EP2483567A1

EP2483567A1 - Radial compressor diffuser

Info

Publication number: EP2483567A1
Application number: EP10760303A
Authority: EP
Inventors: Jean-Paul Komor; Theodor Wallmann
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2009-09-28
Filing date: 2010-09-23
Publication date: 2012-08-08
Also published as: WO2011036206A1; CN102686889A; DE102009043230A1; US20120183395A1

Abstract

The invention relates to a radial compressor diffuser for a radial compressor stage (1), comprising a flow channel (7) which extends radially outwards and which has a cylindrical inlet cross-section (9) on a first radius (10) which extends radially inwards and a cylindrical outlet cross-section (11) which extends radially outwards. A radial diffuser outlet blade (15) is provided in the region of the outlet cross-section (11) in the flow channel (7), said outlet blade can prevent known disadvantages of traditional bladed diffusers.

Description

description

Radial compressor diffuser The invention relates to a radial compressor diffuser for a radial compressor stage, wherein the radial compressor diffuser has a radial diffuser outlet blading.

Radial compressor stages are used in different types of turbocompressors. In this case, the type of flow guidance in the radial compressor stages depending on

Scope of application different. The flow guide in radial compressors has an impeller, a radial diffuser, and a discharge housing as essential elements. This applies in particular to the flow guidance of

single stage centrifugal compressors, single stages of

Transmission compressors, or the power amplifier multi-stage

Single shaft. The radial diffuser can be designed as a shovelless or as a bladed diffuser. The outflow housing is usually as

spiral housing executed.

To achieve best operating characteristics, the

Spiral housing designed and designed so that the static pressure over the impeller circumference or over the circumference of the radial diffuser is constant away. To this, too

It is necessary for the flow cross section of the spiral to be adapted precisely to the flow data prevailing at the outlet of the radial diffuser. But since the flow data during operation along the

Changing the compressor characteristic, this adjustment is often very imperfect: For example, the spiral is adapted for a specific design point exactly to the flow data, whereas at the other operating points ("Off Design operating points") of the compressor no special

Adjustment of the spiral is present. In other words, depending on the respective operating point, a more or less large aerodynamic mismatch exists Impeller and diffuser on the one hand and the volute casing

on the other hand, which has a corresponding negative impact on the performance of the radial diffuser result. The following is an example of a calculation for calculating the cross-sectional dimensioning of a spiral housing to achieve constant static pressure on the impeller or

Diffuser scope described in Eckert / Schnell, "Axial and Radial Compressors", Springer Verlag, 1961, p 417 ff .. Thereafter, as the decisive parameter for the cross-sectional dimensioning a spiral size parameter C is used, which is calculated as follows becomes:

12§nc _u- r

with c _u : tangential component of the flow velocity at the entry into the spiral for the spiral design point, r: the radius at the spiral entry, Q: the

Volume flow at the entrance to the spiral for the

Spiral design point, JI: circle constant.

It follows after conversion:

360

C

b ^■ tan oc,

respectively ,

(360

cc _r = arctan I - with b: width of the diffuser at the spiral inlet

Thus, for a given scroll compressor stage characterized by the scroll size parameter C, a constant pressure over the circumference of the impeller or diffuser is achieved if and only if the flow angle assumes the value _c according to the above relationship. The adjusting itself at the spiral inlet flow angle is determined by the Impeller and the further development of the flow in the radial diffuser coined. This angle is by no means constant, but changes along the compressor curve. Therefore, only at the excellent operating point where = _c holds, is there an optimum balance between impeller, diffuser and spiral. At operating points which deviate from this operating point, losses are to be expected due to + _c .

In addition, the dedicated design of the spiral is often omitted and instead impeller and diffuser are combined with a spiral already existing in the context of a standardized modular system. This is often done for cost reasons, whereby non-optimal operating characteristics are accepted in favor of the cost situation. The problem described above occurs especially with bladeless radial diffusers, but also with bladed radial diffusers. In particular, in the case of vaneless radial diffusers affects

Mismatched spiral housing often has a particularly negative impact on the operating behavior of the compressor stage.

With a bladed radial diffuser, the losses associated with mismatched volute casings can be reduced

be largely avoided. With the help of a bladed diffuser can be achieved efficiency advantages over a bladed diffuser, but this is only achieved if the bladed diffuser is positioned as close to the impeller out. The entrance ratios r / ri (r here denotes the radius at which the

Radial extent of the radial compressor blade inwardly ends, and r i denotes the radius at which the

Inlet cross section of the flow channel or the

Impeller outlet is located) with bladed diffusers are therefore usually between r / ri = 1.05 and r / ri = 1.2. Bladed diffusers, however, are not always desirable and have the disadvantage, among other things

Narrowing the usable driving range and causing increased Compressor noise. In a bladed radial diffuser, under certain circumstances, vibration excitations may occur due to impeller-stator interaction

Interactions between Diffuser schaufein and

Blades, which can lead to a vibration excitation of the highly loaded impeller. So is one

bladed centrifugal compressor diffuser due to follow - up dents of the impeller with significant fluctuations in the inflow to the diffuser Schaufein to be expected, which inter alia by interaction with the Diffusorschaufein also to the above indicated significant increase in the

Compressor noise leads. The adverse effects due to the impeller-impeller interaction are the more pronounced the smaller the radii ratio r / ri is.

The object of the invention is to a centrifugal compressor

which has improved operating characteristics with a non-optimally adapted outflow housing and does not suffer from drawbacks known from conventional bladed diffusers.

According to the invention, a radial compressor diffuser for a radial compressor stage is provided, comprising a

Flow channel, which extends radially outwardly and radially inwardly lying at a first radius cylindrically encircling inlet cross-section and radially outward lying a cylindrical circumferential outlet cross-section and which is designed such that during operation of the

Radial compressor diffuser one arranged from a directly upstream of the radial compressor diffuser

Centrifugal compressor impeller outflowing and through the

Inlet cross section entering the flow channel

Gas flow is delayed to flow through the outlet cross-section in a Abströmspiralgehäuse. In the area of

Outlet cross section in the flow channel is a

Provided radial diffuser exit blading, which causes the of the radial diffuser exit blading

imprinted outflow angle of the gas flow almost unaffected by the operating condition of the

Radial compressor impeller is and that their radial extent terminates inwardly at a third radius, wherein the

Ratio of the third radius to the first radius is at least 1.2. According to the invention is also a

Radial compressor stage created having the radial compressor diffuser according to the invention.

An advantage of the radial compressor diffuser according to the invention is that for the outer region of the radial diffuser

Guiding blading is used, which causes a nearly constant outflow angle with the value _c even with variation of the volume flow along the characteristic, whereby an optimal inflow to the spiral is achieved in the entire range of the curve and losses in efficiency and compressor ^¬ work can be avoided.

According to one development of the invention, the radial diffuser outlet blading of the radial compressor diffuser has a plurality of guide vanes arranged over the circumference, the leading edges of which are arranged circumferentially at the third radius. In this case, the plurality of guide vanes arranged over the circumference preferably has trailing edges which are arranged circumferentially in a region between the third radius and the radius of the outlet cross section.

The radial diffuser exit blading of the present invention has a higher inlet radii r / ri than conventional bladed diffusers, therefore the blading is placed in a zone having a comparatively low speed level (the velocity level in the diffuser is approximately proportional to the reciprocal of the radial Extension). Thus, the incidence of losses at the inlet of the blading on the one hand low, on the other hand there is in the constriction between stages such a low speed ^¬ or Mach number level that even at high volumetric flows the critical mass flux is not achieved. In order to does not occur in the blading according to the invention

Constriction of the operating area, as with

conventional bladed diffusers is the case. Further, at the radii ratio r / ri> 1.2, the trailing dents are largely balanced, so that negative effects caused by impeller-stator interaction are avoided. Preferably, the ratio of the third radius to the first radius is at least 1.35. The radial diffuser exit blading according to the invention causes the impressed outflow angle to ensure an improved flow to the spiral collecting space and its radial extent to the inside ends at the third radius, wherein the ratio of the third radius to the first radius is at least so large that known from conventional bladed radial diffusers disadvantages be avoided .

In the following, a preferred embodiment of a radial compressor diffuser according to the invention will be explained with reference to the attached schematic drawings. It shows:

Figure 1 is a schematic sectional view of a

Radial compressor stage according to an embodiment of the invention; and

Figure 2 is a plan view of the radial diffuser outlet ^¬ blading of the radial compressor stage of Figure 1. In Figure 1 is a schematic sectional view of a

Radial compressor stage 1 shown according to an embodiment of the invention. The radial compressor stage 1 has a radial compressor impeller 3, a radial compressor diffuser 6, and a discharge spiral housing 8. The radial compressor impeller 3 mounted on a shaft 2 for driving the radial compressor impeller ^¬ 3. In operation, the radial compressor stage 1 Gas in the centrifugal compressor impeller 3 enters a impeller inlet radial compressor 4 of the impeller 3, flows through the radial compressor impeller 3 and enters via the impeller ^¬ outlet 5 and a radial compressor diffuser inlet 9 in the radial compressor diffuser 6 a. The radial compressor diffuser inlet 9 is in one

determined, according to Figure 1 as a radius 10 designated radial distance to the axis of the shaft 2. Of the

Radial compressor diffuser 6 also has a channel 7 and an outlet 11, which is arranged at the radius 12 and has a certain width 13. To the diffuser 6, a Abströmspiralgehäuse 8 connects with a Abströmgehäuseeintritt 14. The diffuser 6 also has a

Radial diffuser exit blading 15 on. The

Radial diffuser exit blading 15 is close to

Radialdiffusoraustritt 11 arranged and extends between a radius 16, i. the radius at the entrance of the radial diffuser exit blading 15, and the area between the third radius 16 and the radius 12 of the

Outlet cross-section 11. In that shown in Figure 1

Embodiment is a radial diffuser ^¬ blading 15 in the outer region of the radial compressor diffuser 6, shortly before the entry zone of Abströmspiral ^¬ housing 8 is provided. The Eintrittsradienverhältnis, here the ratio between the radius 16 at the entrance of

Radial diffuser exit blading 15 and radius 10 at Radialdiffusoreintritt 9, is above the Eintritts ^¬ radii ratio in conventional bladed

Radial diffusers. FIG. 2 schematically shows part of the radial diffuser outlet blading 15 of the radial compressor stage from FIG. The blading 15 has a plurality of

Vanes 17 which extend radially between the radius 22 and the radius 16. In each case, the trailing edges 20 of the guide vanes 17 at the radius 22 and the leading edges 19 of the vanes 17 are arranged at the radius 16. Further, the vanes 17 are inclined with respect to a radial direction, so that the adjusting Flow velocity vector 21 downstream of the

Guide vanes 17 and the Radialdiffusoraustritts- blading 15 has the discharge angle, which is designated in Figure 2 with 18.

Claims

claims

1. Radial compressor diffuser for a radial compressor stage (1), with a flow channel (7) which extends radially outwardly and radially inward one at a first

Radius (10) cylindrically encircling inlet cross-section (9) and radially outwardly lying a cylindrical circumferential outlet section (11), wherein the flow channel (7) is designed, one of a directly upstream of the radial compressor diffuser (6) arranged radial compressor ^¬ impeller (3) flowing out and through the inlet cross-section (9) in the flow channel (7) entering gas flow for outflow through the outlet cross-section (11) in a

Retard spiral housing (8) to delay, wherein in the flow channel (7) in the region of the outlet cross-section (11)

Radial Diffuser exit blading (15) is provided, which causes the of the

Radial diffuser exit paddle (15) imprinted

Outflow angle (18) of the gas flow is almost unaffected by the operating state of the radial compressor impeller (3) and that their radial extension ends inwardly at a third radius (16), wherein the ratio of the third radius (16) to the first radius (10) at least 1, 2.

2. Radial compressor diffuser according to claim 1,

wherein the radial diffuser exit paddle (15) has a plurality of circumferentially disposed vanes (17) whose leading edges (19) are circumferentially disposed at the third radius (16).

3. Radial compressor diffuser according to claim 2,

the plurality being arranged circumferentially

Guide vanes (17) trailing edges (20) which are arranged circumferentially in a region between the third radius (16) and the radius (12) of the outlet cross-section (11).

4. radial compressor diffuser according to claim 3,

the ratio of the third radius (16) to the first

Radius (10) is at least 1.35.

5. Radial compressor stage with a radial compressor diffuser (6) according to one of claims 1 to 4.