Dynamics of bubbles across scales
Doctoral thesis, 2023

This thesis presents numerical investigations of bubbly flow phenomena across a wide range of relevant spatial and temporal scales. The aim is to increase our understanding of a great variety of underlying phenomena and to facilitate improved predictions of bubbly flows at all relevant scales. The investigations start at small spatial scales (size of individual bubbles and below). We focus on the evolution of vapour bubbles by formulating a multiphase Direct Numerical Simulation (DNS) framework and a computationally inexpensive 1D framework, which both consider phase change- and thermal effects. These frameworks are used to study laser-induced thermocavitation bubbles that are a part of a promising technology to achieve good control of the properties of the formed crystals in the crystallisation process. Our findings identify plausible mechanisms that induce crystallisation and give guidelines for selecting suitable system parameters to maintain and control the crystallisation process. We continue to larger scales by focusing on the dynamics of individual rising bubbles. An efficient multiscale methodology is developed in an Eulerian-Lagrangian framework that predicts the liquid-phase fluctuations experienced by a bubble rising in a turbulent flow field. The dynamics and deformation of the bubble due to the liquid-phase fluctuations are resolved using a multiphase DNS framework together with a formulated Moving Reference Frame (MRF) technique. This multiscale approach is useful for studying numerous small-scale processes where bubbles are smaller than the Kolmogorov scales and can be used for bubbles, droplets or particles in both laminar and turbulent flows. We use the developed DNS framework with the MRF to study the lift force acting on deformable bubbles in steady shear flows. We formulate a theoretical framework and support it with DNS to provide a comprehensive explanation for the several identified mechanisms behind the lift force. The findings also elucidate the influence of the shear rate and governing parameters on the lift force. Finally, we study, using DNS, the dynamics and mixing properties of bubbly flows at large spatial scales (size of the entire system). We extract and analyse the dynamics and statistics of passive scalars involving O(10-100) bubbles in periodic domains. The results show a significant influence of the bubble-induced turbulence on the scalar spectra and elucidate the influence of the governing parameters on the scalar dynamics and mixing properties.



lift force

scalar mixing

Bubbly flows


EC-salen, Hörsalsvägen 11
Opponent: Prof. Stéphane Zaleski, Sorbonne Université & CNRS, France


Niklas Hidman

Chalmers, Mechanics and Maritime Sciences (M2), Fluid Dynamics

A multiscale methodology for small-scale bubble dynamics in turbulence

International Journal of Multiphase Flow,; Vol. 150(2022)

Journal article

The lift force on deformable and freely moving bubbles in linear shear flows

Journal of Fluid Mechanics,; Vol. 952(2022)

Journal article

N. Hidman, H. Ström, S. Sasic, and G. Sardina. Assessing passive scalar dynamics in bubble-induced turbulence using DNS.

Bubbly flows are important in many industrial and natural processes such as chemical reactors, heat
exchangers, froth flotation tanks and atmosphere-ocean exchanges. This type of multiphase flow is
characterised by good heat and mass transfer properties without the need for mechanical mixing and
therefore requires lower operating and maintenance costs. To understand and design efficient
applications, it is essential that we can accurately predict the bubbly flow dynamics. However,
numerical predictions of bubbly flows are very challenging, mainly because of the wide range of
coupled phenomena where, for example, the motion of individual bubbles interacts with the large
scale motion of the entire bubbly flow.

In this thesis, we develop numerical frameworks to study bubbly flow phenomena across a wide
range of relevant length scales. The frameworks are used to study the growth of micrometer-sized
vapour bubbles, the forces acting on individual rising bubbles and the mixing properties of turbulent
bubbly flows relevant in industrial applications. Our findings increase the current knowledge of
these bubble phenomena and facilitate the development of improved numerical predictions. The
developed numerical frameworks are useful for studying many other relevant bubble phenomena
such as cavitation/boiling, bubble dynamics in turbulence and heat transfer in bubbly flows.
Possible applications and recommendations for future work are also discussed.

Subject Categories

Fluid Mechanics and Acoustics



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5240



EC-salen, Hörsalsvägen 11


Opponent: Prof. Stéphane Zaleski, Sorbonne Université & CNRS, France

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