Scour and three dimensional turbulent flow fields measured by ADV at a 90 ° horizontal forced bend in a rectangular channel

Abstract

The three dimensional turbulent flow fields and scour at a 90° horizontal forced bend were investigated experimentally. Non-cohesive non-uniform sediments with median diameter d 50 equal to 0.3 mm were used. The flow depth and velocity in the upstream section were adjusted to get a shear velocity equal to 1.61 times the critical shear velocity of the bed particles. The time averaged velocity components, turbulent intensity components and Reynolds stresses on a stabilized scoured bed were taken by the Acoustic Doppler Velocimeter (ADV) at different azimuthal sections. The presentation of flow fields through vectors at the horizontal section mainly shows that there is a concentration of flow in the concave bank at the bend. It is found from the measured bed profile that the non-dimensional maximum scour depth (scour depth/width of channel) is approximately 0.17 at the bend under the above flow conditions. The maximum measured velocity was approximately 1.61 times the average velocity. The data obtained in the experimental investigation will be useful for the proper design of protection works at bends.