• Journal of Power System Engineering
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• v.19 no.6
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• pp.19-25
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• 2015

The unsteady-state, incompressible and three-dimensional large eddy simulation(LES) was carried out to analyze the aerodynamic performance of three-dimensional small-size axial fan(SSAF) with the different depth of bellmouth. The static pressure coefficients analyzed by LES predict a little bit larger than measurements except stall region regardless of the installation depth between SSAF and bellmouth. Moreover, static pressure efficiencies analyzed by LES show about maximum 30% at the actual operating point ranges, but measurements do not. Therefore, if the blades of conventional SSAF have some more rigidity and complete dynamic balance, the aerodynamic performance of SSAF will be some more improved. In consequence, LES shows the best prediction performance in comparison with any other Reynolds averaged Navier-Stokes(RANS) method.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.2
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• pp.162-170
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• 2014

A CFD(Computational Fluid Dynamics) analysis is presented to predict hydrodynamic characteristics of a marine propeller. A commercial RANS(Reynolds Averaged Navier-Stokes equation) solver, namely FLUENT, is utilized in conjunction with fully unstructured meshes around rotating propeller. Mesh generation process is greatly accelerated by using fully unstructured meshes composed of both isotropic and anisotropic tetrahedral elements. The anisotropic tetrahedral elements were used in the flow domain near the blade and shaft, where the viscous effect is important, having complex shape yet resolving the thin boundary layers. For other regions, isotropic tetrahedral elements are utilized. Two different approaches simulating rotational effect of the propeller are employed, namely Moving reference frame technique for steady simulation, and Sliding mesh technique for unsteady simulation. Both approaches are applied to the propeller open water (POW) test simulation. The current results, which are thrust and torque coefficients, are compared with available experimental data.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.296-296
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• 2015

The aim of this paper is to numerically explore the feasibility of designing a Mini-Hydro turbine. The interest for this kind of horizontal axis turbine relies on its versatility. For instance, in the field of renewable energy, this kind of turbine may be considered for different applications, such as: tidal power, run-of-the-river hydroelectricity, wave energy conversion. It is fundamental to improve the turbine performance and to decrease the equipment costs for achievement of "environmental friendly" solutions and maximization of the "cost-advantage". In the present work, the commercial CFD code ANSYS is used to perform 3D simulations, solving the incompressible Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations discretized by means of a finite volume approach. The implicit segregated version of the solver is employed. The pressure-velocity coupling is achieved by means of the SIMPLE algorithm. The convective terms are discretized using a second order accurate upwind scheme, and pressure and viscous terms are discretized by a second-order-accurate centered scheme. A second order implicit time formulation is also used. Turbulence closure is provided by the realizable k - turbulence model. In this study, a mini hydro turbine (3kW) has been considered for utilization of horizontal axis impeller. The turbine performance and flow behavior have been evaluated by means of numerical simulations. Moreover, the performance of the impeller varied in the pressure distribution, torque, rotational speed and power generated by the different number of blades and angles. The model has been validated, comparing numerical results with available experimental data.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.3
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• pp.366-372
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• 2019

This study performed a numerical analysis of a 3D unsteady viscous flow in order to investigate ship motion responses running through regular waves of the platform supply vessel. The feasibility of numerical analysis was tested under the three regular wave conditions of the KRISO container ship (KCS) suggested at the 2010 Gothenburg CFD Workshop. The resulting resistance coefficient, heave motion, and pitch angle were compared with the model test of the harmonic analysis. Also, the ship motion response characteristics of the platform supply vessel were performed using the proven method of the KRISO container ship (KCS). The ship motions including the resistance coefficient, heave motion, and pitch angle according to the time series were investigated via harmonic analysis under regular waves condition of ${\lambda}/LPP=1.87$ and $H_S=0.078m$.

• Wind and Structures
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• v.32 no.5
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• pp.487-499
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• 2021

The wind-blown sand effect on the high-speed train is investigated. Unsteady RANS equation and the SST k-ω turbulent model coupled with the discrete phase model (DPM) are utilized to simulate the two-phase of air-sand. Sand impact force is calculated based on the Hertzian impact theory. The different cases, including various wind velocity, train speed, sand particle diameter, were simulated. The train's flow field characteristics and the sand impact force were analyzed. The results show that the sand environment makes the pressure increase under different wind velocity and train speed situations. Sand impact force increases with the increasing train speed and sand particle diameter under the same particle mass flow rate. The train aerodynamic force connected with sand impact force when the train running in the wind-sand environment were compared with the aerodynamic force when the train running in the pure wind environment. The results show that the head car longitudinal force increase with wind speed increasing. When the crosswind speed is larger than 35m/s, the effect of the wind- sand environment on the train increases obviously. The longitudinal force of head car increases 23% and lateral force of tail increases 12% comparing to the pure wind environment. The sand concentration in air is the most important factor which influences the sand impact force on the train.

• The Journal of the Acoustical Society of Korea
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• v.36 no.6
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• pp.371-377
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• 2017

The performance of an air conditioner is closely related to the cooling performance of a split-type outdoor unit so that, in most of the relevant preceding studies, the independent performance of an axial fan in an outdoor unit has been studied. However, there is a lack of research on the effects of other components in an outdoor units was rarely investigated. Therefore, in this paper, the effects of the fan orifice among other parts on the flow performance of the outdoor unit was numerically investigated. A virtual fan tester consisting of 18 million grids was developed for highly resolved flow simulation. The unsteady RANS (Reynolds-averaged Navier-Stokes) equations are numerically solved by using finite-volume CFD (Computational Fluid Dynamics) techniques. In order to verify the validity of the numerical methods, the predicted P-Q curve of the cooling fan in a full outdoor unit is compared with the measured one. Optimization of orifice shape was carried out for maximum flow performance of the outdoor unit using the validated numerical method.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.524-532
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• 2020

In this study, noise radiated from a high-speed fan-motor unit for a cordless vacuum cleaner is reduced by designing splitter blades on the existing impeller. First of all, in order to investigate the flow field through a fan-motor unit, especially impeller, the unsteady incompressible Reynolds-Averaged Navier-Stokes (RANS) equations are numerically solved by using computational fluid dynamic technique. With predicted flow field results as input, the Ffowcs Williams-Hawkings (FW-H) integral equation is solved to predict aerodynamic noise radiated from the impeller. The validity of the numerical methods is confirmed by comparing the predicted sound pressure spectrum with the measured one. Further analysis of the predicted flow field shows that the strong vortex is formed between the impeller blades. As the vortex induces the loss of the flow field and acts as an aerodynamic noise source, supplementary splitter blades are designed to the existing impeller to suppress the identified vortex. The length and position of splitter are selected as design factors and the effect of each design factor on aerodynamic noise is numerically analyzed by using the Taguchi method. From this results, the optimum location and length of splitter for minimum radiated noise is determined. The finally selected design shows lower noise than the existing one.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.575-583
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• 2017

Various types of flow patterns around the stepped weir and spillway, such as the skimming flow over such structures and the wave-type flow with a standing undular hydraulic jump and roller downstream of the structures, are developed in open channels. Unsteady three-dimensional numerical simulations are carried out using a hybrid RANS-LES turbulence modeling approach and the volume of fluid method for resolving free surface fluctuations to represent the turbulent flow including the skimming flow and wave-type flow over a stepped weir installed in a rectangular channel. The comparison of numerical results with an existing experimental measurement reveals that the present numerical simulations reasonably well reproduce the turbulent flow passing the stepped weir, in terms of time-averaged velocity profiles at selected locations downstream of the weir, flow topology characterized by the wave-type and skimming flows, the maximum height and length of the standing wave and the length of reattachment of recirculating zone. The numerical result further elucidates the distinct flow behaviors of the wave-type and skimming flow by presenting instantaneous intense variations of free surface and velocity vectors, the distributions of Reynolds shear stress and turbulent kinetic energy and three-dimensional complex features of coherent structures and total pressure distribution.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.2
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• pp.114-120
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• 2011

The characteristics of a helical turbine to be used for tidal stream energy conversion have been numerically studied with varying a few design parameters. The helical turbines were proposed aiming at mitgating the well known poor cut-in characteristics and the structural vibration caused by the fluctuating torque, and the basic concept is introducing some twisting angle of the vertical blade along the rotation axis of the turbine. Among many potential controling parameters, we focused, in this paper, on the twisting angle and the height to diameter ratio of the turbine, and, based on the numerical experiment, We tried to propose a configuration of such turbine for which better performance can be expected. The three-dimensional unsteady RANS equations were solved by using the commercial CFD software, FLUENT with k-${\omega}$ SST turbulence model, and the grid was generated by GAMBIT. It is shown that there are a range of the twisting angle producing better efficiency with less vibration and the minimum height to diameter ratio above which the efficiency does not improve considerably.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.379-389
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• 2020

In this study, the flow and noise performances of high-speed fan motor unit for cordless vacuum cleaner is improved by optimizing the impeller which drives the suction air through flow passage of the cordless vacuum cleaner. Firstly, the unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equations are solved to investigate the flow through the fan motor unit using the computational fluid dynamics techniques. Based on flow field results, the Ffowcs-Williams and Hawkings (FW-H) integral equation is used to predict flow noise radiated from the impeller. Predicted results are compared to the measured ones, which confirms the validity of the numerical method used. It is found that the strong vortex is formed around the mid-chord region of the main blades where the blade curvature change rapidly. Given that vortex acts as a loss for flow and a noise source for noise, impeller blade is redesigned to suppress the identified vortex. The response surface method using two factors is employed to determine the optimum inlet and outlet sweep angles for maximum flow rate and minimum noise. Further analysis of finally selected design confirms the improved flow and noise performance.