HIGH EFFICIENCY DUAL RAIL SHROUD
Publication Date: 2013-Jun-05
The IP.com Prior Art Database
A technique to reduce fluid leakage flow across gas turbine blades is proposed herein. The technique includes a configuration of dual rail tip shroud and static shroud of the turbine blade. The proposed configuration is such that leakage flow force of fluid follows a torturous path without any change in physical clearance. The physical clearance includes radial/axial gaps. However, effective area of leakage flow is reduced.
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HIGH EFFICIENCY DUAL RAIL SHROUD
The present invention relates generally to gas turbine blades, and more particularly to shrouded turbine blades.
Generally, fluid flow in a turbine provides useful work when it flows through moving buckets of a turbine. The buckets are mounted on a rotor of a turbine. The fluid flow through the buckets is different from that which leaks around radial tips of the bucket. The fluid leaking around radial tips of the bucket produces no useful work. Leakage of the fluid flow around the radial tips of the buckets in a turbine needs to be minimized in order to increase the efficiency of the turbine.
Turbine rotor blades have shrouds that form a band around perimeter of a row of turbine rotor blades attached to a rotating disk (turbine wheel). The shrouded turbine rotor blades effectively reduce combustion gas leakage around the tips of the blades and reduce blade vibration. However, the shrouds in the rotor blades are not effective in reducing fluid leakage across the turbine blade. It is estimated that there is substantial loss of stage efficiency of gas turbine due to clearance flow of fluid between bucket tip shroud and static shroud and cavity required around the tip shroud to provide axial/radial movement.
Several conventional techniques are known in the art for reducing leakage flow across the bucket of the turbine blade. A conventional technique includes a leakage control structure provided between a bucket cover of a turbine and a surrounding diaphragm around the bucket cover. The bucket cover includes a plurality of circumferentially stepped portions extending radially outward and located on the downstream side of the existing or first fin of a turbine. A fin is provided which also extends radially inward from the turbine diaphragm and circumferentially thereabout. The stepped portion dissipates the kinetic energy of the fluid flow leaking through the gap between a fin and outer radial surface of the stepped portion of the bucket cover. The fin further reduces fluid flow leakage which passes by the fin after having interacted with the stepped portion.
Another conventional technique for regulating leakage of fluid flow across bucket includes a tip shroud rail. The tip shroud rail includes a base that is integrally attached to a tip shroud of at least one turbine rotor blade, a top distally from the base, an upstream surface, and a downstream surface. The rail has a height, h, as measured from the base to the top, and a width, w, as measured from the upstream surface to the downstream surface. Such dimensions include, but are not limited to, tip shroud rails with upstream and/or downstream surfaces that are concave in profile. The tip shrou...