Vortex Suppression through Drain Port Sizing

This paper reports on an experimental study motivated by the issue of vortex formation in fuel tanks of liquid propulsion rockets. In this study, vortex funnel (vortex-air core) formation during draining of liquids from cylindrical tanks is suppressed by means of a simple, yet effective method of controlling or adjusting the size of the base drain port. This is particularly relevant in spacecraft and rocket applications where suppression of such vortex-air core is very much warranted because of the possible drain port blockage they cause and the consequent adverse impact (of vortices) on the generation of propulsive thrust. It is found that in the range of rotational speeds provided to the liquid column (between 120 and 200 rpm) in a cylindrical tank, for $d/D\sim 0.03$ (where $D$ is the tank diameter held constant in the study, and $d$ is the port diameter that is varied in the experiments), vortex funnel formation is completely eliminated for concentric drain ports. For eccentric ports, this occurs at a slightly higher value of port size, viz., $d/D\sim 0.04$. The liquid used is water at room temperature with its free surface open to the atmosphere.