BENARD-MARANGONI THERMAL OSCILLATORS - AN EXPERIMENTAL-STUDY

An experimental study of time-dependent Benard-Marangoni convection in small aspect ratio containers and high Prandtl number fluids is prese nted. Two similar systems with the same aspect ratio; depth, and type of fluid are compared: one with adiabatic lateral boundaries and the o ther with open boundaries. In spite of the fact that very different pl an forms and flows appear, both systems exhibit an oscillating plan fo rm and a discrete narrow-band frequency spectrum in the temperature si gnal having the same threshold and similar frequencies. Coincidence in temporal behavior between physical variables (temperature or velocity fields) and signals obtained from a distance representative of plan-f orm evolution or surface curvature is shown in the interval of the con trol parameter studied. The origin of a time-dependent regime arising from a boundary layer instability is discussed. Plan-form, temperature , and velocity measurements confirm this assumption, showing that this mechanism, first proposed in Rayleigh-Benard convection, also appears under the conditions of these experiments, in time-dependent behavior of Benard-Marangoni convection.