Turbulent Flows within Random Arrays of Rigid and Emergent Cylinders with Varying Distribution
Publication: Journal of Hydraulic Engineering
Volume 142, Issue 9
Abstract
The spatial distribution of emergent vegetation in rivers is frequently nonuniform. Here, spatial nonuniformity is simulated in the laboratory by varying longitudinally the stem areal number density (). Time- and space-averaged flow variables, corresponding to different values and gradients of and different stem Reynolds numbers, are calculated from instantaneous velocity maps obtained with particle image velocimetry (PIV). Results show that Reynolds stresses are completely determined by the local spatially averaged number of stems per unit area; they are not sensitive to local spatial gradients of . These variables seem to adjust locally to the spatial variations of the stem distribution. Contrarily, the spatial distribution of the time-averaged flow is influenced not only by the local value of but also by its spatial gradients. Form-induced stresses express this influence. They reveal a subsistence of flow complexity generated by the upstream stem distribution as a form of spatial memory. Thus, the effect of spatial gradients of is always in the direction of increasing form-induced stresses although at different rates depending on the signal of the former.
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Acknowledgments
This study was funded by the Portuguese Foundation for Science and Technology (FCT) through projects PTDC/ECM/117660/2010 and RECI/ECM-HID/0371/2012, and by the grant SFRH/BPD/93903/2013.
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Published In
Journal of Hydraulic Engineering
Volume 142 • Issue 9 • September 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: May 15, 2015
Accepted: Jan 26, 2016
Published online: May 2, 2016
Published in print: Sep 1, 2016
Discussion open until: Oct 2, 2016
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