Flow guide device and fan with a flow guide device

Abstract

The invention relates to a flow guiding device (21) and to a fan (15) comprising a flow guiding device (21). The flow guiding device (21) has an annular wall (23) which completely encloses a central axis (A) in a circumferential direction (U) and delimits an inflow channel (27) on its inner side facing the central axis (A). The downstream end of the annular wall (23) has a trailing edge (31) which does not extend within a single plane oriented perpendicular to the central axis (A). Rather, the trailing edge (31) forms a plurality of depressions (33) and / or a plurality of elevations (32) with respect to a virtual reference plane (E) oriented perpendicular to the central axis (A). The trailing edge (31) can have a wavy and / or jagged profile.

Description

[0001] The invention relates to a flow guide device for a fan and a fan comprising a flow guide device. The flow guide device is configured to guide an air flow to a rotatably driven fan rotor. To this end, the flow guide device defines an inlet channel through which air from the surroundings can flow to the fan rotor.

[0002] Such a flow guide device is described, for example, in DE 10 2021 123 242 A1. The flow guide device has a low-hardness end piece that can be in sliding contact with the fan rotor. This causes the end piece to wear down during initial commissioning, creating a minimal gap between the end piece and the fan rotor. This minimizes leakage flows through the gap between the fan rotor and the flow guide device.

[0003] Grinding the end cap to increase efficiency has its advantages. In some cases, a grinding noise may be noticeable. In addition, some common airflow control devices may produce noises caused by the air flowing toward the fan rotor, such as whistling.

[0004] Therefore, the object of the present invention is to provide a flow guide device for a fan which enables lower noise generation and does not significantly impair the efficiency of the fan.

[0005] This object is achieved by a flow guiding device having the features of patent claim 1 and by a fan having the features of patent claim 15.

[0006] The flow guiding device according to the invention is designed to guide an air flow to a rotatably driven fan rotor. The flow guiding device has an annular wall that completely encloses an inlet duct in a circumferential direction around a central axis. The annular wall is in particular circular and arranged coaxially to the central axis. The annular wall can extend in the flow direction of the air flow parallel to the central axis or at an angle to the central axis. As a result, the shape of the inlet duct can be cylindrical or conical. A conical inlet duct tapers in the direction of air flow. In this case, the annular wall aligned at an angle to the central axis can be referred to as an inlet nozzle.

[0007] The annular wall has a trailing edge in the direction of the airflow. When the flow guide device is installed, the trailing edge is positioned adjacent to the fan rotor. Along its circumferential extension, the trailing edge has varying distances relative to a virtual reference plane oriented perpendicular to the central axis. Thus, the trailing edge has multiple depressions and / or elevations relative to the virtual reference plane.

[0008] The shape of the existing depressions and / or elevations can vary, for example, in order to adapt the geometry and / or dimensions of the depressions and / or elevations of the trailing edge to the operating range of the fan, in particular to a range for a flow velocity of the air flow and / or for an inlet pressure of the air in the region of the trailing edge. The trailing edge can, for example, have a wavy profile, such as a sinusoidal profile, or a jagged profile. It can also be advantageous to combine wavy shapes and jagged shapes in a suitable manner. In all embodiments, the trailing edge can be formed from arcuate sections and / or linear sections in its extension around the central axis.Each arcuate section can be, for example, a circular arc, an elliptical arc, an oval arc or a sinusoidal arc, and one or more arc shapes can be combined.

[0009] At least some or all of the depressions and / or elevations of the trailing edge may be oriented obliquely relative to the central axis. A median plane through one of the depressions and / or elevations may be oriented obliquely relative to the central axis and / or obliquely relative to the circumferential direction around the central axis.

[0010] The extension or course of the trailing edge around the central axis may be without corners or steps. Mathematically formulated, the course of the trailing edge may be continuous and / or differentiable. Optionally, at least one depression and / or at least one elevation may also have one or more edges or one or more steps.

[0011] The distance of a low point of a respective depression and / or a high point of a respective elevation from the reference plane in the direction parallel to the central axis can be the same at any point in the circumferential direction or can vary. Additionally or alternatively, a width of the depressions in the circumferential direction (for example, distance between two immediately adjacent high points in the circumferential direction) and / or a width of the elevations in the circumferential direction (for example, distance between two immediately adjacent low points in the circumferential direction) can be constant or vary. As explained, the dimension and shape or geometry of the depressions and / or elevations can be selected to suit the application and the conditions prevailing there, in particular to suit the pressure and / or flow velocity of the air flow.

[0012] The uneven trailing edge relative to the virtual reference plane eliminates or at least reduces unwanted noise that may occur when air flows through or out of the inlet duct. It has been shown that the uneven trailing edge does not, or only slightly, impair the efficiency of the fan compared to a trailing edge running parallel to the reference plane, for example, with regard to volume flow or outlet pressure.

[0013] Wavy or jagged edges are known in other technical applications, particularly so-called "chevrons" on aircraft engines. However, the jagged or wavy trailing edges are arranged at the flow outlet of an aircraft engine and are intended to better mix a fast-flowing airflow layer on the inside and a slower-flowing airflow layer on the outside. Various "chevrons" are described, for example, in EP 2 245 289 A1, EP 4 015 812 A1, WO 2015 / 036 684 A1, and WO 2023 / 057 704 A1.

[0014] It is advantageous if the flow guide device also has a front wall connected to the annular wall. The front wall and the annular wall can form a monolithic component. The front wall is connected to the annular wall upstream of the trailing edge at the opposite end of the inlet channel. The front wall can be oriented perpendicular to the central axis. In one embodiment, the front wall can be part of a fan housing.

[0015] The flow guide device is particularly designed to direct the air flow exclusively via the inlet channel to the fan rotor. The annular wall is therefore preferably designed to guide an air flow only on its side facing the inlet channel. On the outer side of the annular wall facing away from the inlet channel, air movements may occur as a result of the air flow through the inlet channel, but no air flows from the surroundings to the fan rotor along this outer side of the annular wall.

[0016] It is preferred if the front wall is free of flow openings that allow air to be supplied to the fan rotor. The front wall is preferably free of flow openings that are fluidically connected to the inlet channel. Apart from openings for mechanically connecting the flow guide device to other components of a fan, the front wall may have only a single inlet opening leading to the inlet channel. It is understood that this inlet opening may optionally be covered by a grid and / or a filter to prevent bodies or particles from entering the inlet channel.

[0017] The front wall and the annular wall can be directly connected to one another. Alternatively, the front wall and the annular wall can be indirectly connected to one another, for example, by means of a transition wall. The transition wall is arranged, in particular, coaxially to the central axis and can merge into the annular wall without forming an edge or a step. Additionally or alternatively, the transition wall can merge into the front wall without forming an edge or a step.

[0018] The flow cross-section defined by the transition wall, for example, an inner diameter, can decrease continuously from the front wall to the annular wall. In a section perpendicular to the circumferential direction, the transition wall can be circularly arc-shaped.

[0019] The front wall, the annular wall, and the optional transition wall can together form a monolithic front part of the flow guide device. The front part can be manufactured, for example, by injection molding or another suitable primary forming process.

[0020] In one embodiment, the flow guide device may further comprise an outer wall. The outer wall is connected to the front wall. The outer wall protrudes from the front wall in the same direction as the annular wall. The outer wall may circumferentially enclose the annular wall. Optionally, the outer wall may be a monolithic component of the front part.

[0021] Each existing elevation and each existing depression has a width in the circumferential direction around the central axis and a length perpendicular to the circumferential direction in the direction of flow and / or parallel to the central axis. The length can be characterized, for example, by the distance between a high point of the respective elevation and a low point of an immediately adjacent depression. The widths and / or lengths of all elevations can be the same. Additionally or alternatively, the widths and / or lengths of all depressions can be the same. Alternatively, it is also possible for at least several of the existing elevations and / or several of the existing depressions to have different widths and / or different lengths.

[0022] In all embodiments, at least several of the existing elevations and / or several of the existing depressions can be curved without edges. In all embodiments, at least several of the existing elevations and / or several of the existing depressions can have an edge and / or step. For example, at least several of the existing elevations at their respective high points and / or several of the existing depressions at their respective low points can have an edgeless course in the circumferential direction or have an edge there.

[0023] A central plane containing the central axis can be defined parallel to each high point of an elevation and each low point of a depression. The central plane can divide the respective elevation and / or depression into symmetrical halves. Alternatively, the respective elevation and / or depression can also be asymmetrical to its central plane. For example, an elevation and / or depression can have two flanks with different orientations relative to the central plane, which merge into one another at the high point of the elevation and / or the low point of the depression.

[0024] Any embodiment of the flow-guiding device explained above can be part of a fan. In addition to the flow-guiding device, the fan has a fan rotor that can be driven about the central axis. The fan rotor can also be referred to as a fan wheel. The fan rotor is arranged downstream of the inlet channel of the flow-guiding device. An electric motor driving the fan rotor is preferably arranged downstream of the fan rotor. The fan can be an axial fan, a radial fan, or a diagonal fan.

[0025] In a preferred embodiment of the fan, the fan rotor has an outer ring arranged coaxially to the central axis. The outer ring surrounds the annular wall adjacent to the trailing edge. Preferably, the relative position between the annular wall of the flow guide device and the outer ring is such that all depressions and / or elevations of the trailing edge are arranged at least substantially and preferably entirely within the space enclosed by the outer ring. A total length of the trailing edge along the elevations and / or depressions around the central axis is located at least 70%, 80%, or 90% within the space enclosed by the outer ring.

[0026] Advantageous embodiments of the invention will become apparent from the dependent claims, the description, and the drawings. Preferred embodiments of the invention are explained in detail below with reference to the accompanying drawings. The drawings show: Fig. 1 a perspective view of an embodiment of a fan with an embodiment of a flow guide device according to the present invention, Fig. 2 a sectional view along a central axis through the fan Fig. 1, Fig. 3 a modified embodiment of an annular wall of the flow guide device, which in the fan according to the Fig. 1 and Fig. 2 can be used, Fig. 4-10 each show a highly schematic representation of elevations and / or depressions of a trailing edge of an embodiment of the annular wall of the flow guide device, Fig. 11 and Fig. 12 each shows an example of a characteristic curve describing the distances of the high points of the elevations and the distances of the low points of the depressions of the trailing edge from a reference plane.

[0027] In the Fig. 1 and Fig. Figure 2 shows an embodiment of a fan 15. The fan 15 can be an axial fan, a radial fan, or a diagonal fan.

[0028] The fan 15 has a fan housing 16 with a front part 17 and a rear part 18. The front part 17 and / or the rear part 18 can each be monolithic and manufactured by primary forming, for example, by injection molding. In the exemplary embodiment, the front part 17 and / or the rear part 18 can be made of plastic.

[0029] The front part 17 and the rear part 18 are mechanically connected to one another to form the fan housing 16, in particular detachably connected to one another, for example by means of a positive and / or non-positive connection, such as a screw connection, plug connection or snap connection.

[0030] The fan 15 has a flow guide device 21. In the exemplary embodiment, the flow guide device 21 is part of the front part 17. The flow guide device 21 is designed to direct an air flow in a flow direction F to a fan rotor 22 of the fan 15. For this purpose, the flow guide device 21 has an annular wall 23 arranged coaxially to a central axis A of the flow guide device 21 or of the fan 15. The annular wall 23 extends in a circumferential direction U completely around the central axis A. In the exemplary embodiment, the annular wall 23 has a circular shape in the circumferential direction U around the central axis A.

[0031] In the exemplary embodiment, the annular wall 23 is a component of the front part 17. The front part 17 also has a front wall 24 connected to the annular wall 23. The front wall 24 and the annular wall 23 can be directly connected to one another or directly adjoin one another. In the exemplary embodiment, the front wall 24 is indirectly connected to the annular wall 23 via a transition wall 25.

[0032] In the exemplary embodiment, the front wall 24 extends along a plane oriented perpendicular to the central axis A. An inlet opening 26 is provided in the front wall 24, which has a circular edge around the central axis A. The inlet opening 26 is fluidically connected to an inflow channel 27 delimited by the annular wall 23. The inflow channel 27 is arranged downstream of the inlet opening 26 of an air flow in the flow direction F.

[0033] In the Fig. 1 and Fig. 2, the annular wall 23 is aligned parallel to the central axis A. It thus defines a cylindrical inflow channel 27 around the central axis A. Alternatively, the annular wall 23 can also be aligned obliquely inclined to the central axis A, as is the case, for example, in Fig. 3. The inflow channel 27 thus delimited tapers (for example conically) in the flow direction F or alternatively against the flow direction F, as is shown in a greatly simplified manner by the annular wall 23 shown in dashed lines in Fig. 3. The annular wall 23 can also form an inlet nozzle if it is tapered and, for example, conical.

[0034] In the exemplary embodiment, the connection between the inlet opening 26 and the inflow channel 27 is made along the transition wall 25. In the exemplary embodiment illustrated here, the transition wall 25 is convexly curved toward the central axis A. In a sectional plane along the central axis A, the curvature of the transition wall 25 can be circularly arcuate. Preferably, the transition between the inlet opening and the annular wall 23 is continuous and / or edgeless.

[0035] In the exemplary embodiment, the inlet opening 26 is the only flow opening in the front wall 24. Radially outside the inlet opening 26, the front wall 24 is completely free of flow openings through which an air flow can flow from the environment to the fan rotor 22. In addition to the inlet opening 26, the front wall 24 can optionally have openings for mechanically fastening the front part 17 to the rear part 18.

[0036] In the exemplary embodiment, the flow guide device 21 is a component of the front part 17 and in particular a monolithic component of the front part 17. According to the example, the flow guide device 21 includes at least the annular wall 23 and the front wall 24 with the inlet opening 26 present therein. As explained, the transition wall 25 between the front wall 24 and the annular wall 23 is optional.

[0037] In the flow direction F, the annular wall 23 has a trailing edge 31 at its downstream end. The trailing edge 31 of the annular wall 23 has a reference plane E ( Fig. 2-10) a varying distance. The reference plane E is a virtual plane oriented perpendicular to the central axis A. The position of the reference plane E along the central axis A can be defined differently. In the exemplary embodiment illustrated here, the reference plane E is arranged, for example, at a front end of the annular wall 23 arranged upstream of the trailing edge 31, i.e., in the exemplary embodiment, at the transition point to the transition wall 25. The reference plane E could also be arranged at a different position upstream or downstream of the trailing edge 31, or subdividing the trailing edge. It is merely a virtual auxiliary plane for describing the contour of the trailing edge 31.

[0038] As explained, the trailing edge 31 does not lie entirely in a single plane aligned parallel to the reference plane E. Rather, the trailing edge 31 has elevations 32 and / or depressions 33 that alternately adjoin one another in the circumferential direction U. This creates a wave-shaped and / or zigzag-shaped profile of the trailing edge 31. Each existing elevation 32 has a high point HP and each existing depression 33 has a low point TP. A distance of the low points from the reference plane E is a minimum distance of each depression 33 and a distance of the high points HP of each elevation 32 is a maximum distance of each elevation 32 from the reference plane E.

[0039] Two high points HP directly adjacent in the circumferential direction U define a width b of a depression 33 ( Fig. 4). A distance between two low points TP immediately adjacent in the circumferential direction U defines a width c of an elevation 32 arranged therebetween ( Fig. 4). A distance x of a low point from the reference plane E defines, for example, a minimum length of the annular wall 23 at the depression 33 having the low point TP. A distance y of a high point HP from the reference plane E parallel to the central axis A defines a maximum length of the annular wall 23 at the elevation 32 having the high point HP.

[0040] The widths b of all existing depressions 33 can be the same. The widths c of all existing elevations 32 can be the same. Equal widths b, c are shown as examples in the Fig. 4-9. In a variation of this, the widths b, c can also take two or more different values, as shown schematically in Fig. 10. There, the depressions can have a first width b1 of the depression 33 or a second width b2 of the depression 33, and the elevations can have a first width c1 of the elevation 32 or a second width c2 of the elevation 32. It is understood that the number of different widths b, c is not limited to two different values, but any number of different values ​​can be present for both the width b of a depression 33 and the width c of an elevation 32.

[0041] Analogous to the widths c, b, the distances x, y of the depressions 33 and / or the elevations 32 from the reference plane E can also vary, as shown by way of example in the Fig. 5-8. The distance x of a depression 33 from the reference plane E can, for example, assume at least two different values ​​corresponding to a first distance x1 and a second distance x2 of a depression 33 from the reference plane E ( Fig. 5, Fig. 7 and Fig. 8). Additionally or alternatively, the distance y of an elevation 32 from the reference plane E can assume at least two different values ​​corresponding to a first distance y1 and a second distance y2 of an elevation 32 from the reference plane E ( Fig. 6-8).

[0042] Viewed in the circumferential direction U, the dimensions (width and distance from the reference plane) of the individual elevations 32 and / or depressions 33 can vary in a repeating pattern or irregularly. Fig. 11 and Fig. 12 schematically illustrates, merely by way of example, characteristic curves for changing the distance x of a depression 33 from the reference plane E and the distance y of a projection 32 from the reference plane E depending on the position in the circumferential direction U. The characteristic curves can be continuous and / or differentiable ( Fig. 11) or have cracks ( Fig. 12). The curves of the distances x and y as a function of the circumferential position in the circumferential direction U can be specified according to any characteristic curves, as appropriate for a specific application. For example, rectangular curves with two or more steps for the distances x and / or y can also be used.

[0043] The trailing edge 31 or the elevations 32 and / or depressions 33 may be edgeless and / or stepless. For example, the entire trailing edge 18 may have an edgeless and / or stepless course in its extension around the central axis A, as shown schematically in the Fig. 1-6, 9 and 10. Alternatively, elevations 32 and / or depressions 33 may have an edge or corner ( Fig. 7 and Fig. 8). The geometry or shape of the elevations 32 and the depressions 33 can be selected to suit the application and the flow conditions or pressure conditions in the fan 15. The exemplary configurations of the trailing edge 31 or the elevations 32 and the depressions 33 can be combined with one another as desired.

[0044] In Fig. 9 illustrates an embodiment of a trailing edge 31 in which the elevations 32 and / or depressions 33 are formed asymmetrically with respect to a center plane M, which extends through the high point HP of an elevation 32 or through the low point TP of a depression 33 and is oriented perpendicular to the circumferential direction U. The center plane M divides an elevation 32 or a depression 33 into two unequal parts, as shown schematically in Fig. 9. The elevations 32 and / or depressions 33 can thus be asymmetrical with respect to their respective center plane M. In this case, all elevations 32 and / or all depressions 33 can be asymmetrical, as shown in the Fig. 9, or it may simply be that several of the existing elevations 32 and / or several of the existing depressions 33 are asymmetrical with respect to their respective center plane M. The embodiment according to Fig. 9 can therefore be combined with any other embodiment for the design of the trailing edge 31, as explained above and illustrated in the drawing.

[0045] The described flow guide device 21 is arranged in the fan 15 in the flow direction F upstream of the fan rotor 22. The fan rotor 22 can have an outer ring 22a that surrounds the annular wall 23 in the region of the trailing edge 31. Viewed parallel to the central axis A, the outer ring 22a of the fan rotor 22 and the annular wall 23 overlap with one another. The trailing edge 31 is preferably arranged entirely in this overlap region. In other words, all elevations 32 and depressions 33 formed by the course of the trailing edge 31 are preferably arranged in a space that is enclosed by the outer ring 22a ( Fig. 2). A leading edge 22b of the outer ring 22a arranged upstream in the flow direction F defines an axial position parallel to the central axis A, which can be arranged upstream of the trailing edge 31 of the ring wall 23.

[0046] The fan 15 has an electric motor 37, by means of which the fan rotor 22 can be driven to rotate about the central axis A. For this purpose, the fan rotor 22 is connected in a rotationally fixed manner to a drive shaft which extends from the fan rotor 22 along the central axis A on the downstream side of the fan rotor 22. The drive shaft is rotatably mounted and can be driven to rotate by the electric motor 37. The electric motor 37 is arranged, for example, at least substantially within the rear part 18 of the fan housing 16.

[0047] In the exemplary embodiment, the front part 17 of the fan housing 16 includes an outer wall 39, which extends from the front wall 24 to the rear part 18, for example, in a direction parallel to the central axis A. In the exemplary embodiment, the outer wall 39 encloses an interior space in which the annular wall 23 is arranged. In the exemplary embodiment of the fan 15 described here, the interior space delimited by the outer wall 39 of the front part 17 also contains the outer ring 22a and, optionally, parts of the fan rotor 22 adjoining the outer ring 22a.

[0048] During operation of the fan 15, air is sucked in from the environment through the inlet opening 26 and enters the inlet channel 27. On the outer side of the annular wall 23 facing away from the inlet channel 27, no or only a small amount of air flows along the annular wall 23. The volume flow or mass flow of the air flow flowing to the fan rotor 22 is directed exclusively or at least 80% or at least 90% or at least 95% through the inlet opening 26 and the inlet channel 27 to the fan rotor 22.

[0049] Due to the wavy and / or serrated trailing edge 31 of the annular wall 23, noise caused by the incoming air can be minimized. Although air turbulence does form in the area of ​​this trailing edge 31, it has been shown that this does not result in significant efficiency losses or leakage flows. The fan rotor 22 can surround the annular wall 23 in the area of ​​the trailing edge 31, as is the case in the exemplary embodiment with the outer ring 22a of the fan rotor 22, and contribute to reducing efficiency losses.

[0050] The invention relates to a flow guiding device 21 and a fan 15 comprising a flow guiding device 21. The flow guiding device 21 has an annular wall 23 which completely encloses a central axis A in a circumferential direction U and delimits an inflow channel 27 on its inner side facing the central axis A. The downstream end of the annular wall 23 has a trailing edge 31 which does not extend within a single plane oriented at right angles to the central axis A. Rather, the trailing edge 31 forms a plurality of depressions 33 and / or a plurality of elevations 32 with reference to a virtual reference plane E which is oriented at right angles to the central axis A. The trailing edge 31 can have a wavy and / or jagged profile. List of reference symbols: 15 Fan 16 fan housing 17 Front part 18 back 21 Flow control device 22 Fan rotor 22a Outer ring 22b Ring leading edge 23 Ring wall 24 front wall 25 Transition wall 26 Inlet opening 27 Inlet channel 31 trailing edge 32 Survey 33 Deepening 37 electric motor 39 Exterior wall A central axis b Width of a depression b1 first width of a depression b2 second width of a depression c Width of an elevation c1 first width of an elevation c2 second width of an elevation E Reference plane F Flow direction HP high point M Middle level TP low point U circumferential direction x Distance of a depression from the reference plane x1 first distance of a depression from the reference plane x2 second distance of a depression from the reference plane y Distance of an elevation from the reference plane y1 first distance of an elevation from the reference plane y2 second distance of an elevation from the reference plane QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 123 242 A1

[0002] EP 2 245 289 A1

[0013] EP 4 015 812 A1

[0013] WO 2015 / 036 684 A1

[0013] WO 2023 / 057 704 A1

[0013]

Claims

[1] Flow guiding device (21) for a fan (15), which is designed to guide an air flow to a fan rotor (22) which can be driven in rotation, wherein the flow guiding device (21) has an annular wall (23) which completely encloses an inlet channel (27) extending along the central axis (A) in a circumferential direction (U) around the central axis (A) and has a trailing edge (31) arranged downstream in the flow direction (F) of the air flow, which trailing edge has depressions (33) and / or elevations (32) with respect to a reference plane (E) oriented at right angles to the central axis (A). [2] Flow guiding device according to claim 1, wherein the annular wall (23) is aligned parallel or obliquely inclined to the central axis (A). [3] Flow guiding device according to claim 1 or 2, further comprising a front wall (24) which is connected to the annular wall (23) on a side of the inflow channel (27) opposite the trailing edge (31). [4] Flow guiding device according to claim 3, wherein the front wall (24) is oriented at right angles to the central axis (A). [5] Flow guiding device according to claim 3 or 4, wherein the front wall (24) is free of flow openings which allow air to be supplied to the fan rotor (22). [6] Flow guiding device according to one of claims 3 to 5, further comprising a transition wall (25) which connects the front wall (24) and the annular wall (23) to one another. [7] Flow guiding device according to claim 6, wherein the annular wall (23), the front wall (24) and the transition wall (25) are part of a monolithic front part (17) of the flow guiding device. [8] Flow guiding device according to one of claims 3 to 7, further comprising an outer wall (39) which is connected to the front wall (39) and surrounds the annular wall (23) in the circumferential direction (U). [9] Flow guiding device according to one of the preceding claims, which is designed to guide the air flow exclusively via the inlet channel (27) to the fan rotor (22). [10] Flow guiding device according to one of the preceding claims, wherein the elevations (32) all have the same distance (y) from the reference plane (E) and / or wherein the depressions (33) all have the same distance (x) from the reference plane (E). [11] Flow guiding device according to one of the preceding claims, wherein the elevations (32) in the circumferential direction (U) all have the same width (c) and / or wherein the depressions (33) in the circumferential direction (U) all have the same width (b). [12] Flow guiding device according to one of claims 1 to 10, wherein at least several of the existing elevations (32) have different distances (y1, y2) from the reference plane (E) and / or wherein at least several of the existing depressions (33) have different distances (x1, x2) from the reference plane (E). [13] Flow guiding device according to one of claims 1 to 10 or 12, wherein at least several of the existing elevations (32) have different widths (c1, c2) in the circumferential direction (U) and / or wherein at least several of the existing depressions (33) have different widths (b1, b2) in the circumferential direction (U). [14] Flow guiding device according to one of the preceding claims, wherein each elevation (32) has a central plane (M) extending at right angles to the circumferential direction (U) through its high point (HP) and each depression (33) has a central plane (M) extending at right angles to the circumferential direction (U) through its low point (TP), and wherein at least several of the existing elevations (32) and / or at least several of the existing depressions (33) are asymmetrical with respect to their respective central plane (M). [15] Fan (15) comprising a flow guiding device (21) according to one of the preceding claims and a fan rotor (22) which can be driven to rotate about the central axis (A) and which is arranged downstream of the inlet channel (27). [16] Fan according to claim 15, wherein the fan rotor (22) has an outer ring (22a) which surrounds the annular wall (23) in the region of the trailing edge (31).

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