Computational Fluid and Particle Dynamics (CFPD): An Introduction - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 4

1.3 CFPD and CFD Applications in the Respiratory System

1.3.1 CFPD as a Research Tool

One of the many uses of CFPD is to reveal the physical nature of the interactions
of particles in a fluid around and within designated objects. Fluid and particles are
transported through a domain by many physical processes including dissipation,
diffusion, convection, boundary layers and turbulence. The capabilities of CFPD
are vast and while great advancements have been made there still remains a large
undeveloped territory. CFPD, analogous to wind-tunnel and laser-photography par-
ticle analysis, can be employed as a research tool to perform numerical experiments
in order to better understand the physical nature of the fluid-particle dynamics. By
performing these numerical experiments, advanced models can then be developed
to increase the capabilities of the computational modelling. One area of high level
research activity is in the areas of atomization and sprays which are also applicable
for the drug delivery devices. Models are being developed to account for the complex
nature of atomization which involves a liquid phase breaking up into small droplets,
which in turn experience further breakup and collisions or coagulation.
Figure 1.3 shows a snapshot in time of the unsteady atomization of a spray close
to the nozzle region, which is referred to as the primary breakup. The flow structures
reveal that the liquid exits the nozzle with a wave-like energy and atomizes into small
droplets downstream. Following the primary breakup, the small droplets experience
further atomization, which is referred to as the secondary breakup. This example
illustrates how CFPD can provide detailed visualisation to better understand the
observed flow structures and some important physical aspects of the fluid-particle
flow, similar to a real laboratory experiment. More importantly, the simulations com-
plement the experiments not only providing qualitative comparison but also a means
to interpret some basic phenomenological aspects of the experimental condition.
In addition to the theoretical research into the fundamental physics, numerical
experiments may be performed on problems that are difficult to perform experimen-
tally. This may involve particle tracking and deposition, and particle size distributions
that are involved with chemical species (heliox inhalation, see Sandeau et al. (2010),
porous media (nasal hairs), non-Newtonian fluids (blood flow), and moving body
problems (lung expansion/contraction). These problems highlight the capabilities of
the CFPD as a non-invasive technique to study the human respiratory system.

1.3.2 CFPD and CFD as a Training Tool

Traditional users of CFD had been limited to academic researchers at a graduate or
post-graduate level who were developing their own computational code in pursuit
of code development and applications. Nowadays, as CFD becomes a cornerstone
of engineering practice, many engineers without any post-graduate education are