ISSN:
1089-7674
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Nonlinear evolution of one-dimensional planar perturbations in an optically thin, radiatively cooling medium in the long-wavelength limit is studied numerically. The accepted cooling function generates, in thermal equilibrium, a bistable equation of state P(ρ). The unperturbed state is taken close to the upper (low-density) unstable state with infinite compressibility (dP/dρ=0). The evolution is shown to proceed in three different stages. At the first stage, pressure and density set in the equilibrium equation of state, and velocity profile steepens gradually, as in the case of pressure-free flows. At the second stage, those regions of the flow where anomalous pressure (i.e., with negative compressibility) holds create a velocity profile sharper than in the pressure-free case, which in turn results in formation of a very narrow (short-wavelength) region where gas separates the equilibrium equation of state and pressure equilibrium sets in rapidly. At this stage, the variation in pressure between the narrow dense region and the extended environment does not exceed more than 0.01 of the unperturbed value. At the third stage, gas in the short-wavelength region reaches the second (high-density) stable state, and pressure balance establishes through the flow, with pressure equal to the one in the unperturbed state. In external (long-wavelength) regions, gas forms slow isobaric inflow toward the short-wavelength layer. The duration of these stages decreases when the ratio of the acoustic time to the radiative cooling time increases. The limits in which nonlinear evolution of thermally unstable long-wavelength perturbations develops in isobaric regime are obtained. © 1999 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.873286
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