Page 1 |
Save page Remove page | Previous | 1 of 116 | Next |
|
small (250x250 max)
medium (500x500 max)
Large (1000x1000 max)
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
|
LARGE EDDY SIMULATIONS OF LAMINAR SEPARATION BUBBLE
FLOWS
by
Francois Cadieux
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)
May 2015
Copyright 2015 Francois Cadieux
Object Description
| Title | Large eddy simulations of laminar separation bubble flows |
| Author | Cadieux, Francois |
| Author email | cadieux@usc.edu;francois.cadieux@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Aerospace and Mechanical Engineering (Computational Fluid and Solid Mechanics) |
| School | Viterbi School of Engineering |
| Date defended/completed | 2015-02-27 |
| Date submitted | 2015-04-20 |
| Date approved | 2015-04-20 |
| Restricted until | 2015-04-20 |
| Date published | 2015-04-20 |
| Advisor (committee chair) | Domaradzki, Julian A. |
| Advisor (committee member) |
Spedding, Geoffrey R. Redekopp, Larry G. Lynett, Patrick J. Becker, Thorsten W. |
| Abstract | The flow over blades and airfoils at moderate angles of attack and Reynolds numbers ranging from 10⁴ to 10⁵ undergoes separation due to the adverse pressure gradient generated by surface curvature. In many cases, the separated shear layer then transitions to turbulence and reattaches, closing off a recirculation region—the laminar separation bubble. To avoid body‐fitted mesh generation problems and numerical issues, an equivalent problem for flow over a flat plate is formulated by imposing boundary conditions that lead to a pressure distribution and Reynolds number that are similar to those on airfoils. Spalart & Strelets (2000) tested a number of Reynolds‐averaged Navier‐Stokes (RANS) turbulence models for a laminar separation bubble flow over a flat plate. Although results with the Spalart‐Allmaras turbulence model were encouraging, none of the turbulence models tested reliably recovered time‐averaged direct numerical simulation (DNS) results. The purpose of this work is to assess whether large eddy simulation (LES) can more accurately and reliably recover DNS results using drastically reduced resolution—on the order of 1% of DNS resolution which is commonly achievable for LES of turbulent channel flows. LES of a laminar separation bubble flow over a flat plate are performed using a compressible sixth‐order finite‐difference code and two incompressible pseudo‐spectral Navier‐Stokes solvers at resolutions corresponding to approximately 3% and 1% of the chosen DNS benchmark by Spalart & Strelets (2000). The finite‐difference solver is found to be dissipative due to the use of a stability‐enhancing filter. Its numerical dissipation is quantified and found to be comparable to the average eddy viscosity of the dynamic Smagorinsky model, making it difficult to separate the effects of filtering versus those of explicit subgrid‐scale modeling. The negligible numerical dissipation of the pseudo‐spectral solvers allows an unambiguous assessment of the performance of subgrid‐scale models. Three explicit subgrid‐scale models—dynamic Smagorinsky, σ, and truncated Navier‐Stokes (TNS)—are compared to a no‐model simulation (under‐resolved DNS) and evaluated against the benchmark DNS data focusing on two quantities of critical importance to airfoil and blade designers: time‐averaged pressure and skin friction predictions used in lift and drag calculations. Results obtained with these explicit subgrid‐scale models confirm that accurate LES of laminar separation bubble flows are attainable with as low as 1% of DNS resolution, and the poor performance of the no‐model simulation underscores the necessity of subgrid‐scale modelling in coarse LES with low numerical dissipation. |
| Keyword | computational fluid dynamics; fluid mechanics; direct numerical simulation; large eddy simulation; turbomachinery; UAV |
| Language | English |
| Format (imt) | application/pdf |
| 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-m |
| Contributing entity | University of Southern California |
| Rights | Cadieux, Francois |
| Physical access | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-CadieuxFra-3340.pdf |
| Archival file | Volume1/etd-CadieuxFra-3340.pdf |
Description
| Title | Page 1 |
| Repository email | cisadmin@lib.usc.edu |
| Full text | LARGE EDDY SIMULATIONS OF LAMINAR SEPARATION BUBBLE FLOWS by Francois Cadieux 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) May 2015 Copyright 2015 Francois Cadieux |
