Interaction and clocking effect of unsteady flow in a one and a half axial-flow turbine stage

The unsteady flow in a one and a half of Aachen axial-flow turbine stage was investigated by full three-dimensional viscous numerical simulation, and the main interaction phenomenon of adjacent blade rows and clocking effect were discussed. Results indicate that between adjacent blade rows the interaction of pressure potential field happens, which is more intense between the rotor and the second stator. The interaction of pressure potential field is quantified by the fluctuation of static pressure on the surface of blade and propagates upstream and downstream at certain speed respectively. Truncated by the blade, the wake caused by upstream stator, which is distorted in the rotor passage occurs at certain position in the absolute coordinate system periodically, which creates a condition for clocking effect. The best clocking position for the second stator can be determined through analyzing the space-time diagram of entropy at the exit of rotor. Qualitatively, the entropy at the exit of the turbine decides the efficiency of turbine stage, which provides a new objective parameter for unsteady optimization and design of turbines.