Influence of Density Ratio Between Liquid And Gas On Sloshing Model Test Results Available to Purchase

Pressures induced by sloshing phenomenon are widely studied through small scale model tests. This implies the need to satisfy scaling laws governed by dimensionless numbers. Froude number is the one governing the overall liquid flow within the tank. It means that changing the scale or the fluids would lead to analogous overall flows when Froude number is satisfied. Based on this, the experimental modelling consisting in moving a small scale model tank filled with water and air is commonly considered representative enough to derive sloshing pressures occurring in a full scale tank filled with LNG and its vapour. Nevertheless, impact pressures are strongly influenced by local phenomena, and hence other dimensionless numbers, such as the density ratio between the liquid and the gas, are likely to govern this local behaviour. Aware of possible consequences on sloshing assessment methodology, GTT decided to dedicate a specific R&D program on the density ratio influence, including theoretical, numerical and experimental studies. On the one hand, theoretical (Dias, Ghiadaglia, Le Coq, 2007) and numerical (Braeunig, Brosset, Dias, Ghidaglia, 2009) studies proved that the density ratio has a significant effect on the transfer of momentum between the liquid and gas during the impact: the impact velocity is slowed down, but the overall flow remains almost unchanged. On the other hand, sloshing vapour tests (water and its vapour) at small scale were performed in order to investigate the influence of density ratio on the statistical pressure distributions, the rise times of the impact pressures and the proportion of gas pocket events (impacts with gas entrapment that are likely to be governed by a scaling law other than Froude's). A pressure vessel, able to withstand both low and high pressures, allowed to study a large range of density ratios by using water and its vapour along the phase boundary.