• Proceedings of the Korean Nuclear Society Conference
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• 2003.10a
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• pp.81.1-81.1
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• 2003

• Journal of the korean Society of Automotive Engineers
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• v.7 no.4
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• pp.49-56
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• 1985

This study consists of instrumenting and running tests on variable compression engines and measuring the following combustion characterics: (a)flame speed, (b) emission and (c)performance parameter such as power and economy. The results were as follows: 1) The phase separation diagram of substitute fuels were obtained from phase separation experiment. 2) The flame propagation speed of substitute fuels were higher than gasoline and increased with increasing methanol weight percent of substitute fuels. 3) BEMP of substitute fuels was slightly less than that of gasoline but in the range of small weight percent, BEMP was compatible to gasoline. 4) Concentration of NOx decreased significantly with delaying spark advancing time. Also, it decreased for rich equivalence ratio but increased with high compression ratio. In general, NOx concentration was much lower than that of gasoline. 5) Concentration of HC and CO increased for rich equivalence ratio. Also it was lower than that of gasoline.

• Journal of Ship and Ocean Technology
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• v.8 no.2
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• pp.13-19
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• 2004

Jet flows applied tangential to a foil surface near the leading and/or trailing edges increase the lift of the foil by delaying the separation also known as the Coanda effects. Many experimental and numerical studies have proven the effectiveness of Coanda effects on circulation control and the effects have been found to be useful in practical application in many aerodynamics fields. Most of the previous works have studied the effects of the jet blowing near the trailing edges and investigated the influence of jet momentum on lift. A few experimental studies, however, focused on the separation bubble that develops near the leading edge and applied jet flow the edge to remove the bubble but only to find decrease in lift. In the present paper, a Coanda foil of 20% thickness ellipse with modified rounded leading and trailing edges was investigated, and the flow around the foil was numerically studied. The blowing around the leading edge only decreased the lift, as the experiments showed, but the suction considerably increased the lift.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.356-361
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• 2011

The flow characteristics of synthetic jet depending on rectangular and circular jet exit configuration are investigated using numerical computation with cross flow. In rectangular slot, synthetic jet generates the strong vortex, however, supply fewer momentum and effectiveness of flow control is reduced along flow direction. In circular slot, regular vortex is fanned from slot center to end and developed in flow direction. It affects the wider region than rectangular slot. The distribution of wall shear stress is considered in order to indicate the effectiveness of flow control device for flow separation delay. As a result, circular slot is a more suitable candidate for delaying flow separation.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.491-496
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• 2000

The objective of this study is to increase lift and decrease drag of an airfoil by delaying flow separation with piezo-ceramic actuators. The airfoil used is NACA 0012 and the chord length is 30cm. An experiment is performed at the freestream velocity of 15m/s at which the Reynolds number is $3{\times}10^5$. Seven rectangular actuators are attached to the airfoil surface and move up and down based on the electric signal. At the attack angle of $16^{\circ}$, the separation point is delayed downstream due to momentum addition induced by the movement of the actuators. Drag and lift are measured using an in-house 2-dimensional load cell and the surface pressures are also measured. Lift is increased by 10%, drag is reduced by 50%, and the efficiency is increased to 170%. The flow fields with and without control are visualized using the smoke-wire and tuft techniques.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.1
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• pp.18-25
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• 2017

This study deals with numerically comparing performance according to rudder shape called 'Twisted rudder and Wavy twisted rudder'. In comparison with conventional rudder, rudder with wavy shape has showed a better performance at high angles of attack($30^{\circ}{\sim}40^{\circ}$) due to delaying stall. But most of study concerned with wavy shape had been performed in uniform flow condition. In order to identify the characteristics behind a rotating propeller, the present study numerically carries out an analysis of resistance and self-propulsion for KCS with twisted rudder and wavy twisted rudder. The turbulence closure model, Realizable $k-{\epsilon}$, is employed to simulate three-dimensional unsteady incompressible viscous turbulent and separation flow around the rudder. The simulation of self-propulsion analysis is performed in two step, because of finding optimization case of wavy shape. The first step presents there are little difference between twisted rudder and case of H_0.65 wavy twisted rudder in delivered power. So two kind of rudders are employed from first step to compare lift-to-drag ratio and torque at high angles of attack. Consequently, the wavy twisted rudder is presented as a possible way of delaying stall, allowing a rudder to have a better performance containing superior lift-to-drag ratio and torque than twisted rudder at high angles of attack. Also, as we indicate the flow visualization, check the quantity of separation flow around the rudder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1112-1118
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• 2000

The objective of this study is to increase lift and decrease drag of an airfoil at high angles of attack by delaying flow separation with piezo-ceramic actuators. The airfoil used is NACA 0012 and its chord length is 0.3m. An experiment is performed at the freestream velocity of 15m/s at which the Reynolds number based on the chord length is $2{\times}10^5$. Seven rectangular actuators are attached to the airfoil surface and move up and down based on the electric signal. Drag and lift are measured using an in-house two-dimensional force-balance and the surface pressures are also measured. At the attack angle of $16^{\circ}$, the separation point is delayed downstream due to momentum addition induced by the movement of the actuators. Lift is increased by 10%, drag is reduced by 37%, and the efficiency is increased up to 170%. The flow fields with and without control are visualized using the smoke-wire and tuft techniques.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.10-17
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• 2018

The size of commercial wind turbines has been increased. Generally, the pitch control is used to increase the efficiency of wind turbine. However, the pitch control has difficulty to control the local unsteady flow control which makes fatigue load and decreases the efficiency. In this research, Synthetic Jet Actuators(SJAs) are manufactured and applied into a wing section to delay flow separation and increase aerodynamic performances. The SJAs as a kind of zero-net mass-flux actuators injects and removes fluid through a small orifice with a given frequency. The SJA modules actuated by piezoelectric disks are manufactured and the aerodynamic performances are measured according to the shape of the orifice and the velocity of the jets through the wind tunnel test. It is confirmed that as the velocity of the jets are increased using rectangular shape orifice, drag force is decreased and lift force in increased.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.585-595
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• 2011

The flow characteristics of synthetic jet depending on rectangular and circular jet exit configuration are investigated using numerical computation with cross flow. In rectangular slot, synthetic jet generates the strong vortex but supplies fewer momentum and effectiveness of flow control is reduced along flow direction. In circular slot, regular vortex is formed from slot center to end. It affects the wider region than rectangular slot. The distribution of wall shear stress is considered in order to indicate the effectiveness of flow control device for flow separation delay. Consequently, circular slot is a more suitable candidate for delaying flow separation. In order to derive the optimal shape of a circular slot exit, hole gap and diameter that affect the flow structure and flow control were analyzed. As a result, consider the hole diameter and gap of circular slot exit design, effectiveness of the flow control can be increased.

• Advances in aircraft and spacecraft science
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• v.4 no.2
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• pp.145-167
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• 2017

The presented paper gives an overview of several projects addressing the experimental characterization and control of the buffet phenomenon on 3D turbulent wings in transonic flow conditions. This aerodynamic instability induces strong wall pressure fluctuations and therefore limits flight domain. Consequently, to enlarge the latter but also to provide more flexibility during the design phase, it is interesting to try to delay the buffet onset. This paper summarizes the main investigations leading to the achievement of open and closed-loop buffet control and its experimental demonstration. Several wind tunnel tests campaigns, performed on a 3D half wing/fuselage body, enabled to characterize the buffet aerodynamic instability and to study the efficiency of innovative fluidic control devices designed and manufactured by ONERA. The analysis of the open-loop databases demonstrated the effects on the usual buffet characteristics, especially on the shock location and the separation areas on the wing suction side. Using these results, a closed-loop control methodology based on a quasi-steady approach was defined and several architectures were tested for various parameters such as the input signal, the objective function, the tuning of the feedback gain. All closed-loop methods were implemented on a dSPACE device able to estimate in real time the fluidic actuators command calculated mainly from the unsteady pressure sensors data. The efficiency of delaying the buffet onset or limiting its effects was demonstrated using the quasi-steady closed-loop approach and tested in both research and industrial wind tunnel environments.