• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.55-57
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• 2016

본 연구에서는 초고속 자기부상열차의 단면도를 통하여 2-D형상을 모델링하고 이를 기반으로 항력과 유동 특성에 대한 분석을 수행하였다. 유동의 마하수가 0.3 이상임을 고려하여 압축성 모델이 사용되었고, 난류모델은 Menter's k-w SST(Shear Stress Transport)모델을 적용시켰다. 2-D 해석과 자기부상열차의 특성상 열차가 공기중에서 주행하고 있는 것으로 가정하고 공력 특성을 해석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.109-117
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• 2015

Aircraft needs an inlet duct to supply the airflow to engine face. A fighter aircraft that requires low radar observability has to hide the engine face in the fuselage to reduce the Radar Cross Section(RCS). Therefore, the flow path of the inlet duct is changed into S-shape. The performance of the aircraft engine is known to be influenced by the shape and the centerline curvature of the S-Duct. In this study, CFD analysis of the RAE M 2129 S-Duct has been performed to investigate the influence of aspect ratio of inlet geometry. The performance of the S-Duct is evaluated in terms of the distortion coefficient. To simulate the flow under adverse pressure gradient better, $k-{\omega}SST$ turbulence model is employed. The computational results are validated with the ARA experimental data. The secondary flow and the flow separation are observed for all computational cases, while the semi-circular geometry has been found to produce the best results.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.4
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• pp.33-38
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• 2003

The Physics of the Plume-induced shock and separation Particularly at a high Plume to exit pressure ratio and supersonic speeds up to Mach 3.0 with and without a passive control method, porous extension, were studied using computational techniques. Mass-averaged Navier-Stokes equations with the RNG $\kappa$-$\varepsilon$ turbulence model were solved using a fully implicit finite volume scheme and a 4-stage Runge-Kutta method. The control methodology for plume-afterbody interactions is to use a perforated wall attached at either the nozzle exit or the edge of the missile base. The Effect of porous wall length on plume interference is also investigated The computational results show the main effect of the porous extension on plume-afterbody interactions is to restrain the plume from strongly underexpanding during a change in flight conditions. With control, a change in porous extension length has no significant effect rut plume interference.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.562-570
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• 2009

An Experimental study was conducted on the flow characteristics and interference heating caused by a two-dimensional object protruding from a flat plate using a blow-down type of hypersonic wind tunnel. Inflow condition was a free-stream Mach number of 7.0 and a unit Reynolds number of $2.0{\times}10^6/m$. Experimental conditions were varied with three heights of protuberance for two flat plate models which have different lengths. Experimental data were obtained from Schlieren visualization images and heat flux measurements. Also, this paper suggests hypersonic experimental techniques such as boundary-layer detection method in detail. A Large separation region was observed in front of the protuberance and that region was very sensitive to the height of protuberance and the length of the flat plate. For only the highest protuberance, a severe jump of heat flux was observed at the top station among the measuring points. Measured heat flux is large when the height of protuberance is large and the length of flat plate is long.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.45-49
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• 2006

The flow around a foil with waterjet was investigated using the two-frame PIV(CACTUS 3.1) system. After separation, unsteady recirculation & reattachment region was shown as a result at reading edge. Separation area was decreased to 1/3 more by waterjet system with coanda effect. Angle of attack and waterjet velocity was a variable in the experiment. Each parameters was controlled to $0^{\circ}{\sim}35^{\circ}$ and 0[m/s]${\sim}$9.2[m/s]. The separation of flow appearanced at first when the angle of attack is $17^{\circ}{\sim}18^{\circ}$. However, according to grew up of velocity, beginning of the separation was delayed. In this experiment, vortex and separation region was disappeared by blown when each parameters are low level, and separation controlled more certainly.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.1
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• pp.60-67
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• 2003

Flow around an oscillating circular cylinder was experimentally investigated. With varying Keulegen-Carpenter(KC) number from 10 to 30 the flow field with vortex sheddings and the related hydrodynamic fortes exerting on the cylinder were measured. A newly developed PW(paricle image velocimetry) successfully captured the complex vortical flows varying with the KC number and the flow patterns were 'traverse street', 'single pairing' and 'double pairing' of vortices with increasing KC number, At a certain KC number range the lift force undergoes a transition showing little periodicity due to surrounding complicated shedded vortices.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.211-214
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• 2011

In the present work, a computational study was conducted to investigate characteristic of lateral force on the flow fields inside the propulsion nozzle with step. The unsteady, compressible, axisymmetric, Navier-Stocks equations with SST k-${\omega}$ turbulence model are solved using a fully implicit finite volume scheme. In order to simulate the shut-down process of the engine, NPR is varied from 100.0 to 10.0. It is observed that the separation point and Mach-disk strongly depend on the variation of NPR, and adjusting the step lead to significantly different characteristics in the lateral forces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2267-2276
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• 1996

Twin-fluid atomization has been widely used in combustors and process industries because of its high performance and simple structure. Flow visualization and pressure measurements were conducted to investigate the effects of gas flow in twin-fluid atomization. Schlieren photographs showed that changes in atomizing gas pressure, altered the wave patterns, and the lengths of both recitrculating toroid (impinging stangnation point) nad supersonic flow region in the jet. A longer supersonic wave pattern like net-shape wqas observed as atomizing gas pressure increased. The disintegration phenomenon of liquid delivery tube. The variation of spray angles with gas pressures were obtained by visualization using laser sheet beam. Suction pressuresat the nozzle orifice exit and recirculating region are shown to be used to estimate the stable atomization condition of a twin-fluid atomizer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1173-1183
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• 2009

In order to reduce the download around the Smart UAV(SUAV) at hovering, flow control using synthetic jet has been performed. Many of the complex tilt rotor flow features are captured including the leading and trailing edge separation, and the large region of separated flow beneath the wing. In order to control the leading edge and trailing edge separation, synthetic jet is located at 0.01c, $0.3c_{flap}$, $0.95c_{flap}$. As non-dimensional frequency, the flow pattern is altered and the rate of drag reduction is changed. The results show that synthetic jets shorten the vortex period and decrease the vortex size by changing local flow structure. By using leading edge jet and trailing edge jet, download is efficiently reduced compared to no control case at hovering mode.

• Journal of Power System Engineering
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• v.12 no.5
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• pp.20-26
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• 2008

양산되는 승용차용 토크 컨버터 내부의 유동을 LDV 측정 기술을 이용하여 정량화했다. 속도비 0.4와 0.8 경우에 대한 속도 측정을 통해 임펠러 유로 중간과 출구 영역의 질량 유동율 특성을 분석했다. 측정 단면의 속도 분포는 유로의 위치와 속도비에 따라 많은 차이를 보이며, 특히 속도비 0.8 조건에서 임펠러 유로 중간영역 흡입면 부근의 유동은 유동박리에 의한 재순환 현상을 나타내며, 이와는 대조적으로 출구 영역에서는 흡입면을 따라 역류 현상이 발생한다. 임펠러 유로 내부의 유동은 각 영역에서 속도비에 따라 개별적 유동 특성을 보인다. 질량 유동율은 모든 속도비와 측정단면에서 주기적인 변화를 보이며, 또한 터빈의 순간적인 위치가 임펠러 유로 측정단면의 질랑 유동율에 매우 큰 영향을 미치는 것이 밝혀졌다 따라서 토크 컨버터 임펠러의 유로 방향 유동 특성 변화는 컨버터 설계에 중요하게 고려되어야 할 것으로 보인다.