LNG-solid impacts with gas cushioning and phase change are investigated theoretically in a coupled inviscid liquid and viscous gas regime. Condensation from the gas to the LNG is driven by local increases in the gas pressure above the saturation vapour pressure. This is modelled as a sink term on the kinematic boundary condition at the gas interface. To leading order, the bulk liquid motion is unaffected by condensation, with its evolution governed by the same boundary integral equation used in models of non-volatile gas-cushioned liquid–solid impacts. The proposed model extends the approach used to describe two-dimensional non-volatile gas-cushioned impacts by incorporating phase change and is applied to a range of physically relevant LNG-solid impacts associated with sloshing. As an LNG free-surface approaches touchdown with a solid wall, a gas pressure build-up occurs in the gap separating liquid from solid, which decelerates and deforms the liquid free-surface. This deformation of the free surface may result in gas entrapment. In non-volatile impacts, pockets of trapped gas are associated with oscillatory pressure signals, while previous experiments have shown that these oscillations may be damped by phase change in impacts involving volatile liquids. Compared to impacts with non-volatile liquids, gas condensation is shown to reduce both the impact pressures and the volume of gas trapped. Depending on the impact parameters, the proposed model differentiates between cases where a pocket of trapped gas may or may not be formed. A criterion on the critical normal impact velocity above which gas entrapment is not expected is obtained. This indicates that across a range of length scales that are physically relevant to LNG sloshing, gas entrapment is not expected for impact velocities greater than 0.05 m s−1. Impacts where gas compressibility is important are investigated, as well as impacts into corners of containment tanks with varying angles. The model developed is suitable for the analysis of small and medium-sized LNG-solid impacts, as well as larger-scale sloshing model tests involving impacts of water cushioned by water vapour. The importance of inertia in the gas is identified in larger scale impacts.
|Number of pages||15|
|Journal||Journal of fluids and structures|
|Early online date||22 Mar 2018|
|Publication status||Published - Jul 2018|
- liquid-solid impact
- gas cushioning
- phase change