Preliminary results of the sounding rocket experiment on oscillatory flows in liquid bridge

This paper reports on the preliminary 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 attention has been focused on the three dimensional flow structure that is established in the liquid bridge when the temperature difference between the end disks supporting the bridge exceeds a certain critical value. 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 preliminary analysis of the temperature profiles, measured by four thermocouples located 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. The azimuthal wave number of the oscillatory regime, the oscillation period, the time for the onset of the oscillations are in good agreement with the numerical predictions obtained in the pre-flight analysis. The experiment was fully controlled in Telescience mode by the MARS Center remote control room by using four dedicated ISDN lines.