Optical Quality of Pulsed Electron-Beam Sustained Lasers

Plasma Sources Sci. Technol.

et al. 2012

Recent experiments with a nanosecond-pulse, dielectric barrier discharge at the stagnation point of a Mach 5 cylinder flow have demonstrated the formation of weak shock waves near the electrode edge, which propagate upstream and perturb the bow shock. This is a promising means of flow control, and understanding the detailed physics of the conversion of electrical energy into gas motion will aid in the design of efficient actuators based on the concept. In this work, a simplified configuration with planar symmetry was chosen as a vehicle to develop a physics-based model of nanosecond-pulse discharges, including realistic air kinetics, electron energy transport, and compressible bulk gas flow. A reduced plasma kinetic model (23 species and 50 processes) was developed to capture the dominant species and reactions for energy storage and thermalization in the discharge. The kinetic model included electronically and vibrationally excited species, and several species of ions and ground state neutrals. The governing equations included the Poisson equation for the electric potential, diffusion equations for each neutral species, conservation equations for each charged species, and mass-averaged conservation equations for the bulk gas flow. The results of calculations with this model highlighted the path of energy transfer in the discharge. At breakdown, the input electrical energy was transformed over a time scale on the order of 1 ns into chemical energy of ions, dissociation products, and vibrationally and electronically excited particles. About 30% of this energy was subsequently thermalized over a time scale of 10 µs. Since the thermalization time scale was faster than the acoustic time scale, the heat release led to the formation of weak shock waves originating near the sheath edge, consistent with experimental observations. The computed translational temperature rise (40 K) and nitrogen vibrational temperature rise (370 K) were of the same order of magnitude as experimental measurements (50 K and 500 K, respectively), and the approach appears promising for future multi-dimensional calculations. The effectiveness of flow control actuators based on nanosecond-pulse, dielectric barrier discharges is seen to depend crucially on the rapid thermalization of input energy, in particular the rate of quenching of excited electronic states and the rate of electron-ion recombination.

Section: Acoustic Wavessupporting

confidence: 90%

“…The generation of shock waves by volumetric heat release in pulsed discharges was observed and explained in the 1970s in the context of gas laser technology [13,14]. Early computations by Aleksandrov et al [14] assumed that all the power dissipated in the discharge immediately went into heating the neutral gas.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of nanosecond-pulse electrical discharges

Plasma Sources Sci. Technol.

et al. 2012

“…11,12 The generation of shock waves by volumetric heat release in pulsed discharges was observed and explained in the 1970s in the context of gas laser technology. 13,14 Early computations by Aleksandrov et al 14 assumed that all the power dissipated in the discharge immediately went into heating the neutral gas. Popov,15 however, has proposed a two-stage heating mechanism in which product species and electronically excited species are generated by electron impact, and then the stored chemical energy is converted to thermal energy through quenching and recombination reactions.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of a Nanosecond-Pulse Discharge in Mach 5 Flow

51st AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

et al. 2013

A physics-based model was developed for nanosecond-pulse discharges, including realistic air kinetics, electron energy transport, and compressible bulk gas flow. A reduced plasma kinetic model (23 species and 50 processes) was developed to capture the dominant species and reactions for energy storage and thermalization in the discharge. The kinetic model included electronically and vibrationally excited species, and several species of ions and ground state neutrals. The governing equations included the Poisson equation for the electric potential, diffusion equations for each neutral species, conservation equations for each charged species, and mass-averaged conservation equations for the bulk gas flow. The results of calculations with this model highlighted the path of energy transfer in the discharge. At breakdown, the input electrical energy was transformed over a timescale on the order of 1 ns into chemical energy of ions, dissociation products, and vibrationally and electronically excited particles. About 30% of this energy was subsequently thermalized over a timescale of 10 μs. Since the thermalization time scale was faster than the acoustic time scale, the heat release led to the formation of weak shock waves originating near the sheath edge, consistent with experimental observations.

“…21 The generation of shock waves by volumetric heat release in pulsed discharges was observed and explained in the 1970s in the context of gas laser technology. 22,23 Early computations by Aleksandrov et al 23 assumed that all the power dissipated in the discharge immediately went into heating the neutral gas. Analogous calculations have been carried out recently for two dimensions by Unfer and Boeuf.…”

Section: Introductionmentioning

confidence: 99%

High-Speed Flow Control with Electrical Discharges

42nd AIAA Plasmadynamics and Lasers Conference

et al. 2011

Numerical calculations were carried out to examine the physics of the operation of nanosecond-pulse, single dielectric barrier discharges for high-speed flow control. Conditions were selected to be representative of the stagnation region of a Mach 5 cylinder flow that was the subject of recent experiments. A four-species formulation was employed, including neutrals, ions, electrons, and a representative excited molecular species. The following models were employed to predict particle motion: a drift-di↵usion formulation for the charged particles, a di↵usion equation for the excited molecules, and a five-moment fluid formulation for the neutrals. The Poisson equation was solved for the electric potential. During a 20 kV Gaussian input pulse lasting approximately 120 ns, an average energy density of about 40 J/m 3 was stored in excited molecular states. Quenching reactions released this stored energy within about 10 µs, converting it into translational energy of the neutrals and forming weak shock waves. The maximum neutral gas temperature rise predicted by the model was about 40 K.