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Rational study of incompressible turbulent flows
Title
Rational study of incompressible turbulent flows.
Creator
Pu, Xiaoyan., Florida Atlantic University, Yong, Yan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A new turbulence model is proposed in this dissertation for two-dimensional incompressible turbulent flows. The methodology used in the present study is a unilateral-statistical-average scheme with the concept of orthotropic eddy viscosity. This methodology has never been explored before in any research work of this nature. The distinguished feature of the unilateral-statistical-average scheme, compared to Reynolds averaging, is that the first-order information of the fluctuating velocity...
Show moreA new turbulence model is proposed in this dissertation for two-dimensional incompressible turbulent flows. The methodology used in the present study is a unilateral-statistical-average scheme with the concept of orthotropic eddy viscosity. This methodology has never been explored before in any research work of this nature. The distinguished feature of the unilateral-statistical-average scheme, compared to Reynolds averaging, is that the first-order information of the fluctuating velocity field is retained. This is achieved by dividing the fluctuating velocities into two groups and applying the average only to a single group. It is proved that the mean value of the fluctuating velocities of the first group solutions is not equal to zero. This non-zero quantity, together with a specified length vector, is used to define a 3 x 3 matrix of orthotropic eddy viscosity. In an off-streamline coordinate system, the eddy-viscosity matrix exhibits anisotropy characteristic, where each component of the turbulent stresses is related to all the components of the rate of strains of the mean fluid flow. The present model has been successfully applied to turbulent boundary-layer flow, turbulent free-shear jet flow, and turbulent wall-bounded separation flow without using empirical constants or wall-functions. Good agreements between the numerical results and experimental data or empirical predictions demonstrate that the unilateral-statistical-average scheme and the orthotropic non-linear eddy-viscosity formulation are robust and efficient in modeling basic turbulent flows. Applicability and predictability of the model to more complex engineering turbulence problems are worthy of further investigation in the future research.
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Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/12610
Subject Headings
Turbulence--Mathematical models, Turbulent boundary layer--Mathematical models
Format
Document (PDF)
Numerical simulation of wave energy dissipation in turbulent boundary layers
Title
Numerical simulation of wave energy dissipation in turbulent boundary layers.
Creator
Moneris, Stephanie Sylvie., Florida Atlantic University, Slinn, D. N., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Shoaling surface waves create turbulent shear flows at the sea-bed and thereby contribute to wave energy dissipation in the bottom boundary layer. Turbulent boundary layers are examined using a high-resolution time-dependent three-dimensional numerical model. Simulations estimate the wave energy dissipation in the boundary layer. Results indicate that turbulence levels are coupled to the wave cycle; accelerating flow organizes the boundary layer structure, decelerating flow destabilizes it...
Show moreShoaling surface waves create turbulent shear flows at the sea-bed and thereby contribute to wave energy dissipation in the bottom boundary layer. Turbulent boundary layers are examined using a high-resolution time-dependent three-dimensional numerical model. Simulations estimate the wave energy dissipation in the boundary layer. Results indicate that turbulence levels are coupled to the wave cycle; accelerating flow organizes the boundary layer structure, decelerating flow destabilizes it and flow reversal induces the strongest turbulent bursts. Details of the flow are functions of the Reynolds number, wave frequency, wave complexity, presence of a mean current, and the flow history of the preceding wave period. Mean flow properties are compared between the three-dimensional model and one-dimensional eddy-viscosity based models. Generally, features of the boundary layer are satisfactorily approximated by the eddy-viscosity models, with accuracy depending on the wave amplitude, period, phase, and other forcing conditions.
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Date Issued
2000
PURL
http://purl.flvc.org/fcla/dt/12692
Subject Headings
Waves--Mathematical models, Turbulent boundary layer--Mathematical models
Format
Document (PDF)