Abstracto

Ablative Pressure Pulse

J. A. Grzesik

We examine herein a simple model for the evolution in time of the pressure which a suddenly vaporized, ablating layer exerts upon the subjacent body. The model invokes a plausible construct of surface material instantaneously thrust into a gaseous regime governed by a Maxwell-Boltzmann phase space distribution. The surface pressure per se is gotten by computing the time rate of change of the momentum per unit area which the retrograde molecules, and only those, transfer through impact/reflection to the unvaporized body below. An explicit pressure formula, one alluding to the variable gas temperature within the vaporized layer, is obtained as a single quadrature requiring numerical integration at finite times τ>0 past the onset of impact. Limiting, null pressure values, both close-in, with τ=0+, and in pulse aftermath as τ→∞, can nevertheless be extracted in analytic terms, confirming in particular the indispensable asymptotic evanescence. A universal formula in dimensionless variables is given for pressure versus time, both suitably normalized.