Near-critical fluids as experimental models for geophysical flows: The case of internal gravity waves

We perform a theoretical analysis of internal gravity waves in near-critica l fluids to determine whether they have the same behavior as in classical f luids. Two points are studied: the relevance of classical incompressible eq uations and the possibility of a coupling between internal gravity waves an d the piston effect. Using asymptotic analysis of Navier-Stokes equations, it is shown that incompressible equations are applicable even very close to the critical point, and that the piston effect and internal gravity waves never couple, unlike what happens in the case of forced oscillations. These two conclusions confirm the relevance of using near-critical fluids to sim ulate internal gravity waves in large geophysical systems. (C) 2001 America n Institute of Physics.