Shear Stress Distributions along the Cross Section in Smooth Open Channel Flow

Abstract

Distributions of shear stress throughout the entire cross-section within the fully developedboundary layer region in a smooth and rectangular open channel flow setup areexperimentally determined with the help of a laser Doppler anemometer. Velocity measurements are taken for 24 different sub-critical flow conditions with Froude numbers inthe range: 0.13 Fr 0.78 and with aspect ratios within 1.5 B/H 12.0. For all the flow conditions created in the setup, the shear stress distribution is found to exhibit variations as afunction of the aspect ratio, B/H, which is caused by the flow cells originated by the secondary flows in opposite direction to the main flow. For the aspect ratio between 1.5 and5.0, the shear stress distributions are represented by a third degree polynomial function alongthe cross section. In this case, the maximum shear stress is 12% greater than the averagestress. For B/H≥ 5.0, the dimensionless shear stress distributions are represented by a seconddegree polynomial. Here, the maximum shear stress was 10% greater than the overall average shear stress throughout the entire cross-section.