Turbulence characteristics of shallow open channel flow with and without cylinders

Turbulent flow around bluff bodies has received significant research attention due to its relevance in a variety of engineering applications such as environmental and fluid engineering applications. These include flow over hydraulic structures such as bridge piers and flow over natural and artificial vegetation. Understanding of the turbulence characteristics of the wake over bluff bodies in open channel flows would provide a valuable scientific means to design artificial channels as well as to modify existing open channels complying with eco-hydraulics design considerations. Thus, this thesis describes a comprehensive experimental investigation of the flow in smooth uniform open channels with and without bluff bodies in cross flow. Firstly, velocity distribution of smooth uniform open channel flow was critically re-visited, and the typical log law velocity profile was re-examined. Secondly, wake characteristics behind emergent single and a small group of circular cylinders has been investigated. The selected diameter (D) of the cylinders was 6.35 mm with a blockage ratio of 2.1% which is small enough to eliminate the effect of side walls. The selected flow condition corresponds to ReD = 3300 and ReH = 45000. The selected aspect ratio which is around 14 indicates the slenderness of the cylinder under shallow flow conditions for the given Reynolds number. Methodical Laser Doppler Velocimetry measurements were taken in a very fine grid in three horizontal planes at near bed, mid depth, and near free surface. Both horizontal plane flow profiles and vertical plane flow profiles were obtained. The focus of the experiments was to conceptually understand the wake flow structure in terms of mean velocity profiles and turbulent parameters along the entire water depth.