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Title: Application of dielectric barrier discharge plasma actuators on a highly swept delta wing
Authors: Shen, Lu
Degree: Ph.D.
Issue Date: 2018
Abstract: The interest in the active flow control based on dielectric barrier discharge (DBD) plasma actuators has increased rapidly in the past decade because it is a promising technology in advancing the aerodynamic performance and maneuvering of unmanned aerial vehicles (UAV). This thesis reports an experimental investigation on the application of AC-DBD plasma actuators for active flow control on a highly swept delta wing, particularly for the leading edge vortex (LEV) breakdown control. First, the characteristics of DBD plasma actuators on a flat plate and at the leading edge are investigated in the quiescence air, both with the steady mode and periodic mode. The results show that the steady mode DBD generates a wall jet on the model surface and the periodic DBD induces a vortices queue continually. Parameters that affect the performance of the actuator are also examined. The power efficiency and induce momentum coefficient are measured as well. A pre-seeded smoke flow visualization technique is applied to measure the time history of the LEV breakdown location. Then, an improved peak-valley-counting method is used to decompose the high-frequency low-amplitude oscillations from the dominant one. It is noted that a small-scale oscillation exists in the time history with a frequency in the same band of the helical mode instability, which is detected in the LEV breakdown wake. The vortex-shear flow interaction mechanism is proposed to be responsible for the quasi-periodic anti-symmetric interaction between the LEV breakdown locations. The experimental result shows a good agreement with this mechanism.
The steady DBD plasma actuator at the leading edge shows its feasibility of the LEV control on the delta wing. At a sufficient angle of attack, the symmetric control leads to a delay of both LEV breakdown locations; whereas, the asymmetric control advances the LEV breakdown on the controlled side and delays the one on the other side. The crossflow interaction is responsible for the opposite control effect on the controlled side in these two cases. The particle image velocimetry (PIV) results also indicate that the separated shear layer from the leading edge is deformed by the control, therefore to affect the other flow structures. Based on the above experimental result, the periodic DBD control is applied on the delta wing. The phase-lock PIV clearly demonstrates the evolution of the control effect at the leading edge. It is found that the control effect is dependent on the angle of attack. At a low angle of attack, the DBD plasma actuator destroys the local weak shear layer and entrains a new shear layer attaching on the leeward surface to the inboard side. At a medium angle of attack, the local shear layer is deformed to the inboard bottom. Vortices are generated in the shear layer and finally merge with the LEV. At a high angle of attack, the DBD plasma actuator promotes the shear layer to generate a new LEV at the leading edge. The new LEV further develops with the shear layer and finally dominate the flow field. It is also observed that the periodic control induces an oscillation in the flow field. Through this study, the knowledge of DBD plasma actuators has been improved; and the underling mechanism of DBD-based LEV control on a delta wing has been well understood.
Subjects: Hong Kong Polytechnic University -- Dissertations
Leading edges (Aerodynamics)
Airplanes -- Wings, Triangular
Pages: xxi, 137 pages : color illustrations
Appears in Collections:Thesis

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