Abstract:
This dissertation presents a methodology to simulate the dispersion of water droplets in
the air flow typical of an Icing Tunnel. It is based on the understanding the physical
parameters that influence the uniformity and the distribution of cloud of droplets in the
airflow and to connect them with analytical parameters which may be used to describe
the dispersion process. Specifically it investigates the main geometrical and physical
parameters contributing to the droplets dispersion at different tunnel operative
conditions, finding a consistent numerical approach to reproduce the local droplets
dynamic, quantifying the possible limits of commercial CFD methods, pulling out the
empirical parameters/constant needing to simulate properly the local conditions and
validating the results with calibrated experiment.
An overview of the turbulence and multiphase flow theories, considered relevant to the
Icing Tunnel environment, is presented as well as basic concepts and terminology of
particle dispersion. Taylor’s theory of particle dispersion has been taken as starting
point to explain further historical development of discrete phase dispersion. Common
methods incorporated in commercial CFD software are explained and relative
shortcomings underlined. The local aerodynamic condition within tunnel, which are
required to perform the calculation with the Lagrangian particle equation of motions,
are generated numerically using different turbulent models and are compared to the
historical K-ε model. Verification of the calculation is performed with grid
independency studies. Stochastic Separated Flow methods are applied to compute the
particle trajectories. The Discrete Random Walk, as described in the literature, has been
used to perform particle dispersion analysis. Numerical settings in the code are related
to the characteristics of the local turbulent condition such as turbulence intensity and
length scales. Cont/d.
