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Postdoc: Bubble dynamics in complex two-phase flows

Du 1 janvier 2026 au 31 décembre 2026

LEGI, UMR 5519, Grenoble, France
Contacts : Ms. Zhujun Huang, MCF G-INP zhujun.huang@univ-grenoble-alpes.fr Mr. Alain Cartellier, DR Emeritus CNRS, Alain.Cartellier@univ-grenoble-alpes.fr

Bubble columns are common in processes, i.e. biomethanation, hydrogen production, CO₂ sequestration... but their flow dynamics is not well understood. Indeed, in air–water bubble columns in the heterogeneous regime, collective dynamics plays a significant role [Mezui et al., JFM, 2022, 2023]. Meso-scale structures appear that induce buoyancy driven turbulent convection. Several questions remain: what controls these meso-scale structures? does an asymptotic heterogeneous state at exist high gas flow rates? what is the axial development of the flow?... When surfactants are added, a foam layer formq at the top of the column. A characterization of the bubble size inside the layer are necessary for understanding the dynamics, and for developing efficient separation processes. These flows will be investigated using Doppler optical probes [Lefebvre et al., CES, 2022]. Experiments and measuring technique are available. The post-doc will contribute to the collaboration with Shizuoka University.

Bubble columns are exploited in many processes, such as biomethanation, hydrogen production, CO₂ sequestration, protein purification…. Although simple, the flow dynamics inside a bubble column can be highly complex and the understanding bubble dynamics remains an open challenge. At LEGI, two such flow configurations are currently under investigation. 
In air–water bubble columns operated in the heterogeneous regime, collective dynamics play a significant role, as demonstrated by our recent findings [1, 2]. Meso-scale structures spontaneously emerge within the flow, characterized by regions of high bubble densities (up to 10 times more) or zones of low densities (as little as one-tenth). These uneven distributions create turbulent flows driven by buoyancy. The probability density functions (PDFs) of bubble velocities vary significantly. Furthermore, both the phasic velocities and mean relative velocity are linked to column diameter and average void fraction. However, several questions remain open, such as the mechanisms governing the size and gas concentration of these meso-scale structures, the possible existence of an asymptotic heterogeneous state at high gas flow rates, and the axial development of the flow. A predictive model for both the mean void fraction and its fluctuations is yet to be developed [3]. Finally, the disagreement between experiments and advanced simulations on the bubble velocity PDFs remains to be resolved. 
When surfactants are added, t A thick foam layer may form at the top of the column. The distribution of bubble sizes within the foam is influenced by the size of the injected bubbles, the gas flow rate, and the type and concentration of surfactant used. A detailed characterization of the bubble size distribution along a vertical in the foam, as well as its temporal evolution, are required for developing and optimizing separation processes.
The above two situations will be investigated using recently developed Doppler optical probes [4]. Some adaptations of the signal processing and of the data post-processing will be needed. Besides, recent experiments in foams, in collaboration with Y. Mizushima from Shizuoka University have demonstrated that Doppler optical probes are able to detect thin liquid bridges separating bubbles. Both the experiments and the measuring technique are available. The post-doc will contribute to the collaboration with Shizuoka University.

Candidates: We are seeking a motivated postdoctoral researcher with a strong interest in experimental work. The ideal candidate will have a solid background in physics and/or fluid mechanics, and a keen interest in two-phase flow phenomena. 

Salary: monthly 2900€-3500€ (depending on experience) 

Application: https://emploi.cnrs.fr/

References: 
[1] Y. Mezui, M. Obligado and A. Cartellier, Buoyancy-driven bubbly flows: scaling of velocities in bubble columns operated in the heterogeneous regime, J. Fluid Mechanics, 952, A10 (2022). 
[2] Y. Mezui, M. Obligado and A. Cartellier, Buoyancy-driven bubbly flows: role of meso-scale structures on the relative motion between phases in bubble columns operated in the heterogeneous regime, J. Fluid Mechanics, 962, A40 (2023). 
[3] A. Lefebvre, Y. Mezui, M. Obligado, S. Gluck, A. Cartellier, A new, optimized Doppler optical probe for phase detection, bubble velocity and size measurements: Investigation of a bubble column operated in the heterogeneous regime, Chemical Engineering Science 250 (2022) 117359.