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Boundary layer development over equally spaced fences: technical report




Kung, Robin Jung, author
Plate, Erich J., author
Fluid Dynamics and Diffusion Laboratory, College of Engineering, Colorado State University, publisher

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Experimental studies on a series of fences immerged in a smooth wall turbulent boundary layer are discussed in this report. Fences are placed at equal spacing and they are of equal height. The basic variables are the spacings of the fences and the ambient velocity. Six different experiments were performed by combining two ambient velocities with three fence spacings. The flow field is subdivided into three regions. They are: the "smooth" region upstream from the leading fence; the "rough" region far downstream from the leading fence; and the "transition" region between the smooth region and rough region. Emphasis of this work is placed on the rough region. The flow in the rough region represents the overall effects of all upstream fences, in it the effect of each individual fence on the boundary layer can no longer be identified. Mean velocity profiles, static pressure profiles, turbulence, and form drag of fences are measured. Comparison between the measured results and existing theories are made. The flow in the smooth region can be correlated by the wall law and the defect law of a smooth wall turbulent boundary layer. Flow in the rough region is found to depend on fence height, fence spacing and their ratio. The universal velocity defect law breaks down in the rough region of the present study, however, an empirical expression for the velocity defect law is found. A model law is proposed for modeling the problem of multiple wind breaks. Also discussed is how an optimum wind break can be determined.


June 1970.
Includes bibliographical references (pages 83-89).
U.S. Department of Interior Office of Water Resources Research Contract No. 14-01-0001.

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Fluid mechanics


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