• Ocean Systems Engineering
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• v.8 no.2
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• pp.167-182
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• 2018

RTI (Rayleigh-Taylor instability) is investigated by a multi-liquid MPS (Moving Particle Semi-implicit) method for both viscous and inviscid flows for various density differences, initial-disturbance amplitudes, viscosities, and surface tensions. The MPS simulation can be continued up to the late stage of high nonlinearity with complicated patterns and its initial developments agree well with the linear theoretical results. According to the relevant linear theory, the difference between inviscid and viscous fluids is the rising velocity at which upward-mushroom-like RTI flow with vortex formation is generated. However, with the developed MPS program, significant differences in both growing patters and developing speeds are observed. Also, more dispersion can be observed in the inviscid case. With larger Atwood (AT) number, stronger RTI flows are developed earlier, as expected, with higher potential-energy differences. With larger initial disturbances, quite different patterns of RTI-development are observed compared to the small-initial-disturbance case. If AT number is small, the surface tension tends to delay and suppress the RTI development when it is sufficiently large. Interestingly, at high AT number, the RTI-suppressions by increased surface tension become less effective.

• Journal of the Korean Society for Marine Environment & Energy
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• v.20 no.1
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• pp.37-44
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• 2017

Complexity of multiphase flows due to existence of more than two interface including free-surface in one system, cannot be simulated easily. Since more than two fluids affect to flows and disturb interface, non-linearities such as instabilities can be appeared. Among several instabilities on multiphase flows, one of representative is Rayleigh-taylor instability. In order to examine in importance of density disparity, several cases with numerous Atwood number are set. Moreover, investigation of influence on initial disturbance were also considered. Moving particle simulation (MPS) method, which was employed in this paper, was not widely used for multiphase problem. In this study, by adding new particle interaction models such as self-buoyance correction, surface tension, and boundary condition at interface models, MPS were developed having more strength of physics and robust. By applying newly developed multiphase MPS, considered cases are performed and compared each other. Additionally, though existence of disagreement of magnitude of rising velocity between theoretical values from linear potential theory and that of numerical simulation, agreement of tendency can be proved of similarity of result. the discordance of magnitude can be explained due to non-linear effects on numerical simulation which was not considered in theoretical result.