Flight results on Marangoni flow instability in liquid bridges

This paper reports on the results of the experiment PULSAR (Pulsating and R otating Instabilities in Oscillatory Marangoni Flows), performed on the MAX US 3 Sounding Rocket launched last November from the Swedish base in Kiruna . Aim of the experiment was the study of the oscillatory Marangoni convecti on in a cylindrical liquid bridge of silicone oil with kinematic viscosity of 5cSt. The experiment was motivated by preliminary on-ground numerical si mulations and microscale experimental studies, that have pointed out that t he oscillatory Marangoni instability appears at the beginning in the form o f 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 b ridge was equal to the disk diameter (20mm), and the imposed temperature di fference was 15K during the first 460 s and 20K in the second part of the e xperiment, 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 az imuthal coordinates (shifted at 90 degrees), and the surface temperature di stribution, measured by an infrared thermocamera, show that a pulsating and a mixed pulsating-rotating regimes have been established during the experi ment. Unfortunately during the flight the accelerations level caused by two centr ifuges with some biological samples in an adjacent module were above the ex pected values, so that disturbing g-jitter were encountered at different ti mes during the microgravity mission. The effects are clearly visible and th e numerical simulations had to make different assumptions to correlate the experimental results (C) 2000 International Astronautical Federation. Publi shed by Elsevier Science Ltd. All rights reserved.