|Title:||Applications of dielectric barrier discharge plasma actuator for flow control|
|Advisors:||Wen, Chih-yung (AAE, ME)|
|Department:||Department of Mechanical Engineering|
|Pages:||xix, 130 pages : color illustrations|
|Abstract:||Active flow control using dielectric barrier discharge (DBD) plasma actuators has become a promising technology to promote aerodynamic performance. This thesis presents the investigation of the application of AC-driven DBD plasma actuators and plasma streamwise vortex generators (PSVGs) on a D-shaped bluff body in low Reynolds number and a pulsed nanosecond dielectric barrier discharge plasma actuator (NSDBD) on a supersonic compression corner.|
First, the characteristics of different ACDBD and NSDBD plasma actuators and PSVGs on the flat plate model have been studied experimentally. As one of the most interested in a flow control field, the thermal effects of the NSDBD with varying pulse voltages and pulse repetitive frequencies (PRFs) under different air pressures ranging from 0.1 to 1 bar are studied experimentally. The results will provide references for the mechanism detection of icing mitigation and flow control based on NSDBD plasma actuators.
The control performance of a streamwise-oriented DBD plasma actuator, a set of PSVGs, and a hybrid actuator on the reduction in bluff body flow separation, vortex-induced vibration (VIV), and wake fluctuation is experimentally investigated. Particle image velocimetry (PIV) is used to obtain details on the flow fields over a short D-shaped bluff body. Force measurement is conducted to compare the reduction in drag and vibration oscillations using these three types of plasma actuators. The PIV flow fields show that all of the plasma actuators suppress the flow separation on the bluff body, narrow the size of the wake, and decrease the turbulence kinetic energy (TKE) level in the wake. This stable controlled vortex shedding system can reduce the effect of the natural frequency of the bending stiffness-dominated cylinder structure system, thus avoiding the occurrence of resonance in advance. The reduction in drag and lateral lift oscillation are studied by mapping the changes in force coefficients and fluctuations as a function of Reynolds number. A comparison of these plasma actuators shows that the hybrid actuator achieves best drag reduction, suppression of lift oscillation, and Kármán vortex shedding in the wake at low speed, because three-dimensional flow structures are generated on the surface of the bluff body that consequently enhance the mixing.
The control performance of a pulsed NSDBD plasma actuator with varying pulse voltages and locations for a laminar flow separation on a supersonic compression corner is studied using experiments and numerical simulations under a unit Reynolds number of 7.8 × 10^6 m-1 and Mach number of 4. The plasma actuators are placed either upstream or downstream of the separation point, extending in the spanwise direction. The Schlieren technique is used to visualize the shock wave interaction and estimate the propagation speed of the induced shock by the plasma actuator. The results indicate that the high-speed external fluid is entrained into the original separation region after NSDBD activation upstream of the separation point, resulting in flow reattachment upstream of the corner. The entrained fluid with high momentum compels the main separation to move downstream, accompanied by the fragmentation of the original shear layer. For a supersonic compression corner, excitation near the separation point achieves a higher efficiency in suppressing the separation bubble.
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