Device for reducing vortex-induced vibrations of a fluid-enclosed body

Abstract

The invention relates to a device for reducing vortex-induced vibrations of a fluid-enclosed body (2), comprising a first frame-shaped fastening element (3) that can be placed around the fluid-enclosed body (2) and attached to it, and comprising a second frame-shaped fastening element (4) that can be placed around the fluid-enclosed body (2) and attached to it, wherein several lamellae (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 equidistantly spaced apart from each other.

Description

[0001] The invention relates to a device for reducing vortex-induced vibrations of a body surrounded by fluid.

[0002] In the prior art, it is known that in fluid-enclosed bodies, especially on the downstream side, vortices can form in the flowing fluid near the surface of the body. Such vortices can exert forces on the body, which can cause it to vibrate. This is particularly critical if it excites the body's natural frequencies.

[0003] The problem is particularly significant for bodies with a circular cross-section perpendicular to their longitudinal direction, as vortices are always generated regardless of the direction of the flow. This occurs, for example, with 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 at least partially cylindrical, preferably circularly cylindrical. Wind turbine towers, in particular, are susceptible to excitation of their natural frequency before the nacelle is installed, when the tower is not yet loaded by the nacelle.

[0004] Against this background, an object of the invention is to provide a device that can be attached to bodies exposed to fluid flow, preferably air flow, in particular to at least partially cylindrical bodies with a circular cross-section, in order to reduce vibration excitation. Preferably, such a device should be suitable for being attached to the body only temporarily, e.g., on the tower of a wind turbine, in particular at its upper free end region, especially until a nacelle has been mounted.

[0005] This problem is solved according to the invention by the device comprising a first frame-shaped fastening element that can be placed around the fluid-enclosed body and attached to it, and a second frame-shaped fastening element that can be placed around the fluid-enclosed body and attached to it, wherein several lamellae extend between the fastening elements, which are spaced apart in the circumferential direction of the frame-shaped fastening elements, in particular equidistantly spaced apart from each other.

[0006] 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 restricted, and therefore neither is the shape of the frame-shaped fastening element.

[0007] In a possible preferred embodiment, the first and second fastening elements can have the same internal free cross-section.

[0008] The first and second fastening elements may, in another preferred embodiment, have different internal free cross-sections in order to be attached to tapered, in particular conical structures, e.g. conical towers.

[0009] 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 circular-cylindrical. In such a case, each frame-shaped fastening element is an annular fastening element.

[0010] In particular, the first and second frame-shaped fastening elements are spaced apart from each other in one direction of extension of the body, preferably its longitudinal direction, and in particular the aforementioned lamellae extend in the same direction of the spacing. The fastening elements are connected to each other by the lamellae.

[0011] Such a device, when attached to a fluid-enclosed body, e.g., when attached to the upper end of the tower of a wind turbine, can significantly reduce, or preferably prevent, vortex formation, as the lamellae disrupt the flow around the body.

[0012] It is further preferred that the lamellae have a sufficiently high bending stiffness between their attachment points on the fastening elements, in particular to avoid vibrating themselves.

[0013] Preferably, the bending stiffness of a lamella is greater than E × I / (D / 2) 3 = 50 GPa / m 3 , where E is the modulus of elasticity 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.

[0014] In a preferred embodiment, sufficient bending stiffness can also be achieved by connecting at least some, preferably all, of the lamellae to each other circumferentially around the body or around a central axis running through the two frame-shaped fastening elements. The connections between the lamellae are non-contacting with the surface of the surrounding body.

[0015] In another preferred embodiment, sufficient stiffness can also be achieved by the fact that the lamellae are increasingly developed in cross-section from the fastening areas on the fastening elements towards a central area.

[0016] In another preferred embodiment, sufficient stiffness can also be achieved by ensuring that the cross-section of a lamella has the largest cross-sectional dimension in a direction perpendicular to the surface of the surrounding body, in particular radial to a central axis through the frame-shaped fastening elements.

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

[0018] In yet another preferred embodiment, sufficient stiffness can also be achieved by a lamella being a self-supporting and / or inherently stable component. This preferably means that the lamellae in the device keep the spaced-apart 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 cross-sectional profile consisting of webs; in particular, a rod can have a hollow profile.

[0020] The aforementioned training measures for achieving sufficient stiffness can be implemented alternatively or in any combination.

[0021] By attaching several, and in particular equidistantly distributed, lamellae along the circumferential direction of the fastening elements, it is further achieved that at least a substantial reduction in vortices can be realized, regardless of the direction from which the body is approached by the flow, especially if the body has a circular cross-section. Preferably, at least four, preferably at least six, and more preferably exactly six lamellae are attached to the fastening elements, distributed circumferentially.

[0022] In a preferred embodiment, each fastening element is divided into at least two, preferably exactly two, sub-elements which are detachable from each other and which are connectable to each other, wherein a clamping mechanism is formed between the sub-elements with which the inner free cross-section of the area surrounded by the fastening element can be reduced.

[0023] The term "releasable" refers not only to the ability to separate the components into at least two, but also to the removal of any rigid connection between them, while the components remain movably connected, for example, by a hinge. Preferably, in all embodiments of the release mechanism, the closed frame is open in the released state to allow the fastening element to be placed around a body.

[0024] 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 temporarily attached to it, and to remove it from the body again after a period of use.

[0025] The clamping mechanism allows the respective fastening element to be clamped to the surface of the body.

[0026] In this design, 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 fraction of all lamellae. Preferably, each sub-element of a fastening element is partially annular, in particular semi-annular.

[0027] A preferred embodiment provides that each fastening element has, at least partially, 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 has a fastening surface with which the surface of the body can be contacted.

[0028] This protects the surface of the body, for example if other areas of the fasteners are made of metal, so that no damage remains on the surface after the device is removed.

[0029] If the fastener includes such a protective element, then the surface of the protective element facing the surface of the body forms the fastening surface of the fastener, by which it can be attached to the surface of the body. Otherwise, any other surface of the fastener facing the surface of the body to be enclosed can also form the fastening surface.

[0030] In a further preferred embodiment, it is provided that, in a state mounted on the body, the surface areas of the lamellae facing the surface of the body are spaced apart from the surface of the body.

[0031] This prevents damage to the surface of the body caused by any vibrations of the lamellae generated by the flow of fluid.

[0032] This can be achieved, for example, by spacing the surface areas of the lamellae facing the surface of the body apart from the fastening surface of the fastening elements that 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, and in particular in a radial direction of a body with a circular cross-section.

[0033] Preferably, the aforementioned distance between the surface areas of the lamellae facing the surface of the body and the body surface, or between the surface areas of the lamellae facing the surface of the body and the aforementioned fastening surface of the fastening elements, is less than 5%, and more preferably less than 3%, of the cross-sectional dimension of the inner free cross-section of the fastening elements.

[0034] 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.

[0035] Since bodies with such circular cross-sections constitute the preferred application area of ​​the invention, the fastening elements are preferably designed such that they each surround a circular inner free cross-section.

[0036] In particular, this makes it possible to attach the device to bodies with a circular cross-section, e.g., to masts, cables, towers, e.g., towers of wind turbines.

[0037] In general, when applying the invention, the bodies can be surrounded by gas, e.g., air, as in wind turbines, but also by a liquid, e.g., water in the case of underwater bodies, e.g., cables or channels.

[0038] It is further preferably provided that the outer edges of the lamellae, 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 attached to the surface of a body, or from the body surface, which corresponds to a distance of 3% to 7%, preferably 5%, of the cross-sectional dimension of the inner free cross-section, in particular the diameter, of the fastening elements. This ensures that the arrangement of the lamellae is essentially limited to the area above the surface of bodies where vortices can form.

[0039] 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.

[0040] In particular, all versions may stipulate that the slats terminate at the fastening elements. However, another version may also provide that the slats extend beyond the fastening elements in the direction of their extension. In this case, the slats are longer than the distance between the fastening elements.

[0041] Preferably, the fastening elements and the louvers are materially bonded to one another, in particular by welded elements. Preferably, the louvers and the fastening elements, apart from a protective element mentioned above, are made of metal. In particular, if the louvers and fastening elements are made of different materials, it is preferable that the louvers are connected to the fastening elements by force-fit and / or form-fit, e.g., by screwing.

[0042] The lamellae are further preferably designed in cross-section perpendicular to their extent as a profile with at least one web, in particular I-shaped, L-shaped or T-shaped, preferably wherein a web is oriented perpendicular to the fastening surface and / or radially to the central axis through the fastening elements.

[0043] 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 exemplary embodiment.

[0045] The Fig. 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 sectionally circular cylindrical body 2, for example a tower of a wind turbine.

[0046] The device has an upper fastening element 3 and a lower fastening element 4. Both surround an inner free circular cross-section in an annular manner, which corresponds to the outer diameter of the body 2.

[0047] In the detailed views of the Fig. Figure 1 shows 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 lamellae 5, which ensure that the airflow around the body 2 is disrupted in such a way that no vortices can form, or at least the formation of vortices is reduced.

[0049] The Fig. Figure 1 shows in detail, using the upper fastening element 3 as an example, which also applies to the lower one, that the respective fastening element 3, 4 is divided into two parts and both parts can be connected by means of two opposing clamping devices 6 and clamped to the body surface.

[0050] 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 pulled together by screws. This example, however, does not limit the invention shown.

[0051] The detailed illustration below further shows that, viewed in cross-section perpendicular to the circumferential direction, the ring-shaped fastening element 3, 4 each has two mutually perpendicular webs connected by stiffening ribs 7. One of the webs, which in cross-section is parallel to the surface of the body 2 and perpendicular to the circumferential direction, has the protective element 3a on its side facing the body 2.

[0052] The Fig.Figure 2 further shows that each fastening element 3, 4 is divided at the location of the clamping device 6 into two semi-ring-shaped sub-elements 3-1 and 3-2 or 4-1 and 4-2, respectively, wherein the sub-elements 3-1 and 4-1 are connected by a fraction of all the lamellae 5. The same applies to the sub-elements 3-2 and 4-2, which are not shown. This results in a division of the entire device 1 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 a hinged connection after the clamping device is released.

Claims

[1] Device for reducing vortex-induced vibrations of a body (2) surrounded by fluid, characterized by that they a first frame-shaped fastening element (3) which can be placed around the fluid-flowing body (2) and fastened thereto, and b. comprises a second frame-shaped fastening element (4) which can be placed around the fluid-flowing body (2) 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 bythat 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 are connectable 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 by that each fastening element (3, 4) has, at least in some areas, preferably everywhere, on a surface area facing the surface of the body (2), a protective element (3a), in particular made of an elastomer, which 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 bythat in a state mounted on the body (2), the surface areas of the slats (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 by that the fastening elements (3, 4) each surround a circular inner free cross-section. [6] Device according to one of the preceding claims, characterized by 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 bythat 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 by that the fastening elements (3, 4) and the slats (5) are materially connected to one another, in particular are welded elements. [9] Device according to one of the preceding claims, characterized by 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 bythat 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.

Images