: Figure 1

Description

Title of the invention: Centrifugal compressor with double-impeller rotor and diffuser

[0001] The present application relates to an assembly consisting of a centrifugal turbomachine compressor equipped with a double-impeller rotor arranged in a back-to-back configuration, and a diffuser. Previous technique

[0002] Twin-impeller rotors arranged in a back-to-back configuration, i.e., coupled at the back, are already known from prior art. Their combination with a diffuser is also already known, in the context of research to improve compressor performance. In some configurations, the twin-impeller rotor is directly followed by the diffuser, resulting in disturbances in the airflow exiting both impellers. Indeed, the air exiting the first impeller mixes with the air from the second impeller, and the two airflows mutually disturb each other. This type of twin-impeller configuration thus impacts the local aerodynamics and reduces the pumping margin of the compression stage due to a decrease in the compressor outlet pressure. Summary

[0003] The present disclosure is intended in particular to improve the local aerodynamic behavior, at the exit of the double-wheel rotor arranged back-to-back and in the associated diffuser.

[0004] An assembly is thus proposed comprising a centrifugal compressor with a double-impeller rotor arranged in a back-to-back configuration, and a diffuser arranged radially opposite the outlet of the double-impeller rotor, in which the diffuser includes means for separating the air exiting the centrifugal compressor arranged so that a first airflow exiting a first impeller feeds a first annular conduit of the diffuser and a second airflow exiting a second impeller feeds a second annular conduit of the diffuser.

[0005] The separation means thus reproduce the well-known supply conditions of the centrifugal compressor diffuser in the case of a single-impeller rotor, while taking advantage of the design of a double-impeller rotor, which doubles the flow rate through the compressor. The separation means are therefore particularly advantageous for increasing the operating performance of a turbomachine and maintaining, or even improving, the pumping margin in a technical solution that seeks to use a double-impeller rotor.

[0006] Alternatively or in addition, the first annular conduit and the second annular conduit form an annular airflow channel in which the separation means are arranged.

[0007] Alternatively or in addition, the separation means comprise at least an upstream portion having the shape of a blade. Furthermore, the blade may have a symmetrical profile.

[0008] Alternatively or in addition, the upstream part of the separation means extends along an axis and in which a first distance between an envelope of the upstream part and a wall of the first or second annular conduit represents between 1% and 50% of a second distance between the axis and said wall.

[0009] The separation means may further include a separation wall extending from a trailing edge of said upstream part.

[0010] In addition, the separating wall can be of angled shape.

[0011] Alternatively or additionally, the annular airflow channel has a radial annular portion, an axial annular portion and a bent annular portion for joining the radial portion to the axial portion, the upstream part of the separation means extending at least into the radial portion, and the separation wall extending at least into the bent annular portion.

[0012] In addition, the axial annular portion can extend over a length H1 and the separation wall can include a downstream end of the separation means separated from a downstream end of the annular airflow channel by a distance DI between 10% and 100% of the length Hl.

[0013] Alternatively or in addition, an upstream end of the separation means is arranged upstream of the first and second annular conduits.

[0014] In addition, a trailing edge of the rotor can be separated from the first and second annular conduits by a distance H2, and the upstream end can be arranged at a distance D2 measured from the trailing edge, D2 being between 1% and 100% of the distance H2.

[0015] According to another aspect, a turbine is proposed comprising an assembly as described above. Brief description of the drawings

[0016] Other features, details and advantages will become apparent from reading the detailed description below and from analyzing the accompanying drawings, in which: Fig. 1

[0017] [Fig.1] shows a schematic cross-sectional view of part of a centrifugal compressor according to an example embodiment. Fig. 2

[0018] [Fig.2] shows a schematic cross-sectional view of the diffuser according to the example in [Fig.1]. Fig. 3

[0019] [Fig.3] shows a detailed view of the compressor part of [Fig.1]. Description of the implementation methods

[0020] The terms "upstream" and "downstream" are subsequently defined in relation to an air inlet (upstream) and a gas outlet (downstream) of a turbomachine.

[0021] Figure 1 illustrates an assembly consisting in part of a centrifugal compressor 11 and a diffuser 12. The compressor includes a rotor 50. The rotor 50 is of the twin-impeller type, the two impellers being arranged in a back-to-back configuration. In particular, the rotor 50 comprises a first impeller 15 and a second impeller 17. The first and second impellers 15 and 17 are joined together so that the rotor 50 thus comprises two fluid inlets, the flow directions of which are opposite to each other.

[0022] The rotor 50 further includes an outlet 13, through which the fluid exits the rotor 50. More precisely, the fluid passes through the first and second impellers 15, 17 to the outlet 13 of the rotor 50. The outlet 13 is common to the first and second impellers 15, 17. The outlet 13 thus includes a trailing edge 24.

[0023] The diffuser 12 is also illustrated in [Fig.2]. The diffuser 12 comprises a first annular duct 16 and a second annular duct 18. The first and second annular ducts 16, 18 form an annular airflow channel 22.

[0024] As illustrated in [Fig.2], the annular air flow channel 22 has a radial annular portion 25 and an axial annular portion 26. The annular air flow channel 22 may also include an angled annular portion 30. The angled annular portion 30 connects the radial annular portion 25 to the axial annular portion 26.

[0025] The radial annular portion 25 comprises an upstream radial annular wall 41 and a downstream radial annular wall 42. The upstream and downstream radial annular walls 41, 42 extend parallel to each other. The radial annular portion 25 further comprises the upstream end 31 of the annular airflow channel 22.

[0026] The axial annular portion 26 comprises an internal axial annular wall 43 and an external axial annular wall 44. The radially internal axial annular wall 43 and the radially external axial annular wall 44 extend parallel to each other, i.e., coaxially. The axial annular portion 26 further comprises, downstream, the downstream end 28 of the annular airflow channel 22.

[0027] The angled annular portion 30 is arranged between the radial annular portion 25 and the axial annular portion 26. More precisely, the angled annular portion 30 is the junction between the radial annular portion 25 and the axial annular portion 26. The The angled annular portion 30 therefore extends upstream in a radial direction, from the radial annular portion 25, to end in an axial direction downstream, at the level of the axial annular portion 26. The angled annular portion 30 comprises an internal angled annular wall 45 and an external angled annular wall 46. The internal and external angled annular walls 45, 46 are equidistant from each other at every point.

[0028] The diffuser 12 follows the rotor 50 directly. More precisely, there are no interposed elements between the diffuser 12 and the rotor 50, so that the fluid exits the rotor 50 and flows to the diffuser 12 without coming into contact with any part that might serve as a guide for the fluid between these two elements, such as, for example, a bridging cone. Furthermore, as shown in [Fig. 1], the diffuser 12 and the rotor 50 are not in contact with each other, but separated by a gap, this gap being represented by a distance H2, visible in [Fig. 3]. Consequently, in the absence of a guiding part between the rotor 50 and the diffuser 12, part of the flow may deviate outside the diffuser 12, which leads, for example, to a reduction in the pumping margin.The fluid exiting rotor 50 at point 13 therefore has its local aerodynamics disturbed compared to a classic configuration in the case of a centrifugal compressor with a simple impeller, involving for example a fluid recovery cone.

[0029] Furthermore, the fluid entering the diffuser 12 originates from the first and second impellers 15, 17. The fluid is thus composed of two flows in the rotor 50 (a first flow passing through the first impeller 16 and a second flow passing through the second impeller 17) and then forms a single flow at the inlet of the diffuser 12. This single flow corresponds to the merging of the two upstream fluids. This merging can lead to fluid recirculation or vorticity phenomena and thus create anomalies in the aerodynamic behavior at the inlet of the diffuser 12. These anomalies contribute to the phenomenon of reduced margin during the pumping of the compression stage.

[0030] Figure 1 also illustrates separation means 14. The separation means 14 serve as a guide for the flow between the rotor 50 and the diffuser 12, thereby providing the fluid exiting the rotor 50 with feed conditions to the diffuser 12 as close as possible to those existing in the case of a single-impeller centrifugal compressor. Indeed, the separation means 14 reproduce the phenomenon of fluid streamline contraction encountered in the case of the single-impeller compressor. This contraction phenomenon contributes to the stability of the flow in the rotor / stator area. The separation means thus keep the fluid exiting the rotor 50 towards the diffuser 12 separated into two streams. Consequently, the separation means 14 maintain the division of the flow entering the diffuser 12 into two flow, each of the two flows being directed from outlet 13 to respectively the first annular conduit 16 and the second annular conduit 18. In other words, the separation means 14 separate the annular air flow channel 22 into several annular conduits. For example, as illustrated in the figures, the separation means 14 are arranged in the annular airflow channel 22. The separation means 14 divide the annular airflow channel 22 into two conduits, namely the first and second annular conduits 16, 18. In other words, the separation means 14 extend the two flows passing through the rotor 50, i.e., the first flow passing through the first impeller 16 and the second flow passing through the second impeller 18, into the diffuser 12. The separation means 14 thus act as a physical guide, preventing the flow from merging at the outlet of the rotor 50.

[0031] As illustrated for example in Figures 1 and 2, the separation means 14 may include an upstream part 19. The upstream part 19 extends at least into the radial part 25. More precisely, the upstream part 19 includes an upstream end 23 and a trailing edge 21. The upstream end 23 and the trailing edge 21 may extend beyond the radial part 25, respectively upstream and downstream of the radial part 25.

[0032] Furthermore, the upstream portion 19 can take the form of a blade with a symmetrical profile. By "symmetrical profile," it is understood that the camber of the blade is zero. Moreover, the axis of symmetry of the blade is parallel to the direction of the fluid's approach velocity. In addition, the blade comprises a streamlined body, with a rounded leading edge and a trailing edge 21, the trailing edge 21 being thin compared to the leading edge. The flow then divides around the leading edge, i.e., the upstream end 23, and rejoins at the trailing edge 21 of the blade. The axis of the upstream portion 19 is illustrated in [Fig. 3] by the reference numeral X19. The axis X19 can be an axis of symmetry, which extends radially in the annular airflow channel 22.

[0033] Figure 3 illustrates in more detail the upstream portion of the annular airflow channel 22, i.e., the inlet of the diffuser 12. As can be seen in this example, the upstream end 23 of the separation means 14 is arranged upstream of the annular airflow channel 22. In other words, the upstream end 23 is arranged between the trailing edge 24 of the rotor 50 and the upstream end 31 of the annular airflow channel 22. The upstream portion 19 of the separation means 14 is thus located partly outside the annular airflow channel 22, within the distance H2. More precisely, the upstream end 23 is arranged at a distance D2 measured from the trailing edge 24. The distance D2 can be between 1% and 100% of the distance H2. For example, distance H2 could be 10 mm and distance D2 could be 5 mm. Therefore, distance D2 is equal to 50% of distance H2. In another example, distance H2 could be 10 mm and distance D2 could be 6 mm.The distance. D2 is therefore equal to 60% of the distance H2, and the upstream end 23 of the separation means 14 is arranged 4 mm upstream of the upstream end 31 of the annular airflow channel 22.

[0034] Furthermore, according to [Fig. 3], it can be seen that the upstream portion 19 of the separation means 14 occupies a volume in the annular airflow channel 22. Depending on the size of the upstream portion 19, this occupied volume is more or less significant. In other words, the separation means 14 cause a greater or lesser contraction of a section of the annular airflow channel 22. For example, the larger the volume of the upstream portion 19, the more the airflow channel 22 is obstructed, and therefore its volume is smaller in the portion containing the upstream portion 19. In particular, the ratio between the volume occupied by the upstream portion 19 in the annular airflow channel 22 can be illustrated by a measurement taken at the upstream end 31 of the annular airflow channel 22, with reference to [Fig. 3].For example, the upstream part 19 is arranged radially along the midline of the annular airflow channel 22, which separates the channel into two radially symmetrical parts, with respect to the axis of symmetry X19 in the radial annular portion 25. At the upstream end 31 of the annular airflow channel 22, a first distance L31 is measured between the envelope of the upstream part 19 and the inner surface of the upstream radial annular wall 41, as well as a second distance L19 between the axis of symmetry X19 of the upstream part 19 and the inner wall of the upstream radial annular wall 41. The first distance L31 can represent between 1% and 50% of the second distance L19. For example, for a distance L19 equal to 10 mm, the distance L31 can be equal to 4 mm, which represents 40% of the distance L19.

[0035] Alternatively, the separation means 14 comprise a separation wall 20, illustrated for example in [Fig. 2]. The separation wall 20 extends from the trailing edge 21 of the upstream portion 19 to the downstream end 28 of the annular airflow channel 22. The separation wall 20 terminates with a downstream end 27.

[0036] As shown in [Fig. 2], the separating wall 20 extends primarily into the angled annular portion 30. Furthermore, the separating wall 20 is angled in shape. In other words, the separating wall 20 follows the angled shape of the angled annular portion 30. The separating wall 20 divides the annular airflow channel 22 into an outer annular portion, bounded by the outer angled annular wall 46, and an inner annular portion, bounded by the inner angled annular wall 47. Consequently, the separating wall 20 extends the first and second annular ducts 16, 18 into the angled annular portion 30. The separating wall 20 thus guides the flows from the radial annular portion 25 into the first and second annular ducts 16, 18, enabling an optimal transition. between a radial flow circulation in the radial annular portion 25 and an axial flow circulation in the axial annular portion 26.

[0037] Alternatively, the separating wall 20 also extends, at least in part, into the axial annular portion 26. More precisely, DI can be written as the distance between the downstream end 27 of the separating means 14 and the downstream end 28 of the annular airflow channel 22, in other words, the distance between the free end of the separating wall and the trailing edge of the axial annular portion 26. This distance DI can be between 10% and 100% of the length H1 of the axial annular portion 26. For example, the axial annular portion 26 is 100 mm long and the downstream end 27 is located 60 mm from the downstream end 28 of the annular airflow channel 22. The distance DI therefore represents 60% of the length H1.

[0038] In addition, the separation means 14 can be an added part, inserted into the annular air flow channel 22. Alternatively, the separation means 14 can be manufactured with the annular air flow channel 22, either in one piece or in two half-pieces, for example in additive manufacturing.

[0039] Furthermore, the figures illustrate separation means 14 in the form of a symmetrically profiled blade extending into a separating wall. However, the present description is not limited to this example, as other forms may be envisaged. For example, the separation means 14 may be a fixed wall in the radial annular portion 25, separating the annular airflow channel 22 into first and second annular ducts 16, 18.

Claims

Demands

1. A turbomachine assembly (10) comprising a centrifugal compressor (11) with a rotor (50) having two impellers arranged in a back-to-back configuration, and a diffuser (12) arranged radially opposite the outlet (13) of the rotor (50) with two impellers, wherein the diffuser (12) comprises air separation means (14) for the air exiting the centrifugal compressor (11) arranged such that a first airflow exiting a first impeller (15) feeds a first annular duct (16) of the diffuser (12) and a second airflow exiting a second impeller (17) feeds a second annular duct (18) of the diffuser (12), and wherein the separation means (14) comprise at least an upstream portion (19) having the form of a blade, the separation means (14) comprising a separation wall (20) extending from a trailing edge (21) of said upstream part (19).

2. Assembly according to claim 1, wherein the first annular conduit (16) and the second annular conduit (18) form an annular airflow channel (22) in which the separation means (14) are arranged.

3. Assembly according to claim 1 or 2, wherein the blade has a symmetrical profile.

4. Assembly according to any one of the preceding claims, wherein the upstream part (19) of the separation means (14) extends along an axis (X19) and wherein, a first distance (L31) between an envelope of the upstream part (19) and a wall of the first or second annular conduit (16, 18) represents between 1% and 50% of a second distance (L19) between the axis (X19) and said wall.

5. Assembly according to claim one of the preceding claims, wherein the separating wall (20) is of angled shape.

6. Assembly according to claim 2, wherein the annular airflow channel (22) has a radial annular portion (25), an axial annular portion (26), and a bent annular portion (30) joining the radial annular portion (25) to the axial annular portion (26), the upstream portion (19) of the separation means (14) extending at least into the radial annular portion (25), and the wall separation (20) extending at least into the bent annular portion (30).

7. Assembly according to claim 6, the axial annular portion (26) extending over a length H1 and the separating wall (20) comprising a downstream end (27) of the separating means (14) separated from a downstream end (28) of the annular airflow channel (22) by a distance DI between 10% and 100% of the length Hl.

8. Assembly according to any one of the preceding claims, wherein an upstream end (23) of the separation means (14) is arranged upstream of the first and second annular conduits (16, 18).

9. Assembly according to claim 8, a trailing edge (24) of the rotor (50) being separated from the first and second annular conduits (16, 18) by a distance H2, in which the upstream end (23) is arranged at a distance D2 measured from the trailing edge (24), D2 being between 1% and 100% of the distance H2.

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