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Characterisation of the steady, laminar incompressible flow in toroidal pipes covering the entire curvature range
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.ORCID-id: 0000-0003-3211-4347
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.ORCID-id: 0000-0002-1663-3553
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.ORCID-id: 0000-0001-9627-5903
2017 (engelsk)Inngår i: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 66, s. 95-107Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

This work is concerned with a detailed investigation of the steady (laminar), incompressible flow inside bent pipes. In particular, a toroidal pipe is considered in an effort to isolate the effect of the curvature, δ, on the flow features, and to compare the present results to available correlations in the literature. More than 110 000 numerical solutions are computed, without any approximation, spanning the entire curvature range, 0 ≤ δ ≤ 1, and for bulk Reynolds numbers Re up to 7 000, where the flow is known to be unsteady. Results show that the Dean number De provides a meaningful non-dimensional group only below very strict limits on the curvature and the Dean number itself. For δ>10−6 and De > 10, in fact, not a single flow feature is found to scale well with the Dean number. These considerations are also valid for quantities, such as the Fanning friction factor, that were previously considered Dean-number dependent only. The flow is therefore studied as a function of two equally important, independent parameters: the curvature of the pipe and the Reynolds number. The analysis shows that by increasing the curvature the flow is fundamentally changed. Moderate to high curvatures are not only quantitatively, but also qualitatively different from low δ cases. A complete description of some of the most relevant flow quantities is provided. Most notably the friction factor f for laminar flow in curved pipes by Ito [J. Basic Eng. 81:123–134 (1959)] is reproduced, the influence of the curvature on f is quantified and the scaling is discussed. A complete database including all the computed solutions is available at www.flow.kth.se.

sted, utgiver, år, opplag, sider
Elsevier, 2017. Vol. 66, s. 95-107
Emneord [en]
Bent pipes, Dean number, Friction factor
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-209516DOI: 10.1016/j.ijheatfluidflow.2017.05.014ISI: 000407524500009Scopus ID: 2-s2.0-85020316303OAI: oai:DiVA.org:kth-209516DiVA, id: diva2:1112646
Forskningsfinansiär
Swedish Research Council, 621-2013-5788Knut and Alice Wallenberg FoundationSwedish e‐Science Research Center
Merknad

QC 20170620

Tilgjengelig fra: 2017-06-20 Laget: 2017-06-20 Sist oppdatert: 2018-05-21bibliografisk kontrollert
Inngår i avhandling
1. Of Pipes and Bends
Åpne denne publikasjonen i ny fane eller vindu >>Of Pipes and Bends
2018 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This work is concerned with the transition to turbulence of the flow in bent pipes, but it also includes an analysis of large-scale turbulent structures and their use for flow control.

The flow in a toroidal pipe is selected as it represents the common asymptotic limit between spatially developing and helical pipes. The study starts with a characterisation of the laminar flow as a function of curvature and the Reynolds number Re, since the so-called Dean number is found to be of little use except for infinitesimally low curvatures. It is found that the flow is modally unstable and undergoes a Hopf bifurcation for any curvature greater than zero. The bifurcation is studied in detail, and an effort to connect this modal instability with the linearly stable straight pipe is also presented.

This flow is not only modally unstable, but undergoes subcritical transition at low curvatures. This scenario is found to bear similarities to straight pipes, but also fundamental differences such as weaker turbulent structures and the apparent absence of puff splitting. Toroidal pipe flow is peculiar, in that it is one of the few fluid flows presenting both sub- and supercritical transition to turbulence; the critical point where the two scenarios meet is therefore of utmost interest. It is found that a bifurcation cascade and featureless turbulence actually coexist for a range of curvature and Re, and the attractors of the respective structures have a small but finite basin of attraction.

In 90◦ bent pipes at higher Re large-scale flow structures cause an oscilla- tory motion known as swirl-switching. Three-dimensional proper orthogonal decomposition is used to determine the cause of this phenomenon: a wave-like structure which is generated in the bent section, and is possibly a remnant of a low-Re instability.

The final part of the thesis has a different objective: to reduce the turbulent frictional drag on the walls of a channel by employing a control strategy independent of Re-dependent turbulent scales, initially proposed by Schoppa & Hussain [Phys. Fluids 10:1049–1051 (1998)]. Results show that the original method only gives rise to transient drag reduction while a revised version is capable of sustained drag reduction of up to 18%. However, the effectiveness of this control decreases rapidly as the Reynolds number is increased, and the only possibility for high-Re applications is to use impractically small actuators.

sted, utgiver, år, opplag, sider
KTH Royal Institute of Technology, 2018. s. 51
Serie
TRITA-SCI-FOU ; 2018:25
Emneord
nonlinear instability, bifurcation, flow control
HSV kategori
Forskningsprogram
Teknisk mekanik
Identifikatorer
urn:nbn:se:kth:diva-228225 (URN)978-91-7729-823-6 (ISBN)
Disputas
2018-06-15, F2, Lindstedtsvägen 26, Stockholm, 10:15 (engelsk)
Opponent
Veileder
Merknad

QC 20180521

Tilgjengelig fra: 2018-05-21 Laget: 2018-05-18 Sist oppdatert: 2018-05-21bibliografisk kontrollert

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