|Abstract: ||An eccentric annular duct is a prototype element in many applications, for example
in close-packed tubular heat exchangers and coolant channels of nuclear reactors.
From a fundamental viewpoint, turbulent flow in eccentric annular ducts is an ideal
model for investigating inhomogeneous turbulence. It is also a convenient model to
study the laminar and turbulent interface and may serve as a test case for turbulence
modelling of flows with partly turbulent regimes. Based on the approach of direct
numerical simulation, numerical investigations of turbulent flow in eccentric annular
pipes are carried out in this thesis.
We first investigated the case of fully turbulent flow. A detailed statistical analysis
of turbulent flow and heat transfer was performed. Simulation results, such
as friction factors, mean velocity profiles and the secondary-motion pattern, are in
overall qualitative and quantitative agreement with the existing experimental data.
The components of the Reynolds stress tensor, temperature-velocity correlations
and some others were obtained for the first time for such kind of a flow.
The study of the partly turbulent flow case was then carried out. Three approaches
for detecting interfaces between laminar and turbulent regimes in partly
turbulent flow in rotating eccentric pipes were compared and discussed. Positions of
laminar-turbulent and turbulent-laminar interfaces obtained from profiles of perturbation
enstrophy are the same as those obtained from production terms of enstrophy.
Using patterns of streaks defined by wall shear stresses to determine the locations
of interfaces showed similar results.
The growth rate of a small disturbance in partly turbulent flow case was also
analyzed. Small perturbations were introduced into the initial flow field in two different ways. Both cases show that the global growth rate of the small disturbance
normalized by the global viscous time scale is constant. This constant value is in
a good agreement with that obtained in channel flows and tube flows. A new
approach was proposed to distinguish the interface between laminar and turbulent
flow by introducing the global and local disturbance growth rate.|