Numerical Modelling of Diesel Spray Injection and Turbulence Interaction
Licentiatavhandling, 2006
It has been established by many authors that numerical simulations of
Diesel sprays, using a Lagrangian description for the liquid phase,
are particularly sensitive to the scale of the computational cells
compromising the mesh. There have been many suggestions regarding
means to reduce the dependency on the mesh by improving the component
submodels, but few have addressed the gas phase turbulence modelling.
This thesis covers two main topics. The first is the application of
cavitation models in order to develop a new primary atomization model
for Diesel spray. The second is to investigate the effect of modifying
the length scale used in turbulent dispersion models for particles in
turbulent flows.
The goal of the nozzle flow calculations is to develop a new
atomization model, that does not have the drawback of requiring either
non-physical parameters or information derived from specific
experiments. To validate the cavitation simulations, comparisons with
experimental data obtained at AVL were made. The experiments show
velocity profiles and pressure contour, and are practically
2D. The results of the cavitaiton simulations do not
represent reality to a satisfactory degree yet. Therefore, a new
atomization model has not been developed.
Since most industrial applications are based on eddy viscosity
k-epsilon type models, the spray investigations were limited
to this kind of turbulence model. Three versions were tested, the goal
was to evalute their effect on the spray behaviour and sensitivity to
mesh resolution.
This thesis shows that the turbulence model plays a significant role
in the sprays' behaviour on grids of different spatial resolution, and
a simple and efficient way to reduce the dependency of the mesh
resolution, by limiting the turbulent length scale in the liquid core
region, is proposed. It is shown that this constraint has a positive
effect on the spray behaviour, and reduces grid dependence.
Computational Fluid Dynamics
Spray
Cavitation
Cavitation
Turbulence Model
Atomization
Turbulence Model
Diesel
Atomization