EP3551890B1 - Recirculation stage - Google Patents

Description

The invention relates to a return stage of a radial turbo machine with at least one guide vane stage, the return stage extending in a ring around an axis, the return stage being defined radially inward by an inner boundary contour and radially outward by an outer boundary contour, the return stage along a first flow direction extends radially outward in a first section, wherein the return stage extends in a second section along the first flow direction, describing an arcuate deflection, from radially outside to radially inward, wherein the return stage extends along the first flow direction in a third section from radially outside to extends radially inward, the return stage extending along the first flow direction in a fourth section, describing an arcuate deflection, extending from radially inward to axially, the guide vane stage comprising guide vanes, where in which the guide vanes each comprise an airfoil extending along a span, the surfaces of which extend from an upstream leading edge as a pressure side and as a suction side along a skeleton line spaced apart from one another by profile cross-sections up to a trailing edge, with a tangent on the skeleton line of each Profile cross-section to a radial-axial reference plane includes a vane design angle for each point of the camber line, wherein a difference between a vane construction angle at the leading edge and a vane construction angle at a downstream position defines a deflection angle for each point of the camber line of each profile cross-section, with a mean total deflection angle over is the span of the mean deflection angle at the trailing edge, with the guide vanes extending along at least part of the third section corners and the feedback stage segmented in the circumferential direction into flow channels, the outlet edges being arranged in the third section.

Radial turbo machines are known as either radial turbo compressors or radial turbo expanders. Unless otherwise stated, the following statements refer to the version as a compressor. In principle, the invention can be used for expanders in the same way as for compressors, a radial turbo expander essentially providing a reverse flow direction of the process fluid compared to a radial turbo compressor.

With a radial turbo expander, the energy stored thermodynamically in the process fluid is converted into technical work by means of a drive of the impeller while a process fluid is relaxed and deflected.

In the case of radial turbo compressors, this process is reversed; these convert or store technical work into flow work that is stored thermodynamically in the process fluid. For this purpose, impellers of the compressor usually suck in a process fluid axially to an axis of rotation or at an angle to the axis of rotation with an axial speed component and accelerate and compress this process fluid by means of the respective impeller - which is also referred to as an impeller - which controls the flow direction of the process fluid deflects radial direction. In the case of a multistage radial turbo compressor, the impeller is followed downstream by a return stage if at least one further impeller is provided downstream.

In the scriptures DE102014203251A1 , DE 34 303 07 A1 and EP 592 803 B1 each of the return stages of a multi-stage turbo compressor are shown. An aerodynamic consideration of feedback stages contains the US 2010/0272564 A1 and the WO2014072288A1 .

The WO2016047256 shows a recycle stage that has non-cylindrical guide vanes. Deflection angles are there not specified. The documents US 2010/272564 A1 ,

DE 10 2014 223833 A1 , JP H11 173299 A show aerodynamic designs of comparable configurations.

From the essay " Design exploration of a return channel for multistage centrifugal compressors "of the conference" Proceedings of the ASME Turbo Expo "of the band / year 2016 The authors Vishal Jariwala, Louis Larosiliere and James Hardin provide an analysis of complex guide vane geometries. The proposed guide vanes each extend into the 90 ° deflection of the fourth section of the return stage in order to improve the homogeneity of the outflow over the span. Such feedback stages are complex to manufacture and complex to assemble.

On this basis, the invention has set itself the task of improving the aerodynamics of the feedback stages without having to accept such expenses.

In order to achieve the object of the invention, the invention proposes a recycle stage according to claim 1. The subclaims contain advantageous developments of the invention.

The terms axial, radial, tangential, circumferential direction and the like are here or in this document each related to the central axis around which the return stage extends in an annular manner. In the case of a radial turbo machine, this axis is also the axis of rotation of a rotor or the shaft with the running wheels.

In the case of the terms cylinder or cylindrical, the invention is based on the general mathematical understanding of the term. A plane curve in a plane is shifted by a fixed distance along a straight line that is not contained in the starting plane. Two corresponding points of the curves and the shifted curve are connected by a segment. The entirety of these parallel routes forms the associated cylinder surface (see also definition Wikipedia (https://de.wikipedia.org/wiki/Zylinder_(Geometrie)#Allgemein er_Zylinder)). Accordingly, in the present case the cylinder is not limited to the shape of a circular cylinder. In relation to a blade, a cylindrical design means that the blade - formed from individual profiles that are stacked along a threading line - are stacked along a straight threading line. It is irrelevant here whether the blade extends along a contoured or curved flow channel or whether the flow channel is straight. The decisive factor is the straight extension in the spanwise direction of the blade, which leads to the designation "cylindrical blade".

In the terminology of this invention, a multistage radial turbo machine means that several running wheels are arranged to be rotatable about the same axis of rotation. Here, an impeller is to be equated with a stage of the radial turbomachine. The multistage requires that, in the case of the compressor, the process fluid flowing radially out of the impellers must be guided back in the direction of the axis of rotation and can flow into the subsequent impeller of the downstream stage with an axial speed component. The flow guidance that enables this return of the process fluid is therefore called the "return stage". In the case of the expander, the component can be of identical design and the flow is only flowed through in the opposite direction.

In addition to the return of the process fluid in the direction of the axis of rotation and the deflection of the flow direction of the process fluid in the axial direction, according to the invention, guide vanes are also provided in the return stages, which at least partially or completely neutralize a swirl created in the flow from the upstream impeller or even a swirl in the opposite direction imprint for entry into the next downstream stage.

The embodiment of a return stage preferred according to the invention provides that this entire component is supported and aligned by means of a so-called intermediate floor by means of suitable supports, usually in a housing or some other support device. Furthermore, the return stage comprises a so-called vane bottom, which is attached to the intermediate bottom with the guide vanes already explained, forming a return channel. The process fluid flows through the return channel to the next impeller inlet. In this structure, the guide vanes have two functions. On the one hand, the guide vanes have the aerodynamic function of imposing a counter-swirl on the process fluid to the extent that at least the swirl from the upstream stage is largely compensated, and on the other hand, the guide vanes have the mechanical task of fastening the vane bottom to the intermediate bottom in such a way that, despite the dynamic load, a a secure hold is guaranteed.

The guide vane stage located in the return stage comprises guide vanes which segment the annular shape of the return stage into individual channels in the circumferential direction. In principle, these guide vanes can also have interruptions (split), but according to the invention are preferably designed to be uninterrupted along the first flow direction. The guide vanes have profiles which - if unwound accordingly - can also be represented in two dimensions. A two-dimensional representation is possible, for example, if the annular channel of the return stage is cut along a central surface extending in the circumferential direction. This cut surface of a single guide vane can be developed into a plane, for a two-dimensional representation. A profile center line of the stacked profiles of the guide vanes can be generated by means of centers of inscribed circles in the profile. This profile center line is also referred to below as the skeleton line.

The profile center line can be used to define a profile center line running coordinate or skeletal line running coordinate along the first flow direction along a mean height of the respective guide vane. The length of the guide vane along this coordinate is preferably normalized to a total length of 1 or 100%.

The height direction of the guide vane is defined in the present case as the direction which is oriented perpendicular to the flow direction - in particular to the first flow direction - and perpendicular to the circumferential direction. The height of the blade or the height direction is referred to in this document as the span width or span direction of the blade.

The profile center line of the guide vane directly adjacent to the outer boundary contour of the annular channel of the return stage is referred to here as the outer track of the guide vane and the profile center line of the profile cross section of the guide vane located directly on the inner boundary contour is referred to as the inner track of the guide vane. In this context, the outer boundary contour of the return stage can also be referred to as the boundary contour on the cover disk side, because an impeller provided with a cover disk has this cover disk on the side of the outer boundary contour. The hub-side flow contour of the impeller is located opposite on the inner boundary contour of the return stage, so that the inner boundary contour of the return stage can also be referred to as the hub-side boundary contour. Due to the complex geometry of the return stage, the inner limit contour cannot always be viewed as being located radially further inward than the outer limit contour for the same positions along a central flow line through the return stage, so that such alternative designations are useful for better understanding.

According to the invention, the deflection angle in the middle of the span is greater than the average total deflection angle in each case based on the trailing edges of the guide vanes. The advantageous knowledge of the invention consists in the fact that this shape of the guide vane on the one hand results in a flow to the downstream impeller which is favorable for the efficiency of the return stage and on the other hand is associated with relatively little effort both in terms of manufacture and assembly. Due to the fact that the leading edge is preferably only arranged behind the 180 ° deflection and the trailing edge upstream of the 90 ° deflection from the radially inward flow into the axially directed flow, the guide vanes are essentially located in a radially running flow channel without mandatory Axial components of the flow. The guide vane shape according to the invention prepares the flow behind the 180 deflection and before the diversion in the axial direction so advantageously for the inflow into the impeller that a continuation of the guide vane in the downstream deflection in the axial direction is not necessary. Conventional guide vane shapes in the recirculation stage either accept the unfavorable, inhomogeneous flow distribution in the spanwise direction, or are laboriously continued in the deflections of the second section and / or fourth section of the recirculation stage in order to ensure an advantageous flow to the downstream impeller. The trailing edges brought up close to the impeller, however, ensure an unfavorable excitation of the impeller due to the resulting inhomogeneities in the circumferential direction.

An advantageous further development of the invention provides that the exit edges each describe a straight line. In this design, the differences in the deflection angle are preferably implemented by means of different curvatures of the skeleton lines of different profiles of the span.

Another advantageous development provides that the exit edges are bent or kinked. In that case it is - in other words - not straight designs of the exit edges. Here, the bend of the exit edges can be both in the circumferential direction and in the radial direction be formed and any mixed form of these offsets is also conceivable.

An advantageous development of the invention in this context provides that the skeleton lines of the profile cross-sections there are formed shorter than a mean skeleton line length at least 7% of the span at both ends of the span. Such a design can be achieved if, for example, in the case of a cylindrical blade or a non-cylindrical blade, the trailing edges in these two end regions of the span are shortened or the blade is slightly cut away or cut off at this point. As a result, the reduced deflection required in principle according to the invention in the areas of the span ends is achieved in a particularly cost-effective manner.

Figur 1

ein axialer Längsschnitt durch den Ausschnitt eines Gehäuses einer Radialturbomaschine mit einer Rückführstufe und Laufrädern,

Figur 2

eine schematische perspektivische Darstellung einer erfindungsgemäßen Leitschaufel mit unterschiedlichen Gestaltungen der Austrittskante,

Figur 3

eine schematische perspektivische Darstellung einer erfindungsgemäßen Leitschaufel dargestellt im Zusammenhang mit einer erfindungsgemäßen Rückführstufe,

Figur 4

eine schematische perspektivische Darstellung einer anderen Ausführungsform einer erfindungsgemäßen Leitschaufel mit der dazugehörigen Rückführstufe.

The invention is explained in more detail below using a special embodiment with reference to drawings. They show schematically:

Figure 1

an axial longitudinal section through the section of a housing of a radial turbomachine with a return stage and impellers,

Figure 2

a schematic perspective illustration of a guide vane according to the invention with different designs of the trailing edge,

Figure 3

a schematic perspective illustration of a guide vane according to the invention shown in connection with a return stage according to the invention,

Figure 4

a schematic perspective illustration of another embodiment of an inventive Guide vane with the associated return stage.

Figure 1 shows a feedback stage RCH of a radial turbo machine RTM, which is designed as a radial turbo compressor CO.

The components explained here as an example for a radial turbo compressor CO can also be implemented according to the invention as radial turbo expanders, with a process fluid PF flowing through these components in a radial turbo compressor CO in a first flow direction FD1 and in a radial turbo expander in an opposite, second flow direction FD2. The descriptions in this document always relate to the first flow direction FD1 or a radial turbo compressor CO, unless stated otherwise.

Figure 1 shows parts of two successive stages, a first stage ST1 and a second stage ST2 of a radial turbo machine RTM or a radial turbo compressor CO shown in detail, a return stage RCH between the two stages ST1, ST2 being shown completely schematically. The two stages ST1, ST2 are shown here with impellers arranged to be rotatable about the axis of rotation X, a first impeller IP1 and a second impeller IP2.

In the illustration in FIG. 1, a process fluid PF first flows through the first impeller IP1, flowing in axially and flowing out radially along a first flow direction FD1. An oppositely oriented second flow direction FD2 is also given as an example, as would be the case with a radial expander. Downstream of the first impeller IP1, the process fluid PF flows radially outward and reaches a radially outwardly directed first section SG1 and is decelerated there, passes downstream in an approximately 180 ° deflection of a second section SG2 and then in a radially inward one Return of a third section SG3 of the return stage RCH. Downstream of the third section SG3, the process fluid PF reaches the second impeller IP2 in a fourth section SG4, flowing from radially inward to axially flowing, in order to be accelerated radially outward again there.

The return stage RCH comprises a blade base RR, guide vanes VNS and an intermediate base DGP. The intermediate floor DGP is supported by at least one support SUP in a support device - here in a housing CAS - and positioned there. The support SUP and the supporting section of the housing CAS are designed as a tongue and groove connection in a form-fitting manner.

In a manner not shown in detail, the return stage RCH or the blade bottom RR and the intermediate bottom DGP have a parting joint which runs in a common plane essentially along the axis X. This parting line is conveniently located in the same parting line as a parting line, not shown, of the CAS housing.

In principle, it is also conceivable that the rotor is designed to be divisible between two impellers or the impellers are designed to be axially displaceable in relation to one another for the purpose of assembly, so that the return stages RTC can be designed in one piece and gradually assembled together with the impellers IP1, IP2 of the rotor before merging with a surrounding housing. The housing CAS can in any case be designed to be divided horizontally or vertically.

The conventional design of the feedback stage RCH, which is in the Figure 1 is shown, provides that the blade base RR, the guide vanes VNS and the intermediate base DGP are attached to one another. In the present case, this is done using SCR screws, which are shown in simplified form by means of dash-dotted lines. So that the SCR screws on the one hand the bucket bottom On the other hand, a sufficiently large through-hole must be provided in the guide vanes VNS so that the profile of the guide vanes VNS must be sufficiently strong.

Figure 2 shows a schematic perspective illustration of a guide vane VNS of a return stage RCH according to the invention. The guide vane VNS is shown in connection with the axis X and a radial direction R perpendicular thereto. In the Figure 2 a reference plane PRF, which is spanned by the axis X and the radial direction R, is indicated at different points in order to illustrate geometric relationships.

The guide vane VNS comprises an airfoil VAF extending along a span SPW, the surfaces SFT of which extend from the upstream leading edge LDE as a pressure side PRS and as a suction side PCS along a skeleton line SCL spaced from one another by profile cross sections PRC up to an exit edge TLE. At the end of the span two tangents TGT are drawn on the skeleton line SCL and also on half of the span ½SPW a tangent TGT on the skeleton line SCL shows that for every profile cross section PRC a blade construction angle VCR to the radial-axial reference plane PRF for each point of Skeleton line SCL is defined. Here, a difference between the vane design angle VCA at the leading edge LDE and a vane design angle VCA at a downstream position defines a turning angle RDA (RDA (SPW, SCL)) = VCA (SPW, SCL = LDE) -VCA (SPW, SCL)) for each Point of the skeleton line SCL. From this, a mean total deflection angle RAM can be determined as the deflection angle RDA transmitted over the span SPW at the trailing edge TLE.

The Figure 2 shows in addition to a curved trailing edge TLE also a straight trailing edge TLE 'and one with two kinks provided kinked trailing edge TLE ", which was created by cutting away or leaving out portions of the original blade VAF in the two end regions of the span SPW.

Figure 3 shows a built-in guide vane VNS of a return stage RCH according to the invention. The area in which the guide vane VNS is provided in the return stage RCH extends essentially from radially outside to radially inside along the first throughflow direction FD1 of the process fluid PF. To fasten the arrangement, a screw SCR extends through the blade VAF in the spanwise direction.

The Figure 4 shows the same situation as that Figure 3 with a differently designed guide vane VNS. The guide vane VNS of the Figure 4 is cylindrical and has cut back areas of the trailing edge TLE "at both ends of the span SPW. This embodiment corresponds to the representation of one (TLE") of the three alternatives in FIG Figure 2 .

Claims (6)

1. Return stage (RCH) of a radial turbomachine (RTM) having at least one guide blade stage (VST), wherein the return stage (RCH) extends annularly around an axis (X),
   wherein the return stage (RCH) is defined radially inwards by an inner delimiting contour (IDC) and radially outwards by an outer delimiting contour (ODC),
   wherein, along a first flow direction (FD1), the return stage (RCH) extends radially outwards in a first section (SG1), wherein the return stage (RCH) extends from radially outwards to radially inwards, describing an arcuate deflection, in a second section (SG2) along the first flow direction (FD1), wherein the return stage (RCH) extends from radially outwards to radially inwards in a third section (SG3) along the first flow direction (FD1),
   wherein the return stage (RCH) extends from radially inwards to axially, describing an arcuate deflection, in a fourth section (SG4) along the first flow direction (FD1),
   wherein the return stage (RCH) comprises guide blades (VNS), wherein the guide blades (VNS) each comprise a turbine blade (VAF) which extends along a span width (SPW) and whereof the surfaces around which the flow circulates extend from a leading edge (LDE), located upstream, as a pressure side (PRS) and as a suction side (PCS), spaced from one another along a camber line (SCL) by profile cross-sections (PRC), to a trailing edge (TLE),
   wherein a tangent at the camber line (SCL) of each profile cross-section (PRC) to a radial-axial reference plane (PRF) encloses a blade construction angle (VCA) for each point of the camber line (SCL),
   wherein a difference between a blade construction angle (VCA) at the leading edge (LDE) and a blade construction angle (VCA) at a downstream position defines a deflection angle (RDA) for each point of the camber line (SCL) of each profile cross-section (PRC),
   wherein a mean total deflection angle (RAM) is a deflection angle (RDA) at the trailing edge (TLE) which is averaged over the span width (SPW),
   wherein the guide blades (VNS) extend at least along part of the third section (SG3) and segment the return stage (RCH) into flow channels in the circumferential direction,
   wherein the trailing edges (TLE) are arranged in the third section (SG3),
   characterized in that,
   at the trailing edges (TLE) in the center of the span width (SPW), the deflection angle (RDA) is greater in each case than the mean total deflection angle (RAM),
   wherein, at the two ends of the span width (SPW) to at least 10% of the span width in each case, the deflection angle (RDA) is smaller in each case than the mean total deflection angle (RAM) .
2. Return stage (RCH) according to Claim 1, wherein the leading edges (LDE) are each arranged in the third section (SG3) .
3. Return stage (RCH) according to Claim 1 or 2, wherein the trailing edges (TLS) each describe a straight line.
4. Return stage (RCH) according to Claim 1 or 2, wherein the leading edges (TLE) are designed to be curved or angled.
5. Return stage (RCH) according to Claim 1, 2, 3 or 4, wherein, at the two ends of the span width (SPW) to at least 7% of the span width in each case, the camber lines (SCL) of the profile cross-sections (PRC) there are designed to be shorter than a mean camber line length (SLL).
6. Return stage (RCH) according to Claims 1, 2, 4 and 5, wherein the guide blades (VNS) have a linear leading edge and are designed to be substantially cylindrical up to the region at the two ends of the span width (SPW), wherein, at the trailing edges (TLE) to at least 7% of the span width in each case, the camber lines (SCL) of the profile cross-sections (PRC) there are designed to be shorter than a mean camber line length (SLL).

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