EP3805572A1 - Diffuser, radial turbocompressor - Google Patents

Abstract

The invention relates to a diffuser (DFR) of a radial turbo compressor (RTC), the diffuser (DFR) extending in a ring around a central axis (X), the diffuser (DFR) having an inflow (INL) that runs along at least a first section (SG1) the flow is designed for an at least largely radial flow by means of a process fluid (PFL) during operation, the diffuser (DFR) having stationary guide vanes (VNS) which divides the diffuser (DFR) at least along a radial section into individual circumferential segments , the guide vanes (VNS) extending in the direction of flow from a leading edge (LDG) to a trailing edge (TRG) in the axial center along a mean chord length (MCL), the diffuser (DFR) in the area of the first section (SG1 ) on a first axial side (SRS) a first diffuser delimitation contour (DC1) and on a second axial side (HBS) a second diffuser delimitation contour (D C2), the guide vanes (VNS) extending at least along part of the extent in the flow direction transversely thereto from the first diffuser delimitation contour (DC1) to the second diffuser delimitation contour (DC2) along a vane height (AVH). To reduce flow losses, the invention proposes that the leading edge (LDG) is curved in the tangential projection, with the leading edge (LDG) on the first axial side (SRS) essentially along the direction of flow by an offset (DCL) upstream is offset, where: DCL≥0.3 * AVH.

Description

The invention relates to a diffuser of a radial turbo compressor, the diffuser extending annularly around a central axis, the diffuser having an inflow which is formed along at least a first section of the flow for an at least largely radial flow by means of a process fluid during operation, the Diffuser has stationary guide vanes, which divides the diffuser at least along a radial section into individual circumferential segments, the guide vanes extending in the direction of flow from an entry edge to an exit edge in the axial center along a mean chord length, the diffuser in the area of the first section has a first diffuser delimitation contour on a first axial side and a second diffuser delimitation contour on a second axial side, the guide vanes extending transversely thereto along at least part of the extent in the direction of flow extend from the first diffuser delimiting contour to the second diffuser delimiting contour along a blade height.

In the case of radial compressors, the fluid leaves the impeller radially outwards and from there enters the diffuser, which is typically also flowed through radially from the inside to the outside. The diffuser according to the invention is designed bladed. With regard to the blading, a distinction is made between low solidity diffusers [LSD] with low blade overlap (with guide blades that are relatively far apart in the circumferential direction in relation to their radial extent) and channel diffusers - also known as aerodynamic diffusers [AE diffusers] . A diffuser according to the invention is preferably designed as an LSD.

Diffusers for radial machines are already from the EP 2 650 546 A1 known. It is proposed there to arrange the guide vanes of the diffuser in an inclined shape in a standing diffuser arranged behind the impeller (dihedral vanes). With the LSD in particular, this aerodynamic measure is intended to achieve a reduced pressure loss.

From the WO2019057412A1 , WO2019057413A1 , WO2019057414A1 arrangements of impellers and diffusers of, in particular, turbo-compressors are already known.

From the US4850795A and the EP446900B1 arrangements with rib guide vanes are already known.

In the case of a combined use of fin guide vanes and guide vanes which - unlike the fin guide vanes - extend over the entire axial channel height of the diffuser, the fin guide vanes being upstream of the other guide vanes, it is disadvantageous that the fin guide vanes in the area of their axial end in Flow channel can trigger separation phenomena in the flow. In addition, it is disadvantageous that the rib guide vanes can cause a dead water area extending over part of the channel height downstream, so that in an axial view the flow pattern through the diffuser can also become less uniform through the use of the rib guide vanes, so that positive effects in aerodynamic terms at least to be partially repealed.

In particular, motivated by the avoidance of disproportionate detachment phenomena, the invention has set itself the task of providing a more uniform flow guidance and at the same time offering the advantage that a separate flow guidance on the part of a cover disk side of the diffuser offers - as is done for example by means of rib guide vanes provided upstream.

To solve the problem, a diffuser or a radial turbo compressor with such a diffuser with the features defined at the outset is proposed, which has the additional features of the characterizing part of claim 1. The dependent claims referring back contain advantageous developments of the invention.

Terms such as radial, axial, tangential or circumferential direction relate to the initially defined axis around which the diffuser extends in an annular manner. In the case of a turbo compressor or a radial turbo compressor, this axis is coaxial with the axis of rotation of the rotor.

All angle details always relate to the actual angles on the actual geometric shapes - in short: metal angles.

The invention understands a profile center line to be an imaginary line that extends through the center of a blade profile. Here, the blade profile is understood as a two-dimensional shape. The profile center line can be constructed in this two-dimensional form, for example by connecting the center points of all inscribed circles by means of a line - the profile center line.

The diffuser is defined axially by diffuser boundary contours. The term “diffuser delimitation contours” is not to be understood here in such a way that the diffuser delimitation contours always have an axial surface normal. Rather, this term is intended to mean that the diffuser delimiting contours in any case have a radial extent and - even if they have an oblique course with respect to the radial or axial - delimit the diffuser in the axial direction. Another advantageous development of the invention provides that the axial distance between diffuser delimitation contours widens in the radial direction.

In the case of the radial turbo compressor in particular, the diffuser is a flow-conducting component of the stator, which is located downstream of the impeller outlet. As a rule, the flow rate of the process fluid is delayed in the diffuser, so that a pressure build-up results in accordance with Bernoulli's principles.

In the case of the radial turbo compressor and a diffuser that extends essentially radially outward, the diffuser effect results from the radial increase in the cross-sectional area through which the flow passes. Also of importance is a change in the diffuser channel width, which usually results from the axial extent of the clear width of the diffuser. In principle, the diffuser can also extend in a manner deviating from the radial direction. Most diffusers extend largely radially. The diffuser channel width is limited by diffuser delimitation contours provided on both sides. In the case of a purely radially extending diffuser without axial expansion, the diffuser delimitation contours also run purely radially. Due to the axial suction of a radial turbo compressor and the radial output of the process fluid from the impeller, a deflection from axial to radial takes place in the impeller. The impeller is usually constructed with a wheel disc that connects the impeller to the shaft with a shaft-hub connection. The side that does not have the axial suction of the impeller is referred to here as the hub side. The other opposite axial side is referred to as the housing side. In the case of impellers that have a cover disk on the housing side, this housing side is also often referred to as the cover disk side.

The invention understands a blade height as the extension of the blade perpendicular to the main flow direction. If one follows a - for the main flow direction - representative flow thread through the arrangement of the invention, for example through the diffuser, then this extends Flow filament essentially perpendicular to the direction of the blade height. If this flow thread extends approximately centrally through the arrangement, it will be approximately 50% of the blade height.

The invention understands stationary guide vanes to mean guide vanes that are firmly connected to the stator and cannot be moved relative to the rest of the stator for the purpose of changing fluidic conditions during operation. These guide vanes divide the diffuser at least along a radial section into individual circumferential segments. Such a division does not generally take place by means of purely radially extending guide vanes, but is provided by means of guide vanes extending obliquely to the radial. In the area of the curved leading edge, such a segment division does not exist over the entire axial channel width. The invention provides, however, that the guide vanes extend at least in radial sections over the entire width of the channel and that circumferential segments are thereby separated from one another. The peripheral segments of claim 1 or the set of patent claims are conceptually synonymous with flow channels between the guide vanes of the diffuser which extend essentially from radially inward to radially outward or are flowed through along this direction.

The invention understands an average chord length to be a mean value of the chord length averaged over the axial height of the guide vane. The chord length is the length of the profile chord - that is, an imaginary connecting line between the profile nose and the profile trailing edge or the leading edge of the guide vane and the trailing edge. Since the profile according to the invention is not constant over the vane height, the terminology of the invention refers to a mean chord length averaged over the height of the guide vane.

The special feature of the invention is that the curved leading edge of the guide vane is what comes out of the impeller Exiting process fluid leads significantly earlier or further upstream on the cover disk side than on the wheel disk side or on the hub side. Furthermore, the invention ensures a steady transition between the early acceptance of the process fluid on the cover disk side by the flow guidance of the guide vane and the later or more downstream acceptance of the process fluid by the guide vane on the hub side. This smooth transition through the curved leading edge ensures a more harmonious or uniform flow development overall, so that the flow losses in the area are reduced and the flow is less prone to detachment.

The invention understands the attribute “curved” to mean a “non-angular” course, that is to say a course with a continuous curvature course. In this context, the terms “curved”, “non-angular profile” and “continuous curvature profile” are synonymous for the invention. As a rule, and preferably, it is an arcuate profile with changing curvature.

The invention therefore proposes that on the first axial side, the leading edge of the guide vanes is essentially offset upstream along the direction of flow by an offset, the offset being at least 30% of the axial guide vane height or the axial channel width of the diffuser. According to the invention, an even more uniform flow can often be achieved if the offset is at least 50% of the axial diffuser channel width.

Another advantageous possibility according to the invention of dimensioning the offset according to the invention with regard to the tangential projection of the leading edges is that the offset is at least 20% of the mean chord length of the guide vanes. An offset of at least 30% of the mean chord length of the guide vanes makes sense aerodynamically.

The design of the tangential projection of the leading edge is particularly useful if it has at least one turning point in the area of the axial channel width of the diffuser. The arrangement according to the invention is particularly expedient and aerodynamically efficient when an angle between the tangents on a tangential projection of the leading edge and a tangential projection of the first diffuser boundary contour is at least 45 °, preferably at least 75 °. An advantageous development provides that the angle between the tangent on a tangential projection of the leading edge and a tangential projection of the second diffuser boundary contour is at least 45 °, preferably at least 75 °.

The design of the curved leading edge according to the invention is particularly expedient if the point of inflection of the tangential projection of the leading edge is arranged closer to the first diffuser delimiting contour than to the second diffuser delimiting contour. In this case, it makes sense, in the event that there are several turning points of this type, that this criterion is applicable for at least one turning point.

The invention also relates to a radial turbo compressor with a diffuser of the design according to the invention.

Figur 1

einen schematischen Längsschnitt entlang einer Drehachse durch einen Radialturboverdichter mit einem erfindungsgemäßen Diffusor,

Figuren 2, 3, 4

jeweils das Detail II aus Figur 1 in verschiedenen Varianten,

Figur 5

einen Schnitt V-V entlang einer Hauptströmungsrichtung gemäß Figur 1.

In the following, the invention is illustrated with the aid of various figures for better understanding, showing preferred exemplary embodiments. Show it:

Figure 1

a schematic longitudinal section along an axis of rotation through a radial turbo compressor with a diffuser according to the invention,

Figures 2, 3, 4

detail II in each case Figure 1 in different variants,

Figure 5

a section VV along a main flow direction according to Figure 1 .

Figure 1 shows a centrifugal compressor RTC with a diffuser DFR and an impeller IMP arranged upstream of the diffuser DFR. The impeller IMP and the diffuser DFR extend annularly along a circumferential direction CDR of an axis X with an axis of rotation ROT. The impeller IMP is fastened in a specific axial position to a shaft SHT which is rotatably mounted about the axis of rotation ROT or the axis X arranged coaxially to the axis of rotation ROT. The impeller IMP has a wheel disk H, impeller blades BLD and a cover disk SHR, the impeller blades BLD being attached between the wheel disk H and the cover disk SHR, forming flow channels. A process fluid PFL is sucked in axially and deflected outwards in the radial direction, where it exits the rotating impeller IMP during operation and enters a static diffuser DFR.

An advantageous development of the radial compressor RTC according to the invention is given by the arrangement of an open impeller IMP without a cover plate SHR. This variant is not shown separately, but the SHR cover plate - shown in FIG Figure 1 - can be seen as optional.

The process fluid PFL flows from the diffuser DFR into a collecting spiral VOL. From there, the process fluid PFL from the radial turbo compressor RTC is fed to units located downstream in a manner not shown.

The Figures 2-4 show schematically that in the Figure 1 with II designated detail, whereby different variants of this detail are shown. In tangential projection, the guide vane VNS shown of the diffuser DFR each has a curved leading edge LDG according to the invention. A maximum chord length XCL is indicated in each of the figures, and the minimum chord length YCL is also indicated. Schematically drawn between these two extremes Values is a mean chord length MCL. An offset between the leading edge LDG on the first axial side and the leading edge LDG on the second axial side is indicated according to the invention with an offset DCL. The inlet edge LDG, which is offset upstream by the offset DCL on the first axial side, guides the process fluid entering the diffuser DFR a little further upstream, so that the inhomogeneity of the process fluid flowing out of the impeller IMP over the axial channel width is better taken into account. The guide vane VNS extends at least over a partial section axially over the entire channel width with an axial guide vane height AVH. The tangential projection of the leading edge LDG has at least one turning point WP, which is preferably closer to the first diffuser delimiting contour DC1 than to the second diffuser delimiting contour DC2. An angle α between tangents on a tangential projection of the leading edge LDG and a tangential projection of the first diffuser boundary contour DC1 is preferably at least 75 ° ( Figure 3 ), particularly preferably at least 90 ° ( Figures 2 , 4th ). Here, the angle α means the angle between the two tangents that defines the free space between the first diffuser boundary contour DC1 and the leading edge LDG of the guide vane VNS and not the angle that is within the solid or the material of the guide vane VNS. A second angle β located on the opposite, second diffuser delimiting contour DC2 preferably has the same conditions as in FIG Figures 2, 3 shown.

The variant that appears in Figure 4 is shown, shows essentially two turning points WP, the tangential projection of the leading edge LDG particularly preferably entering the second delimiting contour DC2 essentially at a second angle β of approximately 90 ° or more.

Figure 5 shows an in Figure 3 section illustrated as VV, which shows schematically the arrangement of the guide vanes VNS in the diffuser DFR. The guide vanes VNS extend from a leading edge LDG up to a trailing edge TRG, with a chord length CDL or a mean chord length MCL or, depending on the arrangement of the section along the axial height AVH, a minimum chord length YCL or a maximum chord length XCL are characteristic for the respective profile.

Claims (9)

Diffuser (DFR) of a radial turbo compressor (RTC),
wherein the diffuser (DFR) extends annularly around a central axis (X),
wherein the diffuser (DFR) has an inflow (INL),
which is designed along at least a first section (SG1) of the flow for an at least largely radial flow by means of a process fluid (PFL) during operation,
wherein the diffuser (DFR) has stationary guide vanes (VNS), which divides the diffuser (DFR) at least along a radial section into individual circumferential segments,
wherein the guide vanes (VNS) extend in the direction of flow from a leading edge (LDG) to a trailing edge (TRG) in the axial center along a mean chord length (MCL),
wherein the diffuser (DFR) in the area of the first section (SG1) has a first diffuser delimiting contour (DC1) on a first axial side (SRS) and a second diffuser delimiting contour (DC2) on a second axial side (HBS),
wherein the guide vanes (VNS) extend at least along part of the extent in the flow direction transversely thereto from the first diffuser delimitation contour (DC1) to the second diffuser delimitation contour (DC2) along a vane height (AVH), characterized in that
the leading edge (LDG) is curved in the tangential projection, the leading edge (LDG) on the part of the first axial side (SRS) essentially along the direction of the flow by an offset (DCL) with respect to the leading edge (LDG) at the second diffuser boundary contour ( DC2) is offset upstream, where: $$\mathrm{DCL}\ge 0,3*\mathrm{AVH}\mathrm{.}$$

Diffuser (DFR) according to claim 1,
where: $$\mathrm{DCL}\ge 0,5*\mathrm{AVH}\mathrm{.}$$

Diffuser (DFR) according to at least one of the preceding claims 1, 2,
where: $$\mathrm{DCL}\ge 0,2*\mathrm{MCL}\mathrm{.}$$

Diffuser (DFR) according to at least one of the preceding claims 1 to 3,
where: $$\mathrm{DCL}\ge 0,3*\mathrm{MCL}\mathrm{.}$$

Diffuser (DFR) according to at least one of the preceding claims 1 to 4,
wherein a tangential projection of the leading edge (LDG) has at least one turning point (WP). Diffuser (DFR) according to at least one of the preceding claims 1 to 5,
wherein an angle between tangents on a tangential projection of the leading edge (LDG) and a tangential projection of the first diffuser boundary contour (DC1) is at least 45 °, preferably at least 75 °. Diffuser (DFR) according to at least one of the preceding claims 1 to 6,
wherein the turning point (WP) is arranged closer to the first diffuser delimiting contour (DC1) than to the second diffuser delimiting contour (DC2). Diffuser (DFR) according to at least one of the preceding claims 1 to 7,
wherein the angle between a tangent on a tangential projection of the leading edge (LDG) and a tangential projection of the second diffuser boundary contour (DC2) is at least 45 °, preferably at least 75 °. Radial turbo compressor (RTC) with at least one diffuser (DFR) according to at least one of the preceding claims 1 to 8 and at least one impeller (IMP), which is essentially designed such that there is a process fluid (PFL) axially on the first axial side during operation (SRS) and discharges essentially radially into the downstream diffuser (DFR).

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