Active Tip Clearance Flow Control for an Axial-Flow Turbine Rotor Using Ring-Type Plasma Actuators

Tip leakage flow through the small gap between the blade tip and the casing wall in turbomachinery reduces the aerodynamic performance of the blade. New ring-type dielectric barrier discharge (DBD) plasma actuators have been developed to facilitate active control of the tip leakage flow of a turbine rotor. In the present study, the ring-type plasma actuators consisted of metallic wires coated with insulation material, mounted in an insulator embedded in the tip casing wall. For the fundamental experiments using a flat plate and a single airfoil with tip clearance, particle image velocimetry (PIV) was used to obtain two-dimensional velocity field measurements near the plate and blade tip regions. From flat plate experiments in a static flow field, it was confirmed that the operation of the plasma actuator generates an upward flow at the corner between the blade tip and the casing wall, and this forms a perpendicular obstacle to the tip leakage flow. In flat plate experiments on tip leakage flow in a wind tunnel, the forcibly-induced tip leakage flow was successfully dissipated by means of the plasma actuator flow control. In single airfoil experiments, the tip leakage flow was also reduced by the plasma actuator. In annular turbine rotor experiments, the plasma emission at the blade tip and its motion with blade rotation were determined. Single-element hot-wire anemometry was used to measure the turbulence intensity distributions at the turbine rotor exit. The amplitude of input voltage for the plasma actuator was varied from ±3.0 to ±6.0 kV. The high turbulence intensity region created by the tip leakage flow was reduced with an increase in the input voltage of the plasma actuator.