Experimental Investigation of Turbulent Hydrodynamics in Developing Narrow Open Channel Flow

Abstract

In the present study, a detailed experimental investigation of turbulent hydrodynamics is carried out on developing flow along the centreline of a narrow open channel. The characteristics of flow velocity, normal stresses and Reynolds stresses have been investigated. At the beginning of the modelled region, the time-averaged streamwise velocity increases up to 20% of the flow depth from the channel bed and decreases with further increase in vertical height. With increasing streamwise length, vertical location of the maximum time-averaged streamwise velocity is shifting away from the bed. The time-averaged lateral velocities are positive along the midsection in the modelling region, whereas the time-averaged vertical velocities exhibit negative value. In the modelled region, the maximum value of time-averaged lateral velocity occurs either near the channel bed or in the vicinity of the free surface; however, the peak value of time-averaged vertical velocity appears in the neighbourhood of the channel bed. In the developing flow region, the values of normal stresses in streamwise and lateral directions are maximum near the bed and decrease with vertical distance up to 40% of the flow depth from the channel bed and after that normal stresses increase with further increase in vertical distance from the channel bed. Moreover, the observed magnitudes of streamwise normal stresses are greater than the corresponding values of lateral normal stress. The normal stress in vertical direction increases with increasing vertical height from the channel bed; however, the increasing trend decreases with increasing streamwise distance. Before attaining the fully developed profile, the Reynolds shear stress exhibits a decreasing trend with increasing vertical height up to 60% of the flow depth from the channel bed, and with further increase in vertical distance, the Reynolds shear stress trend starts increasing. An important finding is that in the modelled region, the developing flow zone, the transition zone from developing flow to fully developed flow and the fully developed flow zone are detected. The present study provides a good quality data for further investigations of developing flow in a narrow open channel.