Turbulence--Mathematical models.

An Ocean Current Turbine (OCT) numerical simulation for creating, testing and
tuning flight and power takeoff controllers, as well as for farm layout optimization is
presented. This simulation utilizes a novel approach for analytically describing oceanic
turbulence. This approach has been integrated into a previously developed turbine
simulation that uses unsteady Blade Element Momentum theory. Using this, the
dynamical response and power production of a single OCT operating in ambient
turbulence is quantified.
An approach for integrating wake effects into this single device numerical
simulation is presented for predicting OCT performance within a farm. To accomplish
this, far wake characteristics behind a turbine are numerically described using analytic
expressions derived from wind turbine wake models. These expressions are tuned to
match OCT wake characteristics calculated from CFD analyses and experimental data. Turbine wake is characterized in terms of increased turbulence intensities and decreased
mean wake velocities. These parameters are calculated based on the performance of the
upstream OCT and integrated into the environmental models used by downstream OCT.
Simulation results are presented that quantify the effects of wakes on downstream turbine
performance over a wide range of relative downstream and cross stream locations for
both moored and bottom mounted turbine systems. This is done to enable the
development and testing of flight and power takeoff controllers designed for maximizing
energy production and reduce turbine loadings.

The flow field behavior of axial flow turbines is of great importance, especially in
modern designs that may operate at a low Reynolds number. At these low Reynolds
numbers, the efficiency loss is significantly augmented compared to higher Reynolds
number flows. A detailed incompressible numerical study of a single stage axial-flow
turbine at a low Reynolds number is investigated with the use of multiple eddy-viscosity
turbulence models. The study includes epistemic uncertainty quantification as a form of
numerical error estimation. The numerical results show good qualitative and quantitative
agreement with experimental data. It was found that the shear stress transport (SST) k - ω turbulence model with rotation/curvature correction and inclusion of transition modeling
is most capable at predicting the mean velocity distribution, which is further enhanced
when the URANS formulation is employed. However, all the cases indicate a large
variation in the prediction of the root-mean-squared of the turbulent velocity fluctuations.

Flow Structure and fluid transport via advection around pectoral fin of larval ZebraFish
are studied numerically using Immersed Boundary Method, Lagrangian Coherent
Structure, passive particle tracing, vortex core evolution and four statistically defined
mixing numbers. Experimental fish kinematics for nominal swimming case are obtained
from previous researchers and numerically manipulated to analyze the role of different
body motion kinematics, Reynolds number and fin morphology on flow structure and
transport. Hyperbolic strain field and vortex cores are found to be effective particle
transporter and their relative strength are driving force of varying flow structure and fluid
transport. Translation and lateral undulation of fish; as a combination or individual entity,
has coherent advantages and drawbacks significant enough to alter the nature of fluid
advection. Reynolds number increase enhances overall fluid transport and mixing in varying order for different kinematics and nominal bending position of fin has average
transport capability of other artificially induced fin morphology.