Laboratory Study of Porosity Effect on Drag Induced by Circular Vegetative Patch
Publication: Journal of Engineering Mechanics
Volume 145, Issue 7
Abstract
Laboratory experiments were conducted to directly measure the drag force induced by vegetation patches under unidirectional flow conditions. The drag force was measured with a highly responsive load cell for six patch models, of which the vegetation stems were simulated using rigid cylindrical rods. The measured drag coefficient varies with the Reynolds number and the number of rods included in the patch model. It generally reduces with increasing Reynolds number, and the reduction appears more significant for a patch model with fewer rods. To take into account effects of the patch porosity, this study proposed to redefine the drag coefficient and Reynolds number based on new length and velocity scales, that is, the vegetation hydraulic radius and the average velocity for the flow through the patch. This change produces a monotonic relationship between the redefined drag coefficient and redefined Reynolds number, which is generally applicable for all patch models.
Get full access to this article
View all available purchase options and get full access to this article.
References
Cheng, N. S. 2013. “Calculation of drag coefficient for arrays of emergent circular cylinders with pseudo-fluid model.” J. Hydraul. Eng. 139 (6): 602–611. https://doi.org/10.1061/(ASCE)HY.1943-7900.0000722.
Cheng, N.-S. 2015. “Single-layer model for average flow velocity with submerged rigid cylinders.” J. Hydraul. Eng. 141 (10): 06015012. https://doi.org/10.1061/(ASCE)HY.1943-7900.0001037.
Cheng, N.-S., and H. T. Nguyen. 2011. “Hydraulic radius for evaluating resistance induced by simulated emergent vegetation in open-channel flows.” J. Hydraul. Eng. 137 (9): 995–1004. https://doi.org/10.1061/(ASCE)HY.1943-7900.0000377.
Follett, E. M., and H. M. Nepf. 2012. “Sediment patterns near a model patch of reedy emergent vegetation.” Geomorphology 179 (Dec): 141–151. https://doi.org/10.1016/j.geomorph.2012.08.006.
Ishikawa, Y., K. Mizuhara, and S. Ashida. 2000. “Effect of density of trees on drag exerted on trees in river channels.” J. For. Res. 5 (4): 271–279. https://doi.org/10.1007/BF02767121.
James, C. S., A. L. Birkhead, A. A. Jordanova, and J. J. O’Sullivan. 2004. “Flow resistance of emergent vegetation.” J. Hydraul. Res. 42 (4): 390–398. https://doi.org/10.1080/00221686.2004.9728404.
Kothyari, U. C., K. Hayashi, and H. Hashimoto. 2009. “Drag coefficient of unsubmerged rigid vegetation stems in open channel flows.” J. Hydraul. Res. 47 (6): 691–699. https://doi.org/10.3826/jhr.2009.3283.
Kouwen, N., T. E. Unny, and H. M. Hill. 1969. “Flow retardance in vegetated channels.” J. Irrig. Drain. Div. 95 (2): 329–342.
Lam, K., J. Y. Li, and R. M. C. So. 2003. “Force coefficients and Strouhal numbers of four cylinders in cross flow.” J. Fluids Struct. 18 (3–4): 305–324. https://doi.org/10.1016/j.jfluidstructs.2003.07.008.
Murphy, E., M. Ghisalberti, and H. Nepf. 2007. “Model and laboratory study of dispersion in flows with submerged vegetation.” Water Resour. Res. 43 (5): W05438. https://doi.org/10.1029/2006WR005229.
Nepf, H. M. 1999. “Drag, turbulence, and diffusion in flow through emergent vegetation.” Water Resour. Res. 35 (2): 479–489. https://doi.org/10.1029/1998WR900069.
Schlichting, H. 1979. Boundary-layer theory, New York: McGraw-Hill.
Shimizu, Y., T. Tsujimoto, H. Nakagawa, and T. Kitamura. 1991. “Experimental study on flow over rigid vegetation simulated by cylindrical with equi-spacing.” [In Japanese.] Proc. Jpn. Soc. Civ. Eng. 438/II-17: 31–40.
Stone, B. M., and H. T. Shen. 2002. “Hydraulic resistance of flow in channels with cylindrical roughness.” J. Hydraul. Eng. 128 (5): 500–506. https://doi.org/10.1061/(ASCE)0733-9429(2002)128:5(500).
Tanino, Y., and H. M. Nepf. 2008. “Laboratory investigation of mean drag in a random array of rigid, emergent cylinders.” J. Hydraul. Eng. 134 (1): 34–41. https://doi.org/10.1061/(ASCE)0733-9429(2008)134:1(34).
Tinoco, R. O., and E. A. Cowen. 2013. “The direct and indirect measurement of boundary stress and drag on individual and complex arrays of elements.” Exp. Fluids 54 (4): 1509. https://doi.org/10.1007/s00348-013-1509-3.
Vandenbruwaene, W., et al. 2011. “Flow interaction with dynamic vegetation patches: Implications for biogeomorphic evolution of a tidal landscape.” J. Geophys. Res. Earth Surf. 116 (F1): F01008. https://doi.org/10.1029/2010JF001788.
Wang, X. K., K. Gong, H. Liu, J. X. Zhang, and S. K. Tan. 2013. “Flow around four cylinders arranged in a square configuration.” J. Fluids Struct. 43 (Nov): 179–199. https://doi.org/10.1016/j.jfluidstructs.2013.08.011.
Wilson, C., J. Hoyt, and I. Schnauder. 2008. “Impact of foliage on the drag force of vegetation in aquatic flows.” J. Hydraul. Eng. 134 (7): 885–891. https://doi.org/10.1061/(ASCE)0733-9429(2008)134:7(885).
Zhao, K. F., N. S. Cheng, X. K. Wang, and S. K. Tan. 2014. “Measurements of fluctuation in drag acting on rigid cylinder array in open channel flow.” J. Hydraul. Eng. 140 (1): 48–55. https://doi.org/10.1061/(ASCE)HY.1943-7900.0000811.
Information & Authors
Information
Published In
Journal of Engineering Mechanics
Volume 145 • Issue 7 • July 2019
Copyright
©2019 American Society of Civil Engineers.
History
Received: Jul 1, 2018
Accepted: Dec 5, 2018
Published online: May 6, 2019
Published in print: Jul 1, 2019
Discussion open until: Oct 6, 2019
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.