Investigation Of Control Technique Of Endwall Flow At The Meridional Expansion Turbine Blade

Normally, power turbines are characterized by their longer blades, larger meridional expansion angle and high velocities. The expansion angle of contours could cause a local static pressure increased near the endwall regions, and the same time the expansion of the flow at the leading edge region of the blade passage wasn’t enough to counteract the increased of static pressure. Then lead to a larger and strength horse vortex at the leading edge regions of the turbine blade.In this paper, to improve the turbine stage aerodynamic performance, there are tow optimization measures have been applied to the first stage of a4stages power turbine which has a diverging upper contours.3D numerical simulation was carried out by commercial software NUMECA to analysis the effects on the aerodynamic performance of the power turbine stage stator blade which optimized with compound bow and part forward sweep near the case regions.Firstly, in order to average the reaction and mass flow distribution along with span direction compound bow was applied to the stator blade. Different bowing effects are produced when profile sections stagger angles near the case of the stator blade were increased. Stacking on the leading edge induces a negative bowing effect at the trailing regions of the stator. In order to keep the same overall throat area and hence preserve the mean reaction, the throat at mid-height has been opened by decreasing stagger angles of the profile sections. Then, positive bow was applied to the stator case regions that would lead to a compound bow effects which it was positive bow at the leading edge regions and negative bow at the trailing edge regions. Numerical result shows that the reaction of the turbine stage was increased at the hub regions and decreased at the case regions. At the same time the more and more mass flows were through the mid-span height regions caused by the throat area changed. Then the intensity of the passage vortex was decreased and the energy loss of the stator blade decreased from5.04%to4.91%. Secondly, part forward was adopted to the case regions of the stator blade to optimized static pressure distribution. The curved forward sweep have been provided to25%and35%of the stator blade near the case regions under three sweep angles, so seven sets of the turbine stage case were studied. The results show that the swept blade can improve the static pressure distribution at the case regions. And there are optimal sweep angle and height that make the performance of the turbine stage has a maximum improved. In this paper the efficiency increased from92.36%to92.58%for the optimal part-span forward sweep case.