EP3760871A1 - Diffuser for a turbomachine - Google Patents

Abstract

The invention relates to a diffuser (DFF) for a turbo machine (CMP) with an impeller (BLD), the diffuser (DFF) extending in a ring around an axis (X) along a circumferential direction (CDR), the diffuser (DFF) being a Having a plurality of diffuser guide vanes (VNS), the diffuser guide vanes (VNS) extending along the vane height (AFH) between two diffuser boundary walls (LDW) from a diffuser boundary wall (LDW) on a housing side (CSS) to a diffuser boundary wall (LDW) on a hub side (HBS ), wherein the diffuser guide vanes (VNS) for each position of the vane height (AFH) have a vane cover (SLD), which is defined as the ratio of a chord length (CHD) of the respective diffuser guide vane (VNS) to the circumferential pitch (CCP) of the arrangement of the diffuser guide vanes (VNS). To improve the aerodynamic effect of the diffuser, it is proposed that the blade overlap (SLD) differ between the hub side (HBS) and the housing side (CSS). The invention also relates to an arrangement with such a diffuser (DFF) and a fluid flow machine (CMP).

Description

The invention relates to a diffuser for a turbomachine with an impeller, the diffuser extending in a ring around an axis along a circumferential direction, the diffuser having a plurality of diffuser guide vanes, the diffuser guide vanes extending along the vane height between two diffuser boundary walls from a diffuser boundary wall on a housing side extend to a diffuser boundary wall on a hub side, the diffuser guide vanes for each position of the vane height having a vane overlap which is defined as the ratio of a chord length of the respective diffuser guide vane to the circumferential pitch of the arrangement of the diffuser guide vanes. The invention further relates to an arrangement with such a diffuser and a turbo machine with such an arrangement.

In centrifugal compressors, the fluid leaves the impeller radially outwards and from there into the diffuser, which typically also has a radial flow from the inside to the outside. Diffusers can be bladed or bladed. In the case of the bladed types, a distinction is made between low solidity diffusers [LSD] with little blade overlap (with guide vanes that have a relatively large distance from one another in the circumferential direction in relation to their radial extent) and channel diffusers - also known as aerodynamic diffusers [AE diffuser] - distinguished. Due to the disadvantages with regard to the driving range, AE diffusers are very rarely used. LSDs, on the other hand, offer a significantly better and more extensive driving range than AE diffusers. Almost all bladed diffusers today are LSDs.

• Unterdrücken von Rotating Stall, welcher im Falle eines unbeschaufelten Ringraums ggf. auftreten könnte
• Steigerung des Wirkungsgrades der Stufe durch Aufrichten der Strömung und durch Vergleichmäßigung der Strömung über der Kanalhöhe. Dies führt zu einer Reduktion von Verlusten in den nachgeschalteten Komponenten wie Rückführstufe oder Spirale.
• Besserer Kennlinienanstieg zur Pumpgrenze.

LSDs are used for the following reasons:

• Suppression of rotating stall, which could possibly occur in the case of a non-bladed annulus
• Increase in the efficiency of the stage by straightening the flow and by equalizing the flow above the channel height. This leads to a reduction in losses in the downstream components such as the recirculation stage or spiral.
• Better increase in characteristic curve to surge limit.

• Reduzierter Fahrbereich (schmalere Kennlinie) im Vergleich zur unbeschaufelten Variante
• Höherer Lärmpegel
• Höhere Laufradanregung
• Notwendige radiale Erstreckung des Diffusors größer als für den unbeschaufelten Diffusor
• Notwendige Sammelspiralgehäusegröße nimmt mit LSD zu, da die Umfangskomponente der Geschwindigkeit (Transportgröße in der Spirale) durch den LSD reduziert wird.

Disadvantages of LSDs are:

• Reduced travel range (narrower characteristic) compared to the non-bladed variant
• Higher noise level
• Higher impeller excitation
• The necessary radial extension of the diffuser is greater than that for the unbladed diffuser
• Necessary collecting volute casing size increases with LSD, since the circumferential component of the speed (transport size in the volute) is reduced by the LSD.

A corresponding arrangement is already from the EP 2 650 546 Al 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.

Proceeding in particular from the disadvantages described, the main task of the invention is to reduce the radial space requirement of an LSD so that the otherwise The increased radial space requirement compared to a non-bladed diffuser is no longer so significant.

To solve the problem, a diffuser or an arrangement and a flow machine 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 axis defined at the outset, 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.

According to the invention, the term turbomachine relates to radial turbomachines which provide a deflection of the process fluid. The application for a radial turbo compressor is of primary importance. In the case of the radial turbo compressor in particular, the diffuser is a flow-guiding component of the stator, which is located downstream of the impeller outlet. In the diffuser, the flow rate of the process fluid is generally delayed, so that a pressure build-up results in accordance with Bernulli'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. A change in the width of the diffuser channel is also important, as this generally results in 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, however, extend largely radially. The diffuser channel width is limited by the diffuser boundary walls provided on both sides. In the case of one purely radially extending diffuser without axial expansion, the diffuser boundary walls 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 Laur wheels which 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 representative flow thread through the arrangement of the invention, for example through the diffuser, then this flow thread extends essentially perpendicularly in 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 feature according to the invention that the blade overlap between the hub side and the outer one is different is aimed at ensuring that the respective aerodynamic requirements on the hub side and on the housing side are or can be individually adapted. To this end, an advantageous development of the invention provides that the blade overlap on the hub side is between 0.5 and 0.8 on the housing side between 0.7 and 1.0. Another advantageous development of the invention provides that the leading edge diameter on the housing side and the hub side are different.

Here, the diffuser guide vanes have a vane overlap for each position of the vane height, which is defined as the ratio of a profile chord length of the respective diffuser guide vane to the circumferential pitch of the arrangement of the Diffuser vanes. The profile chord is the imaginary connecting line between the leading edge of the profile and the trailing edge or trailing edge. The circumferential division - also often referred to simply as division - is understood to mean the distance in the circumferential direction between the leading edges of the diffuser guide vanes.

Furthermore, the invention proposes as an advantageous development that the diffuser guide vanes have a curved and profiled profile. Profiled here means that the blade profile does not have a constant thickness over the extent in the main flow direction, but is aerodynamically adapted with regard to the profile thickness distribution.

As a rule, the blade or the blade profile on the pressure side is designed to be more concave over a wider area than on the suction side - accordingly, the blade profile on the suction side is designed to be convex over a further area of extent.

Another advantageous development of the invention provides that for each position along the profile center line of the blade profile of the diffuser guide vanes, an angle of attack is defined as the mathematically positive angle from the circumferential tangent to the tangent at the profile center line. Here, a leading edge angle is an angle of attack at the leading edge and an exit edge angle is an angle of attack at the trailing edge of the diffuser guide vane. The following applies to the difference between the leading edge angle and the trailing edge angle averaged over the blade height: -2> leading edge angle - trailing edge angle> 15 °. A negative value means that the flow exits more tangentially than it enters.

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 centerline can be constructed in this two-dimensional form by, for example the centers of all inscribed circles are connected by a line - the profile center line.

It is particularly preferable for the leading edge angle to vary over the blade height. The leading edge angle on the housing side can be between 10 ° and 20 °. The leading edge angle on the hub side can be between 20 ° and 35 °. It is particularly preferred here if the exit edge angle on the hub side and on the housing side differ by at most 2 °. Accordingly, the process fluid emerges from the diffuser largely homogenized in terms of flow distribution and speeds.

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

An advantageous further development of this feature provides that the diffuser boundary wall on the hub side extends less obliquely to the radial direction than the diffuser boundary wall on the housing side, such that at least 80% of the axial expansion results from the inclination of the diffuser boundary wall on the housing side.

Another advantageous development of the invention provides that the diffuser has ribbed guide vanes upstream of the diffuser guide vanes which, starting from the housing side, extend along 25% -50% of the diffuser channel width in the Extend towards the hub side. These ribbed guide vanes also take into account the fact that the process fluid emerging from the impeller has a different flow distribution and speed distribution on the housing side than on the hub side. To compensate for this difference, the ribbed guide vanes are provided in front of the actual diffuser guide vanes, so that these differences are better compensated and the most homogeneous outflow possible takes place behind the outlet of the diffuser. For the ribbed guide vanes, a rib entry angle REA is defined to the entry angle of the diffuser guide vanes and is preferably between 14 ° and 22 °. With a definition of the rib exit angle analogous to the exit angle of the diffuser guide vanes, a further advantageous development provides that the difference between the rib entrance angle and the rib exit angle between -4 ° and + 10 °, averaged over the vane height, is designed as a metal angle.

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

A negative difference between the entry angle and the exit angle or the rib entry angle and the rib exit angle indicates that the blade tapers out more tangentially than the inlet is designed. A flow fluid that would at least largely or completely follow such a blade design has a more tangential flow orientation after flowing through such a blade arrangement with such a negative difference.

• Eintrittskanten (LEE) Nabenseite (HBS):
  1,15 < RDT < 1,3,
• Eintrittskanten (LEE) Gehäuseseite (SHR):
  1,05 < RDT < 1,15,

wobei gilt: $${\mathrm{RDT}}_{\left(\mathrm{Geh}\ddot{\mathrm{a}}\mathrm{useseite}\left(\mathrm{SHR}\right)\right)}/{\mathrm{RDT}}_{\left(\mathrm{Nabenseite}\left(\mathrm{HBS}\right)\right)}<\mathrm{1.}$$

The invention also relates to an arrangement with a diffuser of the design already defined, the arrangement having an impeller arranged upstream of the diffuser and a smaller distance between the rotor outlet edges of the impeller or the impeller blades and inlet edges of the diffuser guide blades on the housing side and on the hub side is. Particularly preferred The following also applies to the distance that the rotor trailing edges are arranged at a mean rotor trailing edge diameter and the following applies to the ratio RDT of the leading edge diameter of the diffuser to the mean rotor trailing edge diameter:

• Leading edge (LEE) hub side (HBS):
  1.15 <RDT <1.3,
• Leading edge (LEE) housing side (SHR):
  1.05 <RDT <1.15,

where: $${\mathrm{RDT}}_{\left(\mathrm{Go}\ddot{\mathrm{a}}\mathrm{usagepage}\left(\mathrm{SHR}\right)\right)}/{\mathrm{RDT}}_{\left(\mathrm{Hub\; side}\left(\mathrm{HBS}\right)\right)}<\mathrm{1.}$$

In principle, a ratio or a distance between the impeller and diffuser is also provided in such a way that the rotor trailing edges of the impeller blades of the impeller are arranged on a mean rotor trailing edge diameter (TID) and for the ratio (RDT) leading edge diameter (DLE) to the mean rotor trailing edge diameter (TID) ) applies: $$1,04<\mathrm{DLE}/\mathrm{TRD}<1,1.$$

The invention also relates to a turbomachine with an arrangement of the type defined above.

Figur 1

einen schematischen Längsschnitt entlang einer Drehachse durch eine erfindungsgemäße Strömungsmaschine mit einem erfindungsgemäßen Diffusor bzw. einer erfindungsgemäßen Anordnung,

Figur 2

einen Schnitt II-II entlang einer Hauptströmungsrichtung gemäß Figur 1,

Figur 3

das Detail III aus Figur 2,

Figur 4

eine schematische Darstellung eines Längsschnitts durch eine Strömungsmaschine beschränkt auf das Detail des Diffusors,

Figur 5

den Schnitt V-V aus Figur 4,

Figur 6

eine schematische Darstellung eines Längsschnitts durch einen Diffusor mit aufgeweiteter Diffusorkanalbreite,

Figur 7

wie Figur 6 aber mit Rippenleitschaufeln.

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 turbomachine according to the invention with a diffuser according to the invention or an arrangement according to the invention,

Figure 2

a section II-II along a main flow direction according to Figure 1 ,

Figure 3

the detail III Figure 2 ,

Figure 4

a schematic representation of a longitudinal section through a turbomachine limited to the detail of the diffuser,

Figure 5

the section VV Figure 4 ,

Figure 6

a schematic representation of a longitudinal section through a diffuser with an expanded diffuser channel width,

Figure 7

like FIG. 6 but with ribbed guide vanes.

In the figures, the same reference symbols denote functionally identical components.

Figure 1 shows a fluid flow machine CMP with an arrangement ARA with a diffuser DFF and an impeller IMP arranged upstream of the diffuser DFF. The impeller IMP and the diffuser DFF 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 HUB, blades BLD and a cover disk SHR, the blades BLD being attached between the wheel disk HUB and the cover disk SHR, forming flow channels. A process fluid PFL is sucked in axially and deflected outward in the radial direction, where it exits the rotating impeller IMP during operation and enters a static diffuser DFF. Diffuser guide vanes VNS of the static diffuser DFF homogenize and correct the speed distribution of the exiting process fluid PFL before it is introduced into a spiral VLT.

The diffuser DFF has two axially delimiting diffuser delimiting walls LDW, between which there are along a blade height AFH, the diffuser guide vanes VNS extend from a housing side CSS to a hub side HBS.

Figure 2 shows a section according to II-II of FIG Figure 1 schematic. In contrast to the circumferential direction CDR illustrated there, in a direction of rotation RDR, the impeller IMP is shown rotatable about the X axis. The blades BLD of the impeller IMP are schematically illustrated with a concave pressure side PRS and a convex suction side SCS - likewise the diffuser guide vanes VNS. The rotor trailing edges TRI of the impeller blades BLD are set back somewhat on a diameter TID compared to the maximum diameter IPD of the impeller IMP. Downstream there are leading edges LEE of the diffuser guide vanes VNS on a leading edge diameter DLE.

The diffuser guide vanes VNS each have a trailing edge TRE on a trailing edge diameter TRD. The diffuser guide vanes VNS extend in the direction of the vane height AFH in the illustration of FIG Figure 1 between the two diffuser boundary walls LDW over the entire diffuser channel width ADW.

Figure 3 shows a detail that is in the Figure 2 is shown with III. The two exemplary diffuser guide vanes VNS shown there have a vane overlap SLD for each position of the vane height AFH in their arrangement to one another, which is defined as the ratio of a chord length CHD of the respective diffuser vane VNS to the circumferential pitch CCP of the arrangement of the diffuser vanes VNS. It is crucial here that the blade covers SLD differ between the hub side HBS and the housing side CSS. It's in the Figure 3 indicated by the different pitches on the one hand on the housing side CSS with the pitch CCP and on the hub side ABS with the pitch CCP '. The difference in pitch is only slight, rather the difference between the two chord lengths CHD, CHD 'is significant with a longer one on the housing side Profile chord length CHD and a hub-side shorter chord length CHD '. In Figure 1 the leading edge diameter DLE ', which is therefore larger on the hub side, is also shown.

For each position along the profile center line SCL of the blade profile of the diffuser guide vanes VNS, an angle of attack PMA is defined as the mathematically positive angle from the circumferential tangent CDT to the tangent PMD. Here, a leading edge angle LEA is a pitch angle PMA at the leading edge LEE. An exit edge angle EXA is an angle of attack PMA at an exit edge TRE of the diffuser guide vanes VNS. The following applies to a difference between the leading edge angle LEA and the trailing edge angle EXA averaged over the blade height AFH: $$-2°>\mathrm{LEA}-\mathrm{EXA}>\mathrm{15th}°\mathrm{.}$$

The leading edge angle LEA varies over the blade height AFH. The leading edge angle LEA on the CSS side is between 10 ° and 20 °. On the hub side HBS, the leading edge angle LEA is between 20 ° and 35 °. The trailing edge angle EXA is largely constant over the entire blade height AFH and differs between the hub side HBS and the housing side CSS by a maximum of 2 °.

The Figure 4 and FIG. 7 also shows different views of an embodiment with ribbed guide vanes RPV arranged upstream of the diffuser guide vanes VNS, which extend from the housing side CSS along 25% to 50% of the diffuser channel width ADW in the direction of the hub side HBS. Analogous to the illustration of Figure 3 For the rib guide vanes RPV, a rib angle of attack RMA is also defined as the mathematically positive angle from the circumferential tangent CDT to the rib tangent RMT at the rib profile center RHD. A rib entry angle REA is a rib setting angle RMA at the rib entry edge REE. The following applies to the rib entry angle REA:
14 °>REA> 22 °.

A rib exit angle RXA is a rib angle of attack RMA at a rib exit edge RRE of the rib guide vanes RPV. For the difference RFA between the rib entry angle REA and the rib exit angle RXA averaged over the blade height AFH, the following applies: -4 °> RNA -RXA> 10 °.

As in the Figures 1 6 and 6, a smaller distance is provided between the rotor trailing edges TRI of the impeller blades BLD of the impeller IMP and the leading edges LEE of the diffuser guide vanes VNS on the housing side CSS than on the hub side HBS.

FIG. 6 shows an expansion of the axial distance between the axial diffuser boundary walls LDW with increasing radial extent. Here, a leading edge axial distance ALE means the mean axial distance AXD between axial diffuser delimiting walls LDW in the area of the leading edge LEE of the diffuser guide vanes VNS and an exit edge axial distance ATE means the mean axial distance AXD between axial diffuser delimiting walls LDW in the region of the trailing edge TRE of the diffuser guide vanes VNS. Advantageously, the axial distance AXD between axial diffuser boundary walls LDW expands axially in such a way that the leading edge axial distance ALE is smaller than the trailing edge axial distance ATE.

Here, the diffuser boundary walls LDW are designed in such a way that the diffuser boundary wall LDW extends less obliquely to the radial direction on the hub side HBS than the diffuser boundary wall LDW on the housing side SHR. This results in an axial expansion of at least 80% exclusively from the inclination of the diffuser boundary wall LDW on the CSS side of the housing.

FIG. 7 shows the combination of the axial widening of the diffuser channel width or the inclined housing-side diffuser boundary wall LDW with the arrangement of the ribbed guide vanes RPV upstream of the diffuser guide vanes VNS.

Claims (14)

Diffuser (DFF) for a fluid flow machine (CMP) with an impeller (IMP),
wherein the diffuser (DFF) extends annularly around an axis (X) along a circumferential direction (CDR),
wherein the diffuser (DFF) has a plurality of diffuser guide vanes (VNS),
wherein the diffuser guide vanes (VNS) extend along the vane height (AFH) between two diffuser boundary walls (LDW) from a diffuser boundary wall (LDW) on a housing side (CSS) to a diffuser boundary wall (LDW) on a hub side (HBS),
wherein the diffuser guide vanes (VNS) for each position of the vane height (AFH) have a vane cover (SLD) which is defined as the ratio of a profile chord length (CHD, CHD ') of the respective diffuser guide vane (VNS) to the circumferential pitch (CCP) of the arrangement of the diffuser guide vanes (VNS),
characterized in that
the blade overlap (SLD) differ between the hub side (HBS) and the housing side (CSS). Diffuser (DFF) according to claim 1, wherein the leading edge diameter (DLE) on the housing side (CSS) and hub side (HBS) are different. Diffuser (DFF) according to Claim 1 or 2, the blade overlap (SLD) on the hub side (HBS) being between 0.5 and 0.8 and on the housing side (CSS) between 0.7 and 1.0. Diffuser (DFF) according to claim 1, 2 or 3, wherein the diffuser guide vanes (VNS) have an arched and profiled profile. Diffuser (DFF) according to at least one of claims 1 to 4,
wherein, for each position along the profile center line of the blade profile of the diffuser guide vanes (VNS), an angle of attack (PMA) is defined as the mathematically positive angle from the circumferential tangent (CDT) to the tangent (PMT) on the profile center line (SCL),
where a leading edge angle (LEA) is an angle of attack (PMA) at the leading edge (LEE),
wherein a trailing edge angle (EXA) is an angle of attack (PMA) at a trailing edge (TRE) of the diffuser guide vanes (VNS),
where for the difference (DFA) between the leading edge angle (LEA) and the trailing edge angle (EXA) averaged over the blade height (AFH) the following applies: -2 ° <LEA-EXA <15 °. Diffuser (DFF) according to Claim 7, the leading edge angle (LEA) varying over the blade height (AFH). Diffuser (DFF) according to claim 8,
where the leading edge angle (LEA) on the housing side (CSS) is between 10 ° and 20 °,
The leading edge angle (LEA) on the hub side (HBS) is between 20 ° and 35 °. Diffuser (DFF) according to at least one of claims 5,6,7, wherein the exit edge angle (EXA) on the hub side (HBS) and housing side (CSS) differ by at most 2 °. Diffuser (DFF) according to at least one of the preceding claims 1 - 8,
where a leading edge axial distance (ALE) is the mean axial distance (AXD) between axial diffuser boundary walls (LDW) in the area of the leading edge (LEE) of the diffuser guide vanes (VNS),
where a trailing edge axial distance (ATE) is the mean axial distance (AXD) between axial diffuser boundary walls (LDW) in the area of the trailing edge (TRE) of the diffuser guide vanes (VNS),
is smaller than the trailing edge axial distance (ATE), wherein the axial distance (AXD) between axial diffuser boundary walls (LDW) widens axially in the radial direction, so that the leading edge axial distance (ALE) is smaller than the trailing edge axial distance (ATE). Diffuser (DFF) according to claim 9,
wherein the diffuser boundary wall (LDW) on the hub side (HBS) extends less obliquely to the radial direction than the diffuser boundary wall (LDW) on the housing side (SHR), in such a way that at least 80% of the axial expansion results from the inclination of the diffuser boundary wall (LDW) the housing side (SHR) results. Arrangement (ARA) with a diffuser (DFF) according to at least one of the preceding claims 1 - 10 and an impeller (IMP) arranged upstream, with a smaller distance between the rotor trailing edges (TRI) of the impeller blades (BLD) of the impeller (IMP) and leading edges ( LEE) of the diffuser guide vanes (VNS) is provided on the housing side (CSS) than on the hub side (HBS). Arrangement (ARA) according to claim 11, wherein the rotor trailing edges (TRI) are arranged on a mean rotor trailing edge diameter (TID) and the ratio (RDT) leading edge diameter (DLE) to the mean rotor trailing edge diameter (TID) applies to: the leading edges (LEE) on the hub side (HBS) 1.15 <RDT <1.3, the leading edges (LEE) housing side (SHR) 1.05 <RDT <1.15, where RDT _{(housing side (SHR))} / RDT _{(hub side (HBS))} <1 _applies . Arrangement (ARA) with a diffuser (DFF) according to claim 12 and an impeller (IMP) arranged upstream, with rotor trailing edges (TRE) of the impeller blades (BLD) of the impeller (IMP) being arranged on a mean rotor trailing edge diameter (TID) and for the ratio (RDT) Leading Edge Diameter (DLE) for the mean rotor trailing edge diameter (TID) the following applies: 1.04 <DLE / TID <1.1. Fluid flow machine (CMP) with an arrangement (ARA) according to at least one of Claims 11 to 13.

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