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Lagrangian Particles in Turbulence and Complex Geometries
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Wall-dominated turbulent dispersed multiphase flows occur in a variety of industrial, biological and environmental applications. The complex nature of the  arrier and the dispersed phase is elevated to a higher level introducing geometrical complexities such as curved walls. Realising such flows and particulate phases poses challenging problems both from computational and also physical point of view. The present thesis tries to address some of these issues Lagrangian computational frame.

In the first step, turbulent flow in straight pipes is simulated by means ofdirect numerical simulation with a spectrally accurate code nek5000 to examine the Reynolds number effect on turbulent statistics. Adding the effect of the curvature to these canonical turbulent pipe flows generates Prandtl’s secondary motion of first kind. These configurations, as primary complex geometries in this study, are examined by means of statistical analysis to unfold the evolutionof turbulent characteristics from a straight pipe configuration. A fundamentally different Prandtl’s secondary motion of second kind is also put to test by means of adding the side-walls to a canonical turbulent channel flow and the evolution of various statistical quantities with varying the duct aspect ratios is discussed.

After having obtained a characterisation of the turbulent flow in the geometries of bent pipes and ducts, the dispersion of small heavy particles is modelled in the bent pipe by means of point particles which are one-way coupled to the flow. For this purpose a parallel Lagrangian Particle Tracking (LPT) scheme is implemented in the spectral-element code nek5000. Its numerical accuracy, parallel scalability and general performance in realistic situations are scrutinised in various situations. Also, the resulting particle fields are analysed, showing that even a small degree of geometrical curvature has a profound impact on the particle concentration maps.

For each of the aforementioned turbulent flow cases new and challenging questions have arisen to be addressed in the present and upcoming research works. Along with an improved understanding of the particle dispersion in the considered complex geometries, the current project is particularly intended to improve the numerical aspects of the current LPT module suitable for largescale computations.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , v, 41 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:04
Keyword [en]
Direct numerical simulation, wall turbulence, secondary motion
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-141909ISBN: 978-91-7595-032-7 (print)OAI: oai:DiVA.org:kth-141909DiVA: diva2:698903
Presentation
2014-03-11, E2, Linsdtedsvägen 3, KTH, Stockholm, 14:15 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center, 76304
Note

QC 20140226

Available from: 2014-02-26 Created: 2014-02-25 Last updated: 2014-02-26Bibliographically approved
List of papers
1. Direct Numerical Simulation of Turbulent Pipe Flow at Moderately High Reynolds Numbers
Open this publication in new window or tab >>Direct Numerical Simulation of Turbulent Pipe Flow at Moderately High Reynolds Numbers
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2013 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 91, no 3, 475-495 p.Article in journal (Refereed) Published
Abstract [en]

Fully resolved direct numerical simulations (DNSs) have been performed with a high-order spectral element method to study the flow of an incompressible viscous fluid in a smooth circular pipe of radius R and axial length 25R in the turbulent flow regime at four different friction Reynolds numbers Re (tau) = 180, 360, 550 and . The new set of data is put into perspective with other simulation data sets, obtained in pipe, channel and boundary layer geometry. In particular, differences between different pipe DNS are highlighted. It turns out that the pressure is the variable which differs the most between pipes, channels and boundary layers, leading to significantly different mean and pressure fluctuations, potentially linked to a stronger wake region. In the buffer layer, the variation with Reynolds number of the inner peak of axial velocity fluctuation intensity is similar between channel and boundary layer flows, but lower for the pipe, while the inner peak of the pressure fluctuations show negligible differences between pipe and channel flows but is clearly lower than that for the boundary layer, which is the same behaviour as for the fluctuating wall shear stress. Finally, turbulent kinetic energy budgets are almost indistinguishable between the canonical flows close to the wall (up to y (+) a parts per thousand aEuro parts per thousand 100), while substantial differences are observed in production and dissipation in the outer layer. A clear Reynolds number dependency is documented for the three flow configurations.

Keyword
Wall turbulence, Pipes, Channels, Boundary layers, Direct numerical simulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-133634 (URN)10.1007/s10494-013-9482-8 (DOI)000325612100004 ()2-s2.0-84885953214 (Scopus ID)
Funder
Swedish Research Council, 2010 - 4147 2010 - 6965
Note

QC 20131111

Available from: 2013-11-11 Created: 2013-11-08 Last updated: 2017-12-06Bibliographically approved
2. Evolution of turbulence characteristics from straight to curved pipes
Open this publication in new window or tab >>Evolution of turbulence characteristics from straight to curved pipes
2013 (English)In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 41, no SI, 16-26 p.Article in journal (Refereed) Published
Abstract [en]

Fully developed, statistically steady turbulent flow in straight and curved pipes at moderate Reynolds numbers is studied in detail using direct numerical simulations (DNS) based on a spectral element discretisation. After the validation of data and setup against existing DNS results, a comparative study of turbulent characteristics at different bulk Reynolds numbers Re-b = 5300 and 11,700, and various curvature parameters kappa = 0, 0.01, 0.1 is presented. In particular, complete Reynolds-stress budgets are reported for the first time. Instantaneous visualisations reveal partial relaminarisation along the inner surface of the curved pipe at the highest curvature, whereas developed turbulence is always maintained at the outer side. The mean flow shows asymmetry in the axial velocity profile and distinct Dean vortices as secondary motions. For strong curvature a distinct bulge appears close to the pipe centre, which has previously been observed in laminar and transitional curved pipes at lower Re-b only. On the other hand, mild curvature allows the interesting observation of a friction factor which is lower than in a straight pipe for the same flow rate. All statistical data, including mean profile, fluctuations and the Reynolds-stress budgets, is available for development and validation of turbulence models in curved geometries.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Wall turbulence, Pipe flow, Curvature effects, Reynolds-stress budgets, Coiled tube
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-124983 (URN)10.1016/j.ijheatfluidflow.2013.03.005 (DOI)000321078700003 ()2-s2.0-84878568406 (Scopus ID)
Conference
9th International Symposium on Engineering Turbulence Modelling and Measurements (ETMM), JUN 06-08, 2012, Thessaloniki, Greece
Funder
Swedish e‐Science Research Center
Note

QC 20130805

Available from: 2013-08-05 Created: 2013-08-02 Last updated: 2017-12-06Bibliographically approved
3. Aspect ratio effects in turbulent duct flows studied through direct numerical simulation
Open this publication in new window or tab >>Aspect ratio effects in turbulent duct flows studied through direct numerical simulation
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2014 (English)In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 15, no 10, 677-706 p.Article in journal (Refereed) Published
Abstract [en]

Three-dimensional effects in turbulent duct flows, i.e., sidewall boundary layers and secondary motions, are studied by means of direct numerical simulation (DNS). The spectral element code Nek5000 is used to compute turbulent duct flows with aspect ratios 1-7 (at Re-b,Re- c = 2800, Re-tau,Re- c similar or equal to 180) and aspect ratio 1 (at Re-b,Re- c = 5600, Re-tau,Re- c similar or equal to 330), in streamwise-periodic boxes of length 25h. The total number of grid points ranges from 28 to 145 million, and the pressure gradient is adjusted iteratively in order to keep the same bulk Reynolds number in the centreplane with changing aspect ratio. Turbulence is initiated via a trip forcing active during the initial stages of the simulation, and the statistical convergence of the data is discussed both in terms of transient approach and averaging period. Spanwise variations in wall shear, mean-flow profiles, and turbulence statistics are analysed as a function of aspect ratio, and also compared with the spanwise-periodic channel (as idealisation of an infinite aspect ratio duct). The computations show good agreement with experimental measurements carried out in parallel at the Illinois Institute of Technology (IIT) in Chicago, and highlight the relevance of sidewall boundary layers and secondary vortices in the physics of the duct flow. The rich array of secondary vortices extending throughout the upper and lower walls of the duct, and their dependence on Reynolds number and aspect ratio, had not been reported in the literature before.

Keyword
direct numerical simulation, secondary motions, secondary vortices/motions, three-dimensional flows, turbulent duct flow, wall turbulence
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-141942 (URN)10.1080/14685248.2014.925623 (DOI)000340121000003 ()2-s2.0-84904987697 (Scopus ID)
Note

Updated from manuscript to article in journal.

QC 20140908

Available from: 2014-02-26 Created: 2014-02-26 Last updated: 2017-12-05Bibliographically approved
4. Particle dispersion in turbulent curved pipe flow
Open this publication in new window or tab >>Particle dispersion in turbulent curved pipe flow
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-141943 (URN)
Note

QS 2014

Available from: 2014-02-26 Created: 2014-02-26 Last updated: 2014-02-26Bibliographically approved

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