Oscillatory convection in vertical slots

Abstract

Convective flow phenomena in slender vertical slots with larger vertical than horizontal dimension, i.e. Hele Shaw slots, heated from below and subject to specified lateral boundary conditions, are investigated experimentally. Temperature fields in the liquid were visualized by holographic interferometry. Power-density spectra of local time-dependent thermocouple signals are calculated. In these slender slots different steady and time-dependent convection patterns develop with increasing Rayleigh number. The range of oscillatory convective flow exhibits periodic, quasiperiodic or non-periodic structures including possible frequency locking, subharmonics and intermittency. Quasiperiodic and periodic oscillations reappear at higher Rayleigh numbers, with non-periodic flows occurring in-between. These time-dependent flows appear to be caused by an instability of thermal boundary layers at the horizontal walls. Finally, at still higher Rayleigh numbers a reverse transition to a steady-state flow pattern is observed. The transitions between steady and non-steady flows are characterized by hysteresis.