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Abstract

The shock wave boundary layer interaction (SWBLI) occurs in transonic, supersonic and hypersonic applications, for example, the transonic aerofoil, and supersonic inlet. In the occurrence of SWBLI, the incoming boundary layer is subject to an intense adverse pressure gradient caused by the shock wave, leading to a separation. Apart from boundary layer separation, other adverse effects include enhanced turbulence and additional unsteady load to the structure. All those adverse effects will degrade the aerodynamic efficiency and lead to potential structural failure. Flow control is thus needed to address the SWBLI. Recently, the arc-discharge plasma actuator has emerged as a new type of active control device to enhance the SWBLI flow control.

This thesis explores the fundamental characteristic and flow control mechanism of arcdischarge plasma actuators, focusing on the localised arc filament plasma actuator (LAFPA) and the plasma synthetic jet actuator (PSJA). Theoretical, experimental investigations and numerical simulations were conducted to illustrate the performance of these actuators within a wide range of setups and operation conditions, including the operation frequency (0.5-2 kHz), the cavity volume (128-512 mm3) and the discharge energy (2.8-11.3 mJ). The traditional Z-type Schlieren technology was applied to visualise flow structures and capture detailed propagating information of gas dynamic interfaces after the arc discharge (e.g. thermal plasma kernel, shock waves, jet flow). Numerical simulation through ANSYS Fluent was also applied in support of the experimental data and compared with a developed 1D code. Direct numerical simulations (DNS) of the shock wave boundary layer interaction (SWBLI) control through LAFPA were well analysed through collaboration. The effect of PSJAs on the transonic shock wave boundary layer control was conducted by the Unsteady Reynolds-averaged Naiver-stokes equations (URANS).

Several findings have been derived from the investigation at hand. Firstly, the fundamental flow characteristics of LAFPA employing flush electrodes and electrodes located outside the wall have been effectively captured. Schlieren imaging enabled confirmation of the plasma kernel’s shape, blast wave propagation, and thermal fluctuation. Secondly, using five PSJA models, simulations in a quiescent environment are conducted, facilitating detailed analyses of the instantaneous evolution of velocity, pressure, and temperature. By developing a one dimensional code, orifice velocities could be predicted for different input energy levels and cavity volumes, with outcomes consistent with 3D simulations. Additionally, DNS results demonstrated the control mechanism of LAFPA to SWBLI, whereby the high-frequency operation of LAFPA resulted in the emission of precursor shock waves (PSWs) that merged with the separation shock by coalescing into an oblique shock. Lastly, URANS results revealed that the arc-forced micro jets effectively controlled the central separation area of the transonic SWBLI.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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