Experimental and numerical studies of weak blast waves in air

Abstract

Abstract. Effects of viscosity and vibrational nonequilibrium on the profile of a weak, spherical N-wave in air are experimentally and numerically studied. Weak blast waves were generated, in a quiescent air dome, by spark discharges and exploding wires and observed by high frequency response microphones over 40 meters. Some similarity relationships were obtained from the blast wave experiments. For observed N-waves having less than 100 Pa peak overpressure, the peak overpres- Similar trends were also found for the negative phase of the blast wave. Numerical simulations were carried out to compare with the blast wave data. The Navier-Stokes equations for spherical symmetric flows were solved by coupling with a relaxation equation for vibrational excitation of oxygen using the random choice method (RCM) adapted to supercomputing with an operator splitting technique. The resultant N-wave profiles are in good agreement with the experimental results. The numerical results clearly indicate that the wave-easing process due to the dispersive effect of vibrational relaxation plays a dominant role in determining the rise time of the N-wave.

Laboratory-scale experiment to study nonlinear N-wave distortion by thermal turbulence

“…The characteristics of spark-generated N-waves have been previously studied in details in the literature [16][17][18][19][20] and by the present authors. 12,13,21 Hereafter, the main features of the source used in the present study are given.…”

“…Without turbulence, the decrease of the peak pressure with the distance is due to a combination of spherical spreading of the pressure wave, linear absorption, relaxation, and nonlinear effects. 12,19 C. Thermal turbulence…”