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We present results from two-dimensional numerical simulations of a supersonic turbulent flow with parameters characteristic of the interstellar medium at the 1 kpc scale in the plane of the galactic disk. The simulations include heating above a critical density, in order to model heating from stars at unresolved scales, as well as cooling and diffuse heating terms. As a first step, we omit magnetic fields and heating from supernovae. The calculations show segregation of the ISM into a warm, diffuse phase at $\sim 10^4$ K and a cold, denser phase at $\sim 1.5\times 10^3$ K, coexisting in nearly (but not exactly) pressure equilibrium. The model suggests a life cycle for the ISM and cloud formation in which turbulence generates high-density complexes (cloud complexes) by mass advection (ram pressure), while self-gravity and cooling allow the complexes to reach densities high enough to produce star formation, which in turn generates more turbulence. The longest-lived clouds in the simulations have lifetimes $\sim 10^8$ yr, and are the closest to be in virial equilibrium between gravity, thermal pressure, and turbulent kinetic energy, although a variety of energy ratios within the clouds is observed. This suggests that individual clouds do not have a tendency to become virialized; it is only because nearly-virial clouds have longer lifetimes that they are more frequently observed. Other aspects of the cloud energetics and the equivalent equation of state of the flow are briefly discussed. Finally, the system also exhibits large-scale gravito-acoustic waves, equivalent to density waves in galaxies, which appear to be triggered by the initial transients.
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