Geometry, Dissipation, Cooling, and the Dynamical Evolution of Wind-Blown Bubbles
arxiv(2024)
摘要
Bubbles driven by energy and mass injection from small scales are ubiquitous
in astrophysical fluid systems and essential to feedback across multiple
scales. In particular, O stars in young clusters produce high velocity winds
that create hot bubbles in the surrounding gas. We demonstrate that the
dynamical evolution of these bubbles is critically dependent upon the geometry
of their interfaces with their surroundings and the nature of heat transport
across these interfaces. These factors together determine the amount of energy
that can be lost from the interior through cooling at the interface, which in
turn determines the ability of the bubble to do work on its surroundings. We
further demonstrate that the scales relevant to physical dissipation across
this interface are extremely difficult to resolve in global numerical
simulations of bubbles for parameter values of interest. This means the
dissipation driving evolution of these bubbles in numerical simulations is
often of a numerical nature. We describe the physical and numerical principles
that determine the level of dissipation in these simulations; we use this,
along with a fractal model for the geometry of the interfaces, to explain
differences in convergence behavior between hydrodynamical and
magneto-hydrodynamical simulations presented here. We additionally derive an
expression for momentum as a function of bubble radius expected when the
relevant dissipative scales are resolved and show that it still results in
efficiently-cooled solutions as postulated in previous work.
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