An investigation into the flow structure of a generalised open channel intake

Open channel intake structures occur in many different applications such as navigable water courses, irrigation, power station facilities for cooling or steam production and run-of-the-river hydropower facilities. All these applications suffer from problems such as energy losses due to asymmetric flow patterns and the commonly associated problem of sedimentation. The flow structure and the associated energy losses at a generalised open channel intake structure are investigated using three-dimensional numerical and physical modelling techniques. Intake angles of 15, 30 and 45 degrees with flow split ratios (intake channel flow / main channel flow) ranging from 0.5 to 3.0 and Reynolds numbers ranging from 1x105 to 3x105 are investigated. A predictive hypothesis for the position and shape of the dividing streamplane is presented and tested with reasonable correlation. The hypothesis can be applied to channel width ratios of 0.5 (intake channel / main channel) with a plane, smooth, rectangular cross sectional area. The flow structure is also described using flow visualisation techniques in the physical model and streamline plotting, velocity vector and velocity profile graphics. A study is also undertaken to describe the turbulent kinetic energy in the flow domain. Predictions near the bed of the flow domain are poor in all analyses with improved results with depth towards the surface. Areas of secondary circulation cells, flow reversal and stagnation zones are identified by numerical and physical models. Validation of the numerical code is undertaken using three dimensional velocity and root mean square velocity data collected using the Acoustic Doppler Velocimeter (ADV). Calibration of the ADV is undertaken and the results closely match the manufacturers stated calibration data. The numerical code used is a finite volume method solving the Reynolds Averaged Navier Stokes equations and the k-s turbulence model. Validation of the code indicated that it was suitable for the investigation of the flow structure in this instance but failed to predict completely areas of high velocity gradients or flow reversal.