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On minimum aspect ratio for duct flow facilities and the role of side walls in generating secondary flows
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. MMAE Department, Illinois Institute of Technology, Chicago, IL, USA.ORCID iD: 0000-0001-6570-5499
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-9627-5903
2015 (English)In: Journal of turbulence, ISSN 1468-5248, Vol. 16, no 6, 588-606 p.Article in journal (Refereed) Published
Abstract [en]

To the surprise of some of our colleagues, we recently recommended aspect ratios of at least 24 (instead of accepted values over last few decades ranging from 5 to 12) to minimise effects of sidewalls in turbulent duct flowexperiments, in order to approximate the two-dimensional channel flow. Here we compile available results from hydraulics and civil engineering literature, where this was already documented in the 1980s. This is of great importance due to the large amount of computational studies (mainly direct numerical simulations, DNSs) for spanwise-periodic turbulent channel flows, and the extreme complexity of constructing a fully developed duct flow facility with aspect ratio of 24 for high Reynolds numbers with adequate probe resolution. Results from this nontraditional literature for the turbulence community are compared to our recent database of DNS of turbulent duct flows with aspect ratios ranging from 1 to 18 at Re-tau,Re- c values of 180 and 330, leading to very good agreement between their experimental and our computational results at these low Reynolds numbers. The DNS results also reveal the complexity of a multitude of streamwise vortical structures in addition to the secondary corner flows (which extend up to z similar or equal to 5h). These time-dependent and meandering streamwise structures are located at the core of the duct and scale with its half-height. Comparisons of these structures with the vortical motions found in spanwise-periodic channels reveal similitudes in their time-averages and the same rate of decay of their mean kinetic energy similar to T-A(-1), with T-A being the averaging time. However, differences between the two flows are identified and ideas for their future analysis are proposed.

Place, publisher, year, edition, pages
2015. Vol. 16, no 6, 588-606 p.
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-164487DOI: 10.1080/14685248.2014.996716ISI: 000351597400005OAI: diva2:806349

QC 20150420

Available from: 2015-04-20 Created: 2015-04-17 Last updated: 2015-04-20Bibliographically approved

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Vinuesa, RicardoSchlatter, Philipp
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