• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.11
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• pp.964-972
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• 2007

Wind turbine experiment was carried out for the horizontal axis wind turbine with the aerodynamically optimized blade. From the comparison of aerodynamic performance between upwind and downwind type wind turbine rotor, the measured torque fluctuation of the latter is larger than that of the former. This phenomenon is owing to the interaction of wake generated from support column and blades. The wind turbine model satisfies the design condition in that the measured result of the power coefficient at zero pitch angle shows maximum peak at the designed tip speed ratio, λ = 6. It also shows that the decrease in aerodynamic power due to negative pitch change is more sensitive than that of the same positive pitch change.

• Journal of the Korean Society of Visualization
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• v.7 no.2
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• pp.64-71
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• 2010

The flow and noise characteristics of wake behind wind-turbine blades have been investigated experimentally using a two-frame particle image velocimetry (PIV) technique. Experiments were carried out in a POSTECH subsonic large wind-tunnel ($1.8^W{\times}1.5^H{\times}4.3^L\;m^3$) with KBP-750D (3-blade type) wind-turbine model at a freestream velocity of $U_o\;=\;15\;m/s$ and a tip speed ratio $\lambda\;=\;6.14$ (2933 rpm). The wind-turbine blades are connected to an AC servo motor, brake, encoder and torque meter to control the rotational speed and to extract a synchronization signal for PIV measurements. The wake flow was measured at four azimuth angles ($\phi\;=\;0^{\circ}$, $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$) of the wind-turbine blade. The dominant flow structure of the wake is large-scale tip vortices. The turbulent statistics such as turbulent intensity are weakened as the flow goes downstream due to turbulent dissipation. The dominant peak frequency of the noise signal is identical to the rotation frequency of blades. The noise seems to be mainly induced by the tip vortices.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.47-50
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• 2003

The wind flow and pollutant dispersion over a two-dimensional sinusoidal hilly obstacle with slope (the ratio of height to half width) of 0.7 have been investigated experimentally and numerically. Flow over a single sinusoidal hill model was visualized in a subsonic wind tunnel. The mean velocity profiles, turbulence statistics, and pollutant concentration distribution were measured at the Reynolds number based on the obstacle height (H=40mm) oft $2.6\times10^4$. Experimental results for flow over a flat ground were agreed with the theoretical and numerical results. When a pollutant source is located behind the hilly terrain, the pollutant dispersion appeared even in the upstream region due to recirculation flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.67-74
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• 2006

An unsteady blockage-correction method utilizing wall pressure distribution on the test section has been developed for the wall interference correction of a closed test-section subsonic wind tunnel. The pressure distribution along the test section wall was decomposed into Fourier series and a quasi-steady method based on a measured-boundary-condition method was applied to each Fourier coefficient. The unsteady correction for a complete test period was accomplished by recombining each corrected terms. The present method was validated by appling computed unsteady flows over a cylinder and an oscillating airfoil in the test sections. The corrected results by the present method agreed well with free-air condition.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.15-21
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• 1999

The flow characteristics around KRISO 300K VLCC double-body model have been experimentally investigated in a closed-type subsonic wind tunnel. The local mean velocity and turbulence statistics including turbulent intensity. Reynolds shear stress and turbulent kinetic energy were measured using a x-type hot-wire probe. The measurements were carried out at several transverse stations of the stern and near wake regions. The surface flow was visualized using on oil-film technique to see the flow pattern qualitatively. The flow in the stern and near wake region revealed complicated three-dimensional flow characteristics. The VLCC model shows a hook-shaped wake structure behind the propeller boss in the main longitudinal vortex region. The thin boundary layer at midship was increased gradually in thickness over the stern and evolved into a full three-dimensional turbulent wake.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.354-357
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• 2008

Drag reduction is one of main concerns for commercial aircraft companies than ever because fuel price has been tripled in ten years. In this research, Natural Laminar Flow airfoil is designed and tested to reduce drag at cruise condition, $c_l$=0.3, Re=3.4${\times}$10$^6$ and M=0.6. NLF airfoil is characterized by delayed transition from laminar to turbulent flow, which comes from maintaining favorable pressure gradient to downstream. Transition is predicted by solving Boundary Layer equations in viscous boundary layer and by solving Euler Equation outside the boundary layer. Once boundary layer thickness and momentum thickness are obtained, $e^N$-method is used for transition point prediction. As results, KARI's NLF airfoil is designed and shows better characteristics than NLF-0115. The characteristics are tested and verified at low Reynolds numbers, but at high Reynolds numbers, laminar flow characteristics are not obtainable because of fully turbulent flow over airfoil surfaces. Precious experiences, however, relating NLF airfoil design, subsonic and transonic tests are acquired.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.991-996
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• 2002

This paper presents the fabrication method of a micro-riblet film (MRF) using MEMS technology and the experimental results of the drag reduction of an airfoil with MRFs. Riblets having grooved surface in the streamwise direction has been proven as an effective passive control technique of the drag reduction. A V-grooved pattern on (100) silicon wafer is etched with anisotropic bulk micromachining. The MRF is completed by replicating the V-grooved pattern with polydimethylsiloxane (PDMS). Experiments were performed by measuring a velocity field behind the trailing edge of a NACA 0012 airfoil with and without MRFs in a closed-type subsonic wind tunnel using particle image velocimetry (PlV) technique. The MRF provides about 3.8 % drag reduction compared to the drag on a smooth airfoil when the freestream velocity of wind tunnel is 3.3 m/s.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.4
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• pp.345-350
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• 2010

The repetitive vibrating action of an aerodynamic load causes an external fuel tank's horizontal fin to experience a shorter life cycle than its originally predicted one. Store separation analysis is needed to redesign the fin of an external fuel tank. In this research, free-drop tests were conducted using 15% scaled models in a subsonic wind tunnel in order to analyze the store separation characteristics of an external fuel tank. The store separation trajectory based on grid tests was also obtained to verify the results of the free-drop tests. The results acquired from the free-drop tests correlated well with the grid tests in regards to the trajectories and behavior of the stores separated from the aircraft. This agreement was especially noted in the early stages of the store separation.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.27 no.4
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• pp.9-20
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• 2019

A military aircraft generally includes external stores such as fuel tanks or external arming, depending on the purpose of the operation. When a store is dropped from a military aircraft at high subsonic, transonic, or supersonic speeds, the aerodynamic forces and moments acting on the store can be sufficient to send the store back into contact with the aircraft. This can cause damage to the aircraft and endanger the life of the crew. In this study, time accurate computational fluid dynamics (CFD) with dynamic moving grid (moving and deformable mesh, MDM) technique has been used to accurately calculate store trajectories. For the verification of the present numerical approach, a wind tunnel test model for the wing-pylon-finned store configuration has been considered and analyzed. The comparison results for the ejected store trajectories between the present numerical analysis and the wind tunnel test data at the Mach number of 0.95 and 1.2 are presented. It is also importantly shown that the numerical parameter of MDM technique gives significant effect for the calculated store trajectory in the low-supersonic flow such as Mach 1.2.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.955-965
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• 2010

The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.