Flight results on marangoni flow instability in liquid bridges

Abstract

This paper reports on the results of the experiment PULSAR (Pulsating and Rotating Instabilities in Oscillatory Marangoni Flows), performed on the MAXUS 3 Sounding Rocket launched last November from the Swedish base in Kiruna. Aim of the experiment was the study of the oscillatory Marangoni convection in a cylindrical liquid bridge of silicone oil with kinematic viscosity of 5cSt. The experiment was motivated by preliminary on-ground numerical simulations and microscale experimental studies, that have pointed out that the oscillatory Marangoni instability appears at the beginning in the form of a pulsating regime, caused by a hydro-thermal standing wave, and then it turns to a rotating regime, caused by a traveling wave. The height of the bridge was equal to the disk diameter (20mm), and the imposed temperature difference was 15K during the first 460 s and 20K in the second part of the experiment, until the end of the microgravity period. The analysis of the temperature profiles, measured by thermocouples located near the disks at the same radial and axial coordinate but at different azimuthal coordinates (shifted at 90°), and the surface temperature distribution, measured by an infrared thermocamera, show that a pulsating and a mixed pulsating-rotating regimes have been established during the experiment. Unfortunately during the flight the accelerations level caused by two centrifuges with some biological samples in an adjacent module were above the expected values, so that disturbing g-jitter were encountered at different times during the microgravity mission. The effects are clearly visible and the numerical simulations had to make different assumptions to correlate the experimental results