• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.6
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• pp.589-601
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• 2016

The hybrid grid was adopted and numerical prediction analysis of propeller unsteady bearing force considering free surface was performed for mode and full-scale KCS hull-propeller-rudder system by employing RANS method and VOF model. In order to obtain the propeller velocity under self-propulsion point, firstly, the numerical simulation for self-propulsion test of full-scale ship is carried out. The results show that the scale effect of velocity at self-propulsion point and wake fraction is obvious. Then, the transient two-phase flow calculations are performed for model and full-scale KCS hull-propeller-rudder systems. According to the monitoring data, it is found that the propeller unsteady bearing force is fluctuating periodically over time and full-scale propeller's time-average value is smaller than model-scale's. The frequency spectrum curves are also provided after fast Fourier transform. By analyzing the frequency spectrum data, it is easy to summarize that each component of the propeller bearing force have the same fluctuation frequency and the peak in BFP is maximum. What's more, each component of full-scale bearing force's fluctuation value is bigger than model-scale's except the bending moment coefficient about the Y-axis.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.83-86
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• 2002

Numerical simulations are conducted for laminar flow past a sphere rotating In the transverse direction, in order to investigate the effect of the rotation on the characteristics of flow over a sphere. The Reynolds numbers considered are Re=100, 250 and 300 based on the free-stream velocity and the sphere diameter, and the rotational speeds are in the range of $0{\leq}{\omega}{\leq}1$, where ${\omega}^{\ast}$ is the maximum velocity on the sphere surface normalized by the free-stream velocity. At ${\omega}^{\ast}=0$ (without rotation), the flow past the sphere experiences steady axisymmeoy, steady planar-symmetry and unsteady planar-symmetry, respectively, at Re=100, 250 and 300. However, with rotation, the flow becomes planar-symmetric for all the cases investigated and the symmetry plane is orthogonal to the axis of the rotation. The flow is also steady or unsteady depending on both the Reynolds number and the rotational speed, and the vortical structures behind the sphere are significantly modified by the rotation. For example, at Re=300, hairpin vortices completely disappear in the wake at ${\omega}^{\ast}=0.4\;and\;0.6$, and at ${\omega}^{\ast}=1$ vortical structures of a high frequency are newly generated due to the shear layer instability. It is also shown that with increasing rotational speed, the time-averaged drag and lift coefficients increase monotonically.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.258-266
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• 2007

CFD calculations are performed for KRISO 3600TEU container ship(KCS) models with different Reynolds numbers. Numerical calculations of the turbulent flows with the free surface around KCS have been carried out at $Re=0.791{\times}106\;and\;Re=1.4{\times}107$ using a standard Fluent package. In both cases, Froude number is fixed with 0.26 and wave elevation is simulated by using the VOF method. The calculated results at $Re=1.4{\times}107\;and\;Re=0.791{\times}106$ are compared with the experiment data of KRISO towing tank test and RIMS CWC test, respectively. Boundary layer thickness and wake field shows Reynolds number differences. There are some changes in wave pattern behind transom stern.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.67-77
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• 2014

In this study, Explicit Algebraic Reynolds Stress Model (EARSM) which is based on the existing ${\kappa}-{\omega}$ model has been applied to the flow field analysis around ship hulls. Existing transport equations for the turbulent kinetic energy and the dissipation rate are used in almost the same form and anisotropy terms of Reynolds stresses are newly considered. The well-known KVLCC2 and KCS hull forms are selected as validation cases, which were also used in 2010 Workshop on CFD in Ship Hydrodynamics. In case of KVLCC2 double model, comparison of mean velocity distribution, turbulent kinetic energy, and Reynolds stresses near the propeller plane has been carried out and wave elevation and wave profiles have been additionally studied for KCS and KVLCC2 with free surface models. Some improved results for mean velocity distribution at the propeller plane have been obtained while there is little change in free surface wave profiles.

• Wind and Structures
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• v.6 no.6
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• pp.419-436
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• 2003

Large-eddy simulations of the flow around a circular cylinder at a Reynolds number, based on cylinder diameter and free-stream velocity, $Re_D=2{\times}10^4$ are presented. Three different dynamic subgrid-scale models are used, viz. the dynamic eddy-viscosity model and two different mixed two-parameter models. The sensitivity to grid refinement in the spanwise and radial directions is systematically investigated. For the highest resolution considered, the effects of subgrid-scale modeling are also discussed in detail. In particular, it is shown that SGS modeling has a significant influence on the low-frequency modulations of the aerodynamics loads, which are related to significant changes in the near wake structure.

• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.9-14
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• 2000

Computational methods can be classified roughly into two parts: one is the methods based on a potential flow theory, and the other is numerical solvers(CFD) based on Navier-Stockes equation. Methods based on a potential theory are more effective than CFD when the free surface effect is considered. Especially Rankine source method seems to become widespread for simulations of wave making problems. For computations of viscous flow problems, CFD techniques have rapidly been developed and have shown many successful results in the viscous flow calculation. Present paper introduces a computational system 'WAVIS' which includes a pre-processor, potential ant viscous flow solvers and a post-processor. To validate the system, the calculated results for modem commercial hull forms are compared with measurements. It is found that the results from the system are in good agreement with the experimental data, illustrating the accuracy of the numerical methods employed for WAVIS.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.115-120
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• 1998

Aerodynamic noise generated by automobile cooling fan is investigated. Automobile cooling fans radiate both discrete frequency noise as well as broadband noise. In the present work, the former is considered through free-wake panel method coupled with acoustic analogy fully considering the retarded time variation on the blade surface, while the latter is taken into account by three well-established broadband noise components. Experiments were performed to supplement necessary inputs as well as to provide the final comparison with the predicted noise spectrum. The predicted noise levels at blade passing frequencies agree well with the experimental data for the first few harmonics. Although the predicted broadband noise levels at higher frequencies fall below the experimental data due to the fundamental shortcomings of the utilized formulations, the analysis offers a detailed physical understanding of the fan noise generation processes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.116-121
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• 2002

Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time, the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. To calculate the unsteady resultant force over the fan blade in an unsymmetric engine room. Time-Marching Free-Wake Method is used. From the calculations of unsteady force on fan blades, noise signal of an engine cooling fan is calculated by using an acoustic similarity law. Noise optimization is obtained from Neural Network which is constructed based on the calculated flow rate and noise spectrum.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.261-264
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• 2006

This paper describes the effects to wind turbine blade aerodynamics due to interaction between blade and tower on upwind type HAWT. In order to analyze effects of blade-tower interact ion, the analyst s program WINFAS which is based on VLM(Vortex Lattice Method), Free wake and FVE model is used. In this study, the changes of wind turbine blade aerodynamics caused by blade-tower interact ion are Investigated with various parameters windshear, yaw error, TSR and tower diameter.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.43-47
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• 2001

A program to design an axial flow fan, analyze the performance and predict the noise was developed. In order to develop the low noise fan, that program is compulsory. This software is composed of three parts : the geometric design module, the performance analysis module, the fan noise prediction module. In order to analyze the performance, three dimensional vortex panel method is used. The unsteady flow field was analyzed by time-marching free wake method. The unsteady force data is then used in predicting the noise. Farassat's equation is used to predict the noise of fan.