ABSTRACT

The influence of channel confinement in terms of the channel aspect ratio (AR), defined as the ratio between channel width b and flow depth h, has been extensively studied to characterize the structure of turbulence in uniform open-channel flow over a rough bed. The value of AR in the field is typically large such that a central region of two-dimensional flow is maintained. In hydraulic modelling, flume sizing is limited by facility constraints, resulting in AR values smaller than 10, for which channels are classified as narrow. In literature, it is common practice to alter AR by changing h. In the present experimental investigation, the value of AR is altered by changing b with the use of movable sidewalls for dynamic similarity purposes. Particle Image Velocimetry (PIV) measurements are undertaken in the streamwise-vertical central plane for three channels of varying b and constant h. The effect of horizontal confinement on the developing flow over a rough porous bed is explored in terms of the mean velocity field and single point turbulence statistics. It is determined that increasing horizontal confinement (i.e. decreasing b) is found to affect the distributions of streamwise velocity, streamwise turbulence intensity and higher-order turbulence moments.