Holger Homann Maître de Conférence - Chaire CNRS Laboratoire Lagrange UMR7293
Observatoire de la Côte d’Azur
CS 34229, 06304 Nice Cedex 4, France
Tel: +33-4-92-00-30-48
Email: holger.homann@oca.eu

Research interests: Turbulence in fluids and plasmas
  • Fundamental problems: Eulerian and Lagrangian description - intermittency - coherent structures
  • Turbulent transport and mixing: concentrations - interactions - finite-size particles
  • Applications to geophysics and astrophysics: rain formation - planet formation - dynamos
  • Direct numerical simulations: pseudo-spectral schemes - immersed boundary methods - petaflop computing

Hydrodynamics
Hydrodynamics
Solid finite-size particle moving in a turbulent flow (Re=1500) illustrated by a volume rendering of vorticity: Modeling the dynamics of particles with diameters larger than the smallest active scale in turbulent flows is a challenging problem as no analytic solution of the flow around those particles is available. By means of direct numerical simulations we measured their statistics and derived the limit of the validity of point-particle models.
Magnetohydrodynamics
Plasmas
Isosurfaces of vorticity (green) and particles (red) in a slice in 3D magnetohydrodynamic turbulence: Particles tend to concentrate in the vicinity of the strong vortex/current sheet structures in contrast to hydrodynamics where they are expelled from those regions. We found that their density distribution functions only depend on one single parameter which combines their response time with the coarse-graining scale.
High-Performance Computing
HPC
Volume rendering of vorticity of a direct numerical dynamo simulation in a spherical domain: Huge numerical grids are necessary in order to achieve high Reynolds numbers which allow for comparisons to experimental and natural settings. We combine a Fourier- spectral solver with an immersed boundary method which allows for high accuracy and performance on massive parallel architectures such as the BlueGene/Q.

Publications
- H. Homann and F. Laenen (2018): SoAx: A generic C++ Structure of Arrays for handling particles in HPC codes. Comm. Phys. Comm., 224:325-332 [ arXiv ]
- S. Kreuzahler, Y. Ponty, N. Plihon, H. Homann and R. Grauer (2017) : Dynamo enhancement and mode selection triggered by high magnetic permeability. Phys. Rev. Lett., 119:234501 [ arXiv ]
- H. Homann, T. Guillot, J. Bec, C. W. Ormel, S. Ida and P. Tanga (2016): Effect of turbulence on collisions of dust particles with planetesimals in protoplanetary discs. A & A, 589:A129 [ arXiv ]
- J. Friedrich, H. Homann, T. Schäfer, and R. Grauer (2016): Longitudinal and transverse structure functions in high Reynolds-number magneto-hydrodynamic turbulence. New J. Phys., 18:125008 [ NJP ]
- J. Bec, S. S. Ray, E. W. Saw and H. Homann (2016): Abrupt growth of large aggregates by correlated coalescences in turbulent flow. Phys. Rev. E,93:031102(R) [ arXiv ]
- H. Homann and J. Bec (2015): Concentrations of inertial particles in the turbulent wake of an immobile sphere. Phys. Fluids, 27:053301 [ arXiv ]
- S. Kreuzahler, D. Schulz, H. Homann, Y. Ponty and R. Grauer (2014): Numerical study of impeller-driven von Karman flows via a volume penalization method. New J. Phys., 16:103001 [ NJP ]
- J. Bec, H. Homann and G. Krstulovic (2014): Clustering, fronts, and heat transfer in turbulent suspensions of heavy particles. Phys. Rev. Lett., 112:234503 [ arXiv ]
- H. Homann, Y. Ponty, G. Krstulovic and R. Grauer (2014): Structures and Lagrangian statistics of the Taylor-Green Dynamo. New J. Phys., 16:075014 [ NJP ]
- J. Bec, H. Homann and S. S. Ray (2014): Gravity-driven enhancement of heavy particle clustering in turbulent flow. Phys. Rev. Lett., 112:184501 [ arXiv ]
- M.  Cisse, H. Homann and J. Bec (2013): Slipping motion of large neutrally-buoyant particles in turbulence. J. Fluid Mech., 735:R1 [ arXiv ]
- H. Homann, J. Bec, and R. Grauer (2013): Effect of turbulent fluctuations on the drag and lift forces on a towed sphere and its boundary layer. J. Fluid Mech., 721:155 [ arXiv ]
- R. Bitane, H. Homann, and J. Bec (2013): Geometry and violent events in turbulent pair dispersion. J. Turbu., 14:23 [ arXiv ]
- R. Bitane, H. Homann, and J. Bec (2012): Time scales of turbulent relative dispersion. Phys. Rev E, 86:045302 [ arXiv ]
- R. Grauer, H. Homann, and J.-F. Pinton (2012): Longitudinal and Transverse structure functions in high Reynolds-number turbulence. New J. Phys., 14:063016 [ NJP ]
- H. Homann, D. Schulz, and R. Grauer (2011): Conditional Eulerian and Lagrangian velocity increment of fully developed turbulent flow. Phys. Fluids, 23:55102. [ arXiv ]
- T. Hater, H. Homann, and R. Grauer (2011): Lagrangian model for the evolution of turbulent magnetic and passive scalar fields. Phys. Rev. E, 83:017302. [ arXiv ]
- H. Homann and J. Bec (2010): Finite-size effects in the dynamics of neutrally buoyant particles in turbulent flow. J. Fluid Mech., 651:81–91. [ arXiv ]
- H. Homann, J. Bec, H. Fichtner, and R. Grauer (2009): Clustering of passive impurities in mhd turbulence. Phys. Plasmas, 16:082308. [ arXiv ]
- H. Homann, O. Kamps, R. Friedrich, and R. Grauer (2009): Bridging from Eulerian to Lagrangian statistics in 3d hydro- and magnetohydrodynamic turbulent flows. New J. Phys., 11:073020. [ NJP ]
- R. Friedrich, R. Grauer, H. Homann, and O. Kamps (2009): Statistics of a mixed Eulerian-Lagrangian velocity increment in fully developped turbulence. Physica Scripta, 79:055403.
- ICTR, A. Arneodo, R. Benzi, J. Berg, L. Biferale, E. Bodenschatz, A. Busse, E. Calzavarini, B. Castaing, M. Cencini, L. Chevillard, R. Fisher, R. Grauer, H. Homann, D. Lamb, A.S. Lanotte, E. Leveque, B. Luethi, J. Mann, N. Mordant, W.C. Mueller, S. Ott, N.T. Ouellette, J.F. Pinton, S.B. Pope, S.G. Roux, F. Toschi, H. Xu, and P.K. Young (2008): Universal intermittent properties of particle trajectories in highly turbulent flows. Phys. Rev. Lett., 100:254504.
- T. Grafke, H. Homann, J. Dreher, and R. Grauer (2008): Numerical simulations of possible finite time singularities in the incompressible Euler Equations: Comparison of numerical methods. Physica D, 237:1932–1936.
- A. Busse, W.C. Müller, H. Homann, and R. Grauer (2007): Statistics of passive tracers in three-dimensional magnetohydrodynamic turbulence. Phys. Plasmas, 14:122303.
- H. Homann, R. Grauer, A. Busse, and W.C. Müller (2007): Lagrangian statistics of navier-stokes and mhd turbulence. J. Plasma Phys., 73:821–830.
- H. Homann, J. Dreher, and R. Grauer (2007): Impact of the floating-point precision and interpolation scheme on the results of dns of turbulence by pseudo-spectral codes. Comput. Phys. Comm., 177:560–565.
- H. Homann and R. Grauer (2005): Bifurcation analysis of magnetic reconnection in Hall-MHD-systems. Physica D, 205:59–72.

Conference proceedings and other:

- H. Homann (2017): Modeling and Simulation of Finite-Size Particles in Turbulence. CISM book 'Collective Dynamics of Particles', 576:39–66, Springer.
- S. Kreuzahler, R. Grauer, H. Homann and Y. Ponty (2016): Direct Numerical Simulations of Impeller Driven Turbulence and Dynamo Action. Proceedings of the NIC Symposium 2016, Juelich. [ NIC ]
- H. Homann, J. Bec and R. Grauer (2013): Effect of turbulent fluctuations on the drag force and boundary layer of a towed sphere. Proceedings of the 14th EUROMECH European Turbulence Conference, Lyon. [ OpenConf ]
- E.W. Saw, G. Bewley, S.S. Ray, H. Homann, J. Bec and E. Bodenschatz (2013): Relative velocities of inertial particles at the dissipative scales of turbulence. Proceedings of the 14th EUROMECH European Turbulence Conference, Lyon. [ OpenConf ]
- Y. Ponty, S. Kreuzahler, H. Homann and R. Grauer (2013): Numerical Von Kármán flow forcing by two rotating propeller using penalization method. Proceedings of the 14th EUROMECH European Turbulence Conference, Lyon. [ OpenConf ]
- M. Cisse, H. Homann and J. Bec (2013): The slip direction of large-size particles in turbulent flow. Proceedings of the 14th EUROMECH European Turbulence Conference, Lyon. [ OpenConf ]
- J. Bec, R. Bitane and H. Homann, (2013): Statistics of velocity differences between Lagrangian tracers in a developed turbulent flow. Proceedings of the 14th EUROMECH European Turbulence Conference, Lyon. [ OpenConf ]
- H. Homann, J. Bec, and R. Grauer (2010): DNS of finite size particles in turbulent flow. volume 3 of IAS Series, p. 357–364.
- H. Homann, T. Hater, C. Beetz, C. Schwarz, J. Dreher, and R. Grauer (2008): Massively parallel simulations of Lagrangian plasma turbulence. volume 39 of NIC Series, p. 333–341.
- Lukas Arnold, Christoph Beetz, Jürgen Dreher, Holger Homann, Christian Schwarz, and Rainer Grauer (2007): Massively parallel simulations of solar flares and plasma turbulence. In PARCO, p. 467–474.
- H. Homann (2006): Lagrangian statistics of turbulent flows in fluids and plasmas. Dissertation, Ruhr-Universität Bochum. [ PDF ]

© 2010–2017 Holger Homann