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POD analysis of stereoscopic PIV data from swirling turbulent flow through a pipe bend
KTH, School of Engineering Sciences (SCI), Mechanics. 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)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: urn:nbn:se:kth:diva-93728OAI: oai:DiVA.org:kth-93728DiVA: diva2:523476
Note
QC 20120425Available from: 2012-04-25 Created: 2012-04-24 Last updated: 2012-05-14Bibliographically approved
In thesis
1. Experimental study of turbulent flows through pipe bends
Open this publication in new window or tab >>Experimental study of turbulent flows through pipe bends
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
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:nbn:se:kth:diva-93316 (URN)978-91-7501-321-3 (ISBN)
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

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