A Multi-Pronged Investigation of Efflux Time from Cylindrical Tanks Using: Measurements, Analytical/Empirical Approaches, and Free Surface Modeling Methodologies

Abstract Efflux times from a cylindrical tank with exit pipes are reported from: measurements, analytical/empirical approaches and 2D/3D simulations invoking different free surface modeling methodologies in: OpenFOAM, ANSYS FLUENT, and DualSPHysics.A transient mass balance analysis using Torricelli’s equation through an exit orifice resulted in significant errors highlighting the importance of both fluid properties as well as frictional losses.The use of an analytically derived equation that ignored entrance and exit losses but assumes fully developed laminar flow profiles was able to predict both: efflux times within 6% of the measured values and an increase in efflux time with exit pipe length (due to frictional losses) at laminar conditions.A modified Bernoulli’s equation with assumed values of entrance and exit losses [K], and friction factors [f] was able to predict both: efflux times to within 12% of the measured values and a decrease in efflux time with an increase in exit pipe length resulting from a higher pressure head in the turbulent scenarios. However, efflux time estimates varied up to 15% when the values of K and f were varied within reasonable limits.3D OpenFOAM simulations using the Volume of Fluid (VOF) methodology resulted in similar fidelities as the modified Bernoulli’s equation across all scenarios. Using 2D axisymmetric VOF simulations in ANSYS FLUENT showed spurious results near the centerline axis near complete drainage.Efflux time predictions using DualSPHysics were significantly higher than corresponding OpenFOAM, modified Bernoulli equation predictions possibly resulting from inaccurate modeling of fluid-solid interactions at wall boundaries.