Turbulence Measurements in Compound Open Channels

Abstract

An investigation on a 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 engineerings, as well as in fluid mechanics. In this study, accurate measurements in fully-developed compound open-channel flows were conducted by making use of a filder-optic laser Doppler anemometer (FLDA). Secondary velocities could be measured very accurately with the present 3-D measurement system. The characteristics peculiar to compound open channel flows are recognized in a junction region between the main channel and the flood plain, whereas the characteristics in rectangular open channel flows are observed in a region near the side wall of the main channel. Strong inclined secondary currents, which are associated with a pair of longitudinal vortices, are generated in a junction region between the main channel and the flood plain. The primary mean velocity filed is directly influenced by these secondary currents. Turbulence intensisies and the Reynolds stresses are also reveald in detail. Moreover, the effects of channel gemetry and bed roughness on turbulent structures are examined.