Particle Methods in Bluff Body Aerodynamics

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Particle Methods in Bluff Body Aerodynamics
Rasmussen, Johannes Tophøj
Publication date:
2011
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Citation (APA):
Rasmussen, J. T. (2011). Particle Methods in Bluff Body Aerodynamics. DTU Mechanical Engineering. DCAMM
Report No. S146

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Particle Methods in Bluff Body Aerodynamics
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Johannes Tophøj Rasmussen
DCAMM Special Repport No. S146
October 2011

Particle Methods in Bluff Body
Aerodynamics
Johannes Tophøj Rasmussen
A dissertation submitted for the degree of Doctor of
Philosophy
Section of Fluid Mechanics
Department of Mechanical Engineering
Technical University of Denmark
October 2011
ii
Preface
This dissertation is submitted in partial fulfilment of the requirements for
obtaining the Ph.D. degree in mechanical engineering at the Technical Uni-
versity of Denmark (DTU). The Ph.D. Project was funded by the Danish
Research Council of Independent Research (Grant. No. 274-08-0258) and
carried out at the Department of Mechanical Engineering (MEK), section of
Fluid Mechanics at DTU in the period September 1st 2008 - November 1st
2011. Supervisor on the project was Associate Professor Ph.D. Jens Honor´e
Walther from the department.
There is much and many people to appreciate. In the context of the last
three years of Ph.D work at DTU: First and foremost I owe a special thanks
to my tough but supportive ’boss’ Jens Honor´e Walther from whom I have
learned very much. For making me ’keep digging’ and keeping me on track.
I am very grateful for being able to work with you. For our collaboration I
would like to thank Mads M. Hejlesen, Allan Larsen and George-Henri Cot-
tet. I would like to express my gratitude towards my co-workers in building
403, in particular the other Ph.D. students, for the pleasant atmosphere and
the academic discussions. And Laust for our talks on vortices and beyond.
I would furthermore like to thank the following: Ole Christensen for
his pointers on series expansions. Petros Koumoutsakos for my visit to the
CSE lab at ETH. Ivo Sbalzarini and the MOSAIC group at ETH for our
collaboration and in particular I would like to thank Omar Awile for his
support on PPM. I would like to thank George-Henri Cottet and his team
for the pleasant stay at Laboratoire Jean Kuntzmann at UJF. And of course
Bennos Hvile for all the love.
In this dissertation no nomenclature is given but variables are declared
when mentioned.
Parts of the work in the present dissertation have been published in
Journal of Wind Engineering & Industrial Aerodynamics [84] and Journal
of Computational Physics [83]. A third paper is being prepared [43].
iii
Resum´e (in Danish)
Interaktionen mellem strømninger og strukturer studeres ved hjælp af nu-
meriske metoder b˚ade i industrielt og akademisk regi. Strømningers kom-
plekse dynamik ved højeReynolds talkanikke aleneomsættes med r˚abereg-
ningskraft, hvorfor det er nødvendigt med mere effektive og specialiserede
beregningsalgoritmer. Denne afhandling fokuserer p˚a brugen af hvirvelme-
toder ogeffektiv udnyttelse af beregningsressourcer oger inddelt i treemner.
Først præsenteres en ny metode til bestemmelse af den aerodynamiske
admitans gennem numerisk simulering. Metoden bygger p˚a generingen af
turbulente hvirvelpartikler der indsættes opstrøms i strømningen. Turbu-
lensen generes før afviklingen af simuleringen og bygger p˚a atmosfæriske
turbulensspektra og en rummelig korrelationsfunktion. Metoden er valideret
ved simulering af turbulente strømninger forbi en flad plade og Storebælts-
broen, Øresundsbroen og Busan-Geoje broen.
Afhandlingen introducerer endvidere en ny vortex-in-cell algoritme med
varierenderummeligopløsning. Poissonligningensombeskriver forbindelsen
mellem strømningens vorticitet- og hastighedsfelter løses ved hjælp af fast
Fourier transforms i ubegrænsede domæner. Faste legemer p˚atrykkes ved
hjælp af Brinkman penalisering i en semi-implicit formulering. Det vises at
penaliseringen kan p˚atrykkes som en enkel interpolation. Implementeringen
ertodimensionelogsekventiel. Implementeringen valideresmodenanalytisk
løsning til Perlman vorticitetsfeltet, impulsivt startede strømninger omkring
statiske og roterende cylindre samt strømning omkring en brosektion.
Til slut præsenteres en tredimensionel vortex-in-cell implementering som
bygger p˚aet eksisterende opensourcesoftware-biblioteksommuliggørerpar-
allelle tredimensionelle strømningssimuleringer baseret p˚a hvirvelpartikler.
Enhøjere-ordensFourier-baseretPoisson-løser præsenteres ogvalideres. Ved
hjælp af regulariseringsteknikker opn˚as formelt en arbitrært høj rummelig
konvergensrate. Implementeringen er forberedt den udviklede algoritme til
varierendeopløsninghvilket dogikkeerfærdigimplementeret idetunderstøt-
tende softwarebibliotek. Simuleringen af deformerende og bevægende objek-
ter er demonstreret ved hjælp af Brinkman-penalisering og vortex-in-cell al-
goritmen. Modellen er afprøvet p˚a strømning omkring kugler, en brosektion
i opførelsesfasen samt vandmanden Aurelia aurita’s fremdrift.
iv
Abstract
Fluid-structure interaction is studied numerically in academics and the in-
dustry. Shear computational power alone is insufficient to accurately resolve
the complex dynamics of high Reynolds number fluid flow. Therefore the
development of more efficient and applicable computational algorithms is
important. This dissertation focuses on the use of vortex particle methods
and computational efficiency. The work is divided into three parts.
A novel method for the simulation of the aerodynamic admittance in
bluff body aerodynamics is presented. The method involves a model for
describing oncoming turbulence in two-dimensional discrete vortex method
simulations by seeding the upstream flow with vortex particles. The turbu-
lence is generated prior to the simulations and is based on analytic spectral
densities of the atmospheric turbulence and a coherence function defining
the spatial correlation of the flow. The method is validated by simulating
the turbulent flow past a flat plate and past the Great Belt East bridge, the
Øresund bridge and the Busan-Geoje bridge.
The dissertation introduces a novel multiresolution vortex-in-cell algo-
rithm using patches of varying resolution. The Poisson equation relating the
fluid vorticity and velocity is solved using fast Fourier transforms subject to
free-space boundary conditions. Solid boundaries are implemented using the
semi-implicit formulation of Brinkman penalization and it is shown that the
penalization can be carried out as a simple interpolation. The implemen-
tation is two-dimensional and sequential. The implementation is validated
against the analytic solution to the Perlman test case and by free-space sim-
ulations of the onset flow around fixed and rotating circular cylinders and
bluff body flows around bridge sections.
Finally a three-dimensional vortex-in-cell algorithm is implemented into
an existing open source library that enables large scale, three-dimensional
particle-vortex simulations. A high order Fourier based Poisson solver is
presented using novel use of regularization in the vortex-in-cell algorithm
which formally enables arbitrarily high order convergence. The implementa-
tion is prepared for multiresolution though it is currently not supported by
the parallel framework. The simulation of deformable and moving objects
is demonstrated using Brinkman penalization and the vortex-in-cell algo-
rithm. The model is applied to flow around spheres, a bridge section during
the construction phase and the swimming motion of the medusa Aurelia
aurita.
v
vi
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Resum´e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Introduction 1
Dissertation structure . . . . . . . . . . . . . . . . . . . . . . . . 2
1 Fluid-structure interaction 3
1.1 Vortex shedding . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Aerodynamic Admittance . . . . . . . . . . . . . . . . . . . 5
1.3 CFD and fluid-structure interaction . . . . . . . . . . . . . . 8
1.3.1 Computational scaling . . . . . . . . . . . . . . . . . 9
1.3.2 Solid boundaries . . . . . . . . . . . . . . . . . . . . 12
1.3.3 Implementations . . . . . . . . . . . . . . . . . . . . 13
2 Admittance 15
2.1 The discrete vortex method . . . . . . . . . . . . . . . . . . 15
2.2 Synthesizing turbulence . . . . . . . . . . . . . . . . . . . . 18
2.3 Validation, numerical parameters and results . . . . . . . . . 23
2.4 Validation of power spectral density of the velocity . . . . . 25
2.4.1 Sensitivity to upper cutoff and spectral resolution . . 25
2.4.2 Effects of frequency discretisation and circulation in-
tegration . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.3 Influence of circulation correction . . . . . . . . . . . 28
2.4.4 Spatial dependency . . . . . . . . . . . . . . . . . . . 29
2.4.5 Dependency of grid height . . . . . . . . . . . . . . . 31
2.4.6 Dependency of inter-particle spacing . . . . . . . . . 32
2.5 Aerodynamic admittance of a flat plate . . . . . . . . . . . . 34
2.5.1 Comparison with analytic solution . . . . . . . . . . 34
2.5.2 Influence of Reynolds number and turbulence intensity 37
2.6 Aerodynamic admittance of bridge sections and comparison
to experimental results . . . . . . . . . . . . . . . . . . . . . 38
vii