GRAVITATIONAL-INSTABILITY IN A PURE SUPER CRITICAL-FLUID

The hydrodynamic stability of a thermodiffusive interface in near supe rcritical fluid is studied. The Navier-Stokes equations written for a van der Waals gas set above its critical point are solved by means of a finite volume numerical method. The growth rate of the fluctuations shows that a cutoff wave number exists beyond which the short wave len gths are stabilized. The good agreement between the values obtained an d recent theories confirms that a near critical fluid subjected to a t hermal gradient may develop a gravitational instability for which the density gradient is driven by thermal diffusion and high compressibili ty and not by species diffusion.