Three-Dimensional Turbulent Structure and Associated Secondary Currents in Straight Rivers : Field Measurements of River Turbulence

Abstract

Fundamental structures of turbulence in two-dimensional (2-D) and further three-dimensional (3-D) open-channel flows have recently been almost clarified theoretically and experimentally through accurate experimental data which were obtained using a laser-Doppler anemometer system in laboratory flumes ; this detailed knowledge is now available in an IAHR monograph written by Nezu & Nakagawa (1992). Many of these experiments have, however, been conducted at moderate Reynolds numbers, say Re 記号 10⁴. Therefore, it is not yet clear whether such laboratory data of open-channel turbulence can be applied to river turbulence at high Reynolds numbers. In this study, velocity measurements of the Biwako-Sosui River (Re = 8 × 10⁵) in Kyoto and the Aichi Irrigation Channel (Re = 6 × 10⁵) in Nagoya have been conducted, using three-component electromagnetic flow meters. It was first found that multi-cellular secondary currents and free-surface secondary currents were evident in actual rivers. The features of such secondary currents in rivers were in a good agreement with those in laboratory flumes. Key Words : turbulence-driven secondary currents ; river turbulence ; field measurements ; velocity-dip phenomenon ; effects of aspect ratio.