EP0335299A1 - Vibration damper for axial flow blades - Google Patents

Abstract

In the case of axial blades of axial flow turbo-machines, vibrations are damped in that a hollow body (5) with a large internal surface is arranged in the region of large vibration movements, i.e. mainly in the region of the free blade ends, which hollow body (5) contains a damping medium (9). In the case of blades with covering strips, the hollow body is provided in the region of the covering strip. As a result of the movement of the damping medium, which continuously acts against any acceleration, with respect to the movement of the hollow body, damping of the vibration of the blades is achieved which cannot be achieved by the material damping itself or by frictional damping, taking into account tolerable wear. <IMAGE>

Description

The invention relates to vibration damping for axial blades, in particular axially flow-through turbines and compressors, summarized below as turbomachines, with hollow and closed binding pins in the area of the free blade ends, which contain an attenuator and are aligned perpendicular to the centrifugal force, and vibration damping for blades with shroud or plate or support wing, in particular axially flowed through turbomachines with closed cavities provided perpendicular to the direction of centrifugal force in the shroud or in the support wings with a damping fluid.

Due to disturbances in the form of pressure or speed variations, axial blading is excited to vibrate. In order to withstand the additional loads resulting from the vibrations, blade materials with high strength values are required. In order to avoid damage caused by high centrifugal loads with superimposed alternating amplitudes, blades must be made relatively short and with a thick profile. For a high energy conversion, however, these should be made long and thin with respect to the profile, which cannot usually be achieved to the desired extent due to strength requirements.

If the blade vibrations are reduced by suitable measures, the loads are also reduced and the blade profile can be designed to be more flow and energy-efficient (more economical due to higher energy conversion per stage) because of the lower demands on the vibration resistance.

To reduce blade vibrations, the blades can advantageously be connected to one another by means of a shroud or, if the mechanical loads are too high, can be coupled to one another by means of a binding wire or by loosely inserted binding pins.

It has been proposed to introduce cavities (US 2349187) in the blades, in which a cylinder or a ball can move on a concave surface against which the cylinder or the ball is pressed by the centrifugal force, whereby it is from a damping medium are surrounded. The round body (ball or cylinder) is deflected laterally during a swinging movement and a restoring force is caused by the concave surface and the acting centrifugal force. Physically, this means that an additional spring mass system has been created in the blade, which is damped by the damping medium. With specific tuning of the resonance frequency of the single-mass oscillator, a certain resonance frequency of the blade or the coupled blades can be detuned or canceled. This can avoid a dangerous resonance point.

However, the dangerous resonance point must be known beforehand in order to achieve a positive effect, because with the one-mass transducer (as well as with a multi-mass transducer) a new vibration system is created that also has higher amplitudes in certain speed ranges can have under the same excitation conditions. This point is problematic in that resonance frequency - especially in the case of coupled blading with couplings over the disc or coupling elements such as binding pin, shroud, etc. - cannot be calculated precisely enough.

Another proposal (GB 943023) relates to binding pins that are filled with material - here lead balls - that is liquid at operating temperature. In the case of vibratory movements, friction becomes effective, which leads to loss of vibrational energy.

The disadvantage of this construction, however, is that the liquid material is freely movable in the cavity and therefore has only a slight damping effect. The liquid column can also be regarded as an oscillating point mass, which in turn creates a one-mass oscillator (possibly also a multi-mass oscillator) with the disadvantages already mentioned above.

The invention has for its object to provide a vibration damping, the construction of which is easy to manufacture, if possible, the blade is not additionally loaded and is practically wear-free.

The object is achieved in that in the case of binding pins while maintaining the moment of inertia (bending strength), the hollow binding pin is provided with a large inner surface and, in the case of cover tape or plate or with supporting wings, the cavity is provided with a large inner surface.

The free blade end, which has the maximum amplitude of the deflection (and thus also the maximum vibration speed or maximum vibration accelerations) when the free-standing blade vibrates, is provided with a hollow body or a hollow body is arranged in the region of the free end. A damping medium is located in the hollow body, the hollow body advantageously being only partially filled with the damping medium. The damping medium can only move relative to the hollow body within the hollow body, which has a large inner surface, due to its own inertia and due to a toughness which is effective in a shear flow, so that frictional energy is released from the blading, so that the blading can be effectively removed.

The hollow body advantageously connects at least two adjacent blades to one another. This also prevents opposing movements of the blades in the longitudinal direction of the binding pin and thus stiffening the blades.

According to a preferred embodiment, the hollow body is designed as a sleeve. In this embodiment, the cavity lies in the neutral fiber of the sleeve, which has several advantages:
If the hollow body is designed as a binding pin for connecting two blades, the binding pin is subjected to bending due to its longitudinal load due to its own weight in the centrifugal force field. This bending stress is significantly lower in the case of sleeves compared to a solid cylinder with the same outside diameter, because the material in the area of the neutral fiber represents a load without any significant increase in the bending stiffness to contribute this component. The same mode of action is obtained with a hollow cover band.

It follows from this that the binding pin designed as a sleeve, e.g. a hollow binding pin, which usually can absorb lighter damping medium compared to the material of the hollow body, without it having to be significantly reinforced. A small outside diameter is of great importance insofar as the flow cross section is reduced by it and consequently losses in efficiency have to be accepted.

The hollow bodies can advantageously on the blades in a recess provided in the circumferential direction, e.g. a borehole. However, there can also be a hollow body on both longitudinal sides of the blades, e.g. in the form of a support wing, be attached so that the blades or the like through holes. be weakened.

The bores are advantageously introduced into the blades at an angle and laterally offset from the circumferential line, because the free length of the binding pin is shortened and the load thus drops significantly, or the pin can be designed with a smaller outer diameter. If two blades are connected to a hollow body designed as a binding pin, this extends from somewhat in front of the rear edge of the one blade to a point somewhat behind the front edge of the other blade. In addition to bending vibrations, torsional vibrations are also impeded or damped by such a zigzag binding.

The loose insertion of the hollow body into the receptacles of the blades also causes additional damping at relatively low speeds due to the use of micro-friction in the interface between the hollow body and the blade. The simple replacement of damaged hollow bodies is also advantageous.

A further embodiment provides that a hollow body containing a damping medium is arranged in the area of the shroud. This hollow body can be attached to the shroud or integrated in the shroud.

The hollow body is advantageously designed as a circumferential recess, e.g. Bore or the like .. This reduces the weight of the shroud, which leads to a lower static stress on the shroud and the blade itself. Advantageously, several parallel recesses can also be made in the cover band, so that the bending load on the cantilever cover band can be further reduced in a targeted manner and a larger friction surface is available for the damping medium.

In order to be able to effectively transmit the frictional forces resulting from the speed changes of the oscillating movement to the damping medium, the hollow body has a continuous threaded bore on the inside to enlarge the surface. This effect is also achieved by a surface that is rough on the inside in a different way.

A simple sealing of the hollow body is achieved in that it is sealed on both sides with closure elements in a fluid-tight manner. If the hollow body is provided with a thread on the inside, these closure elements can be simple screw plugs, which can also serve as an axial securing means if the binding sleeves are loosely inserted. The closure elements prevent the damping medium from escaping, which would not lead to a reduction in the damping capacity, but could also be disadvantageous in some applications from a system perspective.

The damping medium can be a liquid, e.g. Oil or sodium at a higher temperature can be a granulate or a mixture of the two. The viscosities of the liquids are matched to the working temperature and the required damping in the machine.

The transmission of the oscillating movement from the damping medium can advantageously be increased in that the hollow body has inserted baffles. These baffles can be used as a labyrinth spiral, wire mesh or the like. be trained.

• Fig. 1 ein als Bindestift ausgebildeter Hohlkörper, der an zwei benachbarten Schaufeln festgelegt ist,
• Fig. 2 einen als Deckplatte ausgebildeter Hohlkörper,
• Fig. 3 seitlich an die Schaufelprofile angesetzte Hohlkörper,
• Fig. 4a - 4c Ausschnitte aus den Fig. 1 bis 3, die Beschaffenheit der Innenoberfläche des Hohlkörpers und den Hohlraum in vergrößertem Maßstab zeigend
• Fig. 5a und 5b zeigen jeweils eine vorteilhafte Anordnung der Hohlkörper an den Schaufeln

Further details and advantages of the invention result from the following description, in which reference is made to preferred exemplary embodiments. Show

• 1 is a hollow body designed as a binding pin, which is fixed to two adjacent blades,
• 2 a hollow body designed as a cover plate,
• 3 laterally attached to the blade profiles hollow body,
• 4a-4c sections from FIGS. 1 to 3, showing the nature of the inner surface of the hollow body and the cavity on an enlarged scale
• 5a and 5b each show an advantageous arrangement of the hollow bodies on the blades

Fig. 1 shows a section with two blades (1 and 2) from an impeller (3) which rotates at an angular velocity Omega. A hollow body (5) in the form of a binding pin (6) is arranged in the area of the free blade ends (4). This binding pin (6) is fixed loosely or rigidly in recesses (7), which are designed, for example, as bores (8), on the blades (1 and 2) and connects the two blades (1 and 2) to one another. To accommodate a damping medium (9), the binding pin (6) is hollow in the manner of a sleeve (10), which can be achieved, for example, by means of a through hole. At the ends (11 and 12) of the binding pin (6) each has an internal thread (13) which serves to fix a closure element (14) which closes the cavity of the binding pin (6). The closure element (14), which is designed as a screw-in closure plug (15), also serves, by means of its closure plug (16) projecting beyond the binding pin (6), as an axial securing means against falling out of the recesses (7) of the blades (1 and 2).

Fig. 2 shows a blade (17) which has a shroud (18) at its free blade end (4). In this case, the cover band (18) forms the hollow body (5), which contains the damping medium (9). The cavity (19) is e.g. formed by a through hole (23). In this case screwable plugs (20) serve as closure elements (14).

FIG. 3 shows an impeller (3) in which the blades (1 and 2) have hollow bodies (5) in the form of support vanes (22) attached to the blade profile (21). These support wings (22) are also hollow and contain the damping medium (9). For centering and mutual support, the support wings (22) have wedge-like or groove-like ends that are braced against one another, but without hindering temperature and centrifugal expansion in the circumferential direction.

Instead of attached support wings (22), the blades (1 and 2) can also be provided with hollow bodies (5) which penetrate the blades (1 and 2) in the manner of a binding pin and the blades (1 and 2) each on the opposite Blade profiles (21), as shown in Fig. 3, protrude (not shown).

Figures 4a to 4c show sections of the hollow body (5), in particular the nature of the inner surface (24) of the cavity. In the exemplary embodiment according to FIG. 4a, the inner surface (24) is formed by an internal thread (25). This has the advantage that both the threads for the screw-in closure elements (14) and a rough surface (24) of the cavity are created in one operation. In the exemplary embodiment according to FIG. 4b, the inner surface (24) is roughened artificially or is already present in a rough form due to a correspondingly rough manufacturing process. Due to the roughness, a good transfer of the change in movement of the blades (1, 2 and 17) to the damping medium (9) is effected. In accordance with the damping effect, this damping medium (9) can fill the cavity of the hollow body (5) to more than 50% (see FIG. 4b) or equal to / less than 50% (see FIG. 4a); in addition to the effect of damping other aspects such as weight loading or shifting are taken into account.

In the embodiment according to FIG. 4c, the inner surface 24) of the hollow body (5) is mechanically almost smooth, so that an effective transmission of the movement of the blades (1, 2 and 17) to the damping medium (9) hardly takes place due to the lack of surface unevenness. However, the transmission is achieved in that in the cavity, e.g. can be a bore (8), a chicane (25) for the damping medium (9) is embedded in the form of a wire mesh and this is partially surrounded by the damping medium (9) and flows through.

FIGS. 5a and 5b show advantageous arrangements of hollow bodies (5) designed as binding pins (6). In the exemplary embodiment according to FIG. 5a, two adjacent blades (1 and 2) are connected to one another by means of the binding pin (6) by penetrating one blade (1 or 2) in the region of its rear edge (26) and the other end of the binding pin (6) in the area of the front edge (27) of the adjacent other blade (2 or 1). The recesses (7), e.g. Bores (8) in the blades (1 and 2) laterally offset to the circumferential line (28) and are inclined relative to it by an angle α. Attaching the hollow body (5) in this way has the advantage that the blades (1 and 2) are directly or indirectly connected to one another and also torsional portions of the blades (1 and 2) can be hindered and damped.

This advantage is also achieved by the arrangement of the hollow bodies (5) according to FIG. 5b. Here are the hollow bodies (5), e.g. Tie pins (6), each alternately offset from the circumferential line (28), wherein the distances (a and b) of the hollow body (5) to the circumferential line can be the same or different.

It is of great advantage if, in the case of elongated hollow bodies (5), the longitudinal axis of the hollow body is perpendicular to the direction of centrifugal force and parallel to the main direction of vibration of the blades (1 and 2).

Claims (5)

1) Vibration damping for axial blading, especially axially flowed through turbines and compressors, summarized below as turbomachinery, with hollow and closed binding pins in the area of the free blade ends, which contain a damping fluid and are oriented perpendicular to the centrifugal force, characterized in that while maintaining the moment of inertia (Bending strength) the hollow binding pin is provided with a large inner surface. 2) Vibration damping for blades with cover band or plate or with support wings, in particular turbomachines with axial flow, with closed cavities provided perpendicularly to the direction of centrifugal force in the cover tape or in the support wings with a damping fluid, characterized in that the cavity is provided with a large inner surface. 3) Vibration damping according to claim 1 or 2, characterized in that the rough surface in the hollow body is a threaded bore which can simultaneously serve to close the hollow body. 4) Vibration damping according to one of claims 1, 2 or 3, characterized in that the damping medium is a fluid, a granulate or a mixture of both. 5) Vibration damping according to one of claims 1 to 4, characterized in that the hollow body for the damping medium contains inserted baffles, such as labyrinth spiral, wire mesh or the like ..

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