• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.4
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• pp.670-690
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• 2015

In this paper, numerical investigations for tank sloshing, based on commercial CFD package FLUENT, are performed to study effects of boundary layer grid, liquid viscosity and compressible air on sloshing pressure, wave height and rising time of impact pressure. Also, sloshing experiments for liquids of different viscosity are carried out to validate the numerical results. Through comparison of numerical and experimental results, a computational model including boundary layer grid can predict the sloshing pressure more accurately. Energy dissipation due to viscous friction leads to reduction of sloshing pressure and wave elevation. Sloshing pressure is also reduced because of cushion effect of compressible air. Due to high viscosity damping effect and compressible air effect, the rising time of impact pressure becomes longer. It is also found that liquid viscosity and compressible air influence distribution of dynamic pressure along the vertical tank wall.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.581-591
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• 2011

This paper describes the air compressibility effect in the CFD simulation of water impact load prediction. In order to consider the air compressibility effect, two sets of governing equations are employed, namely the incompressible Navier-stokes equations and compressible Navier-Stokes equations that describe general compressible gas flow. In order to describe violent motion of free surface, volume-of-fluid method is utilized. The role of air compressibility is presented by the comparative study of water impact load obtained from two different air models, i.e. the compressible and incompressible air. For both cases, water is considered as incompressible media. Compressible air model shows oscillatory behavior of pressure on the solid surface that may attribute to the air-cushion effect. Incompressible air model showed no such oscillatory behavior in the pressure history. This study also showed that the CFD simulation can capture the formation of air pockets enclosed by water and solid surface, which may be the location where the air compressibility effect is dominant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.429-445
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• 2008

Two-phase compressible flow fields of air-water are investigated numerically in the fixed Eulerian grid framework. The phase interface is captured via volume fractions of each phase. A way to model two phase compressible flows as a single phase one is found based on an equivalent equation of states of Tait's type for a multiphase cell. The equivalent single phase field is discretized using the Roe‘s approximate Riemann solver. Two approaches are tried to suppress the pressure oscillation phenomena at the phase interface, a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. In discretizing the compressible form of volume fraction equation, phase interfaces are geometrically reconstructed to minimize the numerical diffusion of volume fraction and relevant variables. The motion of a projectile in a water-filled tube which is fired by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one, and several design factors affecting the projectile movement are investigated.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.5
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• pp.271-280
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• 2021

The code developed using a pressure-based method for unified conservation laws of incompressible/compressible fluids is expanded to handle moving or deforming body boundaries using the hybrid Cartesian/immersed boundary method. An instantaneous pressure field is calculated from a pressure Poisson equation for the whole fluid domain, including the compressible gas region. The polytropic gas is assumed for the compressible fluid so that the energy equation is decoupled. Immersed boundary nodes are identified based on edges crossing body boundaries. The velocity vector is reconstructed at the immersed boundary node using an interpolation along the assigned local normal line. The developed code is validated by comparing the time histories of pressure and wave elevation for sloshing in a rectangular and a membrane-type tank. The validated code is applied to simulate air cushion effects in a rectangular tank under sway motion. Time variations of pressure fields are analyzed in detail as the air pocket pulsates. It is shown that the contraction and expansion of the air pocket dominate the pressure loads on the wall of the tank. The present results are in good agreement with other experimental and computational results for the amplitude and the decay of the pressure oscillations measured at the pressure gauges.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.55-63
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• 1997

The empirical factor and reaction force based on published data were involved to investigate compressible flows through sudden enlargement and sudden contraction passages. Analytical solutions of engineering interest were obtained from one-dimensional steady compressible gas dynamic equations. The effects of com- pressibility, cross-sectional area ratio, and inlet Mach number on the air flows were discussed with regards to the total pressure loss and flow choking. The present results provide available information necessary to design the compressible pipe flow systems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.235-244
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• 1997

The empirical factor and reaction force based on published data were involved to investigate compressible flows through sudden enlargement and sudden contraction passages. Analytical solutions of engineering interest were obtained from one-dimensional steady compressible gas dynamic equations. The effects of compressibility, cross-sectional area ratio, and inlet Mach number on the air flows were discussed with regards to the total pressure loss and flow choking. The present results provide available information necessary ta design the compressible pipe flow systems.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.514-519
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.562-567
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.252-255
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• 2006

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.80.2-80.2
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• 2005