• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.25-32
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• 2015

Dielectric barrier discharge (DBD) plasma actuator was designed to reduce aerodynamic drag in a cylindrical model and wind tunnel test was performed at various wind velocities. In addition, computational fluid dynamics (CFD) analysis and flow visualization were used to investigate the effect of the plasma on the flow stream in the cylinderical model. At low wind velocity, the plasma actuator had no effects because flow separation did not appear. The aerodynamic drag was reduced by 14% at 14 m/s and by 27% at 17 m/s, respectively. It was confirmed by CFD analysis and flow visualization that the DBD plasma actuator decreased in pressure difference around the cylindrical model, thus decreasing the magnitude of wake vortex.

• Korean journal of applied entomology
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• v.40 no.2
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• pp.125-129
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• 2001

Some wingless species have evolved take-off behaviors that enable them to become airborne. We examined aerodynamic attributes of dispersal relative to the body size and standing vs. walking postures for three phytoseiids that were suspected to have different take-off behaviors and dispersal abilities, Phytoseiulus persimilis Athias-Henriot, Neoseiulus fallacis (Carman) and N. californicus (McGregor). The average vertical profile of Pp in the walking position was significantly higher than those of Nf and Nc when in walking position. The body height of Nf in the standing posture was significantly greater than the body height of Pp when in the walking position. Cross-section areas also showed similar patterns of difference. Nf in the standing posture would have more than twice the drag force than in walking posture because of more fluid momentum in the wind boundary layer However, Pp in the walking position would have similar drag to Nf in the standing posture because of a higher vertical profile and larger size. Thus we add the scientific evidence of presence and absence of take-off behavior of some phytoseiid mites and evolutionary aspects of aerial dispersal are further discussed.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.4
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• pp.361-372
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• 2019

The flow pattern of air layers and skin-friction drag reduction by air injection are investigated to find the suitable multiphase flow model using unstructured finite-volume CFD solver for the Reynolds-averaged Navier-Stokes equations. In the present computations, two different multiphase flow modeling approaches, such as the Volume of Fluid (VOF) and the Eulerian Multi-Phase (EMP), are adopted to investigate their performances in resolving the two-phase flow pattern and in estimating the frictional drag reduction. First of all, the formation pattern of air layers generated by air injection through a circular opening on the bottom of a flat plate are investigated. These results are then compared with those of MMkiharju's experimental results. Subsequently, the quantitative ratios of skin-friction drag reduction including the behavior of air layers, within turbulent boundary layers in large scale and at high Reynolds number conditions, are investigated under the same conditions as the model test that has been conducted in the US Navy's William B. Morgan Large Cavitation Channel (LCC). From these results, it is found that both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated air cavities so called'air pockets and branches'. However, EMP model is more favorable in predicting quantitatively the percentage of frictional drag reduction by air injection.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.137-145
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• 2008

An experimental study was performed in order to investigate the influence of Reynolds number on the drag coefficient variations of an oscillating airfoil. A NACA 0012 airfoil was sinusoidally pitched at the quarter chord point with an oscillating amplitude of ${\pm}6^{\circ}$. The free-stream velocities were 1.98, 2.83 and 4.03 m/s and the corresponding chord Reynolds numbers were $2.3{\times}10^4$, $3.3{\times}10^4$ and $4.8{\times}10^4$, respectively. The drag coefficient was calculated from the ensemble average velocity measured by an X-type hot-wire probe(X-type, 55R51) in the near-wakes region. In the case of Re=$2.3{\times}10^4$, variation of drag coefficient shows a negative damping (counter-clockwise variation), which implies an unstable state which could be excited by aerodynamic force, whereas the drag coefficient represents the positive damping (clockwise variation) as the Reynolds number increases from Re=$3.3{\times}10^4$ to $4.8{\times}10^4$. Hence, the drag coefficient variations show significant differences between Re=$2.3{\times}10^4$ and $4.8{\times}10^4$이다.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.101-104
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• 2004

CFD simulation is peformed for 2D and 3D frisbees flying at 10m/s. For convenience of simulation, rotation of 3D model is not considered. CFD results show that pitching moment makes the nose down and holes at the leading and trailing edges improve the lift characteristics of the frisbee.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.614-618
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• 2016

본 논문은 EDISON_CFD를 활용하여 화성에서 운용 가능한 풍력터빈에 대해 실험 및 개선 설계하였다. 본 연구에서는 화성의 중력 및 공기밀도 등 화성의 환경 데이터를 적용함으로써 풍력터빈의 형상을 새롭게 설계 하였다. 개선 설계는 기존의 풍력발전기 형상을 변형시키며 해석을 진행하였으며, 받음각과 형상에 따라 생성되는 토크를 확인하였다. 개선설계한 풍력터빈 모델은 단위 미터 당 약 8 W의 전력생산이 가능한 것을 확인하였다.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.3
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• pp.144-157
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• 2021

Brake Horse Power (BHP) reduction ratios by air injection to the underside of the hull surface in an actual ship are predicted using an unstructured finite-volume CFD solver and compared with the sea trial results. In addition, air lubrication system installed on the existing vessel is investigated to find a good solution for additional drag reduction. As a results, it is found that the thickness of the air layer should be minimized within a stable range while securing the area covered by the air layer as much as possible. Furthermore, the amount of frictional drag reduced by air injection is found to be independent of surface roughness and still effective on rough surface. Based on the results of this study, it is expected that systematic and reliable air lubrication system can be designed and evaluated using the proposed method.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.2
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• pp.155-160
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• 2004

Water jet trajectories and velocity deficits from a high pressurize nozzles were experimentally observed. In this article, several parameters affecting plugging and erosion onto the steam generator tube were quantitatively analyzed. Visualization, velocity distribution, and spray growth rate with different nozzle configurations have been mainly focused using a 2-D PDPA (Phase Doppler Particle Analyzer) system. The results indicated that trajectories along the centerline regardless of their momentum has its potential core region. However, the phenomena from the peripheral part need to be meticulosly considered. Accordingly, it is evident that quantitative velocity deficits at the outer region are outstanding due to the aerodynamical drag and entrainment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.191-193
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• 2017

EFD-CFD Comparison Workshop was proposed based on the drag prediction workshop and high lift prediction workshop of AIAA. This workshop is organized to escalate the levels of wind tunnel test and computational fluid dynamics and to escalate the level of domestic aerodynamic technology through the collaboration of both areas. For three benchmark cases of which wind tunnel test results are available, comparison workshops have been held since 2015.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.5
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• pp.14-20
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• 2020

In this study, the overall states of the airflow when a truck with or without side pairing is driven at a maximum speed of 90 km/h, regulated by domestic law, were investigated through computational fluid dynamics numerical analysis. All the tested models showed that the airflow went under the truck body; specifically, the air did not flow along the underside to the rear of the truck but through the sides of its underside. The drag with the drag coefficient at model 3 was clearly higher than those for the other two models. The results of this study could help to improve the truck performance by reducing its resistance against the air flown from it in driving itself.