Open‐channel Flow Measurements with a Laser Doppler Anemometer
Publication: Journal of Hydraulic Engineering
Volume 112, Issue 5
Abstract
A powerful two‐color Laser Doppler Anemometer (LDA) system, with direct digital signal processing has been used to measure accurately the longitudinal and vertical velocity components in two‐dimensional, fully‐developed open‐channel flow over smooth beds. The law of the wall and the velocity defect law were re‐examined because the log‐law has been often applied to open channels without detailed verification. It was found that the log‐law can be applied strictly only to the near‐wall region. In this region, the von rn constant κ and the integral constant A are truly universal, having values of and irrespective of the Reynolds and Froude number. As the Reynolds number becomes larger, the deviation from the log‐law cannot be neglected in the outer region. This deviation can be expressed well by Coles' wake function which involves a Reynolds‐number dependent parameter Π. The distributions of eddy viscosity and mixing length were evaluated and found to depend on Π. All the data including the turbulence intensities will offer valuable information for the further understanding of open‐channel flow and for the development and testing of calculation methods.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 112 • Issue 5 • May 1986
Pages: 335 - 355
Copyright
Copyright © 1986 ASCE.
History
Published online: May 1, 1986
Published in print: May 1986
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