Centrifugal compressor impeller and compressor with said impeller

Description

TECHNICAL FIELD

[0001] The present invention concerns a centrifugal compressor impeller, and to a centrifugal compressor comprising said impeller.BACKGROUND

[0002] WO 2013 / 162897 A1 discloses a turbine hub with a surface discontinuity. US 4 887 940 A discloses a multistage fluid machine. JP H08 170598 A discloses a turbocharger. US 2 390 504 A discloses a centrifugal air compressor.

[0003] A turbomachinery, in particular a centrifugal compressor, may comprise a casing wherein a rotor is rotatingly supported. The rotor may comprise a rotor shaft supported by bearings and seals acting on the rotor shaft may be provided to isolate the interior of the compressor from the environment. In some embodiments, one or more impellers may be mounted on the shaft. The casing defines stator vanes, wherein impellers are positioned and may rotate. The casing (or stator) further defines stator conduits configured to collect the fluid leaving each impeller, and to feed the said fluid to the next compressor stage (if provided). Centrifugal compressors comprising a plurality of impellers are usually referred as multistage centrifugal compressor. Therefore, each impeller provides work to a compression stage.

[0004] An impeller may comprise a plurality of shaped blades extending form an hub. The hub and two adjacent blades form a shaped impeller vane.

[0005] In some embodiments, the impeller is open-faced (namely it is not shrouded) and each blade has a free end, that defines the tip of the blade. In those centrifugal compressor impellers, the tips of the blades are usually flat. When the impeller is mounted in the compressor the tips of the blades face the stator, and between the stator and the tip a gap is formed. As the compressed fluid may flow in the gap creating a recirculation in the compressor, the gap should be as small as possible in order to achieve a good stage performance.

[0006] This secondary fluid flow in the gap is usually called tip leakage flow. In order to reduce the tip leakage flow a recessed blade tip designs, having a U shaped cross section, was used to improve the total-to-total pressure ratio and efficiency over the whole operating range. As a result, the overall stage loss was reduced with recessed blade tip design due to the positive effect of the reduced tip leakage flow.

[0007] However, the recess cavity has an adverse effect on the stage efficiency due to the generation of a vortex in the cavity, hence generating additional losses.

[0008] Moreover, it is costly to form a U-shaped recess on the top of the tip, which may have a width in the order of 2-3mm.SUMMARY

[0009] There is a general need for a centrifugal compressor impeller capable of giving a better stage compression performance.

[0010] The present invention is defined in the accompanying claims.

[0011] An important idea is to provide a centrifugal compressor impeller having blades with a tip surface provided with a rim (also referred to as squealer tip) aligned to the pressure side of the blade, while the tip surface edge in correspondence of the suction side of the blade is almost completely free from said rim.BRIEF DESCRIPTION OF DRAWINGS

[0012] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate exemplary embodiments of the present disclosure and, together with the detailed description, explain these embodiments. In the drawings: Fig. 1 shows a schematic and partial cross section of a centrifugal compressor according to the present disclosure. Fig. 2 shows a schematic section taken along section line II-II of Fig. 1 and II-II of Fig. 3. Fig. 3 shows a top view of a tip surface of the blade represented in Fig. 2. Fig. 4 and 5 show alternative designs of a blade tip surface according to the claimed invention. Fig. 6, 7 and 8 show cross sections taken respectively on section lines VI-VI of Fig. 4, VII-VII of Fig. 5 and VIII-VIII of Fig. 4. DETAILED DESCRIPTION

[0013] The following description of exemplary embodiments refers to the accompanying drawings.

[0014] The following description does not limit the invention. Instead, the invention is defined by the appended claims.

[0015] Fig. 1 shows a centrifugal compressor 1, comprising a stator 2 defining at least a stator vane 3 wherein at least an open impeller 4 is mounted on a shaft 20. In the drawing, only one impeller is shown, but the centrifugal compressor may comprise a plurality of impellers mounted on the shaft 20, each defining a compressor stage. All the impellers or just some of them may be configured as described in the present description.

[0016] The stator 2 may be realized in a single piece or in different parts (diaphragms) mounted in a casing (not shown). The stator defines not only the vane 3 housing the impeller, but also one or more conduits 5 provided to collect a fluid leaving the impeller 4.

[0017] The centrifugal compressor impeller 4 comprises a plurality of blades 6, extending from a hub 7. Each blade 6 have a first wall 6A defining a pressure side of the blade (when the impeller is in operation), and a second wall 6B defining a suction side of the blade 6. Each blade further provides a free end defining a tip 6C of the blade. When the impeller is mounted on the centrifugal compressor the tip 6C of the blades faces the stator 2. A gap G is present between the stator and the tip.

[0018] Moreover, each blade 6 presents a leading edge LE provided at the inlet of the impeller, and a trailing edge TE provided at the outlet of the impeller.

[0019] According to one aspect of the disclosure the tip 6C presents a raised rim 8 aligned (see fig 2) to the first wall 6A. A free edge of the second wall 6B of the blade, instead, is at least partially aligned with a surface 6D of the tip 6C free from the raised rim 8. As it may be clear form Fig. 2, in the same cross section taken where the second wall is free from said rim, the height H1 of the first wall is bigger than the height H2 of the second wall. The ratio between the blade tip width SB and the rim width SR (SB / SR) in any section (Fig. 2) may be higher than 2, depending on the blade tip thickness. The second wall 6B of the blade 6 may be completely aligned (for all its length L) with the surface 6D of the tip free from said raised rim 8.

[0020] Fig 3 shows that the raised rim 8 extends for all the length L of the first wall.

[0021] The configurations of the blade tip according to the claimed invention are provided as shown in Figs. 4 and 5.

[0022] In the description of this embodiment, those parts functionally similar to the ones already described will be indicated with the same reference numbers, and their description will be omitted.

[0023] Fig. 4 shows a blade tip, having a raised rim 8 very similar form the one above described. According to the invention the raised rim 8 is also provided with multiple parts 8A extending from it in the direction of the second wall 6B. Said parts 8A may extend up to the second wall 6B, as shown in Fig. 6, or may be distant from the wall 6B (Fig. 8).

[0024] The parts 8A, may extend in a direction that is perpendicular to the first wall 8A, when seen in a top view as the one of Fig. 4.

[0025] Also in Fig. 5 the raised rim is similar to the one of Fig. 3, but it provides parts 8B that extend from the rim in a direction that is inclined with respect to the first wall 8A. The inclination may be the same for all the parts 8B, or each or some of the parts may have a different inclination with respect to the first wall 6A. The parts 8B may extend up to the second wall 6B or may be distant from it (even if this solution is not represented in the drawings). In the top view of Fig. 5, the inclination α of the axis of the parts 8A with respect to the first wall 6A can be appreciated; the inclination α may be comprised between -45 ° and +45°.

[0026] The presence of the rim 8A, and of the parts 8A or 8B extending form the rim, may reduce leakage flows due to the development of dissipative vortices that may increase stage efficiency.

[0027] Furthermore, an operating range extension due to the reduction of tip leakage flow interaction with main flow at highest pressure ratios (towards left limit) may be achieved.

[0028] While the disclosed embodiments of the subject matter described herein have been shown in the drawings and fully described above with particularity and detail in connection with several exemplary embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without materially departing from the subject matter recited in the appended claims. Hence, the proper scope of the disclosed innovations should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications, changes, and omissions.

Claims

1. Centrifugal compressor impeller (4) comprising a plurality of blades (6) extending from a hub (7), each blade having a first wall (6A) defining a pressure side of the blade, and a second wall (6B) defining a suction side of the blade, and a free end defining a blade tip (6C) arranged to face a centrifugal compressor stator (2), characterized by the blade tip (6C) comprising a tip surface (6D) perpendicular to the second wall (6B) and extending from the edge of the second wall (6B) toward the first wall (6A) and a raised rim (8) aligned to the edge of the first wall (6A) and raised relative to the tip surface (6D), wherein said raised rim (8) presents multiple parts (8A, 8B) raised from the tip surface (6D) and extending from the raised rim (8) in the direction of the second wall (6B).

2. Centrifugal compressor impeller (4) according to claim 1, wherein the raised rim (8) extends for all the length (L) of the first wall (6A) in the first direction.

3. Centrifugal compressor impeller (4) according to claim 1 or claim 2, wherein said multiple parts (8A) extend from the raised rim (8) in a direction perpendicular with respect to the first wall (6A).

4. Centrifugal compressor impeller (4) according to one or more of the previous claims, wherein said multiple parts (8B) extend from the raised rim (8) in a direction inclined with respect to the first wall (6A).

5. Centrifugal compressor impeller (4) according to one or more of the previous claims, wherein said multiple parts (8A, 8B) extend up to the second wall (6B).

6. Centrifugal compressor (1) comprising a stator (2) defining at least a stator vane (3) wherein at least a centrifugal compressor impeller (4) according to one or more of the preceding claims is positioned, and at least a stator conduit (5) provided to collect a fluid leaving the impeller (4), the tip (6C) of the blade facing the stator (2).

7. Centrifugal compressor (1) according to the preceding claim, wherein the compressor comprises a plurality of centrifugal compressor impellers, and a plurality of stator conduits (5) to collect the fluid leaving an impeller and feeding it to the next impeller.