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ON THE SIMULATION OF STRATIFIED TURBULENT FLOWS
by
Yuncheng Lin
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(AEROSPACE ENGINEERING)
December 2010
Copyright 2010 Yuncheng Lin
Object Description
| Title | On the simulation of stratified turbulent flows |
| Author | Lin, Yuncheng |
| Author email | yunchenglin@hotmail.com; yunchenglin@ymail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Aerospace & Mechanical Engineering (Computational Fluid & Solid Mechanics) |
| School | Viterbi School of Engineering |
| Date defended/completed | 2010-12 |
| Date submitted | 2010 |
| Restricted until | Unrestricted |
| Date published | 2010-12-08 |
| Advisor (committee chair) |
Redekopp, Larry G. Domaradzki, Julian Andrzej |
| Advisor (committee member) |
Wilcox, David C. Kukavica, Igor |
| Abstract | In the first part of this report, the effects of numerical dissipation presented in a turbulence Direct Numerical Simulation (DNS) code called SMPM is investigated through the use of the effective numerical eddy viscosity, a concept pioneered by Domaradzki and Xiao in 2003. This SMPM algorithm, which is inherently free of any intrinsic truncation error, employs three numerical stabilizers, i.e., Fourier filtering, Legendre filtering and Penalty method to ensure the numerical stability in the calculations of turbulent flows with very high Reynolds number, for which the simulation is often under-resolved. Numerical data extracted from the simulation of a turbulent wake flow is employed to quantify the effective numerical eddy viscosity for all three explicit numerical stabilizers. The results shown that the effects of the stabilizers can be significant, if not dominated, compared to the physical molecular viscosity. Away from the vertical subdomain interfaces, all three stabilizers behave expectedly to remove the kinetic energy from the system, i.e., dissipative. At the subdomain interfaces, the Legendre filtering and the Penalty scheme exhibit the nexpected anti-dissipative character, i.e., to increase the energy of the system. Such counter-intuitive behavior is attributed to the discontinous formulism of the Penalty scheme, which is absolutely necessary if multi-domain method is employed. This anti-dissipative behavior diminishes quickly only a few grid points away from the subdomain interfaces.; The original formulism of effective numerical viscosity was dedicated to a turbulence DNS code with triply-periodic boundary conditions. It has been successfully extended to our SMPM code whose boundary condition is not periodic in the vertical direction, the direction aligns with the only non-zero external force field, i.e., gravity. The success of this extension gives us the confidence that the same concept can be applied to any numerical algorithm for under-resolved simulation, so long as the baseline case can be defined.; The second part of this report is dedicated to discovering the nature of boundary layer flows induced by the propagation of the internal solitary waves. Long internal waves are common features on the continental shelf and in lakes, but their dissipation via benthic boundary layer drag is largely unknown, particularly when the wave amplitudes are large and the boundary layer corrections based on the linear theory are clearly invalid. In general, the boundary layer induced by a solitary wave of depression experiences a continuous favorable-to-adverse variation of the pressure gradient, undergoes transition, may reach a strongly turbulent state, the lee of the wave. In this study a model for fully-nonlinear solitary waves of depression in a two-layer stratification is employed as the inviscid base state, and a RANS solver with k − ! turbulence model is used to compute the stationary boundary layer under the wave. Local friction coefficients and eddy viscosities are computed in the footprint of the wave. Locations of boundary layer separation are computed as well as the integrated frictional drag over the region of attached boundary layer flow. Boundary layer characteristics are presented for a range of environmental conditions, Reynolds numbers, and surface roughness in an attempt to provide a quantitative measure of the frictional drag of long internal waves in realistic, shallow environments. |
| Keyword | internal solitary waves; turbulent boundary-layer flows; KdV equation; k-\omega model; SMPM; DNS; numerical dissipation; under-resolved simulations; Fourier filtering; Boussinesq approximation; Poisson equation; Legendre polynomial; penalty method; aliasing effect |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3589 |
| Contributing entity | University of Southern California |
| Rights | Lin, Yuncheng |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Lin-4196 |
| Archival file | uscthesesreloadpub_Volume14/etd-Lin-4196.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | ON THE SIMULATION OF STRATIFIED TURBULENT FLOWS by Yuncheng Lin A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (AEROSPACE ENGINEERING) December 2010 Copyright 2010 Yuncheng Lin |
