Mechanisms of free surface vortex formation at water intakes (a review)

The formation of a free surface vortex at water intakes is a hazardous phenomenon due to the vortex’s potential to entrain large quantities of air and debris that reduce the hydraulic efficiency of the equipment, as well as creating pressure surges and surface damage. Therefore, identifying the mechanism of the vortex formation is a critically important element of the process of control and prevention. This paper reviews the latest research on the various mechanisms of vortex formation at water intakes as well as the different interpretations provided by researchers. More specifically, the paper discusses the mechanisms of conical flow development, small vortex stretching, vortex line deformation, multi-circular flow structure and upstream flow orientation dependency. A comparison between the mechanisms suggested by different researchers considers, amongst other things, the accuracy of the correlation between results from numerical and experimental models on one hand and analytical analyses on the other. The effectiveness of different design strategies for control and prevention of vortex formation is discussed by referring to the optimal submergence depth, intake geometry, suitable structural devices (e.g. anti-vortex plates) and hydraulic methods (e.g. water jets). The paper is intended to link the theoretical and practical aspects of vortex formation in context.