• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2009.10a
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• pp.49-52
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• 2009

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.4 no.1
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• pp.1-9
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• 2001

An oscillating body motion with extremely large amplitude has been studied using the viscous flow solver. Time simulations of oscillating ship hull in prescribed heave and roll motions are presented using RANS method with FAM approach (Chen, 1995). For viscous flows, laminar flow and turbulent flow with $textsc{k}$-$\varepsilon$ model are considered and compared. The viscous flow solver of RANS method is performed together with a Chimera type of multi-block grid system to demonstrate the advantage of accurate and efficient zonal approach. In the present study, effects of viscosity and oscillation degree are discussed using Re=1000 and Re=1000000. Large motion of oscillating body shows clear vortex propagation that is not possible for inviscid flow to present.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.157-164
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• 2015

The present work performs three-dimensional flow calculations based on Reynolds Averaged Navier-Stokes (RANS) and Delayed Detached Eddy Simulation (DDES) to investigate the flow field of a transonic rotor (NASA Rotor 37) at near-stall condition. It is found that the DES approach is likely to predict well the complex flow characteristics such as secondary vortex or turbulent flow phenomenon than RANS approach, which is useful to describe the flow mechanism of a transonic compressor. Especially, the DES results show improvement of predicting the flow field in the wake region and the model captures reasonably well separated regions compared to the RANS model. Besides, it is discovered that the three-dimensional vortical flows after the vortex breakdown from the rotor tip region are widely distributed and its vortex structures are clearly present. Near the rotor leading edge, a part of the tip leakage flows in DES solution spill over into next passage of the blade owing to the separation vortex flow and the backflow is clearly seen around the trailing edge of rotor tip. Furthermore, the DES solution shows strong turbulent eddies especially in the rotor hub, rotor tip section and the downstream of rotor trailing edge compared to the RANS solution.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.100-106
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• 1997

Viscous flow around an actual ship is calculated by an use of RANS(Reynolds-averaged Navier-Stokes) solver. Reynolds stress is modelled by using k-$\varepsilon$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the complex boundary of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM(Finite Volume Method). SIMPLE(Semi-Implcit Pressure Linked Equation) method is adopted in the calculation of pressure and the solution of the disssssssscretized equation is obtained by the line-by-line method with the use of TDMA(Tri-Diagonal Matrix Algorithme). The subject ship model of actual calculation is 4,410 TEU class container carrier. For 4 geosim models the calculated viscous resistancce values are compared with the model test results and analyzed on their componentss. The resistance performance of an actual ship is predicted very resonably, so this mothod may be utilized as a design tool of hull form.

• Journal of Ocean Engineering and Technology
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• v.34 no.4
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• pp.237-244
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• 2020

In this study, we investigate surge force, heave force, and pitch moment, which are vertical plane hydrodynamics acting on Manta-type unmanned underwater vehicles (UUVs), using a model test and computational fluid dynamics (CFD) simulation. Assessing the maneuvering hydrodynamic characteristic of an underwater glider in the initial design stage is crucial. Although a model test is the best approach for obtaining the maneuvering hydrodynamic derivatives for underwater vehicles, numerical methods, such as Reynolds averaged Navier-Stokes (RANS) equations, have been used owing to their efficiency in terms of time and cost. Therefore, we conducted an RANS-based CFD calculation and a model test for Manta-type UUVs. In addition, we conducted a validation study through a comparison with a model test conducted at a circular water channel (CWC) in Korea Maritime & Ocean University Furthermore, two RANS solvers (Star-CCM+ and OpenFOAM) were used and compared. Finally, the maneuvering hydrodynamic forces obtained from the static drift and resistance tests for a Manta-type UUV were presented.

• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.183-188
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• 2017

This paper provides numerical results for the estimation of the efficiency of KRISO energy saving devices in the design stage. A finite volume method is used to solve Reynolds averaged Navier-Stokes (RANS) equations, where the SST k-$\omega$ model is selected for turbulence closure. The propeller rotating motion is determined using a rigid body motion (RBM) scheme, which is called a sliding mesh technique. The numerical analysis focuses on predicting the power reduction by the designed KRISO devices (K-DUCT) under a self-propulsion condition. The present numerical results show good agreement with the available experimental data. Finally, it is concluded that CFD can be a useful method, along with model tests, for assessing the performance of energy saving devices for propulsion efficiency improvement.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.250-257
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• 2005

Large eddy simulation{LES) methodology used to model a bluff-body stabilized non-reacting flow. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, the results was compared with that of Reynolds Averaged Navier-Stokes(RANS) using $k-{\epsilon}$ model as well as experimental data. The results showed that the LES and RANS qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. However, in the quantitative analysis, the LES showed a better prediction performance than RANS. Specially, the LES well described characteristics of the recirculation zones, such as air stagnation point and jet stagnation point. Finally, the unsteady phenomena on the Bluff-body, such as the transition of recirculation region and vorticity, was examined with LES methodology.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.341-345
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• 2017

In this study, the Inlet/Isolator model experiments performed at Texas University were performed by 2-dimensional RANS computerized analysis. First, supersonic flow conditions were analyzed and compared with experimental surface pressure results, and the flow structure was analyzed by confirming Mach number distribution and numerical shadowgraph. Then, the inlet unstart condition was given by changing the back pressure, and the URANS analysis was performed to confirm the progress of inlet unstart.

• Journal of Korea Water Resources Association
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• v.50 no.2
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• pp.89-97
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• 2017

Turbulent flow structure in the high amplitude meandering channel is complex due to secondary recirculation with helicoidal motions and shear layers formed by flow separation from the curved sidewall. In this work, the secondary flow and the superelevation of the water surface produced in the high-amplitude Kinoshita channel are reproduced by the unsteady Reynolds-averaged Navier-Stokes (RANS) computations using the VOF technique for resolving the variation of water surface elevation and three statistical turbulence models ($k-{\varepsilon}$, RNG $k-{\varepsilon}$, $k-{\omega}$ SST). The numerical results computed by a second-order accurate finite volume method are compared with an existing experimental measurement. Among applied turbulence models, $k-{\omega}$ SST model relatively well predicts overall distribution of the secondary recirculation in the Kinoshita channel, while all three models yield similar prediction of water superelevation transverse slope. The secondary recirculation driven by the radial acceleration in the upstream bend affects the flow structure in the downstream bend, which yields a pair of counter-rotating vortices at the bend apex. This complex flow pattern is reasonably well reproduced by the $k-{\omega}$ SST model. Both $k-{\varepsilon}$ based models fail to predict the clockwise-rotating vortex between a pair of counter-rotating vortices which was observed in the experiment. Regardless of applied turbulence models, the present computations using the VOF method appear to well reproduce the superelevation of water surface through the meandering channel.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.68-75
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• 2009

In this study, aeroelastic response analyses have been conducted for a 3D wind turbine blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responsed of wind turbine blade. Vibration analyses of rotating wind-turbine blade have been conducted using the general nonlinear finite element program, SAMCEF (Ver.6.3). Reynolds-averaged Navier-Stokes (RANS)equations with spalart-allmaras turbulence model are solved for unsteady flow problems of the rotating turbine blade model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D turbine blade for fluid-structure interaction (FSI) problems. Detailed dynamic responses and instantaneous Mach contour on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating wind-turbine blade model.