Browsing by Subject "Plasma actuator"

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    An investigation of dielectric barrier discharge based plasma actuator designs with enhanced performance in active flow control
    (2013-04) Guo, Song
    This work presents an investigation of various dielectric barrier discharge based aerodynamic plasma actuator designs, in order to make plasma actuators more efficient in the aerodynamic active flow control. Based on the electric wind generation schemes of the AC signal driven plasma actuator, two features intended to explore the controlling of the accumulated surface charges are introduced in the new plasma actuator design: 1. By adding a diode-driven third electrode downstream of the discharge region; 2. By depositing a hundred-nanometer-thick layer of semiconductor material on the dielectric surface. Both measurement of thrust and flow separation control indicate that the new designs have better performance than traditional plasma actuators. Different geometries have been tested by varying the thickness of the hydrogenated amorphous silicon layer and the location of the third electrode. This aims to determine an optimized configuration of the plasma actuator based on performance. More experiments have been performed, focusing on exploration of the physics behind the two added features. Intensified CCD camera images of microdischarges have been recorded to illustrate the effects of added features. Also, surface charge distribution measurements have been performed, which reveal that the third electrode has an influ-ence on the distribution of the deposited surface charges and the semiconductor surface helps to move the surface charges. The effects of the added features have also been studied numerically. The effects in the visible plasma region are simulated using MATLAB and the effects of the downstream region are simulated by a model implemented in COMSOL Multi-physics. The computa-tional results have well explained the observations of enhanced the plasma actuator per-formance.
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    Separation control in low pressure turbines using plasma actuators with passing wakes
    (2013-09) Burman, Debashish
    A Dielectric Barrier Discharge (DBD) plasma actuator is operated in flow over the suction surface of a Pack-B Low Pressure Turbine (LPT) airfoil at a Reynolds number of 50,000 (based on exit velocity and suction surface length) and inlet free-stream turbulence intensity of 2.5%. Preliminary characterization studies were made of the effect of varying actuator pulsing frequency and duty cycle, actuator edge effects, and orientation of the actuator with the flow. Flow control was demonstrated with the actuator imparting momentum opposite to the stream-wise flow direction, showing that it is possible to use disturbances alone to destabilize the flow and effect transition. No frequencies of strong influence were found over the range tested, indicating that a broad band of effective frequencies exists. Edge effects were found to considerably enhance separation control. Total pressure measurements of the flow without passing wakes were taken using a glass total-pressure tube. Corrections for streamline displacement due to shear and wall effects were made, and comparisons with previous hot-wire measurements were used to validate data. Performance features of conventional two-electrode and a novel three-electrode actuator configuration were compared. Hot-wire anemometry was used to take time-varying ensemble-averaged near-wall velocity measurements of the flow with periodic passing wakes. Corrections were made for near-wall effects, temperature effects, and interference of the electric field. The wakes were generated by a wake generator mechanism located upstream of the airfoil passage. The near-suction-surface total pressure field (flow without wakes) and velocity field (flow with wakes) in the trailing part of the airfoil passage, and the wall-normal gradient of these quantities, were used to demonstrate effective prevention of flow separation using the plasma actuator. Both flows (with and without passing wakes) showed fully attached flow (or very thin separation zones) when the actuator was activated. The flow with passing wakes and the actuator on showed relatively little time variation in the boundary layer, and qualitative similarities to the corresponding flow without passing wakes and with the actuator on were noted.