We study the dynamics of phase transitions in the interstellar medium by means of three-dimensional hydrodynamic numerical simulations .
We use a realistic cooling function and generic nonequilibrium initial conditions to follow the formation history of a multiphase medium in detail in the absence of gravity .
We outline a number of qualitatively distinct stages of this process , including a linear isobaric evolution , transition to an isochoric regime , formation of filaments and voids ( also known as “ thermal ” pancakes ) , the development and decay of supersonic turbulence , an approach to pressure equilibrium , and final relaxation of the multiphase medium .
We find that 1 % -2 % of the initial thermal energy is converted into gas motions in one cooling time .
The velocity field then randomizes into turbulence that decays on a dynamical timescale E _ { k } \propto t ^ { - \alpha } , 1 ~ { } \raise 1.29 pt \hbox { $ < $ } \kern - 7.5 pt { \lower 2.795 pt \hbox { $ \sim$ } } ~ { } \alpha~ { % } \raise 1.29 pt \hbox { $ < $ } \kern - 7.5 pt { \lower 2.795 pt \hbox { $ \sim$ } } ~ { } 2 .
While not all initial conditions yield a stable two-phase medium , we examine such a case in detail .
We find that the two phases are well mixed with the cold clouds possessing a fine-grained structure near our numerical resolution limit .
The amount of gas in the intermediate unstable phase roughly tracks the rms turbulent Mach number , peaking at 25 % when { \cal { M } } _ { rms } \sim 8 , decreasing to 11 % when { \cal { M } } _ { rms } \sim 0.4 .