Classical RANS turbulence closure models bring the excessive turbulence level which leads to the unphysical interface motion in the simulation of the sloshing flow. This paper aims to explore the appropriate turbulence modeling method and proposes two modifications to improve the unphysical interface motion. One is to modify the transport equations, in which the density term and buoyancy effect are considered in the equations. The other is to add an eddy-viscosity limiter, particularly a linear limiter is designed. The comparison between this work and the previous experiments shows that both modifications are effective to improve the unphysical interface motion.
As the demand for clean energy increases, two novel vessels are developed to operate on the sea for a long time. They are the FLNG (floating liquefied natural gas) vessel which can collect the natural gas from the sea and the FSRU (floating storage and regasification unit) which is a vital component to transfer the LNG. Those ships are exposed to external excitations caused by wind or sea waves, which inevitably trigger the resonant sloshing in partially filled tanks. Sloshing influences the ship motion and threatens the structural safety. DNV-GL considers that sloshing brings the largest uncertainty in the design stage.
Nowadays, computational fluid dynamics (CFD) becomes an excellent tool to investigate the sloshing phenomenon with the rapid development in computer technology. Sloshing is an interfacial flow with strong turbulence effects. Maillard and Brosset (2009) and Karimi et al. (2016) found that the gas phase plays a crucial role in the sloshing flow, indicating the equal importance of the gas and liquid phase. For the two-phase flow, the numerical methods can be divided into two categories, one is the multi-fluid model, and the other is the single-fluid model. In the multi-fluid model, each phase has its own set of governing equations. In the single-fluid model, the two-phase flow is considered as a new single continuum fluid with immediate jumps of the associated properties across the interface, e.g., the density and the viscosity, resulting a single set of governing equations to be solved. The single-fluid model is more commonly used for the problems related to wave-elevation prediction, and it is adopted by the commercial software, such as ANSYS Fluent and STAR-CCM+, as well as the open-source package, OpenFOAM. Moreover, Reynolds-averaged Navier-Stokes (RANS) simulation is more popular than large eddy simulation (LES) and direct numerical simulation (DNS) because LES and DNS have much larger computation effort than RANS. Volume-of-fluid (VOF) method is used to capture the interface because the mass conservation is essential in such an enclosed tank (Roenby et al. (2016), Bilger et al. (2017)).
