Turbulent Bubble Jets in Microgravity. Spatial Dispersion and Velocity Fluctuations
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A detailed statistical analysis of bubble dispersion in turbulent jets based on data from drop tower experiments is presented here. A stochastic model is also introduced in order to capture these statistics to a large extent, treating bubbles as passive tracers with a local diffusivity given by a k- ε description of the turbulence. Bubble-bubble and bubble-flow interactions are neglected. Simple scaling analysis suggests that this approach is justified sufficiently far downstream. It is also found that, although interactions cannot be neglected very close to the inlet, the model predictions for the overall spatial distribution of the bubble ensemble are compatible with data within experimental uncertainty, and within the limited statistics of the experiments. In addition, the velocity fluctuations from the same experiments are analyzed, obtaining the local standard deviation of bubble velocities. We also find good agreement between experimental data and the effective model. Slight deviations between the model predictions and the experimental data are found at the jet margins, concerning the dependence on Reynolds number of jet angle and the relative velocity fluctuations. Consequently, significant bubble-flow interactions seem to be confined at the boundaries of the jets.
KeywordsTurbulent jet Bubble dispersion Bubble interactions Microgravity Drop tower Velocity fluctuations
We gratefully thank Jordi Carrera for his key role in initiating this line of research. We acknowledge the support from the DLR, German Aerospace Center, for the funding of the drop tower experiments that provided the raw data here analyzed. P.B., X.R. and J.C. acknowledge financial support from MICINN under projects FIS2010-21924-C02-02 and FIS2013-41144-P, and the Generalitat de Catalunya under projects 2009-SGR-14 and 2014-SGR-878. L.R. acknowledges financial support from Ministerio de Economia y Competividad (Spain) and FEDER (European Union), under project FIS2012-37655-C02-01. P.B. also acknowledges MCyT for a pre-doctoral fellowship.
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