Dielectric barrier Discharge Plasma Actuator Characterization and Application

An experimental investigation about nanosecond Dielectric Barrier Discharge (ns-DBD) plasma actuator is presented in this thesis. This work aimed to answer fundamental questions on the actuation mechanism of this device. In order to do so, parametric studies in a quiescent air as well as laminar bounded of free shear layers were performed. Amplitude and location of the input with respect to the receptivity region as well as frequency of flow actuation were investigated. This work required the implementation of acquisition techniques such as Schlieren, Particle Image Velocimetry (PIV), infrared thermography, back current shunt technique and balancemeasurements. Moreover, tools of analysis were employed such as Linear Stability Theory (LST), Proper Orthogonal Decomposition (POD) and Inverse Heat Transfer Problem(IHTP). Results revealed that the effect of a ns-DBD is that of “enhancing” the development of natural hydrodynamic instabilities of the specific field of motion. Therefore, in case of a laminar boundary layer, the effect of a ns-DBD plasma actuator was to amplify Tollmien–Schlichting waves according to linear stability theory. Such results led to understand the influence of the actuator position on the achievement of a specific flow control task. A ns-DBD is capable of producing several effects: a shock wave, a small body force and a thermal gradient within the discharge volume. Thus, three were the possible causes of flow actuation. The shock wave was found to be too weak to be capable of introducing an appreciable disturbance. As the shock wave, also the momentum injection induced by the body force produced by the pulsed discharge was found to be relatively too small to justify a control authority based on momentum redistribution within the boundary layer, for cases of relatively high freestream velocity. Thus, the thermal gradient induced within the discharge volume by the energy deposition of a high voltage nanosecond discharge is the effect capable of inducing a relatively large disturbance into the field of motion. Nevertheless, a thermal gradient within a gaseous flow induces two effects, it reduces density and increases viscosity. At the moment it is still unclear which of these two effects is more relevant. Once identified the thermal gradient as the main cause of flow control mechanism, a characterization study was performed aimed to identify the properties of a ns-DBD plasma actuator (thermal, electrical and geometrical) important tomaximize the induced thermal gradient within the discharge volume. In general, a higher efficiency is achieved by a strong dielectric material concerning thermal energy deposition. A barrier of a ns-DBD plasma actuator should be as thin as possible. However, the thickness affects also the lifetime of the barrier itself. Nanosecond pulsed DBD plasma actuators have shown to have the capability to delay leading edge separation. However, in the relevant literature, an influence of the actuation frequency on the achieved results is always reported. In order to investigate this frequency effect, a parametric study on a Backward Facing Step was performed. This geometry was selected because it mimics a fixed point laminar separation, the flow sceixnario of interest. Such flow scenario is unstable at high frequencies close to the step and low frequencies downstream the step and it naturally develops a most unstable mode within it. However, when a flow is actuated, its stability changes, so do the most unstable frequencies naturally developed within it. Results showed that the effect of actuation is the redistribution of energy among modes and that the optimal frequency of actuation must be based on the new stability achieved by the flow due to the actuation itself. Moreover, results indicated that the optimal frequency of actuation is not related to the most unstable frequencies naturally present within the base non-actuated flow. A method to quantify the efficiency of ns-DBDs in depositing energy within the discharge volume is proposed. This energy is the one that eventually contributes to the formation of the thermal gradient responsible of the flow control capabilities shown by these devices. Such method is based on simultaneous implementation of infrared thermography and back-current shunt techniques. Results showed that the overall efficiency of a ns-DBD plasma actuator is inversely proportional to the thickness of the dielectric barrier. Last part of this thesis is concerned with a demonstrative application of a ns-DBD plasma actuator on a two element airfoil, at Reynolds numbers ranging between 0.2·106 and 2 ·106. Results demonstrated its capability to delay separation, increase lift and reduce drag in the post stall regime. Moreover, the plasma actuator showed the capability to eliminate both a laminar bubble separation for small angles of attack and the hysteresis behaviour of the selected airfoil. In conclusion, this work shed some light on the flow actuation mechanism of a ns- DBD plasma actuator and deepened its basic knowledge.AerodynimicsAerospace Engineerin

Method to quantify the electrical efficiency of a ns-DBD plasma actuator

An experimental investigation was conducted on the effective efficiency of a nanosecond Dielectric Barrier Discharge (ns-DBD) plasma actuator. Back-current shunt technique and infrared thermography measurements were carried out at the same time on an upside-down flat plate in a quiescent environment. The only investigated parameter was thickness of the dielectric barrier. Voltage amplitude and frequency of discharge were kept constant at maximum values allowable by the used power generator, i.e. 10k Volt and 10k Hz respectively. The selected material for the dielectric barrier was Makrolon(r) because of its well know thermal and dielectric propriety. Energy input was calculated as difference between the pulse voltage given and the one reflected back into the system via back current shunt technique. Ideal power flux obtained if all the input energy was converted to heat is then calculated. The actual power flux was obtained by solving an IHTP (Inverse Heat Transfer Problem) once the transient temperature distribution on the surface of the dielectric barrier was measured by means of IR thermography. The ratio between these two values represents a quantification of electrical efficiency of an ns-DBD plasma actuator. Results prove the high performances of ns-DBD plasma actuator in the respect of energy deposition and that the efficiency depends on the thickness of the barrier.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin

Experimental method to quantify the efficiency of the first two operational stages of nanosecond dielectric barrier discharge plasma actuators

A method to quantify the efficiency of the first two operational stages of a nanosecond dielectric barrier discharge (ns-DBD) plasma actuator is proposed. The method is based on the independent measurements of the energy of electrical pulses and the useful part of the energy which heats up the gas in the discharge region. Energy input is calculated via a back current shunt technique as the difference between the energy given and the energy reflected back. The ratio of the difference of the latter two quantities and the energy input gives the electrical efficiency (η E) of a ns-DBD. The extent of the energy deposited is estimated via Schlieren visualizations and infrared thermography measurements. Then, the ideal power flux obtained if all the inputted energy was converted into heat is calculated. Transient surface temperature was measured via infrared thermography and used to solve a 1D inverse heat transfer problem in a direction normal to the surface. It gives as output the actual power flux. The estimated ratio between the two power fluxes represents a quantification of the mechanical fluid efficiency (η FM) of a ns-DBD plasma actuator. Results show an inverse proportionality between η E, and η FM, and the thickness of the barrier. The efficiency of the first two operational stages of a ns-DBD is further defined as η  =  η E centerdot η FM.AerodynamicsWind Energ

Increase quantum computing technology readiness level through experimentation in space

The exploitation of quantum physics and of quantum states superposition and entanglement properties for computing applications has been studied since 1980s [1] [2] for their disrupting potential in the evolution of information theory. Although quantum computing is still in its infancy, experiments have been carried out and proto-types have been developed, showing promising results for future commercial applications [3] [4] [5] [6]. Research in both theoretical and practical areas continues at a frantic pace, and many national governments, research institutions and military funding agencies support quantum computing research to develop quantum computers for both civilian and national security purposes, such as cryptanalysis, genetics, drugs and disease research, materials science and design and so on [2]. Thanks to its computing power, the usage of quantum computing capabilities in orbit would bring priceless benefits to space and enable novel methodologies and technologies to improve both on ground and in space applications. On-board cyber-security, satellite AI, advanced autonomous life support systems for human exploration are only few of the domains which could be dramatically boosted by the availability of this technology. The paper discusses an early study about an experimentation of a quantum computer in orbit as a first step for a future fully qualified flight-ready payload. It discusses the major benefits of a flight experimentation, focusing on the one hand on the objectives and the expected benefits that it will bring to the development of the space borne and on-ground technology, on the other hand on the open questions like the effect of microgravity on the architecture of this technology. It analyses the currently available implementation solutions of quantum computers on ground which are currently prototyped (e.g. IBM Q System One), and provides early results on the identified main technical aspects to be considered to improve the technology readiness level. It highlights the most important challenges to be considered in the design and the added value that the space environment will bring as scientific feedback. Finally, it describes possible scenarios and mission profiles analysed and identified as potential hosting platform candidates, focusing on pros and cons of each of them.Wind EnergyComputer EngineeringFTQC/Bertels Lab(OLD)Quantum Computer Architecture

Flow Separation Control on Airfoil With Pulsed Nanosecond Discharge Actuator

An experimental study of flow separation control with a nanosecond pulse plasma actuator was performed in wind-tunnel experiments. The discharge used had a pulse width of 12 ns and rising time of 3 ns with voltage up to 12 kV. Repetition frequency was adjustable up to 10 kHz. The first series of experiments was to measure integral effects of the actuator on lift and drag. Three different airfoil models were used, NACA-0015 with the chord of 20 cm, NLF-MOD22A with the chord of 60 cm and NACA 63-618 with the chord of 20 cm. Different geometries of the actuator were tested at flow speeds up to 80 m/s. In stall conditions the significant lift increase up to 20% accompanied by drag reduction (up to 3 times) was observed. The critical angle of attack shifted up to 5–7 degrees. The relation of the optimal discharge frequency to the chord length and flow velocity was proven. The dependence of the effect on the position of the actuator on the wing was studied, showing that the most effective position of the actuator is on the leading edge in case of leading edge separation. In order to study the mechanism of the nanosecond plasma actuation experiments using schlieren imaging were carried out. It shown the shock wave propagation and formation of large-scale vortex structure in the separation zone, which led to separation elimination. PIV diagnostics technique was used to investigate velocity field and quantitative properties of vortex formation. In flat-plate still air experiments small scale actuator effects were investigated. Measured speed of flow generated by actuator was found to be of order of 0.1 m/s and a span-wise nonuniformity was observed. The experimental work is supported by numerical simulations of the phenomena. The formation of vortex similar to that observed in experiments was simulated in the case of laminar leading edge separation. Model simulations of free shear layer shown intensification of shear layer instabilities due to shock wave to shear layer interaction.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin