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Evidence of sublaminar drag naturally occurring in a curved pipe
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-9627-5903
2015 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, no 3, 035105Article in journal (Refereed) Published
Abstract [en]

Steady and unsteady flows in a mildly curved pipe for a wide range of Reynolds numbers are examined with direct numerical simulation. It is shown that in a range of Reynolds numbers in the vicinity of Re-b approximate to 3400, based on bulk velocity and pipe diameter, a marginally turbulent flow is established in which the friction drag naturally reduces below the laminar solution at the same Reynolds number. The obtained values for friction drag for the laminar and turbulent (sublaminar) flows turn out to be in excellent agreement with experimental measurements in the literature. Our results are also in agreement with Fukagata et al. ["On the lower bound of net driving power in controlled duct flows," Phys. D 238, 1082 (2009)], as the lower bound of net power required to drive the flow, i.e., the pressure drop of the Stokes solution, is still lower than our marginally turbulent flow. A large-scale traveling structure that is thought to be responsible for that behaviour is identified in the instantaneous field. This mode could also be extracted using proper orthogonal decomposition. The effect of this mode is to redistribute the mean flow in the circular cross section which leads to lower gradients at the wall compared to the laminar flow.

Place, publisher, year, edition, pages
2015. Vol. 27, no 3, 035105
Keyword [en]
Channel Flow, Turbulence, Transition, Laminar, Power
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-166347DOI: 10.1063/1.4913850ISI: 000352309400044Scopus ID: 2-s2.0-84924943480OAI: oai:DiVA.org:kth-166347DiVA: diva2:811198
Funder
Swedish e‐Science Research Center
Note

QC 201505

Available from: 2015-05-11 Created: 2015-05-07 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Particle-laden Turbulent Wall-bounded Flows in Moderately Complex Geometries
Open this publication in new window or tab >>Particle-laden Turbulent Wall-bounded Flows in Moderately Complex Geometries
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wall-bounded turbulent dispersed multiphase flows occur in a variety of industrial, biological and environmental applications. The complex nature of the carrier and the particulate phase is elevated to a higher level when introducing geometrical complexities such as curved walls. Realising such flows and dispersed phases poses challenging problems both from computational and also physical point of view. The present thesis addresses some of these issues by studying a coupled Eulerian–Lagrangian computational framework.

The content of the thesis addresses both turbulent wall flows and coupled particle motion. In the first part, turbulent flow in straight pipes is simulated by means of direct numerical simulation (DNS) with the spectrally accurate code nek5000  to examine the Reynolds-number effect on turbulence statistics. The effect of the curvature to these canonical turbulent pipe flows is then added to generate 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 evolution of turbulence characteristics from a straight pipe. A fundamentally different Prandtl’s secondary motion of the second kind is also put to test by adding side-walls to a canonical turbulent channel flow and analysing the evolution of various statistical quantities with varying the duct width-to-height aspect ratios.

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 these configurations 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 is scrutinised. The analysis of the resulting particle fields shows that even a small amount of secondary motion has a profound impact on the particle phase dynamics and its concentration maps.

For each of the aforementioned turbulent flow cases new and challenging questions have arisen to be addressed in the present research works. The goal of extending understanding of the particle dispersion in turbulent bent pipes and rectangular ducts are also achieved.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 71 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2015:09
Keyword
turbulent, complex geometry, particle
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-177310 (URN)978-91-7595-785-2 (ISBN)
Public defence
2015-12-04, F3, Lindstedtsvägen 26, KTH, Stockholm, 11:01 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20151118

Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2015-11-18Bibliographically approved

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