Flow Analysis of Compound Channels With Converging Floodplains

Abstract

The main objective of this research analyses is to study the flow behavior of both prismatic and non-prismatic compound channels having converging floodplains of width ratio varies from 1.8 to 1.0 and main channel aspect ratio of more than 5. Experiments were conducted for these channels in the Fluid Mechanics and Hydraulics laboratory of National Institute of Technology, Rourkela, India by making smooth, rigid, straight and converging within a concrete flume. Micro-ADV, Preston tube, notch, pointer gauge, manometers and other hydraulic equipment have been used to measure 3-d velocity, boundary shear stress, and water surface profile at different sections of the channels. The research investigates the modeling of water surface profile, distribution of longitudinal velocity, depth-averaged velocity, boundary shear stress and energy loss for overbank flow cases in both prismatic and non-prismatic sections of converging compound channels. As a complementary study to the experimental research, numerical hydrodynamic tools viz. ANSYS is applied to simulate the flow for both prismatic and non-prismatic sections of converging compound channels. All the important flow parameters are extracted numerically from the simulation results to study them vis a vis their observed values. As a prediction of flow variables in a non-prismatic converging compound channel is a much complex phenomenon, so an ANN has also been employed for prediction of depth-averaged velocity, boundary shear, and energy loss for different flow conditions.
From the experimental study, new expressions for the water surface, energy loss and stage-discharge relationship for converging compound channels have been developed and validated with the present data and data sets from previous research projects. The distribution of boundary shear stress over different zones of a compound section of prismatic and non-prismatic compound channels are analyzed with several data sets of other researchers, new models for predicting subsection shear force are also suggested. Using the proposed shear models, the stage–discharge relations in case of both prismatic compound channels having different width ratio and non-prismatic compound channel of different converging angles are then evaluated. These developed models are well validated with new experimental data as well as with datasets of another researcher. The efficiency of the model has also been verified by applying natural river data sets and comparing well with other existing models.