Stationary vane assemblies for axial turbines

Abstract

An axial flow turbine is described having a casing defining a flow path for a working fluid therein, a rotor co -axial to the casing, a plurality of stages, each including a stationary row of vanes circumferentially mounted on the casing a rotating row blades, circumferentially mounted on the rotor, with within a stage n vanes have an extension such that at least a part of the trailing edge of each of the n vanes reaches into the annular space defined by the trailing edges of the remaining N-n vanes and the leading edges of rotating blades of the same stage.

Description

technical field [0001] The present invention generally relates to an assembly of stationary vanes for axial flow turbines, in particular for low pressure steam turbines. Background technique [0002] As described in US Patent No. 4,165,616, achieving the maximum possible stage efficiency and avoiding negative reaction forces on all turbine blades requires maintaining the axial velocity within a certain range. The axial velocity of the steam leaving the rotatable turbine blades is one of the most important parameters for determining the stage load, the probability of negative reaction force and the probability of negative work performed by the turbine stage. The last stage blades or exhaust blades in a turbine are the most difficult blades to design optimally because they experience widely varying pressure ratios due to part load and overload operation. [0003] Last stage blade optimization becomes even more difficult as the exhaust pressure downstream of the exhaust stage ...

AI Technical Summary

Problems solved by technology

Operation in the choked flow region will result in no additional turbine power output, but will increase the heat rate of the cycle, while operation outside the zero work region will cause work generated by the remaining turbine blades to be consumed rather than produced

[0004] An additional disadvantage of operating outside the zero work point is that the final stage will eventually experience unsteady flow phenomena, which can cause particularly large blade vibrations

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