Aspect ratio effects in turbulent duct flows studied through direct numerical simulation
2014 (English)In: Journal of turbulence, ISSN 1468-5248, Vol. 15, no 10, 677-706 p.Article in journal (Refereed) Published
Three-dimensional effects in turbulent duct flows, i.e., sidewall boundary layers and secondary motions, are studied by means of direct numerical simulation (DNS). The spectral element code Nek5000 is used to compute turbulent duct flows with aspect ratios 1-7 (at Re-b,Re- c = 2800, Re-tau,Re- c similar or equal to 180) and aspect ratio 1 (at Re-b,Re- c = 5600, Re-tau,Re- c similar or equal to 330), in streamwise-periodic boxes of length 25h. The total number of grid points ranges from 28 to 145 million, and the pressure gradient is adjusted iteratively in order to keep the same bulk Reynolds number in the centreplane with changing aspect ratio. Turbulence is initiated via a trip forcing active during the initial stages of the simulation, and the statistical convergence of the data is discussed both in terms of transient approach and averaging period. Spanwise variations in wall shear, mean-flow profiles, and turbulence statistics are analysed as a function of aspect ratio, and also compared with the spanwise-periodic channel (as idealisation of an infinite aspect ratio duct). The computations show good agreement with experimental measurements carried out in parallel at the Illinois Institute of Technology (IIT) in Chicago, and highlight the relevance of sidewall boundary layers and secondary vortices in the physics of the duct flow. The rich array of secondary vortices extending throughout the upper and lower walls of the duct, and their dependence on Reynolds number and aspect ratio, had not been reported in the literature before.
Place, publisher, year, edition, pages
2014. Vol. 15, no 10, 677-706 p.
direct numerical simulation, secondary motions, secondary vortices/motions, three-dimensional flows, turbulent duct flow, wall turbulence
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-141942DOI: 10.1080/14685248.2014.925623ISI: 000340121000003ScopusID: 2-s2.0-84904987697OAI: oai:DiVA.org:kth-141942DiVA: diva2:699112
Updated from manuscript to article in journal.
QC 201409082014-02-262014-02-262015-11-18Bibliographically approved