CONTROL OF LOW VOLUMETRIC FLOW INSTABILITES IN STEAM TURBINES
Configuration of the last stage of a steam turbine where rotor blades rotate encircled by a vane carrier, such that a plurality of passages are located in the vane carrier, such that a fluid is blown through these passages forming a flow that impinges onto the rotor blades, the number of passages, the location of the passages in the vane carrier and the velocity of the flow impinging onto the rotor blades, being calculated in such a way that rotating flow instabilities in the rotor blades when the steam turbine operates at low volumetric flow conditions are avoided.
1 . Configuration of a last stage of a steam turbine where rotor blades rotate encircled by a vane carrier, characterized in that a plurality of passages are located in the vane carrier, such that a fluid is blown through these passages upstream of the rotor blades and arranged to form a flow that impinges onto the rotor blades with an injection angle of between zero to −90 degrees against the rotation of the rotor blades such that rotating flow instabilities in the rotor blades when the steam turbine operates at low volumetric flow conditions are reduced.
2 . Configuration according to claim 1 , wherein the passages are configured and arranged to blow fluid towards a point that is approximately 80% of a height of the last stage rotor blade taken from a base to a tip of the rotor blade.
3 . Configuration according to claim 1 , wherein the plurality of passages are circumferentially uniformly spaced in the vane carrier.
4 . Configuration according to claim 3 , wherein the plurality of passages circumferentially uniformly spaced in the vane carrier number eight.
5 . Configuration according to claim 3 , wherein the plurality of passages (circumferentially uniformly spaced in the vane carrier number twelve.
6 . Configuration according to claim 1 , wherein the passages are circumferentially shaped in such a way that a circumferential coverage in the vane carrier is increased.
7 . Configuration according to claim 1 , wherein the injection angle is in a range from −45 to −75 degrees.
8 . Configuration according to claim 1 , wherein the injection angle is about −60 degrees.
9 . Configuration according to claim 1 wherein in that the flow injected through the passages is up to 10% of the mainstream flow circulating through the rotor blades and the vane carrier.
10 . Configuration according to claim 1 wherein in that the flow injected through the passages is approximately 10% of the mainstream flow circulating through the rotor blades and the vane carrier.
11 . Configuration according to claim 1 , wherein the fluid blown through the passages is steam.
12 . A steam turbine comprising a last stage configuration according to claim 1 .