The boundary effects of the shock wave dispersion in discharges

Abstract

Investigation on oblique shock wave control by arc discharge plasma in supersonic airflowInteraction of shock waves with a weakly ionized gas generated by discharges has been studied. An additional thermal mechanism of the shock wave dispersion on the boundary between a neutral gas and discharge has been proposed ͓A. Markhotok, S. Popovic, and L. . This mechanism can explain a whole set of thermal features of the shock wave-plasma interaction, including acceleration of the shock wave, broadening or splitting of the deflection signals and its consecutive restoration. Application has been made in the case of a shock wave interacting with a laser induced plasma. The experimental observations support well the results of calculation based on this model.

Shock wave refraction enhancing conditions on an extended interface

“…For a smooth boundary, 19 the coefficient b in the velocity ratio (15) is equal 1 = 2 exactly (1/R ¼ 0) since the Mach number does not change across the interface. For a sharp boundary, 21 the coefficient b is remarkably smaller than 1 = 2 since the velocity ratio (2) is dependent also on the Mach number ratio.…”

“…The thermal plasma/gas regions are always present, for example, in the energy deposition experiments and they are described, in the absence of diffusion, as nonuniform gas objects, with a temperature profile for the initial temperature distribution that can be approximated with a Gaussian function. 17 The boundary effects in the shock wave refraction for the two dimensional cases of sharp [18][19][20] and smooth 21 boundaries have been discussed recently. In this paper, we generalize those results for a case when a plasma boundary is extended over some distance and has a steep parameter distribution across it, as defined in Sec.…”

The cumulative energy effect for improved ignition timing

“…Changes in the shock propagation direction due to its refraction on the interface may result in the shock missing the point of ignition at the desired timing schedule. There is also a possibility that under certain conditions a shock wave propagating through such an interface may arrive at a point where it collapses 19 thus reaching a limit of the use of the cumulation effect.…”

“…While the energy transfer processes on a molecular/atomic level (such as electronic excitation, vibrational excitation or relaxation, chemical reactions, ionization and dissociation, or radiation) can significantly contribute in nonequilibrium state, the pure thermal mechanisms would be more important in the flows with established local equilibrium. 20 Such flows can be present in MHD generators, rocket plumes, plasma chemical reactors, and molecular lasers. The local equilibrium can be established, for example, at the last stages of decaying plasmas or pulsed laser energy deposition in quiescent air.…”

“…16 The shock front shape can be changed from plane to curved and back, with the possibility of gaining an additional dimension. [17][18][19][20] The specific details of the gas state, such as electron kinetic, ionization/dissociation processes, radiation, atomic/molecular transitions, energy exchange processes in collisions, chemical processes, boundary effects, heat, charge (in plasma), or radiation convection, 21,22 add to the variety and complexity of the final state of the gas/plasma or the shock wave structure after the interaction.…”