The invention relates to gas turbine blade tip shrouds and particularly to a seal rail and cutter tooth configuration for a tip shroud.
A gas turbine blade has a tip that closely brushes a surrounding shroud. The shroud channels the working gas flow through circular arrays of blades. Each circular array is called a turbine stage, the first stage being just after the combustion section. The inner lining of the shroud is made abradable so that the blade tips can cut a path in it to minimize the blade tip-to-shroud clearance. This minimizes leakage of the working gas from the pressure side to the suction side of each blade. Some blade designs include a tip shroud as shown in
A disadvantage of adding a tip shroud and seal rail to a blade design is added weight. Cantilevered portions of the tip shroud must be rigid to resist flexing from centrifugal force. This limits possible weight reductions.
The invention is explained in the following description in view of the drawings that show:
The teeth 48, 50 may be smoothly rounded or bumps extending upstream and downstream from the seal rail 32C. The top leading edge of each tooth (the edge touched by lead lines 48, 50) may be sharp, with an included angle B (
The rail 32C may have front and back portions 54, 56 with respect to the rotation direction 29. The front portion 54 of the rail is ahead of the teeth 48, 50. It may be aligned with the rotation direction 29 as shown by centerline 58. The back portion 56 of the rail is behind the teeth. It may be angled back to the extended front centerline 58 as shown so that the back end 62 of the rail aligns with the front end 64 of the rail on the following tip shroud 23C. The back portion 56 of the rail may span linearly from the peak 66 or maximum lateral extent of the back tooth 50 to the back end of the rail 62 centered on the extended centerline 58. This configuration minimizes mass in the back portion 56 of the rail for a given width thereof, since the shortest distance between two points is a straight line. The angle A between centerlines 58, 60 of the front and back portions of the rail may be in a range such as 2 to 3 degrees.
The tip shroud and seal rail as shown in
The teeth 68, 70 may be formed by smoothly rounded lateral departures or bumps on the seal rail 32D as shown. The top leading edge of each tooth (the edge touched by lead lines 68, 70) may be sharp, while the sides 69, 71 may be smoothly rounded. Only one tooth 68, 70 is needed on each side of the rail 32D.
The rail 32D may have front and back portions 74, 76 with respect to the rotation direction 29. The front portion 74 is ahead of the teeth 68, 70, and may be aligned with the rotation direction 29. The back portion 76 is behind the teeth. It may span linearly from the peak 78 or maximum lateral extent of the back tooth 70 to a back end 62 of the seal rail that is centered on an extended centerline 60 of the front portion 72 of the rail. This configuration minimizes mass in the back portion 76 of the rail for a given width thereof, since the shortest distance between two points is a straight line. The front and back portions 74, 76 of the rail may have a common uniform thickness, although this is not a requirement.
The tip shroud and seal rail as shown in
The teeth pairs 48/50, 68/70 may be formed in a comma shape as viewed from above (
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
This application is the US National Stage of International Application No. PCT/US2014/038700 filed May 20, 2014, and claims the benefit thereof. The International Application claims benefit of the 21 May 2013 filing date of U.S. provisional patent application No. 61/825,601. All applications are incorporated by reference herein.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/US2014/038700 | 5/20/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2014/189875 | 11/27/2014 | WO | A |
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