Particle growth in Turbulence


March 20-31 (2023)


Nordita, Stockholm (Particle growth in turbulence)


Axel Brandenburg (Nordita), Bernhard Mehlig (GU), Gunilla Svensson (SU)


How particles or droplets can grow in a turbulent environment is of great current interest in many fields, in astrophysics, cloud microphysics, in biology, and in the engineering sciences. For example, coagulation and condensation in turbulent clouds turn microscopic cloud droplets into rain drops. In astrophysics, planetesimals are thought to form by aggregation of microscopic dust grains in the turbulent environment surrounding a forming star. In many cases, turbulence is believed to be a crucial factor for particle growth. Yet the microscopic mechanisms determining this growth are far from understood.

In the past few years there has been substantial progress in understanding the mechanisms that determine how particles move in turbulence, through experiments, numerical simulations, and the analysis of statistical models.

The challenge is now to understand how and under which circumstances particles grow in turbulence. The program is aimed at scientists interested in the dynamics and the growth particles in turbulence, applications in the atmospheric sciences, astrophysics & engineering, or the mathematical analysis of these phenomena.


We intend to organize the program around the following themes

  • Condensation and coagulation in clouds
  • Collisions and aggregation in turbulence
  • Non-spherical particles in turbulence

Condensation and coagulation in clouds. Condensation and coagulation in clouds. Suggested topics include models for evolution of cloud-droplet-size distributions and how it is affected by turbulent fluctuations on different scales. Studies of entrainment and other effects of  inhomogeneities of the system and condensation and coagulation of atmospheric aerosol particles affected by turbulent fluctuations are also welcome.     

Collisions and aggregation of particles in turbulence. Suggested topics are models for particle aggregation, fragmentation, and erosion that take into account turbulent fluctuations, and their applications in astrophysics. We also intend to discuss recent progress and open questions in the mathematical analysis of statistical models for the dynamics and for aggregation of particles in turbulence. Regarding particle collisions, key topics are the effect of hydrodynamic interactions, as well as models for and measurements of collision and coalescence efficiencies.     

Non-spherical particles. Suggested topics are the dynamics of ice crystals in turbulent clouds, and also the dynamics of plankton in the turbulent ocean, their feeding rates for example, and more generally the survival strategies of small organisms and smart particles in turbulence.

We encourage participants to apply for the whole two-week period. The aim of this program is to initiate interdisciplinary collaborations. The above topics are just suggestions. We will only have short talks (15+5 mins) during the program, to leave free time for discussions and collaborations during the afternoons. There will be plenty of time for discussions in a relaxed atmosphere.

Schedule week 1

Mon 10-12 Condensation and coagulation in clouds (room 4205 house 3)
10:00 Sisi Chen Ice-droplet interactions in turbulent clouds
10:20 Ilona Riipinen Trace gas condensation in clouds

10:40-11:00 Break
11:00 Anna Frishman Predator-prey dynamics in rain formation and fall-out

11:20 Michael Wilkinson Rainfall from warm clouds
11:40 Federico Toschi Fully resolved simulations of yield-stress fluids 

Mon 13:30-14:30 Introduction (A. Brandenburg, room 4205 house 3)
Wed 13-16 Non-spherical particles in turbulence (B. Mehlig, room 11 house 2)
13:00 Jeremie Bec Velocity and acceleration statistics of inertial spheroids in homogeneous turbulence

13:20 Fabien Candelier Inertial torque on a squirmer

13:40 Navid Mousavi Active strategy to avoid high strain regions in plankton navigation

14:00 Akshay Bhatnagar Statistics of relative velocity and orientation of microswimmers in turbulence

14:20-14:40 Break

14:40 Greg Voth  Orientation and relative velocity of sedimenting non-spherical particles in turbulence

15:00 Theresa Oehmke 3D reconstruction of flat, anisotropic particles in turbulence

15:20 Liang-Ping Wang Simulation and analysis of turbulent flows laden with spherical and non-spherical particles
15:40 Prasad Perlekar Kolmogorov turbulence coexists with pseudo-turbulence in buoyancy-driven bubbly flows

Wed 18 Dinner (Restaurant Proviant)

Thu 13-15:40 Collisions, aggregation, fragmentation (B. Mehlig,  room 4205 house 3)
13:00 Luca Biferale Heavy and light particle aggregates in isotropic homogeneous turbulence. A study on breakup and stress statistics
13:20 Anders Johansen Ice nucleation in protoplanetary discs around young stars

13:40 Urs Dannenberg The streaming instability: A source of turbulence and a mechanism for the aggregation of dust and the formation of planetesimals in protoplanetary disks

14:00-14:40 Break

14:40 Dhruba Mitra Lagrangian particles in models of compressible flows

15:00 Alain Pumir Effect of turbulence on the collision rate between settling ice crystals and droplets

15:20 Michael Wilczek Prediction of sling events at high Reynolds numbers

Fre 10-12  Discussion Equations of motion, interactions, and collisions of particles in turbulence (B. Mehlig, room 4205 house 3)

Schedule week 2

Mon 13-15 Condensation and coagulation in clouds (G. Voth, room 4205 house 3)

13:00 Axel Brandenburg Super-droplet simulations of droplet growth in turbulence

13:20 Wojciech Grabowski Impact of turbulence on CCN activation and growth of cloud droplets

13:40-14:20 Break

14:20 Jörg Schumacher Turbulent mixing inside a cloud as an aggregation of supersaturation filaments
14:40 Bernhard Mehlig Lagrangian supersaturation distributions at the cloud edge

15:00 Alex Liberzon Inertial particles and entrainment across turbulent interfaces with density variations

Tue 15-17 Discussion Cloud microphysics (W. Grabowski, room 4205 house 3) 

Wed 13-16:00 Non-spherical particles in turbulence  (B. Mehlig, room 4205 house 3)
13:00 Eric Climent Plankton cells in turbulence, elongated swimmers, and chains

13:20 Kristian Gustavsson Dynamics of ice crystals settling in air

13:40 Samriddhi Sankar Ray Non-spherical particles in turbulence

14:00-14:20 Break
14:20 Fredrik Lundell Hydrodynamic manipulation of nanofibrils for material assembly

14:40 Luca Brandt The interaction of droplet dynamics and turbulence cascade

15:00-15:20 Break

15:20 Erik Thomson Ice particles in clouds: origins, processing, and cloud lifetime

15:40 Gautier Verhille Dynamics of long fibers in turbulence
16:00 Gaetano Sardina Passive scalar dynamics in turbulent suspensions of deformable bubbles
Wed 17-18 Discussion Non-spherical particles in turbulence (G. Voth, room 4205 house 3)

Wed 18  Dinner (Restaurant Proviant)

Thu  10-11 Discussion Non-spherical particles in turbulence (G. Verhille, room 4205 house 3)

Fri 9:30-11:50  Collisions, aggregation, fragmentation  (B. Mehlig, room 4205 house 3)                      
9:30 Tobias Baetge Correlated collisions accelerate the growth of lucky droplets

9:50 Mahdi Esmaily Proposing a 1D model problem to explain the behavior of inertial particles in turbulence 

10:10 Fabiola A. Gerosa Clusters of heavy particles in two-dimensional Keplerian turbulence

10:30-10:50 Break

11:10 Jan Meibohm Optimal path to caustic formation in turbulent aerosols
11:30 Grigory Sarnitsky Stochastic models for turbulence

11:50 Viktor Kurasov Formation of macroscopic fluxes in spatial systems under gravity