Vertical mixing layer development

A new generation of current and wave testing tanks is required to simulate more realistic sea conditions at larger scales. One means of producing a current is by using groups of impellers arranged around the perimeter of a circular tank. Each propeller produces a single flow velocity which may be different to its neighbours. These differences can lead to a stepped or curved plan view velocity profile in the test section of the tank where a plug profile is required. It is important to understand what the maximum allowable velocity difference between each impeller can be before the required plug profile in the test section is compromised. The situation where two individual fluid streams combine, leading to a turbulent mixing layer, is found in many applications and is therefore of great interest in wider fluid dynamics. In the experimental work presented a setup is described which combines two water flows at different velocities to create a vertical shear. The evolution of the combined flow is studied using Particle Image Velocimetry (Ply). When analysed, these results lead to an understanding of various aspects of mixing layer flow recovery and how the bulk flow rates and velocity ratio affected them. (C) 2013 Elsevier Masson SAS. All rights reserved.