| Vortices have been a subject of common and scientific interest since early times. Typical examples of vortices include tornadoes, hurricanes, dust devils, and whirlpools. The hydraulic intake vortex occurs at submerged marine structures that withdraw water for transport to another location. These vortices are of considerable importance when designing and operating intakes. The presence of a vortex at an intake can reduce pumping efficiency, and in extreme cases, completely disable the intake. Despite the universal familiarity of the problem, existing literature provides little on the detailed mechanics of hydraulic vortex formation.; An analytical, computational, and experimental study was conducted to better describe the process of vortex formation at hydraulic intakes. Three experimental apparatuses were constructed to examine hydraulic vortices in free-draining and steady state conditions. Three dimensional PIV measurements, and flow visualizations of the vortex formation process were made in the experimental program. CFD simulations were performed for two of the three experimental apparatuses, and a hydrodynamic stability analysis was completed for the third.; Results indicated that the vortex formation process could be broken down into discrete stages, some of which are described by existing fluid mechanics literature. Careful observations revealed that two distinct types of vortex may form at hydraulic intakes, these are referred to as self-sustaining and non-self-sustaining vortices. Self-sustaining vortices require minimal ambient vorticity to form and to persist, due to strong stretching conditions that exist between the intake and water surface. Non-self-sustaining vortices require a significant and continuous supply of ambient vorticity to form and persist, owing to the weak stretching influence present. Core formation in the non-self-sustaining vortex requires the presence of a rotating "pre-core envelope". Inertial waves are suggested as a possible mechanism for the rapid transition from pre-core to core in these vortices.; Finally, as an addition to the details of "how" hydraulic vortices form, principles of self-organization theory are applied to the vortex formation process to offer a possible account of "why" they form. |
