The physics of the atomization in air-assisted atomizer involves many complex
phenomena. Indeed, thin liquid sheet is sheared by co-flowing air streams giving
rise to a small droplets spray. The process involves different scales of space
and time, from some microns, which is the size of the smallest droplets, to some
tenth of cm which is the typical size of a combustion chamber. No CFD code can
efficiently handle the whole process, from the large scale liquid sheet
instability to the droplets formation. The strategy planned at ONERA is to
couple a multifluid solver, for capturing the large scale instabilities very
near the injector, with a dispersed-phase solver for handling droplets
transport, evaporation and combustion. The first solver will simulate the small
region very close to the injector. The second one will work on the remaining
part of the computational domain. The main difficulties of the coupling approach
are, first, to determine the droplets characteristics coming from the multifluid
zone and secondly to have a robust and mass conserving algorithm. ONERA has
developed its own DNS incompressible interface capturing AMR (Adapted Mesh
Refinement) flow solver for accurate atomization simulations. In the first part
of the COFFECI program the numerical treatment of the interface has been
improved by implementing a coupled Level Set/Volume of Fluid algorithm,
enhancing the robustness and mass conservation properties. A new Lagrangian
module was developed to track the small liquid structures the Eulerian solver
fails to treat in case of local under resolution.

A 12 month year post-doctoral position is open in this framework. The candidate
will carry on validations, simulations and model development on the DNS code,
focusing on the Eulerian-Lagrangian coupling. Relevant three-dimensional test
cases of atomization will be simulated for a better understanding of the physics
underlying the ligaments and droplets formation. Numerical issues will be
overcome, in particular the transfer between the Eulerian and Lagrangian solvers
at the coupling location. The candidate will propose a model for the droplet
formation for a future implementation in the multi-fluid solver and will
validate it by performing direct comparison between a full DNS and the
equivalent simulation using the atomization model. He will have at his disposal
experimental results and simulations from other codes based on the diffused
interface technique. Some relevant publications are expected.

Both numerical and theoretical advanced skills are required for this
application. Due to the funding agency (STAE) policy, applicant must come from
outside of the Toulouse region. Salaries ranges from 2300 to 2500 euros per
month (net income), depending on the research experience after the PhD.