Investigation of 3D blade design on flow field and performance of a low pressure turbine stage

To investigate the effect of blade geometry profiling by 3D bowing and twisting independently and jointly on entropy, efficiency and performance for the turbine cascades, the paper describes the mechanism of how bowed and twisted blades affect the secondary flow. The efficiency of the turbine stage improves considerably and flow structure has been optimized by applying the bowed and twisted blade. An optimization of low pressure turbine with bowed stator has been performed using steady and transient RANS simulations. Cases with varying bow angles including both positive bow angle and negative bow angle have been discussed to show how bow angle influence the performance of rotor and stator. An optimal case with positive 18-degree bow angle was obtained. It indicates that the entropy increase rises slightly in the region near mid-span, while it reduces distinctly near the hub and shroud in the stator. In addition to the varying bow angles, further deliberate modification has been made to present a detailed study on the effect of twisted and bowed blade with different stator exit angles. Due to the varying exit flow angles of stator, the mass flow in the spanwise direction has been changed. Meanwhile, the circumferential mass-averaged efficiency in spanwise direction is different. Therefore, the mass flow changing in the spanwise direction leads to redistribution of low energy fluid in the flow passage. The variation of exit flow angles also affects secondary flow and it can be controlled actively by changing the angles. A considerable increase of efficiency has been achieved in this part of investigation. Considering the unsteady interaction of rotor and stator influenced by applying bowed and twisted stator, the flow through the LPT with relatively low aspect ratio was numerically simulated. It shows clearly how the secondary flow develops in the passage of the stage with bowed and twisted stator and proves several results achieved previously. At the same time, it shows how wakes of the stator and passage vortex develop in the rotor passage.