ROTOR BLADE OF A WIND TURBINE AND AERODYNAMIC ATTACHMENT

Description

[0001] The present invention relates to a wind turbine rotor blade having an aerodynamic add-on element. The invention also relates to an aerodynamic add-on element for mounting to a wind turbine rotor blade.

[0002] It is known to provide a variety of aerodynamic add-on elements on the outer surface of wind turbine rotor blades in order to improve the performance of the rotor blade or, for example, to reduce noise levels produced by the rotor blades in use. Typical aerodynamic add-on elements include flaps such as Gurney flaps, vortex generators, and other trailing edge devices such as serrations. The aerodynamic add-on elements may be mounted to the outer surface of the blade shell. These aerodynamic add-on elements are often generally referred to as 'add-ons', and may be provided on the rotor blade during the rotor blade manufacturing process, or later to existing rotor blades as a retrofit.

[0003] Specifically, vortex generators are used to generate vortices on the rotor blade surface. These vortices transport high energetic (fast) airflow from outside the aerodynamic boundary layer closer to the rotor blade surface. Thus, the flow energized is more able to follow the airfoil contour against the adverse pressure gradient. A flow separation is avoided. Thus, the overall aerodynamic performance of the rotor blade at high angels of attack can be efficiently increased.

[0004] WO 2017 / 088881 A1 relates to wind turbine blades and more specifically to a wind turbine blade having an aerodynamic device mounted to a surface of the blade.

[0005] EP 3 510 276 A1 relates to wind turbine blades, and more specifically to a device for mounting to a surface of the blade in order to, for example, improve the performance of the blade.

[0006] EP 3 510 276 A1 relates to wind turbine blades, and more specifically to a device for mounting to a surface of the blade in order to, for example, improve the performance of the blade.

[0007] Vortex generators are typically attached to the rotor blade surface by either double sided tape or adhesive / glue. In both cases a defined bond line (or tape) thickness is required to fulfil structural needs.

[0008] One object underlying the invention is to specify a concept for an aerodynamic add-on element of a wind turbine rotor blade which contributes to a particularly flow-optimized assembly.

[0009] According to an aspect of the invention a wind turbine rotor blade is disclosed according to claim 1. The wind turbine rotor blade comprises an aerodynamic add-on element comprising a baseplate. The baseplate has an upper side and a bottom side. The aerodynamic add-on element is mounted with the bottom side of the baseplate to an outer surface of the wind turbine rotor blade. The whole bottom side is inclined relative to the outer surface of the wind turbine rotor blade along a downstream direction of an operational wind flow, such that a gap is formed between the bottom side and the outer surface in which a distance between the outer surface and the bottom side increases along the downstream direction. Adhesive is provided in the gap to bond the aerodynamic add-on element to the outer surface of the wind turbine rotor blade.

[0010] From an aerodynamic point of view the thickness of the adhesive, i.e. a bond line, is very critical, as it introduces a step and a certain distance of the baseplate from the outer surface of the rotor blade. If this step becomes too high, there will be a negative impact on the local air flow and the aerodynamic properties of the rotor blade. Disturbances of the flow cause additional drag and make the flow more prone to flow separation. Thus, the overall performance of the wind turbine rotor blade decreases.

[0011] The above mentioned aerodynamic requirements are contrary to structural design requirements. The main loading of the bond line arises from strains in the rotor blade shells in longitudinal direction, which, due to the comparatively low stiffness of adhesive materials, is not transferred into the add-ons. Hence, the adhesive must compensate these differences, which introduces shear loads in the bond line. The loading level can be assumed linearly proportional to bond line thickness wherein a thicker bond line leads to smaller shear loading.

[0012] To mitigate the aerodynamically unfavorable step while keeping a structurally required adhesive thickness, the baseplate, in particular its underside or bottom side, is inclined or tilted with respect to the outer surface of the wind turbine rotor blade. Thus, a gap is formed between the bottom side and the outer surface, which gap increases along the downstream direction. In other words, height of the gap or thickness of the respective adhesive in the gap increases. This allows a tilted add-on element with a very small step at the up-wind side, in particular the up-wind edge and a larger, aerodynamically much more tolerable step at the down-wind side, in particular the down-wind edge. Simultaneously, a sufficient bond-line thickness due to the increasing gap height is obtained. Optionally, the step at the down-wind edge of the add-on element could be thicker than structurally necessary. This design fulfills structural need and is aerodynamically much more favourable than a larger or wider gap over the full length.

[0013] The gap beneath the add-on may either be completely filled with adhesive or, alternatively, spacers or barriers can be introduced. This would reduce adhesive material if the spacers are not filled, would allow the adhesive to start with a structurally sufficient thickness in the supposedly down-wind section or may act as crack stoppers to prevent cracks in the adhesive to run from one section into the other one if adhesives are applied to both. For a gap with a small height, this may be a non-structural adhesive, for example to prevent water ingress. We refer to the further details and embodiments below.

[0014] The proposed solution enables both structural and aerodynamic requirements as an inclined bottom side (and thus an increasing gap height / adhesive thickness in down-wind direction) is combined with a sufficiently thick bond line. The invention provides further advantages: The aerodynamic performance of the add-on element and thus of the whole wind turbine can be increased due the better working add-on elements with less drag and less air flow disturbance (compared to overall thick bond line). A cost of energy reduction can be achieved. In particular, a cost of energy optimum can be achieved. Standard adhesives can be used. Reduced effort in rotor blade finish is possible since adhesive enables larger tolerance against surface waviness. A defined bond line thickness can be guaranteed. This increases production quality and reduces the risk of expensive service jobs Structural as well as aerodynamic needs can be fulfilled in one design.

[0015] The term "gap" can also be interpreted as a space, which is defined by the outer surface of the blade and the bottom side. This space can be filled with adhesive. Due to the mentioned design, gap height and thus adhesive thickness increases. Different geometries can be applied to the gap and thus the adhesive in the gap, for example a triangular shape (profile) or trapezoidal shape (profile).

[0016] As already indicated above, the "aerodynamic add-on element" means an element which is attached to the rotor blade, in particular to the outer surface of the shell, and has aerodynamic impacts on the rotor blade. The aerodynamic add-on element is mounted on the rotor blade in a mounting region, which comprises the outer surface. The aerodynamic add-on element may be any blade add-on, for example it may be a flap or a turbulence generating device such as a vortex generator. Such devices typically include a baseplate having an inner surface or bottom plate for bonding to the rotor blade surface. An outer surface of the baseplate may include one or more turbulence generating features such as the fins of vortex generators. Alternatively, a flap may extend from the baseplate. The device may be located either on the pressure side surface or the suction side surface of the rotor blade, at the leading edge or trailing edge of the blade, or at any other suitable position on the blade surface.

[0017] The baseplate may be made of any suitable material, but preferably it is made from a plastics material. In preferred embodiments, the baseplate is an injection-moulded component. Aerodynamic features of the device, such as serrations or turbulence-generating features may advantageously be integrally-formed with the baseplate. This reduces the number of parts and reduces cost, and increases the structural integrity and ease of mounting of the device.

[0018] The baseplate may have any suitable shape, for example rectangular or substantially rectangular or substantially trapezoidal. The baseplate is preferably relatively thin, typically of the order of a few millimeters in thickness. The baseplate is also preferably substantially planar. The baseplate may therefore have some flexibility allowing it to conform to contours of the outer surface of the rotor blade. The mounting region of the baseplate preferably occupies a substantial portion (e.g. a majority) of the inner surface of the baseplate. Maximizing the area of the mounting region is advantageous since it maximizes the bond area between the baseplate and the surface of the rotor blade. The mounting region may have any suitable shape, but preferably corresponds substantially in shape to the baseplate (e.g. substantially rectangular or trapezoidal) and is located inwardly of an outer perimeter of the baseplate.

[0019] According to an embodiment, the aerodynamic add-on element is a vortex generator.

[0020] According to an embodiment the baseplate is tilted relative to the outer surface of the wind turbine rotor blade. That means that the upper side respectively outer surface is inclined or tilted with respect to the outer surface of the wind turbine rotor blade as well. This contributes to the above advantages and effects.

[0021] According to an embodiment a height of the gap increases along the downstream direction. The gap / space is such that the adhesive thickness (or gap height) increases over length in downstream direction. The thickness increases continuously or gradually. Alternatively, the thickness increases stepwise. Also, combinations thereof are possible, e.g. different sections with stepwise or continuously increasing thickness. This contributes to the above advantages and effects.

[0022] According to an embodiment a height of the gap increases from 0,1 mm, preferably 0,2 mm, to 1 mm, preferably 0,7 mm, 0,6 mm or more preferably 0,5 mm. This particularly contributes to the above advantages and effects.

[0023] According to an embodiment the wind turbine rotor blade comprises a gradual transition between the outer surface of the wind turbine rotor blade and the aerodynamic add-on element at the up-wind side. This contributes to the above advantages and effects.

[0024] According to an embodiment the distance between an upper side of the aerodynamic add-on element and the surface of the wind turbine rotor blade at the up-wind side is smaller than at the down-wind side of the aerodynamic add-on element. Thus, the aerodynamic add-on element comprises none or only a small step at the up-wind side of the aerodynamic add-on element. This contributes to the above advantages and effects.

[0025] According to an embodiment a structural relevant thickness of the adhesive in the gap to bond the add-on element to the blade, e.g. 0,5 mm, is reached at a certain distance from the up-wind side of the adhesive in the gap with regard to the downstream direction. This contributes to the above advantages and effects.

[0026] According to an embodiment at least one section of the bottom side comprises one or more spacers, the spacers being in direct contact with the outer surface of the wind turbine blade. The spacers define the distance between the inner surface of at least one add-on section and the outer surface of the rotor blade. In other words, the spacers guarantee a correct position and orientation, e.g. tilting, of the aerodynamic add-on element on the outer surface. Further, the spacers guarantee a defined amount of adhesive in the gap.

[0027] According to an embodiment the spacers are formed as line shaped spacers, cylindrical spacers or point spacers. Thus, different kinds of spacers are provided. For example, an area support, a line support, a point support or combinations thereof are possible, which can be selected depending on the design of the add-on element and / or blade, for example.

[0028] According to an embodiment at least one section of the bottom side comprises a web running traverse to the operational wind flow, the web being in direct contact with the outer surface of the wind turbine rotor blade, wherein the web separates the gap into a first gap section and a second gap section, such that the adhesive is divided into a first and a second gap section. The web essentially has two functions. Basically, it acts as a line-spacer. Additionally, it serves as a crack stopper, if the adhesive get cracks. By providing a separation of the gap into at least two gap sections, the applied adhesive is divided into corresponding sections. In other words, the adhesive in the first gap section has no contact with the adhesive in the second gap section. Thus, a potential crack cannot run through the whole adhesive from the up-wind side to the down-wind side, since it cannot surpass the web. This provides a particular reliable and robust fixation of the add-on element on the rotor blade.

[0029] According to an embodiment a further section of the add-on element bottom side is directly arranged on the wind turbine rotor blade outer surface . In this "close contact" section no adhesive is provided between the baseplate and the outer surface of the rotor blade. Therefore, the baseplate and thus the add-on element are attached particularly close to the outer surface, thereby improving the aerodynamic effects of the add-on element and reducing adhesive material use.

[0030] According to an embodiment the further section of the bottom side is arranged upstream of at least one section of the bottom side. In particular, the further section is a front section of the bottom side. This is related to the downstream direction of operational wind flow. This contributes to the above advantages and effects, in particular a small or no step can be provided at the up-wind side.

[0031] According to an embodiment the further section comprises spacers or is formed as a spacer section. For example, the further section comprises spacers formed as ribs. It is referred to the above functions and advantages.

[0032] According to a further aspect, an aerodynamic add-on element for mounting to an outer surface of a wind turbine rotor blade, according to claim 15, is disclosed. The add-on element comprises a baseplate which has an upper side and a bottom side. The aerodynamic add-on element is configured to be mounted with the bottom side of the baseplate to an outer surface of the wind turbine rotor blade. The aerodynamic add-on element is configured such that - in a mounted state - the bottom side is inclined relative to outer surface of the wind turbine rotor blade along a downstream direction of an operational wind flow, such that a gap is formed between the bottom side and the outer surface in which a distance between the outer surface and the bottom side increases along the downstream direction, and such that adhesive can be provided in the gap to bond the aerodynamic add-on element to the outer surface of the wind turbine rotor blade.

[0033] The add-on element according to the further aspect enables the above mentioned effects, functions and advantages. Further advantages, features and further embodiments result from the following description of embodiment examples explained in connection with the figures. Identical, similar or similarly acting elements may be provided with the same reference signs in the figures.

[0034] In the figures: Figure 1 shows a schematic view of a wind turbine, Figure 2 shows a schematic view of a wind turbine rotor blade, Figures 3 to 5 show schematic views of a wind turbine rotor blade with an aerodynamic add-on element according to embodiments of the invention, and Figures 6 to 20 show aerodynamic add-on elements according to further embodiments of the invention in different views.

[0035] Figure 1 shows a schematic view of a wind turbine 100, which comprises a tower 102. The tower 102 is fixed to the ground by means of a foundation 104. At one end of the tower 102 opposite to the ground a nacelle 106 is rotatably mounted. The nacelle 106, for example, comprises a generator which is coupled to a rotor 108 via a rotor shaft (not shown). The rotor 108 comprises one or more (wind turbine) rotor blades 110, which are arranged on a rotor hub 112.

[0036] During operation, the rotor 108 is set in rotation by an air flow, for example wind. This rotational movement is transmitted to the generator via the rotor shaft and, if necessary, a gearbox. The generator converts the mechanical energy of the rotor 108 into electrical energy.

[0037] Figure 2 shows an exemplary rotor blade 110. The rotor blade 110 has the shape of a conventional rotor blade and has a rotor blade root area 114 facing the rotor hub 112. The rotor blade root area 114 typically has an essentially circular cross-section. The rotor blade root area 114 is followed by a transition area 116 and a profile area 118 of the rotor blade 110. The rotor blade 110 has a pressure side 122 and an opposite suction side 124 with respect to a longitudinal extension direction 120 (also main extension direction). The rotor blade 110 is essentially hollow inside.

[0038] In the rotor blade root area 114 a rotor blade root end 126 with a flange connection 128 is provided, by means of which the rotor blade 110 can be mechanically connected to a pitch bearing or an extender.

[0039] Figure 3 shows a schematic view of a rotor blade 110 according to an embodiment of the invention. The rotor blade 110 comprises an outer surface 130. The rotor blade 110 comprises an aerodynamic add-on element 132 (short: add-on element), which is a vortex generator. The aerodynamic add-on element 132 has a baseplate 134, which has an upper side 136 and a bottom side 138 opposing the upper side 136. The upper side 136, which not necessarily needs to be flat, comprises one or more turbulence generating features 140 such as vortex generators. With the bottom side 138, the aerodynamic add-on element 132 is mounted to the outer surface 130 of the rotor blade 110 in a mounting region 142 thereof.

[0040] Particularly, the add-on element 132, in particular its baseplate 134, is tilted with regard to the outer surface 130. The bottom side 138 is inclined with respect to the outer surface 130 (in the schematic view the whole bottom side is inclined), such that a gap 144 is formed between the bottom side 138 and the outer surface 130. A distance 146 between the bottom side 138 and the outer surface 130, i.e. a gap height, increases continuously along a downstream direction 148 of an operational wind flow (wind flow during operation of wind turbine 100 with such rotor blade 110). The gap 144 is filled with adhesive 150, wherein an adhesive thickness 152 correspondingly increases continuously along the direction 148. The adhesive 150 firmly bonds the add-on element 132 to the rotor blade 110.

[0041] The rotor blade 110 as described above enables the above mentioned functions and advantages. In particular, only a small step 154 is provided at an up-wind side 156 (or up-wind edge) of the add-on element 132. In other words, a distance between the upper side 136 of the add-on element 132 and the outer surface 130 of the rotor blade 110 is smaller at the up-wind side 156 than at the down-wind side 158 (or down-wind edge) of the add-on element 132. For example, the height of the gap 146 / adhesive thickness 152 increases from 0,2 mm to 0,7 mm.

[0042] A structural relevant thickness 162 of the adhesive 150 is reached at a certain distance 160 from the up-wind side 156. Such structural relevant thickness 162 is for example 0,5 mm.

[0043] In other embodiments a gradual transition between the outer surface 130 of the rotor blade 110 and the add-on element 132 at the up-wind side 156 is provided, i.e. there is essentially no step 154.

[0044] According to the embodiment of figure 3, the adhesive 150 has a triangular shape. In other words, the gap 144 is triangularly formed.

[0045] Figures 4 and 5 show rotor blades 110 according to further embodiments of the invention, which are similar to the embodiment shown in figure 3. Thus, we refer to the above description of features with regard to the reference signs (which are not repeatedly shown in figure 4).

[0046] According to figure 4, the only difference to the embodiment of figure 3 is the design of the gap 140 and thus the adhesive 150 applied therein, wherein a trapezoidal shape is provided.

[0047] According to figure 5, the baseplate 134 differs from the above embodiments in that the bottom side 138 (or baseplate 134) comprises a first section 164 and a second section 166 along the downstream direction 148. The second section 166 is inclined similar to the above described embodiments, such that the adhesive 150 has an increasing thickness 152 corresponding to the gap 144. The first section 164 is arranged upstream of the second section 166 and is in direct contact with the outer surface 130 of the rotor blade 110.

[0048] The bottom side 138 of the above embodiments, including the first and second sections 164, 166, may comprise spacers or the like, being in direct contact with the outer surface 130, which will be described in the following with regard to further embodiments shown in the figures 6 to 20.

[0049] Figure 6 to 8 refer to an add-on element 132 according to an embodiment of the invention. Figure 6 shows a perspective top view of the add-on element 132, figure 7 shows a perspective bottom view of the add-on element 132 and figure 8 shows a side view of the add-on element 132. The add-on element 132 comprises a baseplate 134 with an upper side 136 and a bottom side 138. On the upper side 136, several turbulence generating features 140 are provided.

[0050] To ensure the inclination of the bottom side 138 as described above, the bottom side 138 comprises spacers 168. As can be seen in figure 7, the spacers 168 are formed cylindrically.

[0051] The spacers 168 are in direct contact with the outer surface 130 of the rotor blade 110 and comprise different sizes in order that the baseplate 134, in particular the bottom side 138, is inclined with respect to the outer surface 130 of the rotor blade 110. Similar to the above description, a suitable gap 144 is formed, in which the adhesive 150 can be provided. Figure 8 shows a respective inclination angle α.

[0052] Figures 9 to 11 show a similar embodiment, with the only difference to the embodiment of figures 6 to 8, that the spacers 168 are line-shape, running in the downstream direction 148. We refer to the above description of further details.

[0053] Figures 12 to 14 show a similar embodiment. The embodiment differs from the above embodiments according to figures 6 to 11, that the bottom side 138 comprises a first section 164 and a second section 166, e.g. as described with regard to figure 5. In the first section, spacers 168 are provided, which are line-shaped and running in the downstream direction 148. The second section 166 is form such that a direct contact to the outer surface 130 of the blade 110 is established. The second section 166 is made of full material and can also be seen as front spacer region. This design allows the structural adhesive to exhibit a structurally sufficient thickness from the start and reduces the risk of crack initiation. We refer to the above description of further details.

[0054] Figures 15 to 17 show another embodiment. In difference to the embodiment of the figures 12 to 14, the second section 166 comprises spacers 168 formed as ribs, whereas the first section 164 does not comprise any spacers. The spacers 168 of the second section 166 (front section) serve for constant material thickness in the whole add-on element 132, which is important for high pressure injection moulding.

[0055] Figures 18 to 20 show a further embodiment, similar to the above embodiments. As difference, at the bottom side 138, the baseplate 134 comprises webs 170, running traverse to the downstream direction 148. The webs 170 act as spacers functioning as described above. The spacers 168 are again in direct contact with the outer surface 130 of the blade 110 and define the gap 144 to be filled with adhesive for bonding the add-on element 132 to the blade 110. Along the downstream direction 148, in the present shown example, the gap 144 has a first height h1 of 0,2 mm at the up-wind side 156, a second height h2 of 0,5 mm in approximately the middle of the add-on element 132, and a third height h3 of 0,7 mm at the down-wind side 158. In the first gap section 172 a rather small gap for adhesive 150 to be applied is provided, in order to achieve good aerodynamic properties resulting from the wind flow in downstream direction. The first gap section 172 for example is not especially provided for structural means. The second gap section 174 is designed for structural bonding, wherein a sufficient height of the gap is provided for adhesive to be applied.

[0056] The middle web 170 of the three webs 170 separates the gap 144 into a first gap section 172 and a second gap section 174, such that adhesive 150, which is provided in the gap sections 172, 174, is divided into the first and second gap sections 172, 174, wherein the adhesive in the first gap section 172 has no contact to the adhesive in the second gap section 174. Thus, the middle web 170 serves as a crack stopper, as explained above.

[0057] Features of the different embodiments can be mixed, if necessary, e.g., the embodiment according to the figures 9 to 11 can additionally be provided with a rib in the middle of the bottom side 138 running traverse to the downstream direction 148.Reference signs

[0058] 100wind turbine 102tower 104foundation 106nacelle 108rotor 110rotor blade 112rotor hub 114rotor blade root area 116transition area 118profile area 120longitudinal extension direction 122pressure side 124suction side 126rotor blade root end 128flange connection 130outer surface 132aerodynamic add-on element 134baseplate 136upper side 138bottom side 140turbulence generating feature 142mounting region 144gap 146distance 148downstream direction 150adhesive 152adhesive thickness 154step 156up-wind side 158down-wind side 160distance 162structural relevant thickness 164first section 166second section 168spacers 170web 172first gap section 174second gap section h1first height h2second height h3third height αinclination angle

Claims

1. Wind turbine rotor blade (110), comprising an aerodynamic add-on element (132) comprising a baseplate (134), the baseplate (134) having an upper side (136) and a bottom side (138), wherein the aerodynamic add-on element (132) is mounted with the bottom side (138) of the baseplate (134) to an outer surface (130) of the wind turbine rotor blade (110), the whole bottom side (138) is inclined relative to the outer surface (130) of the wind turbine rotor blade (110) along a downstream direction (148) of an operational wind flow, such that a gap (144) is formed between the bottom side (138) and the outer surface (130) in which a distance (146) between the outer surface (130) and the bottom side (138) increases along the downstream direction (148), and adhesive (150) is provided in the gap (144) to bond the aerodynamic add-on element (132) to the outer surface (130) of the wind turbine rotor blade (110).

2. Wind turbine rotor blade (110) according to claim 1, wherein the baseplate (134) is tilted relative to the outer surface (130) of the wind turbine rotor blade (110).

3. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein a height of the gap (144) increases along the downstream direction (148).

4. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein a height of the gap (144) increases from 0,1 mm, preferably 0,2 mm, to 1 mm, preferably 0,7 mm, 0,6 mm or more preferably 0,5 mm.

5. Wind turbine rotor blade (110) according to anyone of the preceding claims, comprising a gradual transition between the outer surface (130) of the wind turbine rotor blade (110) and the aerodynamic add-on element (132) at the up-wind side (156).

6. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein a distance between the upper side (136) of the aerodynamic add-on element (132) and the wind turbine rotor blade (110) at the up-wind side (156) is smaller than at the down-wind side (158) of the aerodynamic add-on element (132).

7. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein a structural relevant thickness (162) of the adhesive (150) in the gap (144) to bond the add-on element (132) to the blade, e.g. 0,5 mm, is reached at a certain distance (160) from the up-wind side (156) of the adhesive (150) in the gap (144) with regard to the downstream direction (148).

8. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein the at least one section of the bottom side (138) comprises one or more spacers (168), the spacers (168) being in direct contact with the outer surface (130) of the wind turbine blade.

9. Wind turbine rotor blade (110) according to claim 8, wherein the spacers (168) are formed as line shaped spacers, cylindrical spacers or point spacers.

10. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein the at least one section of the bottom side (138) comprises a web running traverse to the operational wind flow, the web being in direct contact with the outer surface (130) of the wind turbine blade, wherein the web separates the gap (144) into a first gap section (172) and a second gap section (174), such that the adhesive (150) is divided into the first and second gap sections (172, 174).

11. Wind turbine rotor blade (110) according to anyone of the preceding claims, wherein a further section of the bottom side (138) of the add-on element (132) is directly arranged on the outer surface (130) of the wind turbine rotor blade (110).

12. Wind turbine rotor blade (110) according to claim 11, wherein the further section of the bottom side (138) is arranged upstream of the at least one section of the bottom side (138), in particular the further section is a front section of the bottom side (138).

13. Wind turbine rotor blade (110) according to claim 11 or 12, wherein the further section comprises spacers (168) or is formed as a spacer section.

14. Wind turbine rotor blade (110) according to claim 11, wherein the further section comprise spacers (168) formed as ribs.

15. Aerodynamic add-on element (132) for mounting to an outer surface (130) of a wind turbine rotor blade (110) according to anyone of the preceding claims, comprising a baseplate (134) which has an upper side (136) and a bottom side (138), wherein the aerodynamic add-on element (132) is configured to be mounted with the bottom side (138) of the baseplate (134) to an outer surface (130) of the wind turbine rotor blade (110), the aerodynamic add-on element (132) is configured such that - in a mounted state - the whole bottom side (138) is inclined relative to outer surface (130) of the wind turbine rotor blade (110) along a downstream direction (148) of an operational wind flow, such that a gap (144) is formed between the bottom side (138)and the outer surface (130) in which a distance (146) between the outer surface (130) and the bottom side (138) increases along the downstream direction (148), and such that adhesive (150) can be provided in the gap (144) to bond the aerodynamic add-on element (132) to the outer surface (130) of the wind turbine rotor blade (110).