• Journal of Mechanical Science and Technology
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• 제14권11호
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• pp.1267-1275
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• 2000

A series do wind tunnel tests were conducted for Korean high-speed train model with various shape components to assess the contributions to aerodynamic drag. In order to elucidate the ground effects, two different wind tunnels, one with a moving ground system and the other with a fixed ground, were used for the same model and the results of both were compared and analyzed in detail. The result show that a suitable ground simulation is necessary for the test of a train model with many cars and detailed underbody. But the relative difference of the drag coefficients for the modifications of shape components can be measured by a fixed ground test with high accuracy and low cost. The effects of the nose shape, the inter-cargap and the bogie-fairing on total drag were discussed and some ideas were prosed to decrease the aerodynamic resistance of high speed train.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.605-610
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• 2000

A series of wind tunnel test were conducted on Korean high speed train model to understand the flow physics around the vehicle related to the aerodynamic drag. For the wind tunnel test on high-speed ground vehicle, a moving ground simulation is necessary to predict the aerodynamic drag accurately. So, the models were tested in three wind tunnels with various ground simulation facility including moving belt ground plane system and tangential blowing system. The test results including measured aerodynamic drag and flow visualization showed that a tangential blowing method can be an alternative ground simulation method in short time using conventional wind tunnel.

• 한국자동차공학회논문집
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• 제4권3호
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• pp.31-39
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• 1996

The effect of rear-spoiler attached at rear end of automobile trunk on the aerodynamic characteristics of a MIRA reference car model was experimentally investigated. For different shapes and positions(G/H) of the rear-spoiler, the aerodynamic forces on the automobile were measured at various flow speed(ReL). The effect of rear-spoiler on the wake structure behind the automobile was also investigated using flow visualization and hot-wire anemometer. The rear-spoiler modifies the near wake structure and decreases aerodynamic drag and increases driving stability compared with those of the conventional automobile without rear-spoiler. From the experimental results, rear-spoiler of airfoil shape installed at the position of G/H=0.084 shows the best aerodynamic performance.

• 항공우주시스템공학회지
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• 제2권2호
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• pp.46-50
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• 2008

Aerodynamic characteristics, such as drag and lift, play an important role in automobile design under certain speed conditions. Such characteristics are essential to design an automobile since they are directly related to automobile's performance such as passenger safety and fuel consumption. There is a huge demand for the automobile to have safe performance at high speed. Reduction in drag is also important and it could lead to the solution of air flow induced noise and dust problems. The objective of this research is to find out the aerodynamic differences between conventional side mirror and a modified one using CFD. Although drag generated around a side mirror is only about 7% of the total drag when a car runs, it is very closely related to driver's field of vision and noise generation. CFD simulation of the flowfield around a car side-view mirror was performed using a commercial code; Gambit and FLUENT.

• 한국전산유체공학회지
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• 제21권3호
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• pp.71-76
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• 2016

In speed skiing, aerodynamic forces play an important role in determining performance of the skier. To predict aerodynamic effects of the posture of the skier on alpine downhill skiing, we constructed equation of motion of the skier and performed the corresponding CFD simulations. Comparing drag and lift of three different skier postures, it has been shown that drag decreases significantly by tucking upper body to lower body and stretching arms forward. Also, aerodynamic lift which worked as downforce in standing posture worked upward in tuck posture, reducing friction force between snow and ski. This indicates that tuck posture have advantages over standing posture in dual mechanism, namely by reducing drag and also increasing lift. By this two-dimensional initial study we could reveal the general tendency of the aerodynamic force over the skier's body. This study not only provides a theoretical foundation for the athletes to understand the aerodynamic effects of skier postures but also shed a light on towards more accurate and rational three-dimensional CFD simulation of skiers in the near future study.

• Journal of Electrical Engineering and Technology
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• 제9권5호
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• pp.1712-1718
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• 2014

Experimental analysis according to the plasma actuator design variables was performed in order to verify the effects of sliding discharge plasma on aerodynamic drag reduction of a high-speed train. For the study, sliding discharge plasma actuator and high-frequency, high-voltage power supply were developed and experimented to figure out the best design variables for highest ionic wind velocity which could reduce the drag force. And then, 5% reduced-scale model of a high-speed train was built for wind tunnel test to verify it. From the results, it was confirmed that sliding discharge plasma had contribution to reduce the drag force and it had the potential to be applied to real-scale trains.

• 한국ITS학회 논문지
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• 제10권6호
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• pp.140-146
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• 2011

지능형교통체계(ITS) 정책의 일환으로 도로전광표지의 보급이 확대됨에 따라 그에 따른 유지보수의 비용 증가하고 있다. 본 논문은 도로전광표지의 공기저항 저감을 위하여 곡면 U형, 곡면 C형, 통풍형 공기저항 저감 구조를 제안하였으며 유동해석을 통해 제안한 공기저항 저감 표출부 함체의 풍하중 영향을 분석하였다. 풍직각 방향과 좌우 $45^{\circ}$ 방향, 상하 $45^{\circ}$ 방향에 대한 유동해석 결과, 곡면 C형 모델과 통풍형 세 가지 모델의 경우 풍방향 전 방향에 걸쳐 기본형 도로전광 표지에 대해 약 30% 정도의 풍하중 저감율이 있는 것으로 분석되었다. 또한 곡면 U형 모델은 기본형 도로전광표지 대비풍직각 방향과 풍방향 좌우 $45^{\circ}$ 방향에 대해서는 풍하중 저감효과가 있으나 풍방향이 상하 $45^{\circ}$ 방향으로 작용할 경우 풍하중 저감 효과가 미비한 것으로 나타났다. 향후 본 연구의 분석 결과를 토대로 도로전광표지의 공기저항을 줄여 태풍으로 인한 피해가 예상되는 곳에 적용 가능하고, 나아가 도로전광표지 지지구조물의 경량화가 가능해짐으로써 도로전광표지의 설치장소 제약을 완화시킬 수 있을 것으로 예상된다.

• 한국전산유체공학회지
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• 제19권2호
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• pp.66-71
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• 2014

Aerodynamic design of a vehicle has very important meaning on the fuel economy, dynamic stability and the noise & vibration of a moving vehicle. In this study, the correlation of aerodynamic effect between two model vehicles moving inline on a road was studied with the basic SAE model vehicle. Drag and lift are two main physical forces acting on the vehicle and both of them directly effect on the fuel economy and driving stability of the vehicle. For the research, the distance between two vehicles is varied from 5m to 30m at the fixed vehicle speed, 100km/h and the side-wind was assumed to be zero. The main issue for this numerical research is on the understanding of the interaction forces; lift and drag between two vehicles formed inline. From the study, it was found that as the distance between two vehicles is closer, the drag force acting on both the front and rear vehicle decreases and the lift force has same trend for both vehicle. As the distance(D) is 5m, the drag of the front vehicle reduced 7.4% but 28.5% for the rear-side vehicle. As the distance is 30m, the drag of the rear vehicle is still reduced to 22% compared to the single driving.

• 대한조선학회논문집
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• 제61권2호
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• pp.68-76
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• 2024

The rotor sail is one of the representative devices in eco-friendly wind-assisted propulsion systems that have been practically applied to commercial ships. The present study proposes an asymmetric vertical folding rotor sail (AFRS) designed for small ships, featuring asymmetric geometry along the vertical direction and the function of vertical folding. To evaluate the aerodynamic performance of rotor sail, the drag, lift and lift-to-drag ratio were derived using computational fluid dynamics. The aerodynamic performance of AFRS was compared with that of normal rotor sail with different aspect ratios and spin ratios. The effect of geometric parameters on the aerodynamic performance of AFRS was assessed by varying the asymmetric diameter ratio. The maximum improvement in lift-to-drag ratio for AFRS was approximately 12% in the considered case. Additionally, the resistance is decreased when AFRS is vertically folded without rotating. Throughout the present study, improved aerodynamic and resistance performances for AFRS were confirmed, which will successfully provide additional propulsion to small ships.

• 한국전산유체공학회지
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• 제18권3호
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• pp.8-13
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• 2013

Drag reduction of a running vehicle is very important issue for the energy savings and emission reduction of its power train. Especially for a solar powered electric vehicle, the drag reduction and weight lightening are two serious problems to be solved to extend its driving distance under the given energy condition. In this study, the ground effect of an airfoil shaped road vehicle was studied for an optimum body design of an ultra-light solar powered electric vehicle. Clark-Y airfoil type was adopted to the body shape of the model vehicle to reduce aerodynamic drag. From the study, it was found that the drag of the model vehicle was reduced as the height(h) between ground and the lower surface of the model vehicle was decreased. It is due to the reduction of the down-wash decreasing the induced drag of the vehicle. The lift was also decreased as the height decreased. It is due to the turbulent boundary layer developed beneath the vehicle body. The drag is classified into two types; the form and friction drag. The fraction of form drag to friction one is 76 to 24 on the model vehicle. As the height(h) of the model vehicle from the ground surface increases the form drag also increases but the friction drag is in reverse.