STUDIES OF THE POINT BLAST NUMERICAL EXPERIMENT

V.M. Ktitorov, V. Yu. Meltsas
VANT. Ser.: Mat. Mod. Fiz. Proc 1997. Вып.1. С. 57.

      The problem of finding the cases of unstable evolution of the, point blast in perfect gas was actually formulated since 1980’s when the self-similar, approach applied to 2-D linearized hydrodynamic equations showed [1,2] that for the gas adiabatic ratio close to unity (less than 1,20) Raleigh-Taylor instability occurs at the front of such blast when the gas compressed by the shock wave to a thin dense shell is decelerated by the arriving flow relative to low density gas.
      The difficulty in experimental validation of this instability and on the other hand the significance of this result both conceptually and for astrophysical applications motivated the wish to verify it in a numerical experiment.
      This work examines the evolution of 2-D perturbations in the blast with a gas adiabatic ratio close to unity (1,15). The initial values were represented by various sets of 2-D perturbations:
      - perturbations with harmonic number n = 2,4,8,16;
      - linear combinations;
      - bubble perturbation on the axis.
      The computations allowed:
      1. To show that irrespectively of initial conditions the evolution mode of perturbations in a short time (the increase in the shock wave radius by 3-4 times) becomes self-similar further behaving in accordance with [1,2].
      2. To study quantitatively further decay (with the perturbation amplitude increase) of the linear self- similar mode [1,2] followed by the transition to turbulization. The critical amplitudes are found after which the evolution pattern becomes nonlinear.
      3. Ktitorov V.M. // Voprosy Atomnoy Nauki i Tekhniki. Ser. Teoreticheskaya i Prikladnaya Fizika. 1984. N 2(2). P. 28.
      4. Ryu D. and Vishniac E.T. // Astrophys. J. .1987. Vol. 313. P. 820. Vishniac E.T. and Ryu D. // Ibid. 1989. Vol. 337. P. 917.