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Speth, Rachelle LeaParametric Study of the Effects of the Flapping Mode Excitation on the Near Field Structures of a Mach 1.3 Cold Jet
Master of Science, The Ohio State University, 2012, Aero/Astro Engineering
This effort investigates numerical and physical parameters influencing an ideally-expanded Mach 1.3 jet excited by the m=+/-1 flapping mode. The excitation is imposed by eight Localized Arc Filament Plasma Actuators (LAFPA) placed around the periphery of the circular nozzle exit. The devices are modeled with a proven surface heating approach. The reference case considers the most amplified (jet column mode) frequency corresponding to a Strouhal number of 0.3, based on the diameter of the nozzle and the jet velocity, with an actuator-imposed temperature of 1500K and a duty cycle of 20%. Relative to this reference, the effects of changing frequency, duty cycle and actuator model temperature are explored. In some cases, e.g., actuator temperature, experimental data is not available, but for frequency, there is. The results are analyzed with several different quantitative and qualitative metrics, including time-averaged centerline decay and jet half width as well as phase-averaged coherent structures. Raising the frequency affects the dynamics in several ways. The number of vortical features observed in the phase-averaged data increases and the rate of decay of the centerline velocity is reduced. Furthermore, the alternating vortex ring interactions observed in the reference case are not distinct but are rather replaced by smaller structures, trends which are also observed in experiment. The flow mixes the fastest around the jet column mode (St~0.22). The higher duty cycles exhibits strengthened coherent structures and slightly higher jet growth along the flapping plane, but the overall dynamics remain the same. The response of the jet is relatively insensitive to actuator temperature model within reasonable limits. The latter two studies, with different duty cycles and actuator temperatures, are consistent with previous analyses demonstrating that instability manipulation, rather than heat deposition is the primary mechanism of control.

Committee:

Datta Gaitonde, PhD (Advisor); Mo Samimy, PhD (Committee Member); Mei Zhuang, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Mechanical Engineering

Keywords:

supersonic jets; Large Eddy Simulation; plasma actuators

Yugulis, Kevin LeeHigh Subsonic Cavity Flow Control Using Plasma Actuators
Master of Science, The Ohio State University, 2012, Aero/Astro Engineering

Localized arc filament plasma actuators have been used to control pressure fluctuations in a cavity with a length to depth ratio of 4.86. The rear wall of the cavity is inclined 30° above the horizontal plane and the cavity length is 61.7 mm, measured from the leading edge of the cavity to the mid-plane of the ramp. Five actuators have been uniformly distributed along the span of the wind tunnel at 1 mm upstream to the cavity leading edge. Experiments were conducted at Mach 0.6 and a Reynolds number of approximately 2x105 based on cavity depth. Forcing was conducted quasi-two-dimensionally and three-dimensionally. With this Mach number and geometry, the cavity was strongly resonating at the 2nd Rossiter mode corresponding to a frequency of 2.5 kHz.

Time-resolved pressure measurements were used to assess the effectiveness of the actuators. Forcing quasi-two-dimensionally was found to be very effective, achieving a reduction in peak tone magnitude of over 20 dB and a reduction in broadband SPL of up to 5 dB. In general, the results for forcing in this manner were extremely sensitive to forcing frequency. The most effective forcing frequency was found at approximately 3300 Hz. Forcing was also conducted in several three-dimensional configurations. Overall certain three-dimensional configurations were found to be more effective than the quasi-two-dimensional forcing, and significantly less sensitive to frequency.

Particle image velocimetry was used to understand how the forcing affected the shear layer. Interesting vortex dynamics such as possible vortex merging was observed, the details of which help to understand why certain frequencies are more effective than others. It was determined that the vortices in the shear layer are significantly weaker under three-dimensional forcing compared to quasi-two-dimensional forcing. This could help to explain the overall increase in effectiveness seen with three-dimensional forcing.

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Committee:

Mo Samimy, Dr. (Committee Co-Chair); James Gregory, Dr. (Committee Co-Chair)

Subjects:

Aerospace Engineering

Keywords:

aerodynamics; plasma actuators; cavity flow; active flow control

Atkinson, Michael D.Control of Hypersonic High Angle-Of-Attack Re-Entry Flow Using a Semi-Empirical Plasma Actuator Model
Doctor of Philosophy (Ph.D.), University of Dayton, 2012, Aerospace Engineering

The aim of this dissertation was to explore the possibility of using flow control to stabilize re-entry flight at very high angle-of-attack. This was carried out in three steps: 1) study the structure of representative high angle-of-attack re-entry flows; 2) develop a semi-empirical plasma actuator model that can be applied to control high angle-of-attack re-entry flows; 3) application of the plasma actuator model to study the control of representative re-entry flows. The calculations include viscous and thermochemical non-equilibrium effects, and a high-fidelity physical model to resolve complex flow structure.

The contribution of this dissertation was to provide a detailed description of hypersonic viscous flow around blunt-nosed elliptical cone at very high angle-of-attack. High-fidelity, thermochemical non-equilibrium numerical solutions of high angle-of-attack re-entry flows were not published prior to this research, and thus this research can provide a foundation to calculate, analyze, and describe very high angle-of-attack hypersonic re-entry flows.

Paramount to this dissertation was the development of a new phenomenological MHD plasma actuator model. A semi-empirical actuator model was developed by adding source terms to the momentum equation, vibrational energy equation, and total energy equation, employing an exponential decay function based on the formulations of Kalra et al. and Poggie. This new plasma actuator model was extended from Poggie's model to include thermochemical non-equilibrium effects and expanded from Kalra's et al. two-dimensional model to include three-dimensional effects. Development, validation, and calibration of the plasma actuator model was based on a qualitative comparison to the experiment of Kalra et al. on manipulating turbulent shock-wave/bounday layer interaction using plasma actuators. The effect of the plasma actuators on turbulent shock-wave/boundary-layer interaction was simulated numerically and a detailed description of the complex flow structure with and without actuation was provided.

Finally, application of the plasma actuators to control the complex flow structure of high angle-of-attack re-entry flight vehicles was investigated. To the best of the author's knowledge, no prior research on high angle-of-attack re-entry vehicle control using plasma actuators has been published. Lastly, this dissertation serves as a foundation to compute, analyze, and control complex flow generated around re-entry vehicles at high angle-of-attack.

Committee:

José A. Camberos, PhD (Committee Chair); Jonathan Poggie, PhD (Committee Co-Chair); Aaron M. Altman, PhD (Committee Member); Youssef N. Raffoul, PhD (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Hypersonic, Reentry; CFD; Plasma actuators; Flow Control; High angle of attack

Singhal, Achal SudhirUnsteady Flow Separation Control over a NACA 0015 using NS-DBD Plasma Actuators
Master of Science, The Ohio State University, 2017, Mechanical Engineering
Flow field surrounding a moving body is often unsteady. This motion can be linear or rotary, but the latter will be the primary focus of this thesis. Unsteady flows are found in numerous applications, including sharp maneuvers of fixed wing aircraft, biomimetics, wind turbines, and most notably, rotorcraft. Unsteady flows cause unsteady loads on the immersed bodies. This can lead to aerodynamic flutter and mechanical failure in the body. Flow control is hypothesized to reduce the load hysteresis, and is achieved in the present work via nanosecond pulse driven dielectric barrier discharge (NS-DBD) plasma actuators. These actuators have been effective in the delay or mitigation of static stall. The flow parameters were varied by Reynolds number (Re=167,000-500,000), reduced frequency (k=0.025-0.075), and excitation Strouhal number (Ste=0-10). It was observed that the trends of Ste were similar for all combinations of Re and k, and three major conclusions were drawn. It was first observed that low Strouhal number excitation (Ste<0.5) results in oscillatory aerodynamic loading in the stalled stage of dynamic stall. At high Strouhal number excitation (Ste>2), this behavior is not observed, as in the static stall cases. Second, all excitation resulted in earlier flow reattachment. Lastly, it was shown that excitation resulted in reduced aerodynamic hysteresis and dynamic stall vortex strength. The decrease in the strength of the dynamic stall vortex is achieved by the formation of excited structures that bleed the leading edge vorticity prior to the ejection of the dynamic stall vortex. At sufficiently high excitation Strouhal numbers (Ste˜10), the dynamic stall vortex was suppressed.

Committee:

Mo Samimy (Advisor); Datta Gaitonde (Committee Member); James Gregory (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Flow Control; Aerospace; Dynamic Stall; Plasma Actuators