3D Blade Stacking Strategies and Understanding of Flow Physics in Low Pressure Steam Turbines: Part I — 3D Stacking Mechanisms

Optimization of blade stacking in the last stage of Low Pressure (LP) steam turbines constitutes one of the most delicate and time consuming parts of the design process. This is the first of two papers focusing on the stacking strategies applied to the last stage guide vane (G0). Following a comprehensive review of the main features that characterize the LP last stage aerodynamics, the 3D CFD code used for the investigation and options related to modeling of wet steam are described. Aerodynamic problems related to the LP last stage and the principles of 3D stacking are reviewed in detail. In this first paper the results of a systematic study on an isolated LP stator row are used to elucidate the effects of stacking schemes such as lean, twist, sweep and hub profiling. These results show that stator twist has the most powerful influence on the reaction variation but it also produces undesirable spanwise variations in angular momentum at stator exit. These may be compensated by introducing a positive stagnation pressure gradient at entry to the last stage.