Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Experimental study of turbulent flows through pipe bends
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).ORCID iD: 0000-0001-8127-8124
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow.

The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated.

The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated.

Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods.

The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2012. , viii, 85 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:05
Keyword [en]
Turbulent flow, swirl, pulsation, pipe bend, hot-wire anemometry, cold-wire anemometry, laser Doppler velocimetry, stereoscopic particle image velocimetry.
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-93316ISBN: 978-91-7501-321-3 (print)OAI: oai:DiVA.org:kth-93316DiVA: diva2:515647
Presentation
2012-05-03, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20120425Available from: 2012-04-25 Created: 2012-04-13 Last updated: 2012-04-25Bibliographically approved
List of papers
1. Experimental investigation on the effect of pulsations on turbulent flow through a 90degrees pipe bend
Open this publication in new window or tab >>Experimental investigation on the effect of pulsations on turbulent flow through a 90degrees pipe bend
2010 (English)In: Proc. of 3rd Int. Conf. on Jets, Wakes & Separated Flows 2010, 2010Conference paper, Published paper (Other academic)
Abstract [en]

Pulsatile turbulent flows in curved pipes at high Dean numbers are prevalent in various components of internal combustion engines, particularly the intake of exhaust manifolds. Despite their technological importance, there is a clear lack of experimental data. The present paper provides preliminary, albeit unique, data from an experimental investigation, thereby addressing this gap and depicts impressions of the phase evolution of the complex flow including a back flow region. It is also shown, that due to the scale separation of the pulsations and the turbulence, the pulsatile flow can statistically be decomposed into its large-scale pulsations and the steady case.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-93738 (URN)
Conference
3rd Int. Conf. on Jets, Wakes & Separated Flows 2010
Note
QC 20120425Available from: 2012-04-25 Created: 2012-04-25 Last updated: 2012-04-25Bibliographically approved
2. Pulsatile turbulent flow through pipe bends at high Dean and Womersley numbers
Open this publication in new window or tab >>Pulsatile turbulent flow through pipe bends at high Dean and Womersley numbers
2011 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 318, 092023- p.Article in journal (Refereed) Published
Abstract [en]

Turbulent pulsatile flows through pipe bends are prevalent in internal combustion engine components which consist of bent pipe sections and branching conduits. Nonetheless, most of the studies related to pulsatile flows in pipe bends focus on incompressible, low Womersley and low Dean number flows, primarily because they aim in modeling blood flow, while internal combustion engine related flows have mainly been addressed in terms of integral quantities and consist of single point measurements. The present study aims at bridging the gap between these two fields by means of time-resolved stereoscopic particle image velocimetry measurements in a pipe bend with conditions that are close to those encountered in exhaust manifolds. The time/phase-resolved three-dimensional cross-sectional flow-field 3 pipe diameters downstream the pipe bend is captured and the interplay between different secondary motions throughout a pulse cycle is discussed.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-83120 (URN)10.1088/1742-6596/318/9/092023 (DOI)000299774100023 ()2-s2.0-84856347465 (Scopus ID)
Conference
13th European Turbulence Conference, ETC13; Warsaw;12 September 2011 through 15 September 2011
Note
QC 20120213Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2017-12-07Bibliographically approved
3. Dean vortices in turbulent flows: rocking or rolling?
Open this publication in new window or tab >>Dean vortices in turbulent flows: rocking or rolling?
2012 (English)In: Journal of Visualization, ISSN 1343-8875, E-ISSN 1875-8975, Vol. 15, no 1, 37-38 p.Article in journal (Refereed) Published
Abstract [en]

Flows in pipe bends have been studied extensively over the last decades due to their occurrence both in the human respiratory and blood systems as well as in many technical applications. When a fluid flows through a pipe bend an adverse pressure gradient is generated forcing high velocity fluid towards the outer wall which is then replaced by low velocity fluid moving along the wall towards the inner side of the bend. The physical effect is that the high velocity fluid is experiencing a large centrifugal force, resulting in an unstable ‘‘stratification’’ making the high velocity fluid in the centre deflect outwards along the pipe bend, thereby forming two counter-rotating roll cells, so-called Dean vortices. While their behavior in laminar flows has been nicely visualized, the picture of their unsteady behavior in turbulent flows still remains rather blurry, and in fact ‘‘the questions, for example, whether the Dean vortices stay symmetric with respect to the geometric plane of symmetry or whether the strength of the Dean vortices varies with time are hardly addressed’’ (Rütten et al 2005). In the present study, stereoscopic particle image velocimetry has been employed to seize the unsteady behavior of the Dean vortices at the exit of a 90 degree pipe bend at a Reynolds number and Dean number of 34,000 and 19,000, respectively. While the time-averaged flow field shows two symmetrical roll cells, that can be observed both in the streamwise and cross stream velocities, as well as in the streamwise vorticity, the instantaneous snapshots reveal an unsteady behavior where the roll cells are pushing one another alternatively towards the lower or upper half of the pipe, in what could be described as a ‘‘rocking’’ motion of the high speed ‘‘stem’’ in between the roll cells. Hence, the real question is not whether ‘‘to be, or not to be’’ in regards to the instantaneous existence of the Dean vortices in turbulent flows, but rather why, when and how they roll (as their time-averaged counterpart) or rock between the states caught in the presented snapshots.

Place, publisher, year, edition, pages
Springer, 2012
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-83164 (URN)10.1007/s12650-011-0108-8 (DOI)000302382600003 ()2-s2.0-84862658176 (Scopus ID)
Funder
StandUp
Note

QC 20120216

Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2017-12-07Bibliographically approved
4. Experimental investigation on the effect of pulsations on exhaust manifold-related flows aiming at improved efficiency
Open this publication in new window or tab >>Experimental investigation on the effect of pulsations on exhaust manifold-related flows aiming at improved efficiency
2012 (English)In: Institution of Mechanical Engineers - 10th International Conference on Turbochargers and Turbocharging, 2012, 377-387 p.Conference paper, Published paper (Refereed)
Abstract [en]

The gas flowing through the exhaust manifold of the internal combustion engine to the inlet of the turbine side of a turbocharger is highly pulsating and turbulent. The gas enters the turbine after travelling through a complex curved and branched pipe system where the effect of centrifugal (from the acute curvature), inertia and viscous forces result in a three-dimensional, non-symmetric flow field. Additionally, vortical structures are being formed and dissolved due to the co-existence of these forces that change in magnitude under a pulse period. This complex flow field, typical for the inflow condition to the turbine, is the focus of the present study. Instantaneous mass flow rate and pressure measurements that provide information on changes in the turbine map when a sharp bend is mounted at the inlet of the turbine are performed and complemented with time-resolved stereoscopic particle image velocimetry measurements of the pulsating turbulent flow downstream a 90° pipe bend. The results indicate, that the time-averaged operation point in a turbine map is only marginally affected by the inflow conditions and the pulsation frequency. The hysteresis loops, on the other hand, exhibit differences not only for different pulsation frequencies, but also for different inflow conditions as a comparison between a straight and a curved pipe section upstream the turbine shows.

Keyword
Centrifugation, Exhaust manifolds, Flow fields, Internal combustion engines, Superchargers
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-83153 (URN)2-s2.0-84865479030 (Scopus ID)978-085709209-0 (ISBN)
Conference
10th International Conference on Turbochargers and Turbocharging; London;15 May 2012 through 16 May 2012
Funder
StandUp
Note

QC 20120425

Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2013-04-16Bibliographically approved
5. POD analysis of stereoscopic PIV data from swirling turbulent flow through a pipe bend
Open this publication in new window or tab >>POD analysis of stereoscopic PIV data from swirling turbulent flow through a pipe bend
2012 (English)Report (Other academic)
Abstract [en]

Coherent structures in turbulent swirling flow through a pipe bend are investigated experimentally by means of stereoscopic particle image velocimetry. Inparticular, the effect of the imposed swirling motion on the Dean vortices aswell as the very-large-scale structures is examined for a wide range of swirlnumbers. Proper orthogonal decomposition is employed to rank the spatialmodes by energy content and extract the underlying secondary swirling motionas well as the large-scale structures present in the flow field. Moreover theoriginal snapshots are reconstructed by using only a few of the most energeticmodes and ease visualization of the structures by inhomogeneously filtering theflow fields. Phenomena such as the unsteady motion of the Dean vortices, theso called swirl switching, in the non-swirling turbulent flow case and the tiltingof the very-large-scale structures in a highly swirling turbulent flow are capturedand presented. The results presented here are preliminary and furtheranalysis is planned in the future. Nevertheless, this work is believed to provideunique data as the first experimental study on swirling flows through a pipebend which is not restricted to single-point measurements.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-93728 (URN)
Note
QC 20120425Available from: 2012-04-25 Created: 2012-04-24 Last updated: 2012-05-14Bibliographically approved

Open Access in DiVA

fulltext(7376 kB)30437 downloads
File information
File name FULLTEXT02.pdfFile size 7376 kBChecksum SHA-512
0ac6e2ac2013e2b4697b94bb928279251a1cc51ff11e2576e9dd5d182d4aec11d32abaecf0b48077a517dbe2430a0f7694aaccceebf51dc126243e63f374c51e
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Kalpakli, Athanasia
By organisation
Linné Flow Center, FLOWCompetence Center for Gas Exchange (CCGEx)
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
Total: 30437 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 936 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf