Numerical simulation of nanosecond-pulse electrical discharges

Abstract

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.

Effects of pulse polarity on nanosecond pulse driven dielectric barrier discharge plasma actuators

“…This is in contrast to the behavior of the dielectric surface which does not readily give up electrons. Modeling and simulation of nanosecond pulse discharges are a subject of current research [26][27][28][29][30][31][32][33][34][35][36][37] and the exact kinetic mechanisms responsible for near-surface gas heating and subsequent aerodynamic flow control are not completely clear. However, the importance of electrons as a driver for this process is generally accepted and supports the suggestion in this paper regarding the role of the exposed electrode.…”

Simulation of Nanosecond Pulsed DBD Plasma Actuation with Different Rise Times

“…Classical boundary conditions were employed for plasma model. On the surface of upper electrode and dielectric barrier, second electron and electron energy emission were considered: where α s and α ′ s (=− α s ) is the switch function and is equal to 0 when the ion flow is away from the surface, else equal to 1. γ i , the secondary electron emission coefficient, is set as 0.05, same as that in Ref . It has to be mentioned that, the secondary electron emission coefficient is set as a constant value, as currently there hasn't been a systematical and deep insight into the mechanism on how this value will affect nanosecond pulsed plasma discharge .…”

“…where a s and a 0 s (¼Àa s ) is the switch function and is equal to 0 when the ion flow is away from the surface, else equal to 1. g i , the secondary electron emission coefficient, is set as 0.05, same as that in Ref. [20][21][22][23] It has to be mentioned that, the…”

Hypersonic Flow over a Cylinder with a Nanosecond Pulse Electrical Discharge

“…This assumption may be reevaluated in future work, but it is unlikely that its inclusion into the model will strongly influence the formation of the subsequent compression wave, given that the ion wind would induce a transverse velocity (in contrast to the upstream traveling compression wave). In addition, recent high-fidelity 1-D computations [22] of the ns-DBD showed that the device created a very small region of relatively high ion density and electric field required for the ion wind effect, and that the very high electric field only existed for a short period of time prior to space-charge shielding suppressing the ion wind. As such, acceleration of neutral particles through ion-neutral collisions was very limited, and the majority of the fluid motion was associated with rapid thermal energy transfer into the translational energy mode.…”