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Description
The effect of the dielectrophoretic forces in convective flows under microgravity conditions were experimentally investigated to examine the onset and behavior of the hydrodynamic instability. A dielectric fluid confined within a differentially heated, vertically aligned cylindrical annulus was subjected to an alternating electric field at a frequency of 200 Hz during sounding rocket flight, which provides 300 seconds of microgravity conditions and parabolic flights, which in turn provide 22 seconds of microgravity conditions. The combination of differential heating and high alternating electric potential induced artificial electric gravity, triggering the instability.
Flow patterns of the dielectric fluid are studied qualitatively with the use of Shadowgraph technique and additional quantitative analysis was performed using the Particle Image Velocimetry (PIV). During the Parabolic flights two-plane PIV was realized to have three-dimensional view on the flow field.
First experimental set is devoted to the study of near-critical thermal and electrical forcing parameters during the long-term microgravity in sounding rocket flight on the instability onset and growth rate.
The second experimental set is devoted to the investigation of the initial condition of the fluid on the onset and saturation of the flow instability. Different mixing times were applied during the higher gravity phases to break the symmetry of the base flow, formed by Rayleigh-Bénard convection cells. Three different aspect ratios of the cylindrical cell were investigated under the same forcing parameters.
After saturation of the instability was achieved, the results allowed the calculation of saturation times under varying thermal and electrical conditions, providing a basis for comparison with linear stability theory. In addition, the sounding rocket flight data facilitated the determination of perturbation amplitude growth rates and near-critical experimental parameters, confirming numerical simulations.
Based on the previous results of the parabolic flight experiment, the findings from the second set allowed to make a conclusion, that breaking of the initial pattern symmetry helps to reach the saturation of the flow earlier, although the gap ratio influenced the onset time. With the higher aspect ratio, the instability sets up earlier, whereas the mixing time could be adjusted to find the most stable flow mode during microgravity.
These both results offer significant insights into the interaction of thermal and electrical forces in microgravity, advancing the understanding of thermo-electrodriven instability.
Acknowledgement: The project ‘Dielektrophoretisch induzierte Konvektion (DEPIK)’ was supported by the BMWi via the space administration of the DLR under grant no. 50WM2244.
