This invention relates to a seal assembly between a rotor and a stator especially of a turbo-machinery with a close clearance gap there between according to the introductory part of claim 1.
A type of close clearance gap that is often applied in turbo-machinery is the labyrinth seal. Labyrinth seals generate large magnitude, destabilizing forces on turbo-machinery rotors especially when operating in high density fluids. Over the years several alternative labyrinth configurations have been developed in an attempt to reduce the destabilizing forcing function and at the same time increase the damping properties. Honeycomb style seals are an example in this context. These have been quite successfully applied in high pressure, centrifugal compressors especially in gas reinjection applications. Honeycomb style labyrinths have however a very high direct stiffness and are sensitive to actual rotor position and running gap geometry. This has led to several incidents in the industry where corrective actions were required to bring units within specifications.
Rotation of the high density gas inside the labyrinth is a root cause for the large magnitude, destabilizing forces inside labyrinth seals. These forces have a pronounced effect on the design of high density turbo-machinery: they limit the maximum possible running speed, the maximum number of impellers at the rotor, the maximum process pressure, the minimum diameter of the rotor shaft, and the efficiency or a combination of these.
Besides labyrinth seals the destabilizing forces can occur in any close clearance gap where a fluid fills the gap between stator part and rotor part.
The object of the present invention is to reduce the destabilizing forces acting on the rotor of rotating turbo-machinery.
Starting from a seal assembly according to the introductory part of claim 1 the object is achieved by the features of the characterizing part of claim 1. Advantageous embodiments of the invention are described in the subclaims
Through the invention one or more annular chamber(s) between the stator and rotor are created that have multiple openings towards the fluid side. Through the openings the chamber is in contact with the close clearance gap, i.e. the fluid side.
The chambers with these openings have the following characteristics:
- They minimise circumferential swirling of the fluid thereby minimizing the destabilizing forces. This is accomplished through pressure equalisation in angular direction inside the chamber(s). Through the openings the pressure inside the fluid gap will also be equalized by flow leakage through the openings.
- They act as an dynamic damper of dynamics pressure fluctuations through the special combination of the openings and the pressure equalizing chambers. This damping effect can be further enhanced by installation of special damping material in the pressure equalizing chamber.
The inventive seal assembly is therefore capable to reduce the flow induced excitation forces inside the close clearance gap.
The invention will be described by way of example with reference to the accompanying drawing in which:
Fig. 1 is a longitudinal section of a seal assembly with a close clearance gap;
Fig. 2 is a partial sectional view along line II - II of Fig. 1 and
Fig. 3 is a longitudinal section through a labyrinth seal.
A rotor 1 is pivoted in a stator 2. The rotor 1 and the stator 2 belong to a rotating turbo-machinery for example a compressor, a steam turbine, a gas turbine, an expander, an electric motor, or a pump. For sealing a close clearance gap 3 is present between a rotor surface of the rotor 1 and a stator surface 4 of the stator 2. The surfaces surrounding the clearance gap 3 basically can have any geometry ranging from single diameter, staggered, conical, etc.
The rotor surface or the stator surface 4 or both surfaces are provided with openings 5 which open into at least one chamber 6 arranged at that side of the openings 5 turned away from the clearance gap 3. As shown more clearly in Fig. 1 and 2 a perforated plate 7 having openings 5 is fastened to the stator 2. At the back side of the perforated plate 7, that is the side turned away from the clearance gap 3, webs 8 or ribs are provided in circumferential direction. The webs 8 surround annular chambers 6 which inner width is greater than the inner width of the openings 5 and into which a series of openings 5 opens. The various annular chambers 6 can be axially interconnected through holes 9 in the webs 8 of the perforated plate 7, thus forming one large annular chamber.
The close clearance gap 3 is filled with a fluid which is the result of the rotating rotor surface and the stationary stator surface 4 that are in close proximity to each other. Through the openings 5 the annular chambers 6 are in contact with the close clearance gap 3 and the fluid therein. Because of a leakage of fluid through the openings 5 there is annular pressure equalizing.
The labyrinth seal shown in Fig. 3 consists of a labyrinth holder 10 that has several labyrinth teeth 11. The labyrinth holder 10 is arranged in the stator 2. The labyrinth teeth 11 face the surface of the rotor 1 defining a small clearance 3. The rotor surface basically can have any geometry ranging from single diameter, staggered, conical, etc.
Between each labyrinth tooth 11 a perforated section 12 having perforations or openings 5 is present creating pressure equalizing chambers 6 at the backside of this perforated section 12. The openings 5 are typically arranged more or less perpendicular to the sealing surface and can have special geometry optimizing the dynamical behaviour of the labyrinth. The chambers 6 may be filled with damping material.
1. Seal assembly between a rotor (1) and a stator (2) especially of a turbo-machinery with a close clearance gap (3) there between which clearance gap (3) is bordered by a rotor surface at the side of the rotor (1) and by a stator surface (4) at the side of the stator (2), characterized in that the rotor surface or the stator surface (4) or both are provided with openings (5) which open into at least one chamber (6) arranged at that side of the openings (5) turned away from the clearance gap (3).
2. Seal assembly as claimed in claim 1, characterized in that the inner width of the chambers (6) is larger than the inner width of the openings (5).
3. Seal assembly as claimed in claim 1 or 2, characterized by one or more annular chambers (6) extending in circumferential direction, into which or into each of them a plurality of openings (5) open.
4. Seal assembly as claimed in claim 3, characterized in that the annular chambers (6) are axially interconnected by holes (9).
5. Seal assembly as claimed in claim 3, characterized in that the openings (5) are perforations of a perforated plate (7) fastened to the stator surface (4) and that the chambers (6) are arranged at the back side of the perforated plate (7).
6. Seal assembly as claimed in claim 1, characterized in that the axes of the openings (5) are basically perpendicular to the axis of the rotor (1) to be sealed.
7. Seal assembly as claimed in claims 1, characterized in that the chambers (6) are filled with damping material.
8. Seal assembly comprising labyrinth teeth (11) with chambers (6) in between as claimed in claim 1, characterized in that a perforated section (12) having openings (5) is installed between the labyrinth teeth (11) and the chambers (6).