Turbulent Structure in Compound Open‐Channel Flows

Abstract

An investigation of three‐dimensional (3‐D) turbulent structure, including turbulence‐driven secondary currents in compound open‐channel flows, is a very important topic in hydraulic and river engineering, as well as in fluid mechanics. In this study, accurate measurements in fully developed compound open‐channel flows are conducted by means of a fiber‐optic laser Doppler anemometer (FLDA). Secondary velocities can be measured very accurately with the present 3‐D measurement system. The characteristics of compound open‐channel flows are recognized in the junction region between the main channel and flood plain, whereas the characteristics of rectangular open‐channel flows are observed in a region near the sidewall of the main channel. Strong, inclined secondary currents, which are associated with a pair of longitudinal vortices, are generated in the junction region between the main channel and the flood plain. The primary mean velocity field is directly influenced by these secondary currents. Turbulence intensities and the Reynolds stresses are also revealed in detail. Moreover, the effects of channel geometry and bed roughness on turbulent structure are examined.