Device for reducing vortex-induced vibrations of a body around which fluid flows

Abstract

The invention relates to a device for reducing vortex-induced vibrations of a body (2) around which fluid flows, which device comprises a first frame-shaped fastening element (3) which can be placed around the body (2), around which fluid flows, and can be fastened to it, and which device comprises a second frame-shaped fastening element (4) which can be placed around the body (2), around which fluid flows, and can be fastened to it, wherein a plurality of slats (5) extend between the fastening elements (3, 4), which slats are spaced apart in the peripheral direction of the frame-shaped fastening elements (3, 4), in particular are spaced apart equidistantly among one another.

Description

[0001] Device for reducing vortex-induced vibrations of a fluid-flowing body

[0002] The invention relates to a device for reducing vortex-induced vibrations of a body surrounded by fluid.

[0003] The problem that can occur in fluid flow around bodies, especially on the downstream side, is known in the art. Vortices can form in the flowing fluid near the surface of the body. Such vortices can exert forces on the body that can cause it to vibrate. This is particularly critical if they excite the body's natural frequencies.

[0004] The problem is particularly significant for bodies with a circular cross-section perpendicular to their longitudinal direction, which are subject to flow perpendicular to the longitudinal direction, since vortices are always generated regardless of the direction of the flow. This occurs, for example, in masts or towers, such as the towers of wind turbines. This problem can also occur with cables or ducts, or generally with bodies that are cylindrical, preferably circularly cylindrical, at least in some sections. Wind turbine towers are particularly susceptible to excitation of the natural frequency before the nacelle is mounted on the tower.

[0005] Against this background, it is an object of the invention to provide a device that can be attached to bodies around which fluid flows, preferably air or water flows, in particular to bodies that are at least partially cylindrical or at least partially frustoconical, preferably with a circular cross-section, in order to reduce vibration excitation. Such a device should preferably be suitable for only temporary attachment to the body, e.g., in the case of wind turbines, to the tower, in particular to its upper free end region, especially as long as no nacelle has yet been installed.

[0006] This object is achieved according to the invention in that the device comprises a first frame-shaped fastening element that can be placed around the body around which fluid flows and fastened thereto, and a second frame-shaped fastening element that can be placed around the body around which fluid flows and fastened thereto, wherein a plurality of slats extend between the fastening elements, which are spaced apart in the circumferential direction of the frame-shaped fastening elements, in particular are equidistant from one another. The slats extending between the fastening elements are preferably fastened to the fastening elements.

[0007] "Fastened" is preferably understood to mean that the device and its components are immovable and / or stationary relative to the body around which fluid flows. In particular, after fastening, the two fastening elements are thus immovably (i.e., preferably stationary and non-rotatably) attached to the body around which fluid flows. Further preferably, the slats are arranged immovably (i.e., preferably stationary and non-rotatably) relative to the fastening elements and thus preferably also relative to the body around which fluid flows.

[0008] A frame-shaped fastening element is understood to be an element that completely surrounds an inner free cross-section in which the aforementioned body can be accommodated. The shape of the inner free cross-section is not limited, and thus neither is the shape of the frame-shaped fastening element.

[0009] In one possible preferred embodiment, the first and second fastening elements can have the same internal free cross-section. In another preferred embodiment, the first and second fastening elements can have different internal free cross-sections in order to be fastened to tapered structures, in particular structures that are at least partially conical or have a conical segment shape, e.g., towers that are at least partially conical or have a conical segment shape.

[0010] Preferably, the inner free cross-section of each fastening element is circular, e.g., if the device is to be attached to wind turbine towers that are at least partially circularly cylindrical. In such a case, each frame-shaped fastening element is an annular fastening element.

[0011] In particular, the first and second frame-shaped fastening elements are spaced apart from one another in a direction of extension of the body, preferably its longitudinal direction, in particular with the said slats extending in the same direction of spacing. The fastening elements are connected to one another by the slats.

[0012] By means of such a device, after its attachment to a body surrounded by fluid flow, e.g. after attachment to the upper end region of the tower of a wind turbine, vortex formation can be significantly reduced, preferably avoided, since the slats disrupt the flow around the body.

[0013] It is further preferably provided that the slats have a sufficiently high flexural rigidity between their fastening points on the fastening elements, in particular in order not to vibrate themselves.

[0014] Preferably, the bending stiffness of a lamella is greater than E x I / (D / 2) 3 = 50 GPa / m 3 , where E is the elastic modulus of the material used for the lamella, I is the area moment of inertia, and D is the diameter of the body surrounded by the device. In a preferred embodiment, sufficient flexural rigidity can also be achieved by interconnecting at least some, preferably all, of the lamellae in the circumferential direction around the body, or around a central axis running through the two frame-shaped fastening elements, preferably in a region between the fastening elements. The connections between the lamellae are preferably contact-free with the surface of the surrounding body.

[0015] In another preferred embodiment, sufficient rigidity can also be achieved by the lamellae being formed so that they increase in cross-section starting from the fastening areas on the fastening elements in the direction of a central area.

[0016] In another preferred embodiment, sufficient rigidity can also be achieved in that the cross section of a lamella (in particular for each lamella) has the largest cross-sectional dimension in a direction perpendicular to the surface of the surrounding body, in particular radially to a center axis through the frame-shaped fastening elements.

[0017] In yet another preferred embodiment, sufficient rigidity can also be achieved by forming a lamella from a fiber composite component.

[0018] In yet another preferred embodiment, sufficient rigidity can also be achieved simply by having a slat as a self-supporting and / or inherently stable component. This preferably means that the slats in the device keep the spaced fastening elements at a distance, in particular at a fixed, predetermined distance.

[0019] Preferably, each lamella can be designed as a rod. Such a rod preferably has a profile shape made up of webs in cross section; in particular, a rod can have a hollow profile shape. Regardless of whether a lamella is hollow or solid, the invention preferably provides that each lamella forms a rod with edges, preferably at least three edges, in particular with four edges, which run in the longitudinal direction of the rod. The edges form transitions between the adjacent surfaces of the rod, at which transitions the flow separates when exposed to the airflow. As a result of the design with edges, a lamella has, in cross-section perpendicular to its longitudinal extent, at least substantially an n-cornered shape, preferably with n>=3, in particular with n=4.

[0020] The edges of the fins provide a defined flow separation point, so that the flow always separates at the same points, regardless of the structure's size (diameter) and flow velocity. This prevents the so-called Karman vortex street and the associated harmonic fluctuation of flow forces (especially the force perpendicular to the flow direction). As a result, resonant oscillations are not induced. Due to the fixed distribution of the fins across the circumference, this passive flow control is equally effective for all flow directions.

[0021] Relative to a central longitudinal axis passing through the device, the lamellae preferably have a greater extension in the radial direction than in the circumferential direction around the central longitudinal axis, in particular which increases the flexural rigidity.

[0022] It is further preferably provided that of the opposite ends of a lamella (preferably of each lamella) in the radial direction (e.g. relative to a central longitudinal axis passing through the fastening elements), the radially outer end is sharper than the radially inner end. For example, this can be achieved by a respective lamella being narrower at the radially outer end in the circumferential direction around a central longitudinal axis passing through the fastening elements than at the radially inner end. For example, this is the case when the cross-section of a lamella (viewed perpendicular to its longitudinal direction) tapers radially outwards, e.g.This is the case with a triangular cross-section of the lamella if two of the three corners point towards the central longitudinal axis and one of the three corners points away from the central longitudinal axis or if, in the case of a trapezoidal cross-section, the shorter of two trapezoidal sides of different lengths is located radially outwards.

[0023] The aforementioned designs of a lamella, in particular to achieve sufficient rigidity, can be designed alternatively or in any combination.

[0024] By attaching a plurality of fins, particularly those distributed equidistantly, along the circumferential direction of the fastening elements, it is further achieved that at least a substantial reduction in turbulence can be achieved regardless of the direction from which the body is subjected to air flow, particularly if the body has a circular cross-section. Preferably, at least four, preferably at least six, and more preferably exactly six fins are attached to the fastening elements, distributed in the circumferential direction.

[0025] In a preferred embodiment, it is provided that each fastening element is divided into at least two, preferably exactly two sub-elements which are detachable from one another and which are connectable to one another, wherein a clamping mechanism is formed between the sub-elements, with which the inner free cross-section surrounded by the fastening element can be reduced.

[0026] The fact that the sub-elements are detachable from one another does not only mean that they can be separated into at least two sub-elements, but also that a rigid connection between the sub-elements is eliminated, but the sub-elements are still movably connected to one another, e.g. by a hinged connection. Preferably, in all embodiments of the detachability, the closed frame is open in the released state in order to be able to place the fastening element around a body. This makes it possible to open the frame-shaped, preferably ring-shaped fastening element, e.g. to disassemble it into several parts and place it around a body, e.g. so that it remains on it temporarily, and to remove it from the body again after a period of use.

[0027] The clamping mechanism allows the respective fastening element to be clamped to the surface of the body.

[0028] In this construction, the entire device is preferably multi-part, in particular two-part, wherein each of several, preferably two, sub-elements of a fastening element is connected to another of several, preferably two, sub-elements of the other fastening element via a partial number of all lamellae. Preferably, each sub-element of a fastening element is partially annular, in particular semi-annular.

[0029] A preferred embodiment provides that each fastening element has, at least in some areas, preferably everywhere, a protective element, in particular made of an elastomer, on a surface area facing the surface of the body to be surrounded, which protective element has a fastening surface with which the surface of the body can be contacted.

[0030] This can protect the surface of the body, e.g. if the remaining areas of the fastening elements are made of metal, so that no damage remains in the surface after removal of the device.

[0031] If the fastening element comprises such a protective element, then the surface of the protective element facing the surface of the body forms the fastening surface of the fastening element, with which the fastening element can be fastened to the surface of the body. Otherwise, any other surface of the fastening element facing the surface of the body to be enclosed can also form the fastening surface.

[0032] In a further preferred embodiment, when mounted on the body, the surface areas of the slats facing the body's surface are spaced apart from the body's surface. This prevents damage to the body's surface caused by possible vibrations of the slats caused by the flow of the fluid.

[0033] This can be achieved, for example, in that the surface areas of the slats facing the surface of the body are spaced from the fastening surface of the fastening elements which comes into contact with the surface of the body in a direction perpendicular to the direction of the spacing of the fastening elements, in particular in a direction perpendicular to the surface of the body or the fastening surface, in particular in a radial direction of a body with a circular cross-section.

[0034] Preferably, the aforementioned distance between the surface areas of the slats facing the surface of the body and the body surface or between the surface areas of the slats facing the surface of the body and the aforementioned fastening surface of the fastening elements is less than 5%, more preferably less than 3% of the cross-sectional dimension of the inner free cross-section of the fastening elements.

[0035] For bodies with a circular cross-section, the cross-sectional dimension corresponds to the diameter of the body or the diameter of the inner free circular cross-section of the respective fastening element.

[0036] Since bodies with such circular cross-sections form the preferred field of application of the invention, the fastening elements are preferably designed such that they each surround a circular inner free cross-section.

[0037] In particular, this makes it possible to attach the device to bodies with a circular cross-section, e.g. masts, cables, towers, e.g.

[0038] Wind turbine towers.

[0039] In general, when applying the invention, the bodies can have a gas flowing around them, e.g. air, as in wind turbines, for example, but can also have a liquid flowing around them, e.g. water in the case of bodies located under water, e.g. cables or ducts. It is further preferably provided that the outer edges of the slats pointing away from the fastening elements and / or the body surface have a distance from the fastening surface of the fastening elements with which the fastening elements can be fastened to the surface of a body, or from the body surface, which distance corresponds to 3% to 7%, preferably 5% of the cross-sectional dimension of the inner free cross-section, in particular diameter, of the fastening elements. This ensures that the arrangement of the slats is essentially limited to the area above the surface of bodies where vortices can form.

[0040] Furthermore, it is preferably provided that the distance between the fastening elements is 100% to 200% of the inner free cross-section, in particular diameter, of the fastening elements.

[0041] In particular, all designs can be designed so that the slats end at the fastening elements. However, another design can also provide for the slats to extend beyond the fastening elements in the direction of the slats' extension. In this case, the slats are longer than the distance between the fastening elements.

[0042] Preferably, the fastening elements and the slats are connected to one another in a materially bonded manner, in particular by welded elements. Preferably, the slats and the fastening elements, apart from a protective element mentioned, are made of metal. In particular, if the slats and fastening elements are made of different materials, it can preferably be provided that the slats are connected to the fastening elements in a force-fitting and / or form-fitting manner, e.g., by screwing.

[0043] The slats are further preferably designed in cross-section perpendicular to their extension as a profile with at least one web, in particular I-shaped, L-shaped, or T-shaped, preferably with one web oriented perpendicular to the fastening surface and / or radially to the center axis through the fastening elements. For a particularly stable design of the fastening elements, it is preferably provided that each fastening element has two mutually perpendicular webs in cross-section perpendicular to its circumferential direction, in particular between which stiffening ribs are arranged at several, in particular equidistant, circumferential positions.

[0044] The invention is explained below with reference to the figures and an embodiment.

[0045] Figure 1 shows in several different views and detailed representations a device 1 for reducing vortex-induced vibrations on a body 2, such as a partially circular cylindrical body 2, for example a tower of a wind turbine.

[0046] The device comprises an upper fastening element 3 and a lower fastening element 4. Both annularly surround an inner free circular cross-section corresponding to the outer diameter of the body 2.

[0047] In the detailed views of Figure 1, it can be seen that the upper fastening element 3 is supported on the surface of the body 2 by means of a protective element 3a, e.g., made of an elastomer, e.g., rubber. This also applies to the lower fastening element 4.

[0048] Between the fastening elements 3, 4 extend slats 5, which ensure that the air flow around the body 2 is disturbed in such a way that no vortices can form, or at least the formation of vortices is reduced.

[0049] Such a lamella is preferably formed as a solid or hollow rod, more preferably with an at least substantially n-cornered cross-section, resulting in n edges extending in the longitudinal direction of the lamella, at which the separation of a flow can be effected. n is preferably >=3. In particular, n=4. More preferably, a lamella 5 is thinner, viewed in the circumferential direction around the body 2, than it is thick in the direction radial to the body, in particular resulting in high flexural rigidity in the direction toward the body.

[0050] Figure 1 further shows in the detailed representation using the example of the upper fastening element 3, which also applies to the lower one, that the respective fastening element 3, 4 is divided into two parts and that both parts can be connected by means of two opposing clamping devices 6 and clamped to the body surface.

[0051] The respective clamping device 6 is essentially formed by two flange plates at the ends of the two parts of each fastening element 3, 4, which can be tightened toward each other by screws. However, this example does not limit the invention shown.

[0052] Due to the fastening, the device and its components are arranged in a fixed and immovable manner on the body 2.

[0053] The lower detailed illustration further shows that, viewed in cross-section perpendicular to the circumferential direction, the annular fastening element 3, 4 each has two webs oriented perpendicular to each other, which are connected by stiffening ribs 7. One of the webs, which, viewed in cross-section perpendicular to the circumferential direction, lies parallel to the surface of the body 2, has the protective element 3a on its side facing the body 2.

[0054] Figure 2 additionally shows that each fastening element 3, 4 is divided at the location of the clamping device 6 into two semi-annular sub-elements 3-1 and 3-2 or 4-1 and 4-2, wherein the sub-elements 3-1 and 4-1 are connected by a partial number of all slats 5. The same applies to the sub-elements 3-2 and 4-2 not shown. This results in the entire device 1 being divided into two parts. In this example, the sub-elements are completely separable from one another. It can also be provided that they remain movably connected by an articulated connection after the clamping device is released. Figures 3 and 4 show, as a detail of Figure 1, possible cross-sections 5' of a respective slat 5 in a dashed view through the fastening element 3.

[0055] Figure 3 shows an embodiment in which the cross section 5' is quadrangular, in particular rectangular, and Figure 4 shows an embodiment in which the cross section 5' is quadrangular, in particular trapezoidal, wherein the narrower end of the cross section 5' is located radially outward with respect to a central longitudinal axis 8 passing through the device, which is indicated by dashed lines in Figure 1.

[0056] The cross-section 5' of the lamella 5, viewed perpendicular to its direction of extension, which here is preferably parallel to the central longitudinal axis 8, is thus tapered in the radially outward direction, whereby the radially outer end of the lamella 5 is also sharper than the radially inner end of the lamella 5.

Claims

Patent claims 1 . Device for reducing vortex-induced vibrations of a body (2) around which fluid flows, characterized in that it comprises a. a first frame-shaped fastening element (3) which can be placed around the body (2) around which fluid flows and fastened thereto, and b. a second frame-shaped fastening element (4) which can be placed around the body (2) around which fluid flows and fastened thereto, c. wherein a plurality of slats (5) extend between the fastening elements (3, 4), which are spaced apart in the circumferential direction of the frame-shaped fastening elements (3, 4), in particular are equidistant from one another.

2. Device according to claim 1, characterized in that each fastening element (3, 4) is divided into at least two, preferably exactly two sub-elements (3-1, 3-2 / 4-1, 4-2) which are detachable from one another and which can be connected to one another, wherein a clamping mechanism (6) is formed between the sub-elements (3-1, 3-2 / 4-1, 4-2), with which the inner free cross-section surrounded by the respective fastening element (3, 4) can be reduced.

3. Device according to one of the preceding claims, characterized in that each fastening element (3, 4) has, at least in some areas, preferably everywhere, a protective element (3a), in particular made of an elastomer, on a surface area facing the surface of the body (2), which protective element has a fastening surface with which the surface of the body (2) can be contacted.

4. Device according to one of the preceding claims, characterized in that in a state mounted on the body (2) the Surface areas of the lamellae (5) facing the surface of the body (2) are spaced from the surface of the body (2).

5. Device according to one of the preceding claims, characterized in that the fastening elements (3, 4) each surround a circular inner free cross-section.

6. Device according to one of the preceding claims, characterized in that the outer edges of the slats (5) pointing away from the fastening elements (3, 4) have a distance from the fastening surface of the fastening elements (3, 4) with which the fastening elements (3, 4) can be fastened to the surface of a body (2) which corresponds to 3% to 7%, preferably 5% of the cross-sectional dimension of the inner free cross-section, in particular diameter, of the fastening elements (3, 4).

7. Device according to one of the preceding claims, characterized in that the distance between the fastening elements (3, 4) is 100% to 200% of the inner free cross-section, in particular diameter, of the fastening elements (3, 4).

8. Device according to one of the preceding claims, characterized in that the fastening elements (3, 4) and the slats (5) are connected to one another in a materially bonded manner, in particular are welded elements.

9. Device according to one of the preceding claims, characterized in that the slats (5), preferably the slats (5) designed as a rod, are designed in cross-section perpendicular to their extension as a profile with at least one web, in particular I-shaped, L-shaped or T-shaped, preferably with one web oriented perpendicular to the fastening surface.

10. Device according to one of the preceding claims, characterized in that a respective slat (5), preferably the slat (5) designed as a rod, has in the longitudinal direction of the slat (5) extending edges, in particular in cross-section perpendicular to the longitudinal direction is n-angular, preferably with n>=3.

11. Device according to one of the preceding claims, characterized in that a respective lamella (5), preferably the lamella (5) designed as a rod, has a greater extension in the radial direction than in the circumferential direction with respect to a central longitudinal axis (8) passing through the device.

12. Device according to one of the preceding claims, characterized in that in a respective lamella (5), preferably a lamella (5) designed as a rod, of the ends of the lamella lying opposite one another in the radial direction, the radially outer end is designed to be sharper than the radially inner end, in particular that the cross section (5') of the lamella (5) tapers radially outwards.

13. Device according to one of the preceding claims, characterized in that each fastening element (3, 4) has, in cross-section perpendicular to its circumferential direction, two mutually perpendicular webs, in particular between which stiffening ribs (7) are arranged at several, in particular equidistant, circumferential positions.

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