Oscillatory and relaxation studies in the convection of supercritical [formula omitted

Abstract

We analyze the observed temporal profile Δ T( t) of the temperature difference, measured across a very compressible supercritical 3 He fluid layer in the convective state. The experiments were done along the critical isochore in a Rayleigh–Bénard cell after starting the vertical heat flow q. For q> q ons (“convection onset”), the transient Δ T( t) under given conditions of q and ε≡(T−T c )/T c (T c =3.318 K) shows a damped oscillatory profile with period t osc modulating a smooth base profile. The latter forms the tail of the transient which relaxes exponentially to the steady-state Δ T(∞) with a time constant τ tail. The scaled times t osc/ t D and τ tail/ t D from all the data could be collapsed onto two curves as a function of the Rayleigh number over ∼3.5 decades. Here t D is the diffusion time.