• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.413-422
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• 2012

The ducted fan for a small UAV propulsion can reconnoiter and observe in a town and a small area, it has better thrust efficiency and a long endurance than propeller. Thrust characteristics of hover and for ward flight condition for the ducted fan UAV is important issue to improve a endurance. The unsteady 3-dimensional flow fields of the ducted fan UAV is essential to stable flight. In this paper, to verify the design results of the ducted fan and to investigate a stable aeronautical characteristic, the thrust performance and the unsteady 3-dimensional flow fields are measured. Thrust characteristics for the hovering and the forward flight conditions are measured by the 6-components balance system in the subsonic wind tunnel. The unsteady 3-dimensional flow fields are analyzed by using a stationary $45^{\circ}$ slanted hot-wire technique. The swirl velocity is almost removed behind the stator blades. Therefore, the thrust performance of the ducted fan is improved and the flight stability is maintained.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.305-310
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• 2007

For the understanding of the complex flow characteristics in the counter-rotating axial flow fan, it is necessary to investigate the three-dimensional unsteady flow fields in the counter-rotating axial flow fan. This information is also essential for the prediction of the aerodynamic and acoustical characteristics of the counter-rotating axial flow fan. Experimental study on the three-dimensional unsteady flow in the counter-rotating axial flow fan is carried out at the design point(operating condition). Three-dimensional unsteady flow fields in the counter rotating axial flow fan are measured at the cross-sectional planes of the upstream and downstream of each rotor using the $45^{\circ}$ inclined hot-wire. Three-dimensional unsteady flow fields in the counter-rotating axial flow such as the wake, the tip vortex and the tip leakage flow are shown the form of the velocity vectors and the velocity contours.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.879-888
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• 2009

Unsteady three-dimensional reacting flowfield generated by transverse hydrogen injection into a supersonic mainstream is numerically investigated using DES and finite-rate chemistry model. Comparisons are made with experimental results to investigate the turbulent reacting flow physics. The numerical OH distribution describes well the experimental OH-PLIF result, while the numerical ignition delay time shows some disparity due to the restricted available experimental data. The intermittency phenomena are identified by the comparative analysis between RANS and DES. Those effects are also quantified by the temperature distributions along streamlines and superimposed OH mass fraction along with time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.863-878
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• 2009

Unsteady three-dimensional flowfield generated by transverse fuel injection into a supersonic mainstream is simulated with a DES turbulence model. Comparisons are made with experimental results in terms of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the large eddy structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly over-predict the eddy formation frequency. The large eddy structures are generated as the counter-rotating vortices are detached alternately in the upstream recirculation region.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.205-215
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• 2009

The conventional numerical models to analyze flow in subsurface porous media under the transient state usually generate numerical oscillation and unstability due to local flux domain for critical cases such as infiltration into initially dry soil during rainfall period. In this case, it is required refined mesh and small time step, but it decrease efficiency of computation. In this study, numerical unstability in discontinuity domain is removed by applying particle tracking algorithm to simulate unsteady subsurface flow with inflow boundary condition. Finally the hybrid LE FEM improving numerical stability is proposed. The hypothetical domains with unsteady uniform and nonuniform flow field were used to demonstrated algorithm verification. In comparison with analytic solution, we obtained reasonable results and conducted simulation of hypothetical 3-D recharge/pumping area. The proposed algorithm can simulate saturated/unsaturated porous media with more practical problems and will greatly contribute to accuracy and stability of numerical computation.

• Proceedings of the SAREK Conference
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• 2003.07a
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• pp.7-7
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• 2003

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.822-827
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• 2003

Experiments were done for the three dimensional unsteady flow in a counter rotating axial flow fan under stable operating condition. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional flow patterns were investigated through the acquired data by the $45^{\circ}$ inclined hot-wire. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential velocity vector plot. Swirl velocity, which was generated by the front rotor, was recovered in the form of static pressure rise by the rear rotor except for hub and tip regions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.201-209
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• 2011

An unsteady RANS analysis study of the 3-D flow around the NREL Phase VI horizontal axis wind turbine(HAWT) was performed using sliding mesh approach. Two different analysis models such as rotor-only and rotor with tower/nacelle were constructed to investigate the blade/tower interaction. Analysis results for the rotor with tower/nacelle were compared with the corresponding NREL's experimental data which produced fairly good validation of the present CFD model. Comparison of flows around those two models also clearly showed the blade/tower interaction even it was small for upwind configuration. Other visualization results and integrated aerodynamic loads including torque of the blade demonstrated the effective unsteady flow simulation capability of the present CFD model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.41-44
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• 2003

In spite of many researches made on the supersonic jets until now, detailed three-dimensional structures of supersonic jets are not well hewn. In the current study, the detailed structures of three-dimensional supersonic jets are numerically investigated using a CFD method. The total variation diminishing (TVD) scheme is used to solve the unsteady, three-dimensional, compressible Euler equations. Computational results are visualized to investigate the major features of supersonic jets. The three-dimensional computation results show that the structures of the supersonic jets are significantly different from those of the two-dimensional or axisymmetric supersonic jets.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.8-16
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• 2003

Aerodynamic characteristics over Micro Aerial Vehicle(MAV) in low Reynolds number regime are numerically studied using 3-D unsteady, incompressible Navier-Stokes flow solver with single partitioning method for multi-block grid. For more efficient computation of unsteady flows, this flow solver is parallel-implemented with MPl(Message Passing Interface) programming method. Firstly, MAV wing with not complex geometry is considered and then, we analyze aerodynamic characteristics over full MAV configuration varying the angle of attack. Present computational results show a better agreement with the experimental data by MACDL(Micro Aerodynamic Control and Design Lab.), Seoul National University. We can also find the conceptually designed MAV by MACDL has the static stability.