The Effects of the Tangential Leans for the Last Stage Nozzles of Steam Turbine

Abstract

In general, since the aspect ratio defined by the ratio of blade height and blade cord length of the last stage blades (LSBs) of a low pressure steam turbine is considerably larger compared to those of other stages, there is anxiety concern about the possibility of flow separation in the vicinity of the root section of the blades. In addition to the above fact, possible efficiency deterioration due to supersonic inflow resulting from the usage of longer blades has to be avoided to obtain an efficient steam turbine. In this paper, the effects of various types of leans for the last stage nozzles have been studied with the help of 3D-CFD. Then, several characteristics charts related to the stage performance for each type of lean including the s-shaped lean were created. By applying well-designed s-shaped lean nozzles, the undesirable effect of supersonic inflow could be significantly mitigated, giving a fair improvement in stage efficiency.