1. Field of the Invention
The present invention relates generally to a labyrinth seal, and more specifically to a honeycomb seal used in a gas turbine engine.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
Honeycomb seals are used in gas turbine engines such as those used to power an aircraft or a marine craft, or to produce electrical power. A gas turbine engine includes a turbine section that converts the energy in a hot gas flow passing through the turbine into mechanical work to drive the rotor shaft. The rotor shaft drivers the compressor and, in the case of an industrial gas turbine, drives the electric generator. The turbine includes a plurality of stages of rotor blades and stator vanes. In an industrial gas turbine engine, four stages of blades are found in the turbine. The rotor blades include blade tips with seal teeth extending outward that form a labyrinth seal with a honeycomb surface on the stationary part of the engine that also forms the flow path of the hot gas flowing through the turbine. The engine efficiency can be increased by reducing the flow leakage across the blade tips. Also, excess hot gas flow across the blade tip can cause thermal damage to the labyrinth seal, resulting in the life of the seal assembly to be reduced. In an industrial gas turbine engine, it becomes very costly to stop operation of the engine for unnecessary inspection and/or repairs due to worn parts.
Labyrinth seals have been used in gas turbine engines because they provide an effective seal for the hot gas flow between the rotating part and the stationary part. Also, labyrinth seals make use of a plurality of teeth with a cavity formed between adjacent teeth, the cavity functioning to provide a higher pressure against the gap between the tooth and the honeycomb seal face. This functions to limit leakage from one gap to another. A typical gas turbine engine labyrinth seal assembly will include three to five teeth forming two to four cavities in which the leakage would have to traverse.
U.S. Pat. No. 6,652,226 B2 issued to Albrecht, Jr. et al on Nov. 25, 2003 and entitled METHODS AND APPARATUS FOR REDUCING SEAL TEETH WEAR discloses a stepped labyrinth seal which is shown in FIG. 1 of this application. The labyrinth seal includes teeth extending from the rotating part toward the honeycomb material secured on the stationary part. Two teeth are shown in FIG. 1 to represent the concept of this seal. A gap or space will exist between the tooth and the honeycomb seal in which leakage will occur. In the prior art labyrinth seal of FIG. 1, the teeth are offset to form a stepped labyrinth seal in order that the gaps are not aligned along the leakage path. This results in less leakage.
The U.S. Pat. No. 5,244,216 issued to Rhode on Sep. 14, 1993 and entitled LABYRINTH SEAL shows this stepped labyrinth seal. The labyrinth seal is generally characterized by a series of cavities or grooves formed along the adjacent surfaces of two relatively movable members, where these members define a partial barrier between areas of high and low pressures. At successive stations or steps along the seal, the adjacent surfaces of these rotatable members are situated in close juxtaposition to each other such as to define annular slit-like orifices. Further in this type of seal design, a series of cavities or chambers are formed between these stations in order to retard fluid flow through the seal.
In operation, the previously described labyrinth design forms a seal between the rotatable members by forcing high velocity fluid to navigate the irregularly spaced adjacent surfaces formed between these relatively movable members, said fluid sequentially passing through the slit-like orifices to enter the enlarged cavities where the velocity of the fluid is largely dissipated in turbulence. In this, the basic concept of any labyrinth seal design is to create a highly frictional flow passage. Such a flow path will convert pressure energy into velocity energy, a large portion of which will be dissipated into heat via turbulent action.
In another such design, U.S. Pat. No. 1,482,031 issued to Parsons on Jan. 29, 1924 and entitled PACKING FOR ROTATING BODIES, a labyrinth seal is characterized by a radially stepped surface provided along the rotor, the stator being provided with a corresponding set of barrier members or collars disposed in close relationship thereto. In this fashion, high pressure fluid moving across the sealing surface will encounter interference; thus, minimizing leakage. In yet another design, U.S. Pat. No. 3,940,153 issued to Stocker on Feb. 24, 1976 and entitled LABYRINTH SEAL, the labyrinth seal is characterized by a succession of annular orifices or clearances between sealing teeth or knives on one member, and generally cylindrical surfaces or lands on the other. In combination, the sealing system defines a doubly re-curved flow path from each orifice to the orifice next downstream.
An improvement to the above cited prior art labyrinth seals is shown in U.S. Pat. No. 6,164,655 issued to Bothien et al on Dec. 26, 2000 and entitled METHOD AND ARRANGEMENT FOR SEALING OFF A SEPARATING GAP, FORMED BETWEEN A ROTOR AND A STATOR, IN A NON-CONTACTING MANNER in which a vortex flow is generated in a chamber downstream from the choke point (similar to the teeth gap) in order to reduce the leakage across the seal.
IN U.S. Pat. No. 6,276,692 B1 issued to Beeck et al on Aug. 21, 2001 and entitled NON-CONTACT SEAL OF GAPS IN GAS TURBINES, in which a seal is formed between a rotating member and a stationary member by inducing a vortex flow within a chamber formed between the two members. A secondary flow is injected into the vortex chamber from the stationary member to form the vortex flow. A guide lip and a guiding web formed from a plurality of curved guiding members fixed to the rotating member that induces further vortex flow in the chamber to seal the gap formed between the stationary member and the rotating member.