Dr. Christian Focke
Direct Numerical Simulations and Computational analysis of binary droplet collisions for complex fluids
The background of our research is the prediction of properties of particulate products formed in spray processes. Such products are solids in powder form, manufactured in the chemical, pharmaceutical or medical technology or related industries. The properties of particulate systems depend on the primary atomization of the fluid and of droplet collisions inside the spray.
The droplet collisions are investigated by means of Direct Numerical Simulation (DNS) using the two-phase Navier-Stokes solver Free Surface 3D (FS3D) developed at the Institute of Aerospace Thermodynamics at University of Stuttgart.
The major aim of the project is to develop improved closure laws that describe the outcome of droplet collisions. The closure laws can then be used in Eulerian-Eulerian or Eulerian-Lagrangian simulations. In applications dealing with polymers, non-Newtonian rheological behavior comes into focus. To gain a more thorough understanding of the elementary sub-processes inside a spray, FS3D must be extended to account for shear thinning and viscoelastic flow behavior. The aim is the prediction of the outcome of these collisions.
A major difficulty appears concerning the numerical simulation of the thin lamella structure which arises during the extension of the collision complex. If the lamella ruptures during the collision because of insufficient resolution, the result is a severe deterioration of the collision physics. A stabilization of the lamella in the computation of the free surface flow could be achieved in the present project which does not affect the mass and momentum balance but leads to a major improvement in the computation of the collision complex.
The project is supported by the German Science Foundation within the priority program 1423 “Process-Spray”.