THE UNEXPECTED RESPONSE OF NEAR-CRITICAL FLUIDS TO LOW-FREQUENCY VIBRATIONS

The response of a slab-shaped container filled with a near-critical fluid and subjected to mechanical vibrations is studied by means of matched asymptotic expansions applied to the Navier-Stokes equations. The different characteristic regimes of the fluid's vibration are explored and described. In particular, a specific low-frequency regime is highlighted, in which the mechanical response couples with thermo-acoustic convection (piston effect). In this particular regime, the bulk part of the fluid behaves almost like a solid which bounces back and forth between two highly compressible thermal boundary layers. Such a response is entirely specific to near-critical fluids and is never witnessed in perfect gases. (C) 1995 American Institute of Physics.