Wind turbine outer rotor housing with enhanced magnet cooling

Abstract

The invention relates to an outer rotor housing of a wind turbine with enhanced magnet cooling. A housing wall (100) of a rotor housing for a rotor (40) of an external generator (10) of a direct drive wind turbine, for example, or a housing wall (100) of a rotor housing for a rotor of an external rotor of an electric machine, for example a generator or an electric motor, is disclosed. The housing wall (100) is an outer housing wall and has: an inner wall surface (110), an outer wall surface (114) and an axial length (124). The inner wall surface (110) is cylindrical. The outer wall surface (112) has at least one indentation (130) extending over at least a portion of the axial length (124) of the outer wall surface (112), in particular extending over the total axial length (124) of the outer wall surface (112).

Description

Technical Field

[0001] The present disclosure relates to a housing wall for a rotor of an external generator, for example a direct drive wind turbine, or to a housing wall of a rotor housing for a rotor of an external rotor of an electrical machine, such as a generator or a motor. The present disclosure also relates to a rotor for an external generator of a wind turbine. Background Art

[0002] Will refer to Figures 1 to 3 In part, the technical background of the present disclosure is discussed.

[0003] The wind turbine 10, in particular a direct drive wind turbine, may have an external wind generator 30 (see Figure 1 ), which is not arranged in the nacelle 60 of the wind turbine 10, but is directly adjacent to the wind driven rotor hub 22, which supports the blades 24 of the wind turbine 10. This external wind turbine 30 extends axially between a drive end 32 and a non-drive end 34 and has a rotor 40 and an internal stator 50, the rotor 40 having an external rotor housing (not shown), and the internal stator 50 having a stator axis 58 (see Figure 2 ). The rotor 40 is configured to rotate about the stator 50, and in particular about the stator axis 58. The rotation of the rotor 40 is achieved by one or more bearings 46 that rotatably couple the rotor 40 to the stator 50 (see Figure 2 ).

[0004] like Figure 2 As shown, the stator 50 includes: a shaft 52, which is connected to and supported by a nacelle 60 and is substantially rotationally symmetrical about a stator axis 58; first and second substantially circular stator plates 53, each of which is fixed to (e.g., bolted to) the shaft 52; and a plurality of stator segments 55, each of which is supported by (e.g., bolted to) the stator plate 53, and the stator segments 55 are circumferentially distributed around the stator axis 58. Each stator segment 55 includes a plurality of radially and tangentially extending steel sheets (not shown) and a plurality of windings 56, which are typically copper.

[0005] The rotor housing has an outer or outer casing wall 100, which is part of the rotor 40 of the generator 30 of the wind turbine 10. The outer casing wall 100 generally has a substantially cylindrical shape. Moreover, the outer casing wall 100 is directly exposed to the ambient air (or wind) that has passed through the blades 24 and drives the blades 24 to rotate. There are so-called permanent magnet exciters, in which the rotor 40 of the generator 30 includes, in addition to the outer casing wall 100, a plurality of permanent magnets or permanent magnet elements 46 (see Figure 2 and 3), which extend longitudinally and parallel to the axis 102 of the rotor 40 and / or the substantially cylindrical outer housing wall 100, and which are supported on the inner wall surface 110 of the outer housing wall 100 of the rotor 40. As an alternative to and instead of using permanent magnets 46, in a so-called electric exciter, a field excitation coil may be used, which is driven by a substantially constant current in order to generate a permanent magnetic field.

[0006] Rotor 40 (see Figure 1 ) also has a first base plate 42 and a second base plate 44, the first base plate 42 is basically annular in shape and is arranged perpendicular to the axis 102 at the axial drive end 12 of the rotor 40 facing the wind-driven rotor hub 22, the second base plate 44 can be used as a brake disk during operation of the generator 30, and the second base plate 44 is basically annular in shape and is arranged perpendicular to the axis 102 at the axial non-drive end 34 of the rotor 40 facing away from the wind-driven rotor hub 22 and toward the nacelle 60.

[0007] There are trends in the technical development of direct drive wind turbines 10 that include ever-increasing sizes (including diameters) of the wind drive rotor hub 22 and sizes (including diameters) of the generator 30 (including the rotor 40 and its substantially cylindrical outer casing wall 100), as well as ever-increasing nominal electrical output power of the generator 30.

[0008] Power losses occur in the generator 30 , particularly in the rotor 40 , due to, among other reasons, eddy currents periodically generated in the main components of the rotor 40 , which include a substantially cylindrical outer casing wall 100 , first and second base plates 42 , 44 , and permanent magnets 46 .

[0009] Power losses in rotor 40 become a critical issue, especially in direct drive wind generators 30 , as they may even limit the power output of wind turbine 10 .

[0010] These power losses will result in lower performance, lower power capacity and lower derating ambient temperature. The latter term (i.e. derating ambient temperature) refers to the external ambient temperature at which the temperature limit of the generator 30 is reached. This can occur in various components, such as the windings 56 or the permanent magnets 45. When the temperature rises above this threshold, the turbine power output must be reduced to avoid overheating. Therefore, these power losses will more generally result in lower Annual Energy Production (AEP) and higher Cost of Energy (CoE).

[0011] The problem of power losses in the rotor 40 has hitherto been solved on the one hand by methods aimed at reducing the losses themselves, for example by implementing well-developed techniques such as magnet segmentation. Segmentation consists in dividing each longitudinal magnet element 46 into a plurality of smaller blocks in order to reduce the generation of eddy currents. However, the reduction in the size of the magnet blocks has only a limited effect and is generally associated with lower performance and / or higher costs.

[0012] Other approaches aim to increase heat dissipation from heat sources (i.e., components that generate eddy currents, particularly magnets). One approach is to add cooling fins (not shown) to the outer surface of the outer housing wall 100 of the rotor housing. This may be effective, however the fixing of the fins may involve a reduction in thermal conductivity along the heat dissipation path, which is caused by the specific technology known to fix the fins to the surface. Such fin fixing techniques include gluing the fins to the surface (which involves a thin layer of adhesive between the fins and the surface), or welding or bolting the fins to the surface (which may involve a thin layer of air between the fins and the surface). For this technology, this reduction in thermal conductivity may be disappointing. Another disadvantage of using cooling fins is the maintenance work required to keep the cooling fins fixed or replace them.

[0013] Another method to increase heat dissipation may be forced cooling by air or liquid. The disadvantages of forced cooling are the increased cost and the maintenance required for the forced cooling system. Summary of the invention

[0014] The present disclosure is generally directed to avoiding or mitigating disadvantages of conventional methods for increasing heat flow from a rotor and / or improving heat dissipation from a rotor.

[0015] An object of the present disclosure is to provide a housing wall 100 for a rotor housing of a rotor 40 for, for example, directly driving an external generator 30 of a wind turbine, wherein the housing wall 100 provides enhanced heat transfer from the interior of the housing wall 100 via an exterior or outer wall surface 112 of the housing wall 100 to the external air environment, and in particular from generator magnets 46 supported on the inner wall surface 110 through the housing wall 100 via the exterior or outer surface 112 of the housing wall 100 to the external air environment.

[0016] This object is solved by the subject matter having the features according to the independent claim. Further embodiment examples are presented in the dependent claims.

[0017] Generally, the invention proposes to increase the cooling surface of the outer surface of the housing wall of the rotor, namely by implementing indentations or grooves in the outer surface of the housing wall.

[0018] According to an example of an embodiment of the invention, a housing wall of a rotor housing for a rotor of an external generator of a direct drive wind turbine, for example, and / or a housing wall of a rotor housing for an external rotor of an electric machine, for example a generator or an electric motor, is established. The housing wall is an outer housing wall and has an inner wall surface, an outer wall surface and an axial length. The inner wall surface is cylindrical. The outer wall surface has at least one indentation (or groove) extending over at least a portion of the axial length of the outer wall surface, in particular extending over the total axial length.

[0019] In an exemplary embodiment example of the present invention, the outer wall surface may have a plurality of indentations (or grooves), at least some of the plurality of indentations (or grooves) extending over at least a portion of the axial length of the outer wall surface, in particular extending over the total axial length of the outer wall surface. In particular, a first portion of the plurality of indentations may extend over only a portion of the axial length of the outer wall surface, and a second portion of the plurality of indentations may extend over the total axial length of the outer wall surface.

[0020] Providing dimples (or grooves) in the outer wall surface increases the surface area that interfaces with the surrounding air, thereby increasing the total heat flow of heat to be dissipated. At the same time, providing the dimples eliminates thermal conductivity issues associated with fixing fins to the outer surface. In particular, providing the dimples avoids the contact thermal resistance of conventional fins that are separately provided and fixed to the outer wall surface of the housing wall. In addition, providing the dimples instead of conventional fins provides a maintenance-free solution for increasing heat flow and / or improving heat dissipation.

[0021] It should be noted that the embodiment examples of the present disclosure do not only relate to the housing wall of a rotor housing for a rotor of an external generator, for example, for a direct drive wind turbine. Rather, the present disclosure relates to and can also be applied to the housing wall of a rotor housing of an external rotor of any electrical machine, for example a generator or a motor.

[0022] In an exemplary embodiment example of the present disclosure, in one or more regions of the outer wall surface outside at least one indent, in particular each indent, the outer wall surface may be cylindrical. In an exemplary embodiment example of the present disclosure, at least one indent, in particular each indent, has a indent bottom that is cylindrical, or in other words forms part of the outer cylindrical surface. In an exemplary embodiment example of the present disclosure, the at least one indent, in particular each indent, may be machined into the outer wall surface of the housing wall. Machining the indent into the cylindrical outer surface and making the bottom of the excavated indent also cylindrical is particularly convenient and cost-effective to perform. Moreover, as a result of machining the indent into the outer wall surface, the indents and the areas between the indents form an integral part of the housing wall, and there is no problem of reduced thermal conductivity due to, for example, fixing techniques for fixing structures that increase the surface area to the outer surface of the housing wall.

[0023] The size, shape, number, distribution and arrangement of the dimples may be optimized for each turbine generator design.Some exemplary embodiments are described below.

[0024] In exemplary embodiment examples of the present disclosure, the indentations may be equally spaced apart in a circumferential direction around the outer wall surface at a circumferential pitch and / or at a corresponding angular pitch.

[0025] Alternatively, in alternative exemplary embodiment examples of the present disclosure, the dimples may not all be equally spaced apart in the circumferential direction around the outer wall surface. In particular, the plurality of dimples may include at least two groups of equally spaced dimples, wherein the at least two groups have different mutual circumferential spacings of adjacent dimples in the circumferential direction.

[0026] In an exemplary embodiment example of the present disclosure, the outer wall diameter of the outer wall surface may be in the range of 4.0m to 12m, in particular in the range of 5.0m to 10m, and more particularly in the range of 6.0m to 8.0m. Alternatively or additionally, the total radial wall thickness of the outer wall surface may be in the range of 30mm to 60mm, in particular in the range of 32mm to 50mm, and more particularly in the range of 34mm to 40mm. Still alternatively or additionally, the ratio of the total radial wall thickness of the outer wall surface to the outer wall diameter of the outer wall surface may be in the range of between 0.4% and 1.0%, in particular in the range of 0.5% to 0.8%.

[0027] In an exemplary embodiment example of the present disclosure, the at least one indentation, in particular each indentation, may extend at a helix angle relative to the axial direction of the housing wall. The helix angle may be optimized so that air can flow optimally along and through the one or more indentations, i.e. with a thin interface layer, in particular depending on the wind speed and the rotation speed of the wind rotor of the generator and the connected rotor housing. In particular, the helix angle may be in the range of 12° to 20°, in particular in the range of 13° to 19°, more particularly in the range of 14° to 18°, and still more particularly in the range of 15° to 17°.

[0028] In an exemplary embodiment example of the present disclosure, when observed in the axial direction of the shell wall, in a cross-section perpendicular to the axial direction of the shell wall, at least one indentation, in particular each indentation, may have a cross-sectional shape selected from the group consisting of a basic rectangular shape, a basic trapezoidal shape, a basic sawtooth shape, and a basic wavy shape.

[0029] In an exemplary embodiment example of the present disclosure, the cross-sectional shape may be a substantially rectangular or substantially trapezoidal shape. Then, the cross-sectional shape of the groove has a radial height, a circumferential width, and the cylindrical outer wall surface between adjacent grooves has a circumferential length; and at least some of the plurality, in particular three, of the dimples are equally spaced in the circumferential direction with a circumferential pitch and / or with a corresponding angular pitch. Based on these definitions, at least one of the following conditions may hold:

[0030] - the radial height may be in the range of 10 mm to 50 mm;

[0031] - the circumferential width is in the range of 100 mm to 600 mm, in particular in the range of 100 mm to 500 mm;

[0032] - the circumferential length may be in the range of 10 mm to 70 mm, in particular in the range of 10 mm to 50 mm, or in the range of 100 mm to 500 mm, in particular in the range of 100 mm to 350 mm;

[0033] - the number of indentations along the entire circumference may be in the range of 30 to 250, in particular in the range of 50 to 150, more particularly in the range of 70 to 140;

[0034] - the circumferential pitch may be in the range of 100 mm to 500 mm, in particular in the range of 125 mm to 400 mm, and more particularly in the range of 150 mm to 300 mm;

[0035] - the angular pitch may be in the range of 2° to 10°, in particular in the range of 2.5° to 8°, and more particularly in the range of 3° to 6°;

[0036] - a ratio between the radial height of the indentation and the radial wall thickness of the housing wall, in particular the radial wall thickness measured in a surface area outside the indentation or indentations, is in the range of 0.5 to 1.0; and

[0037] If the cross-sectional shape is a trapezoid, the inclination angle of the side wall of the indentation relative to the radial direction is 30° to 75°, in particular 40° to 60°.

[0038] In exemplary embodiment examples of the present disclosure, the substantially trapezoidal cross-sectional shape may differ from the substantially rectangular cross-sectional shape in at least one of the following features:

[0039] - the transition from the outer wall surface to the side surface of the indentation is chamfered;

[0040] - the side surface of the indentation is inclined, in particular inclined at an inclination angle;

[0041] The transition from the side surface of the indentation to the indentation bottom is chamfered.

[0042] In other exemplary embodiments of the present disclosure, the cross-sectional shape may be a substantially sawtooth shape or a substantially wavy shape. Then, the cross-sectional shape of the dimple has a radial height, a circumferential width, at least a portion of the side surface of the dimple has an inclination angle relative to the radial direction, and at least some of the plurality, in particular three, dimples are equally spaced in the circumferential direction with a circumferential pitch and / or with a corresponding angular pitch. Based on these definitions, at least one of the following conditions holds:

[0043] - the radial height may be in the range of 10 mm to 50 mm;

[0044] - the circumferential width may be equal to the circumferential pitch and be in the range of 20 mm to 75 mm, in particular in the range of 30 mm to 60 mm;

[0045] - the ratio between the radial height of the indentation and the radial wall thickness of the housing wall (in particular the radial wall thickness measured in the surface area outside the one or more indentations, in particular the radial wall thickness measured through the peaks) may be in the range of 0.5 to 1.0;

[0046] - at least a portion of the side surface of the indentation may have an inclination angle β of the side wall of the indentation relative to the radial direction, the inclination angle β being 30° to 75°, in particular 40° to 60°, and more particularly 45°;

[0047] The number of indentations along the entire circumference of the outer wall surface may be in the range of 250 to 1000, in particular in the range of 300 to 750, more particularly in the range of 400 to 600.

[0048] In an exemplary embodiment example of the present disclosure, the outer wall surface may have a tapered section in the range of 100 mm, in particular 75 mm, more particularly 50 mm measured from an axial end of the housing wall, in a section outside at least one indentation, in particular outside each indentation and in the axial direction, the axial end facing the blades and the hub of the wind turbine to be connected to the rotor housing. When viewed in a cross section from the outer wall surface to the bottom of the indentation containing the axis of the housing wall, the tapered section may taper in the direction towards the axial end. In particular, the tapering may be performed in a linear shape or in a curved shape, the curved shape being selected from the group consisting of an elliptical shape, a parabolic shape, a hyperbolic shape. The tapering is arranged to smooth the transition from the outer surface of the wind rotor hub to the outer wall surface of the housing wall.

[0049] In an exemplary embodiment example of the present disclosure, the plurality of indents may include a first group of indents and a second group of indents, wherein the indents in the first group differ from the indents in the second group in at least one parameter, the one parameter being selected from the group consisting of: an axial length of the indent, a position of the indent in an axial direction of the shell wall, and a shape of the indent in a cross section perpendicular to the axial direction of the shell wall when viewed in the axial direction of the shell wall.

[0050] In exemplary embodiment examples of the present disclosure, the inner wall surface of the housing wall can support a plurality of, in particular, axially elongated magnet elements (eg in a permanent magnet exciter) or field excitation coils (eg in an electric exciter).

[0051] According to another embodiment example of the present disclosure, a rotor for an external generator, for example a direct drive wind turbine, and / or a rotor for an external rotor of an electric machine, such as a generator or a motor, is established. The rotor has a rotor housing having an outer housing wall as described above.

[0052] In exemplary embodiment examples of the rotor of the present disclosure, the inner wall surface of the housing wall can support a plurality of, in particular, axially elongated magnet elements (eg in a permanent magnet exciter) or field excitation coils (eg in an electric exciter). BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Hereinafter, exemplary embodiments of the present disclosure are described in detail with reference to the accompanying drawings.

[0054] Figure 1A direct drive wind turbine with a conventional external generator is shown in side view, wherein the generator has a conventional rotor housing with a substantially cylindrical outer wall surface.

[0055] Figure 2 A cross-sectional view of a conventional generator having a conventional rotor housing and main components of the generator in a plane including the axis is shown.

[0056] Figure 3 A portion of a conventional housing wall of a conventional rotor housing is shown in cross-sectional view, with magnets supported on the inner wall surface.

[0057] Figure 4 A plan view of a housing wall of a rotor housing for a rotor according to a first embodiment example of the present invention, seen in the axial direction, is shown, which has indentations in the outer wall surface.

[0058] Figure 5 Shown according to Figure 4 The illustrated example of a first embodiment of the present invention is a plan view of a housing wall viewed perpendicularly to the axial direction.

[0059] Figure 6 Shown according to Figure 4 A perspective view of a housing wall is shown showing a first exemplary embodiment of the invention.

[0060] Figure 7 Shown according to Figure 4 The modified housing wall of the first embodiment example of the present invention shown is viewed perpendicularly to the axial direction and is Figure 5 Similar in plan view, the housing wall has an indentation in the outer wall surface.

[0061] Figure 8 A plan view of a housing wall of a rotor housing for a rotor according to a second embodiment example of the present invention, seen in the axial direction, is shown, which has indentations in the outer wall surface.

[0062] Fig. 9 Shown according to Figure 8 The second embodiment example of the present invention is shown in a plan view of a housing wall viewed perpendicularly to the axial direction.

[0063] Fig.10 Shown according to Figure 8 A perspective view of a housing wall is shown of a second exemplary embodiment of the invention.

[0064] Fig.11 The plan view along the axial direction shows the Figure 4 An enlarged section of a housing wall of an example of a first embodiment of the invention is shown, wherein certain geometrical dimensions are shown, which characterize the shape of the indentation and the shape of the outer wall surface.

[0065] Fig.12 A plan view of a housing wall of a rotor housing for a rotor according to a third embodiment example of the present invention, seen in the axial direction, is shown, which has indentations in the outer wall surface.

[0066] Fig.13 Shown according to Fig.12 The third embodiment example of the present invention is shown in a plan view of a housing wall viewed perpendicularly to the axial direction.

[0067] Fig.14 Shown according to Fig.12 A perspective view of a housing wall is shown in accordance with a third exemplary embodiment of the present invention.

[0068] Fig.15 Shown according to Fig.12 The third embodiment of the present invention is shown as an example Fig.14 A perspective view of an enlarged portion of a housing wall is shown.

[0069] Fig.16 A plan view of a housing wall of a rotor housing for a rotor according to a fourth embodiment example of the present invention, seen in the axial direction, is shown, which has indentations in the outer wall surface.

[0070] Fig.17 Shown according to Fig.16 The fourth embodiment example of the present invention is shown in a plan view of a housing wall viewed perpendicularly to the axial direction.

[0071] Fig.18 Shown according to Fig.16 A perspective view of a housing wall is shown in accordance with a fourth exemplary embodiment of the present invention.

[0072] Fig.19 Shown according to Fig.16 The fourth embodiment of the present invention is shown as an example Fig.14 A perspective view of an enlarged portion of a housing wall is shown.

[0073] Fig. 20 The plan view along the axial direction shows the Fig.12 An enlarged section of a housing wall of a third exemplary embodiment of the invention is shown, wherein certain geometrical dimensions are shown which characterize the shape of the indentation and the shape of the outer wall surface.

[0074] Fig.21 Shown according to Figure 4 A perspective view of an enlarged portion of a housing wall of another modified example of the first embodiment of the present invention is shown, similar to Figure 6 of the view.

[0075] Fig. 22 Shown according to Figure 4 A perspective view of an enlarged portion of a housing wall of another modified example of the first embodiment of the present invention is shown, similar to Figure 6 and 21 of the view.

[0076] Fig.23 A portion of a housing wall according to a fifth embodiment example of the invention is shown in a cross-sectional view, wherein the cross-sectional view cuts through the peak line of the area between two adjacent indentations according to any one of the first to fourth embodiments in a plane including the axis.

[0077] Similar or similar components in different drawings are provided with the same reference numerals. The drawings are not necessarily drawn to scale and may be schematic, e.g. Figures 4 to 7 , Figures 8 to 10 , Figures 12 to 15 as well as Figures 16 to 20 . DETAILED DESCRIPTION

[0078] Figure 4 A plan view, seen in the axial direction 104 , of a housing wall 100 of a rotor housing for a rotor 20 according to a first embodiment example of the invention is shown, which has an indentation 130 in an outer wall surface 112 . Figure 5 Shown according to Figure 4 The first exemplary embodiment of the present invention is shown in a plan view of a housing wall 100 viewed perpendicularly to the axial direction 104 . Figure 6 Shown according to Figure 4 A perspective view of a housing wall 100 is shown according to a first exemplary embodiment of the present invention.

[0079] Figures 4 to 6 The housing wall 100 shown is used, for example, to directly drive an external generator 10 of a wind turbine (not shown) (see Figure 1 ) of the rotor 40 (see Figure 2 The housing wall 100 is an outer housing wall of the rotor housing, such that an outer wall surface 112 of the housing wall 100 is exposed to ambient air in an environment of the wind turbine.

[0080] The housing wall 100 has an inner wall surface 110, an outer wall surface 112, and an axial length 124 (in Figure 5 As shown in Figure 6 As best shown in FIG. 1 , the inner wall surface 110 is cylindrical.

[0081] Housing wall 100 (see Figure 4) of the outer wall surface 112, more specifically, the outer wall diameter 114 of the outer wall surface 112 is in the range of 4.0 m to 12 m. The outer wall diameter 114 may be in particular in the range of 5.0 m to 10 m, and more particularly in the range of 6.0 m to 8.0 m. The total radial wall thickness 116 (see Figure 4 ) is in the range of 30 mm to 60 mm. In particular, the total radial wall thickness 116 may be in the range of 32 mm to 50 mm, and more particularly in the range of 34 mm to 40 mm. The ratio of the total radial wall thickness 116 of the outer wall surface 112 to the outer wall diameter 114 of the outer wall surface 112 is in the range of 0.4% to 1.0%, and in particular in the range of 0.5% to 0.8%.

[0082] If you can Figures 4 to 6 As can be seen in each of the figures, the outer wall surface 112 has at least one dimple 130 extending over the total axial length 124 of the outer wall surface 112. Of course, preferably, the outer wall surface 112 has a plurality of dimples 130, each of which extends over the total axial length 124 of the outer wall surface 112 (see Figure 5 Providing the dimples 130 or grooves in the outer wall surface 112 increases the surface area that interfaces with the surrounding air, thereby increasing the overall heat flow and, therefore, the heat dissipation from the magnet element 46 that may be secured to the inner wall surface 110 of the housing wall 100, as shown. Figure 3 At the same time, the provision of the dimples 130 eliminates thermal conductivity issues associated with the fixation of the fins on the outer wall surface 112 .

[0083] If you can Figure 4 and 6 As can be seen in FIG, in the region of the outer wall surface 112 outside at least one dimple 130, in particular outside and between each dimple 130, the outer wall surface 112 is also cylindrical. At least one dimple 130, in particular each dimple 130, has a dimple bottom 134, which is also cylindrical and forms part of the outer cylindrical surface.

[0084] Each of the dimples 130 is obtained by a machining process in the outer wall surface 112 of the housing wall 100. In other words, each of the dimples 130 has been machined into the outer wall surface 112 of the housing wall 100. Machining the dimples 100 into the cylindrical outer surface, so that the hollowed-out dimple bottom 134 of the dimples is also cylindrical, is particularly convenient and cost-effective to perform. Moreover, as a result of machining the dimples 130 into the outer wall surface, the dimples 130 and the areas between the dimples 130 form an integral part of the housing wall 100, and there is no problem of reduced thermal conductivity due to, for example, fixing techniques for fixing structures of increased surface area to the outer surface of the housing wall.

[0085] If you can also Figure 4 and 6 As seen in , the dimples 130 are equally spaced along the circumferential direction 108 around the outer wall surface 112 .

[0086] Figure 7 Shown according to Figure 4 The modified housing wall 100 of the first exemplary embodiment of the present invention shown is viewed perpendicularly to the axial direction 104 and is Figure 5 Similarly in plan view, the housing wall 100 has an indentation 130 in the outer wall surface 112 .

[0087] If you can Figure 7 As can be seen in FIG. 1 , at least one indentation 130, in particular each indentation 130, may extend at a helix angle 132 relative to the axial direction 104 of the housing wall 100. The helix angle 132 may be optimized depending on the wind speed relative to the rotation speed of the wind rotor and thus the rotation speed of the housing wall 100. In the result of a corresponding calculation, the helix angle 132 may be in the range of 12° to 20°, in particular in the range of 12° to 20°, more particularly in the range of 13° to 19°, more particularly in the range of 14° to 18°, more particularly in the range of 15° to 17°, and even more particularly about 16°.

[0088] Generally, the size, shape, location, number, distribution, and arrangement of the dimples 130 may be optimized for each turbine generator design. Figures 4 to 6 A first exemplary embodiment is shown, Figures 8 to 10 A second exemplary embodiment is shown, Figures 12 to 15 A third exemplary embodiment is shown, and Figures 16 to 18 A fourth exemplary embodiment is shown. These exemplary embodiments will be described in more detail below.

[0089] When viewed in the axial direction 104 of the housing wall 100, in a cross section perpendicular to the axial direction 104 or the axis 102 of the housing wall 100, at least one indentation 130, in particular each indentation 130, may have a shape selected from a substantially rectangular shape 140 (e.g. Figures 4 to 6 As shown), the basic trapezoidal shape 142 (as Figures 8 to 10 As shown), the basic sawtooth shape 144 (as Figures 12 to 15 ) and the basic wavy shape 146 (as shown Figures 16 to 19 The cross-sectional shape of the group).

[0090] Not only for Figure 7The substantially rectangular indentation 130 is shown, and for each of the proposed cross-sectional shapes, namely the substantially rectangular shape 140 , the substantially trapezoidal shape 142 , the substantially sawtooth shape 144 and the substantially wavy shape 146 , the respective indentation 130 may extend at a helix angle 132 relative to the axial direction 104 of the housing wall 100 .

[0091] In such Figures 4 to 6 In the illustrated example of the first embodiment of the present invention, the cross-sectional shape of the indentation 130 has a substantially rectangular shape 140. Note again that Figures 4 to 7 This is merely schematic and serves to illustrate the indentation 130 having a substantially rectangular shape 140 in a cross section cut perpendicularly to the axial direction 104. In a modification of the first embodiment example of the present invention, the indentation 130 having a substantially rectangular shape 140 may be similar to Fig.21 and 22 The embodiments are shaped and distributed according to the embodiment examples shown in FIG.

[0092] Figure 8 A plan view, seen in the axial direction 104 , of a housing wall 100 of a rotor housing for a rotor 20 according to a second embodiment example of the invention is shown, which has an indentation 130 in the outer wall surface 112 . Fig. 9 Shown according to Figure 8 A second exemplary embodiment of the invention is shown in a plan view of a housing wall 100 viewed perpendicularly to the axial direction 104 . Fig.10 Shown according to Figure 8 A perspective view of a housing wall 100 is shown according to a second exemplary embodiment of the present invention.

[0093] In such Figures 8 to 10 In the second embodiment example of the present invention shown in , the cross-sectional shape of the dimple 130 has a substantially trapezoidal shape 142. Note again that Figures 8 to 10 This is merely schematic and serves to illustrate the indentation 130 having a substantially trapezoidal shape 142 in a cross section cut perpendicularly to the axial direction 104. In a modification of the second embodiment example of the present invention, the indentation 130 having a substantially trapezoidal shape 142 may be similar to Fig.21 and 22 The dimples 130 shown in FIG.

[0094] Fig.11 The plan view seen along the axial direction 104 shows the Figures 4 to 6 An enlarged portion of a housing wall 100 of a first embodiment example of the present invention is shown in FIG. 1 (where the indentation 130 has a substantially rectangular shape 140), wherein specific geometric dimensions are shown that characterize the shape of the indentation 130 and the shape of the outer wall surface 112. The following also applies to Figures 8 to 10A second embodiment example of the present invention is shown in (wherein the indentation 130 has a substantially trapezoidal shape 142).

[0095] When the cross-sectional shape of the indentation 130 is a substantially rectangular shape 140 (eg Figures 4 to 6 ) or a substantially trapezoidal shape 142 (such as Figures 8 to 10 ), the cross-sectional shape of the dimples 130 may be characterized by a radial height 150 and a circumferential width 152. The cylindrical outer wall surface 112 between adjacent dimples 130 may be characterized by a circumferential length 154. The dimples 130 are equally spaced apart in the circumferential direction 108 and may be characterized by a circumferential pitch 156 and / or a corresponding angular pitch 158 (angle π).

[0096] With regard to the geometric shapes and sizes of the substantially rectangular dimples and the substantially trapezoidal dimples, at least one of the following conditions may be established: the radial height 150 is in the range of 10 mm to 50 mm; the circumferential width 152 is in the range of 100 mm to 600 mm, in particular in the range of 100 mm to 500 mm; the circumferential length 154 is in the range of 10 mm to 70 mm, in particular in the range of 10 mm to 50 mm, or in the range of 100 mm to 500 mm, in particular in the range of 100 mm to 350 mm; the number of dimples 130 along the entire circumference of the outer wall surface 112 is in the range of 30 to 250, in particular in the range of 50 to 150, more particularly in the range of 70 to 145; the circumferential pitch 156 is in the range of 100 mm to 50 mm; 0 mm, in particular in the range of 125 mm to 400 mm, and more particularly in the range of 150 mm to 300 mm; the angular pitch 158 (or angle π) is in the range of 2° to 10°, in particular in the range of 2.5° to 8°, and more particularly in the range of 3° to 6°; the ratio between the radial height 150 of the indentation 130 and the radial wall thickness 116 of the housing wall 100 (in particular the radial wall thickness 116 measured in the surface area outside one or more indentations 130) is in the range of 0.5 to 1.0; if the cross-sectional shape of the indentation 130 is a basically trapezoidal shape 142, the inclination angle 160 (angle α) of the side wall 136 of the indentation 130 relative to the radial direction 106 is 30° to 75°, in particular 40° to 60°.

[0097] When the general Figures 4 to 6 and Figures 8 to 10When compared, it can be seen that the cross-section of the basic trapezoidal shape 142 differs from the cross-section of the basic rectangular shape 140 in at least one of the following features: the transition from the outer wall surface 112 to the side surface 137 of the indentation 130 is chamfered; the side surface 137 of the indentation 130 is inclined, in particular, inclined at an inclination angle 160 (angle α); the transition from the side surface 137 of the indentation 130 to the bottom 134 of the indentation is chamfered.

[0098] Fig. 20 The plan view seen along the axial direction 104 shows the Fig.12 An enlarged section of a housing wall 100 is shown for a third exemplary embodiment of the present invention, wherein certain geometrical dimensions are shown, which characterize the shape of the indentation 130 and the shape of the outer wall surface 112 .

[0099] When the cross-sectional shape of the dimples 130 is a substantially sawtooth shape 144 or a substantially wavy shape 146, the cross-sectional shape of the dimples 130 may be characterized by a radial height 150 and a circumferential width 152. At least a portion of a side surface 137 of the dimples 130 may be characterized by an angle of inclination 160 (angle β) relative to the radial direction 106. The dimples 130 are equally spaced apart in the circumferential direction 108 and may be characterized by a circumferential pitch 156 and / or a corresponding angular pitch 160 (angle π).

[0100] With regard to the geometry and dimensions of the basic sawtooth-shaped indentations and the basic wave-shaped indentations, at least one of the following conditions may be true: the radial height 150 is in the range of 10 mm to 50 mm; the circumferential width 152 is equal to the circumferential pitch 156 and is in the range of 20 mm to 75 mm, in particular in the range of 30 mm to 60 mm; the ratio between the radial height 150 of the indentation 130 and the radial wall thickness 116 of the housing wall 100 (in particular the radial wall thickness 116 measured in the surface area outside one or more indentations 130, in particular the radial wall thickness measured by the peak 164) is in the range of 0.5 to 1.0; at least a portion of the side surface 137 of the indentation 130 has an inclination angle 160 (angle β) of the side wall of the indentation 130 relative to the radial direction 106, which inclination angle 160 (angle β) is 30° to 75°, in particular 40° to 60°, and more in particular 45°. The number of the dimples 130 along the total circumference of the outer wall surface 112 is in the range of 250 to 1000, specifically in the range of 300 to 750, and more specifically in the range of 400 to 600.

[0101] Fig.21 Shown according to Figure 4 A perspective view of an enlarged portion of another modified housing wall 100 of the first embodiment example of the present invention is shown, similar to Figure 6 of the view. Fig. 22 Shown according to Figure 4 The perspective view of an enlarged portion of a housing wall 100 of another modified example of the first embodiment of the present invention is shown, similar to Figure 6 and 21 of the view.

[0102] exist Fig.21 and 22 In the illustrated example of the embodiment, the dimples 130 are significantly wider (e.g., 3 to 8 times, particularly 4 to 6 times, and more particularly about 5 times) than the areas between the dimples 130 when measured in the circumferential direction 108. In such a geometry, the areas between the dimples 130 may be referred to as "fins". However, these "fins" differ from conventional fins in that Fig.21 and 22 The "fins" shown are integral with (or in other words part of) the housing wall 100, whereas conventionally known fins are provided separately and fixed to a surface by a specific fixing technique, such as gluing or bolting.

[0103] exist Fig.21 In the embodiment example shown, the “fins” have a radial height 150 of 50 mm and a circumferential length 154 of 50 mm; the “fins” are arranged at an angular pitch of 5°, so that a total of 72 “fins” are provided along the circumference of the housing wall 100 .

[0104] exist Fig. 22 In the embodiment example shown, the “fins” have a radial height 150 of 10 mm and a circumferential length 154 of 10 mm; the “fins” are arranged at an angular pitch of 2.5°, so that a total of 144 “fins” are provided along the circumference of the housing wall 100 .

[0105] exist Fig.21 In the embodiment example shown, the surface area of ​​the outer wall surface 112 is increased by 28% due to the machining of complementary indentations 130, the "fins" having a radial height of 50 mm and a circumferential length of 50 mm. Thermal simulations have shown that heat flow through the housing wall 100 is increased by 25%.

[0106] exist Fig. 22 In the embodiment example shown, the surface area of ​​the outer wall surface 112 is increased by 28% due to the machining of complementary indentations 130, the "fins" having a radial height of 50 mm and a circumferential length of 50 mm. Thermal simulations have shown that the heat flow through the housing wall 100 is increased by 22%.

[0107] For comparison purposes, further thermal simulations have been performed with the aim of estimating the disadvantages of the prior art.

[0108] In one such simulation, it has been assumed that the fins are bolted to the outer surface. In this simulation, an air gap of 0.1 mm thickness has been assumed between the bottom surface of the fin and the outer wall surface. In this simulation, the air gap was found to have a thermal conductivity of 0.02 W / mK. This fixing technique showed a reduction in heat flow of about 11% due to contact thermal resistance.

[0109] In another such simulation, it has been assumed that the fins are glued to the outer surface. In this simulation, the adhesive is assumed to be an epoxy-based glue with a thermal conductivity of 2 W / mK and a film thickness of 0.5 mm between the bottom surface of the fin and the outer wall surface. This fixing technique shows a reduction in heat flow of approximately 2% due to contact thermal resistance.

[0110] Fig.23 A section of a housing wall 100 according to a fifth exemplary embodiment of the present invention is shown in cross-sectional view, wherein the cross-sectional view is taken along a line including the axis 102 (see FIG. Figure 6 , 10 , 14 and 19) in a plane that cuts through a peak or peak line 164 in the area between two adjacent dimples 130 according to any one of the first to fourth embodiments.

[0111] exist Fig.23 In the embodiment example shown, the outer wall surface 112 tapers in the direction towards an axial end 180 of the housing wall 100 which will face the wind turbine blade and the hub to be connected to the rotor housing. The taper of the outer wall surface 112 is provided in a section outside at least one indentation 130, or generally in a section outside each indentation 130.

[0112] The taper is formed to be carried out in the range of 100 mm, particularly 75 mm, more particularly 50 mm along the axial direction 104, as measured from the axial end 180 of the housing wall 100. When viewed in a cross section containing the axis 102 of the housing wall 100, the tapered section 170 is shown to taper from the outer wall surface 112 to the dimple bottom 134 in the direction toward the axial end 180.

[0113] The tapering may be in a linear shape 172 or in a curved shape 174. If the tapering occurs in a curved shape 174, this may be selected from the group consisting of an elliptical shape 176, a parabolic shape 178, a hyperbolic shape (not shown).

[0114] The tapering is arranged to smooth the transition from the outer surface of the wind rotor hub (not shown) to the outer wall surface 112 of the housing wall 100 .

[0115] exist Figures 4 to 23In the illustrated embodiment, the housing wall 100 is an outer housing wall 100 for a rotor 40 of an external generator 10, such as may be used in a direct drive wind turbine (not shown). In this application, a plurality of axially elongated magnet elements 46 will be disposed on an inner wall surface 110 of the housing wall 100, such as Figure 3 shown.

[0116] In this specification, exemplary embodiments have been presented according to a selected set of details. However, it will be appreciated by those skilled in the art that many other exemplary embodiments including different selected sets of these details may be implemented. It is intended that the appended claims cover all possible exemplary embodiments.

[0117] In addition, it should be noted that "having" or "including" does not exclude other elements or steps, and "one" or "an" does not exclude a plurality. In addition, it should be noted that the features or steps described above with reference to one of the above embodiment examples can also be used in combination with other features or steps of other embodiment examples described above. The reference numerals in the claims should not be interpreted as limitations.

Claims

1. A housing wall (100) of a rotor housing for a rotor (40) of an external generator (10) of a wind turbine, or a housing wall (100) of a rotor housing for an external rotor of an electric machine, wherein: The housing wall (100) is an outer housing wall and has: an inner wall surface (110), an outer wall surface (112) and an axial length (124), wherein the inner wall surface (110) is cylindrical, and The outer wall surface (112) has at least one indentation (130), and the at least one indentation (130) extends over at least a portion of the axial length (124) of the outer wall surface (112). wherein the dimples (130) are not all equally spaced along a circumferential direction (108) around the outer wall surface (112), wherein the plurality of dimples (130) comprises at least two groups of equally spaced dimples (130), wherein the at least two groups of equally spaced dimples (130) have different mutual circumferential spacings of adjacent dimples (130) in the circumferential direction (108), wherein the outer wall diameter (114) of the outer wall surface (112) is in the range of 4.0 m to 12 m, and wherein the total radial wall thickness (116) of the outer wall surface (112) is in the range of 30 mm to 60 mm, and Wherein, a ratio of a total radial wall thickness (116) of the outer wall surface (112) to an outer wall diameter (114) of the outer wall surface (112) is in a range between 0.4% and 1.0%.

2. The housing wall (100) according to claim 1, wherein: The wind turbine is a direct drive wind turbine.

3. The housing wall (100) according to claim 1, wherein: The electric machine is a generator or an electric motor.

4. The housing wall (100) according to claim 1, wherein: The at least one indentation (130) extends over a total axial length (124) of the outer wall surface (112).

5. The housing wall (100) according to claim 1, wherein: The outer wall surface (112) has a plurality of indentations (130), at least some of the plurality of indentations (130) extending over at least a portion of an axial length (124) of the outer wall surface (112).

6. The housing wall (100) according to claim 5, wherein: At least some of the plurality of dimples (130) extend over a total axial length (124) of the outer wall surface (112).

7. The housing wall (100) according to claim 5, wherein: A first portion of the plurality of dimples (130) extends over only a portion of the axial length (124) of the outer wall surface (112), and a second portion of the plurality of dimples (130) extends over the entire axial length (124) of the outer wall surface (112).

8. The housing wall (100) according to any one of claims 1 to 7, wherein In one or more regions of the outer wall surface (112) outside the at least one indentation (130), the outer wall surface (112) is cylindrical.

9. The housing wall (100) according to any one of claims 1 to 7, wherein: In one or more regions of the outer wall surface (112) outside each indentation (130), the outer wall surface (112) is cylindrical.

10. The housing wall (100) according to any one of claims 1 to 7, wherein: The at least one indentation (130) has an indentation bottom (134), and the indentation bottom (134) is cylindrical.

11. The housing wall (100) according to any one of claims 1 to 7, wherein: Each indentation (130) has an indentation bottom (134) which is cylindrical.

12. The housing wall (100) according to any one of claims 1 to 7, wherein: The at least one indentation (130) has been machined into the outer wall surface (112) of the housing wall (100).

13. The housing wall (100) according to any one of claims 1 to 7, wherein: Each indentation (130) has been machined into the outer wall surface (112) of the housing wall (100).

14. The housing wall (100) according to any one of claims 1 to 7, wherein: The at least one indentation (130) extends at a helix angle (132) relative to an axial direction (104) of the housing wall (100).

15. The housing wall (100) according to any one of claims 1 to 7, wherein Each indentation (130) extends at a helix angle (132) relative to an axial direction (104) of the housing wall (100).

16. The housing wall (100) according to claim 14, wherein: The helix angle (132) is in the range of 12° to 20°.

17. The housing wall (100) according to claim 14, wherein: The helix angle (132) is in the range of 13° to 19°.

18. The housing wall (100) according to claim 14, wherein: The helix angle (132) is in the range of 14° to 18°.

19. The housing wall (100) according to claim 14, wherein: The helix angle (132) is in the range of 15° to 17°.

20. The housing wall (100) according to any one of claims 1 to 7, wherein When viewed in the axial direction (104) of the housing wall (100), in a cross section perpendicular to the axial direction (104) of the housing wall (100), the at least one indentation (130) has a cross-sectional shape selected from the group consisting of a basic rectangular shape (140), a basic trapezoidal shape (142), a basic sawtooth shape (144), and a basic wavy shape (146).

21. The housing wall (100) according to any one of claims 1 to 7, wherein When viewed in the axial direction (104) of the housing wall (100), in a cross section perpendicular to the axial direction (104) of the housing wall (100), each indentation (130) has a cross-sectional shape selected from the group consisting of a basic rectangular shape (140), a basic trapezoidal shape (142), a basic sawtooth shape (144), and a basic wavy shape (146).

22. The housing wall (100) according to claim 20, wherein: The cross-sectional shape is a substantially rectangular shape (140) or a substantially trapezoidal shape (142), wherein the cross-sectional shape of the dimple (130) has a radial height (150), a circumferential width (152), the cylindrical outer wall surface (112) between adjacent dimples (130) has a circumferential length (154), and at least some of the plurality of dimples (130) are equally spaced apart in the circumferential direction (108) at a circumferential pitch (156) and / or at a corresponding angular pitch (158), and wherein at least one of the following conditions is met: - the radial height (150) is in the range of 10 mm to 50 mm; - the circumferential width (152) is in the range of 100 mm to 600 mm; - the circumferential length (154) is in the range of 10 mm to 70 mm, or in the range of 100 mm to 500 mm; - the number of indentations along the entire circumference of the outer wall surface (112) is in the range of 30 to 250; - the circumferential pitch (156) is in the range of 100 mm to 500 mm; - the angular pitch (158) is in the range of 2° to 10°; - a ratio between a radial height (150) of the indentation (130) and a radial wall thickness (116) of the housing wall (100) is in the range of 0.5 to 1.0; and If the cross-sectional shape is a substantially trapezoidal shape (142), the inclination angle (160) of the side wall (136) of the indentation (130) relative to the radial direction (106) is 30° to 75°.

23. The housing wall (100) according to claim 22, wherein: At least some of the three dimples are equally spaced apart in the circumferential direction (108) at a circumferential pitch (156) and / or at a corresponding angular pitch (158).

24. The housing wall (100) according to claim 22, wherein: The circumferential width (152) is in the range of 100 mm to 500 mm.

25. The housing wall (100) according to claim 22, wherein The circumferential length (154) is in the range of 10 mm to 50 mm.

26. The housing wall (100) according to claim 22, wherein The circumferential length (154) is in the range of 100 mm to 350 mm.

27. The housing wall (100) according to claim 22, wherein: The number of the dimples along the entire circumference of the outer wall surface (112) is in the range of 50 to 150.

28. The housing wall (100) according to claim 22, wherein The number of dimples along the entire circumference of the outer wall surface (112) is in the range of 70 to 145.

29. The housing wall (100) according to claim 22, wherein: The circumferential pitch (156) is in the range of 125 mm to 400 mm.

30. The housing wall (100) according to claim 22, wherein The circumferential pitch (156) is in the range of 150 mm to 300 mm.

31. The housing wall (100) according to claim 22, wherein: The angular pitch (158) is in the range of 2.5° to 8°.

32. The housing wall (100) according to claim 22, wherein: The angular pitch (158) is in the range of 3° to 6°.

33. The housing wall (100) according to claim 22, wherein: The radial wall thickness (116) is measured in a surface region outside of the at least one indentation (130).

34. The housing wall (100) according to claim 22, wherein: The inclination angle (160) of the side wall (136) of the indentation (130) relative to the radial direction (106) is 40° to 60°.

35. The housing wall (100) according to claim 20, wherein The cross-section of the substantially trapezoidal shape (142) differs from the cross-section of the substantially rectangular shape (140) by at least one of the following features: - the transition from the outer wall surface (112) to the side surface (137) of the indentation (130) is chamfered; - the side surface (137) of the indentation (130) is inclined; - The transition from the side surface (137) of the indentation (130) to the indentation bottom (134) is chamfered.

36. The housing wall (100) according to claim 35, wherein The side surface (137) of the indentation (130) is inclined at an inclination angle (160).

37. The housing wall (100) according to claim 20, wherein: The cross-sectional shape is a substantially sawtooth shape (144) or a substantially wavy shape (146), wherein the cross-sectional shape of the dimple (130) has a radial height (150), a circumferential width (152), at least a portion of a side surface (137) of the dimple (130) has an inclination angle (160) relative to a radial direction (106), and at least some of the plurality of dimples (130) are equally spaced apart in the circumferential direction (108) at a circumferential pitch (156) and / or at a corresponding angular pitch (158), and wherein at least one of the following conditions is met: - the radial height (150) is in the range of 10 mm to 50 mm; - the circumferential width (152) is equal to the circumferential pitch (156) and is in the range of 20 mm to 75 mm; - a ratio between a radial height (150) of the indentation (130) and a radial wall thickness (116) of the housing wall (100) is in the range of 0.5 to 1.0; - at least a portion of the side surface (137) of the indentation (130) has an inclination angle (160) of the side wall of the indentation (130) relative to the radial direction (106), and the inclination angle (160) is 30° to 75°; - The number of the dimples (130) along the entire circumference of the outer wall surface (112) is in the range of 250 to 1000.

38. The housing wall (100) according to claim 37, wherein At least some of the three dimples are equally spaced apart in the circumferential direction (108) at a circumferential pitch (156) and / or at a corresponding angular pitch (158).

39. The housing wall (100) according to claim 37, wherein The circumferential width (152) is in the range of 30 mm to 60 mm.

40. The housing wall (100) according to claim 37, wherein The radial wall thickness (116) is measured in a surface region outside of the at least one indentation (130).

41. The housing wall (100) according to claim 37, wherein The radial wall thickness (116) is measured via the peak (164).

42. The housing wall (100) according to claim 37, wherein The inclination angle (160) is 40° to 60°.

43. The housing wall (100) according to claim 37, wherein The inclination angle (160) is 45°.

44. The housing wall (100) according to claim 37, wherein The number of the dimples (130) along the entire circumference of the outer wall surface (112) is in the range of 300 to 750.

45. The housing wall (100) according to claim 37, wherein The number of the dimples (130) along the entire circumference of the outer wall surface (112) is in the range of 400 to 600.

46. ​​The housing wall (100) according to claim 14, wherein The outer wall surface (112) has a tapered section (170) in a section outside the at least one indentation (130) and within 100 mm measured along the axial direction (104) from an axial end (180) of the housing wall (100), the axial end (180) facing a blade and a hub of a wind turbine to be connected to the rotor housing, When viewed in a cross section from the outer wall surface (112) to the recess bottom (134) containing the axis (102) of the housing wall (100), the tapered section (170) tapers in a direction toward the axial end (180).

47. The housing wall (100) according to claim 46, wherein In a section outside each indentation (130) and within a range of 100 mm measured from an axial end (180) of the housing wall (100) along the axial direction (104), the outer wall surface (112) has a tapered section (170).

48. The housing wall (100) according to claim 46, wherein In a section outside the at least one indentation (130) and within a range of 75 mm measured along the axial direction (104) from an axial end (180) of the housing wall (100), the outer wall surface (112) has a tapered section (170).

49. The housing wall (100) according to claim 46, wherein In a section outside the at least one indentation (130) and within a range of 50 mm measured along the axial direction (104) from an axial end (180) of the housing wall (100), the outer wall surface (112) has a tapered section (170).

50. The housing wall (100) according to claim 46, wherein The tapering of the tapered section (170) is performed in a linear shape (172) or in a curved shape (174), and the curved shape (174) is selected from the group consisting of an elliptical shape (176), a parabolic shape (178), and a hyperbolic shape.

51. The housing wall (100) according to any one of claims 1 to 7, wherein The plurality of indentations (130) include a first group of indentations and a second group of indentations, wherein the indentations in the first group differ from the indentations in the second group in at least one parameter, the one parameter being selected from the group consisting of: an axial length of the indentation (130), a position of the indentation (130) in an axial direction (104) of the housing wall (100), and a shape of the indentation (130) in a cross section perpendicular to the axial direction (104) of the housing wall (100) when viewed in the axial direction (104) of the housing wall (100).

52. A rotor (40) for an external generator (10) of a wind turbine, or a rotor for an external rotor of an electric machine, wherein: The rotor (40) comprises a rotor housing having an outer housing wall (100) according to any one of claims 1 to 51.

53. A rotor (40) according to claim 52, wherein: The wind turbine is a direct drive wind turbine.

54. The rotor (40) of claim 52, wherein: The electric machine is a generator or an electric motor.

55. The rotor (40) of claim 52, wherein: The inner wall surface (110) of the outer shell wall (100) supports a plurality of magnetic elements (46) or magnetic field excitation coils.

56. The rotor (40) of claim 52, wherein: The inner wall surface (110) of the outer shell wall (100) supports a plurality of axially elongated magnetic elements (46) or magnetic field excitation coils.

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