Turbulence modelling and role of compressibility on oil spilling from a damaged double hull tank

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThe viscosity plays an important role and a multi-phase solver is necessary to numerically simulate the oil spilling from a damaged double hull tank (DHT). However, it is uncertain whether turbulence modelling is necessary, which turbulence model is suitable; and what the role of compressibility of the fluids is. This paper presents experimental and numerical investigations to address these issues for various cases representing different scenarios of the oil spilling, including grounding and collision. In the numerical investigations, various approaches to model the turbulence, including the large eddy simulation (LES), direct numerical simulation (DNS) and the Reynolds Average Navier-Stokes equation (RANS) with different turbulence models, are employed. Based on the investigations, it is suggested that the effective Reynolds numbers (Re) corresponding to both the oil outflow and the water inflow shall be considered when classifying the significance of the turbulence and selecting the appropriate turbulence models. This is confirmed by new lab tests considering the axial offset between the internal and the external holes on two hulls of the DHT. The investigations conclude for numerically simulating oil spilling from a damaged double hull tank (DHT) that when the effective Re is smaller the RANS approaches should not be used and LES modelling should be employed; while when the effective Re is large, the RANS models may be used as they can give similar results to LES in terms of the height of the mixture in the ballast tank and discharge but costing much less CPU time. The investigation on the role of the compressibility of the fluid reveals that the compressibility of the fluid may be considerable in a small temporalspatial scale but plays an insignificant role on macroscopic process of the oil spilling.

Effects of tank sloshing on submerged oil leakage from damaged tankers

“…The previous numerical works (e.g. Yang et al, 2017) have confirmed that such assumption is acceptable in the numerical practices.…”

“…In order to reveal the hydrodynamic feature of the oil leakage process, which has been confirmed in the above-mentioned experimental studies, the computational fluid dynamics (CFD) has also been attempted (e.g. Chang III and Lin, 1994;Cheng and Gomes, 2010;Tavakoli et al, 2011Tavakoli et al, , 2012Yang et al, 2014Yang et al, , 2016Yang et al, , 2017. Similar to the experimental studies, the majority of the numerical work did not take into account of the effects of the tank motion on the oil leakage.…”

“…The surface tension is not taken into account. These assumptions have been proven to be acceptable in our previous numerical practices (Yang et al, 2017). Based on these assumptions, three-dimensional mass and momentum conservation equations can be described as follow, respectively.…”