• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.619-630
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• 2005

A two-frame PIV (Particle Image Velocimetry) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from $ 0^{\circ} $ to $ 80^{\circ} $, one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors En the propeller wake legion. The slipstream contraction occurs in the near-wake region up to about X/D : 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.94-101
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• 2016

In this paper, aerodynamic effects on the flow field under the wing with varying aspect ratio were investigated by measuring pressures on the lower surface of wing and analysing velocity components using Particle Image Velocimetry at Reynolds numbers of $1.384{\times}10^5$ and $2.306{\times}10^5$. In case of aspect ratio 4.8 which keeps the wing tip at a distance of 80% chord length from the pylon, the vortex from the wing tip influenced the flow field under the wing by reducing static pressures on the lower surface and increasing the velocity in proximity of the wing tip. Throughout the results, it is observed that aerodynamic effects of wing tip on the flow field around pylon under wing become insignificant as the aspect ratio increases.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.39-45
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• 2010

The optimal design is needed for the blade geometry of the quad-rotor blades which is mainly used for Unmanned Aerial Vehicle. To do this, it is important to analyze the wakes under the blades. In the present study, the flow around the rotating blades was analyzed using PIV(Particle Image Velocimetry) and CFD(Computational Fluid Dynamics). The maximum axial velocity was measured at about 60% position toward the radial direction of the blade. The positions of vorticities in the test section obtained by PIV and CFD were turned out to be almost alike. The values in the difference of pressure coefficients at the upper and the lower blades were increased depending on the radial direction. Then, the values were decreased at the blade tip. The data of the flow analysis in the present study are expected to be served as the design of blades and ducts for the thrust improvement in the future.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.477-487
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• 2012

We investigated the aerodynamic characteristics of a three-dimensional (3D) wing with an endplate in the vicinity of the free surface by solving incompressible Navier-Stokes equations with the turbulence closure model. The endplate causes a blockage effect on the flow, and an additional viscous effect especially near the endplate. These combined effects of the endplate significantly reduce the magnitudes of the velocities under the lower surface of the wing, thereby enhancing aerodynamic performance in terms of the force coefficients. The maximum lift-to-drag ratio of a wing with an endplate is increased 46% compared to that of wing without an endplate at the lowest clearance. The tip vortex of a wing-with-endplate (WWE) moved laterally to a greater extent than that of a wing-without-endplate (WOE). This causes a decrease in the induced drag, resulting in a reduction in the total drag.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.60-66
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• 2010

Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

• Journal of Power System Engineering
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• v.21 no.5
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• pp.20-28
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• 2017

The steady-state, incompressible and three-dimensional numerical analysis was performed to investigate the flow fields around the seabed tiller used for soil improvement in coastal fisheries and the pulling force and buoyancy generated by tiller operation. The turbulence model used in this study is a realizable $k-{\varepsilon}$. As a results, at a stationary current or a current speed of 1.2 knots, where rotor rotates in a clockwise direction, a typical vortex pair appears near the tip of the rotor except for the edge, and the strength of the vortex pair increases with the number of revolutions of the rotor. The pulling force of the tiller rotating in the counterclockwise direction increases with the number of revolutions. Also, when the current flows at 1.2 knots and the rotor rotates clockwise, the pulling force of the tiller acts on the upstream side irrespective of the number of rotations of the rotor, so that no force is applied. The buoyancy of the tiller acts on the seawater surface if the flow direction inside the rotor is the same as the direction of rotation of the rotor, regardless of the current velocity, otherwise it acts on the seabed.

• Journal of Institute of Convergence Technology
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• v.5 no.1
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• pp.37-40
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• 2015

Numerical analyses on the aerodynamic characteristics of a counter rotating axial flow fan is carried out using the frequency domain panel method. Front rotor and rear rotor blades of a counter rotating axial fan are designed by using the simplified meridional flow analysis method with the radial equilibrium equation and the free vortex design condition, according to design requirements. Performance characteristics of a counter rotating axial flow fan are estimated for the variation of design parameters such as the hub to tip ratio, the taper ratio and the solidity. Pressure losses were higher at leading edge and hub region of rotor blades. Characteristic curve of the counter rotating fan was overpredicted without consideration of viscous effect.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.84-90
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• 2000

Ground effect of three-dimensional wing is studied. LU-factored Implicit upwind TVD scheme and Baldwin-Lomax turbulence model are used for this calculation. To investigate ground effect, NACA 4415 wing at M=0.5 calculated. Two different angles of attack and three cases of flight height are calculated. As increasing angle of attack, the ground effect becomes strong. In case of NACA 4415 wing in ground effect, strength of wing tip vortex becomes stronger than that of free flight.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.269-274
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• 2014

In this study, low noise designs for a Savonius wind turbine were numerically investigated. As was reported in our previous study, the harmonic components with a fundamental frequency higher than the BPF were identified as being dominant in the noise spectrum of a Savonius wind turbine, and these components were a result of vortex shedding. On a basis of this observation, an S-shaped blade tip is proposed as a means of reducing the noise generated by small vertical(Savonius) wind turbines. This blade induces phase differences in the shedding vortices from the blades, and thus reduces the noise from the wind turbine. The aerodynamic noise characteristics of the conventional and "S-shaped" Savonius turbines were investigated by using the Hybrid CAA method where the flow field around the turbine is computed using the CFD techniques and the radiated noise are predicted by applying acoustic analogy to the computed flow field data. The degree of noise reduction resulting from the proposed design and its reduction mechanism were confirmed by comparing the predicted noise spectrum of these turbines and the flow characteristics around them.

• Journal of computational fluids engineering
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• v.20 no.4
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• pp.21-27
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• 2015

Flow field around the KRISO 3600TEU container ship is computed using a surface generated based on interpolations of station lines, which are given in a body plan of the ship, without using any CAD program. An interpolation method is suggested based on inscribed circles to generate curves between two neighboring station lines. The interpolated surface is saved in a STL format to use the snappyHexMesh utility of the openfoam. Computed resistance of the ship is compared with experimental and other computational results and the effects of the interpolation of neighboring station lines on the computed resistance are investigated. The suggested method is applied to calculate the flow field around a submarine with appendages. The surface triangulations for the hull and the appendages are generated without consideration of each other, then those surface triangulations are simply combined to provide a grid generator with the body boundary. The junctures of the hull and the appendages are identified automatically during the grid generation procedure. Tip vortex is captured, which travels downstream from the tip of the appendages.