• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.373-379
• /
• 2001

When a train runs into a tunnel at high-speed, aerodynamic drag suddenly increases and the booming noise is generated at the exit of tunnel. The noise shape is very important to reduce the aerodynamic drag in tunnel as well as on open ground, and the micro-pressure wave that is a source of booming noise is dependent on nose shape, especially on area distribution. In this study, the nose shape has been optimized employing the response surface methodology and the axi-symmetric compressible Navier-Stokes equations. The optimal designs have been executed imposing various conditions of the aerodynamic drag and the micro-pressure wave on object functions. The results show that the multi-objective design was successful to decrease micro-pressure wave and aerodynamic drag of trains.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.5
• /
• pp.1712-1718
• /
• 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.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.6 no.1
• /
• pp.7-20
• /
• 1998

A reduction of induced drag is an important problem in order to save fuels. In this study, the aerodynamic characteristics of wing tip devices to reduce induced drag, such as end plate, plain ring, helical ring wing tip device, was experimentally investigated in a low speed wind tunnel. The experimental results showed that the wing model with a helical ring wing tip device reduced a induced drag and increased lift-drag ratio.

• Aerospace Engineering and Technology
• /
• v.7 no.1
• /
• pp.24-29
• /
• 2008

Aircraft fuel efficiency is one of main concerns to aircraft manufacturers and to aviation companies because jet fuel price has tripled in last ten years. One of simple and effective methods to increase fuel efficiency is to reduce aircraft induced drag by using of wingtip devices. Induced drag is closely related to the circulation distribution, which produces strong wingtip vortex behind the tip of a finite wing. Wingtip devices including winglets can be successfully applied to reduce induced drag by wingtip vortex mitigation. Winglet design, however, is very complicated process and has to consider many parameters including installation position, height, taper ratio, sweepback, airfoil, toe-out angle and cant angle of winglets. In current research, different shapes of winglets are compared in the view of vortex mitigation. Appropriately designed winglets are proved to mitigate wingtip vortex and to increase lift to drag ratio. Also, the results show that winglets are more efficient than wingtip extension. That is the reason B-747-400 and B-737-800 chose winglets instead of a span increase to increase payload and range. Drag polar comparison chart is presented to show that minimum drag is increased by viscous drag of winglet, but at high lift, total drag is reduced by induced drag decrease. So, winglets are more efficient for aircraft that cruises at a high lift condition, which generates very strong wingtip vortex.

• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.647-652
• /
• 2016

To reduce drag force at supersonic speeds, sharp leading edge is hugely efficient. It is, however, incompatible with leading edge shape to have fine aerodynamic characteristics at subsonic and transonic speeds. It is critical to reduce drag force for enhanced cruise performance and higher efficiency. An air superiority fighter, however, required to have high maneuverability for survivability, and sharp leading edge is not proper. Consequently, variable leading edge is demanded to reduce drag force significantly at supersonic speeds for cruise performance. Leading edge altering system is constructed with rigid material to improve possibility of realization, and minimized movement of its components in altering for reduce effects on flight. It is compared with bi-convex airfoil and NACA 65-006 airfoil, which have comparable maximum thickness. At Mach number 1.7 and zero angle of attack, supersonic mode of designed airfoil indicates approximately 17% higher drag coefficient than the bi-convex airfoil indicates, it is, however, 23% lower than the NACA 65-006 indicates. Also, subsonic mode of the designed airfoil shows fine aerodynamic characteristics in comparison with NACA 65-006 airfoil in subsonic and transonic speed range. In this regard, design of the airfoil achieved the object of this study satisfactorily.

• Journal of the Korean Society for Railway
• /
• v.19 no.6
• /
• pp.709-716
• /
• 2016

To reduce the aerodynamic drag of high speed trains, aerodynamic drag of KTX-Sancheon was analyzed in detail according to individual components. Aerodynamic drag values of the power cars (front car, rear car) and bogies are about 42.9% and 10.1% of the total aerodynamic drag, respectively. For the aerodynamic drag reduction of a power-car, a nose shape optimization was conducted using the Broyden-Fletcher-Goldfarb-Shanno optimum method. Shape change of a power car and bogie fairing adaptation are used to reduce the aerodynamic drag of a car body. The aerodynamic drag of the optimized train-set dropped by 15.0% compared to the aerodynamic drag of the KTX-Sancheon; a running resistance reduction of 12% is expected at the speed of 350km/h.

• Journal of the Korean Society of Visualization
• /
• v.21 no.2
• /
• pp.8-13
• /
• 2023

The primary challenge in improving fuel efficiency and reducing air pollution for commercial vehicles is reducing their aerodynamic drag. Various flow control devices, such as cab-roof fairing, gap fairing, cab extender, and side skirt have been introduced to reduce drag, however, the drag reduction effect and applicability are different depending on each commercial vehicle model. To evaluate the fuel consumption of heavy vehicles, a comprehensive research approach, including drag force measurement, flow field analysis is required. This study investigated the effect of a cab extender, which installed rear region of cab, on a drag coefficient of commercial vehicle through wind tunnel experiments and CFD. The results showed that the cab extender significantly modified the flow structure around the vehicle, leading to 8.2% reduction in drag coefficient compared to the original vehicle model. These results would provide practical application for enhancing the aerodynamic performance and fuel efficiency of heavy vehicle.

• 한국전산유체공학회:학술대회논문집
• /
• 1995.10a
• /
• pp.154-159
• /
• 1995

Numerical optimization technique with Navier-Stokes code has been used to reduce the drag of conventional ogival nose. Forebody optimizations are performed for supersonic laminar and turbulent flow conditions. To alleviate the computing time of aerodynamic drag calculation, axisymmetric boundary condition is implemented in the 3-dimensional Navier-Stokes code. The automated optimization procedure with gradient based method results in a drag reduction of $4\;\%$.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.04a
• /
• pp.562-566
• /
• 1997

The main torsional vibration source of the driveline is the fluctuation of the engine torque. The gear rattle is impacts generating in the backlash of the free gear due to this torsional vibration Optimization of the clutch torsional characteristic is one of the effective methods to reduce the idle gear rattle. Many researches have been reported on this problem but only few of them give sufficient consideration to the full clutch design parameters(stiffness, hysteresis torque, preload, first stage length) and drag torque This paper pays attention to the gear impact mechanism, clutch design parameters and drag torque to reduce the idle gear rattle with computer simulation.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2002.04a
• /
• pp.140-145
• /
• 2002

At present, wind tunnel test or CFD is used for predicting aerodynamic drag coefficient in motor company. But, wind tunnel test requires much cost and time, and CFD has about 30% error. In this study a predicting program of the aerodynamic drag coefficient based on empirical techniques was developed. Also a mathematical optimization method using GRG method was added to the program. The program was applied to six cars. Aerodynamic drag coefficient values of six cars were Predicted with 4.857% average error. The optimization method was also applied to six cars. Three parameters selected from sensitivity analysis were determined to reduce the afterbody drag coefficient to the value established by a designer and when some parameters were changed for a developing automotive, optimal modifiable parameters were determined to preserve the same drag coefficient as the original automotive. It was verified that this program could predict the aerodynamic drag coefficient effectively and accurately, and this program with GRG method could determine optimal values of parameters.