Study of dye-core vortices at submerged water intakes

Dye-core vortices are of considerable importance when designing and operating submerged water intakes. These vortices are capable of entraining debris, zebra mussels and frazil ice located near the surface, and throughout the water column, into deep-water intakes. This problem often leads to blockage and a reduction of the hydraulic conveyance capacity of the intake.; A 1m x 1m x 1m experimental tank was designed to study dye-core vortices and examine potential methods to suppress their formation. Three-dimensional velocity measurements were made with an Acoustic Doppler Velocimeter (ADV) and a programmable three axis positioning system. Two flow regimes of identical withdrawal rates were considered: a radial flow and a vortical flow. Comparison of velocity vector plots, sectional streamlines, vorticity figures, and select velocity profiles, delineated significant differences in the two flow fields. Investigation indicated the withdrawal envelope for vortical flow was several times larger than for radial flow. The vortical envelope extent exceeded the radial in width, and extended well above the radial, to the water surface. It followed that the dye-core vortex substantially increased the likelihood of foreign material entrainment. Additionally, the vortical flow demonstrated local withdrawal velocities twice that of the radial case. Further examination of the dye-core vortex structure revealed a nearly horizontal flow field in the outer free-region, and a more complex three-dimensional form, in the forced or rotational core. Flow visualization of the core showed the presence of a secondary helix structure spiraling around the primary core. This phenomenon was confirmed in a streamline plot of the data.