Aerodynamic Effects of Coolant Ejected from Trailing Edge Cut-Back Profiles in a Two-Stage Turbine

The present work has been focused on the experimental study of the aerodynamic interaction between the coolant ejected from the trailing edge of cut-back blade profiles and the main flow in a two-stage axial research turbine. The flowfield has been investigated upstream and downstream of the second stator row in order to study the aerodynamic interaction between coolant and main flow under realistic perturbations associated with both upstream wakes and potential effects induced by the downstream bladings in relative motion. Measurements have been carried out by means of a 5-hole aerodynamic probe and a 2-sensor hot-wire anemometer. The Reynolds number based on the turbine axial velocity and stator blade chord has been set equal to Re = 500000. A phase-locked ensemble-averaged technique has been adopted, in order to distinguish the perturbations induced by the first rotor blades from those due to the potential flow interaction associated with the downstream blading. Phase-locked velocity and turbulence intensity distributions have been measured in the rotor-stator axial gap in the blade-to-blade plane at midspan downstream of the second turbine stator. The aerodynamic interaction between coolant and main flow has been investigated for different flow rates (in the range 0-4% of the through flow) at three different incidence angles representative of nominal and off-design operating conditions.