• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2004년도 춘계학술대회 논문집
• /
• pp.889-896
• /
• 2004

A series of filed tests have been performed to investigate the aerodynamic effects on platform of the railway station during the passage of train that can be unpleasant and even dangerous to the pedestrians. To assess the aerodynamic effects on the platform, two aerodynamic properties has been measured; one is the wind gust induced by the train and the other is the pressure pulses generated when the nose and the tail of train passes. To measure these aerodynamic properties during the train passage, an array of hot-wire type anemometers and several sets of pressure transducers have been used, respectively. This paper deals with the filed test on conventional railway at about l00km/h operational speed, in which total 34 measurements has been made at the Bugok station in Seoul-Busan line for Saemaul and Mugungwha train. The results showed dramatic differences in the aerodynamic features between the two trains that are supposed to originate from the contrasting nose shapes of the trains.

• 대한조선학회논문집
• /
• 제36권3호
• /
• pp.15-21
• /
• 1999

KRISO 300K VLCC 이중모형선 주위의 유동특성을 풍동실험을 통해 연구하였다. 선체 선미 주위유동과 후류유동의 평균속도 성분, 난류강도, 레이놀즈 전단응력 및 난류 운동에너지 분포를 열선풍속계를 이용하여 측정하였다. 실험은 선미와 후류의 횡단면에서 수행하였으며, 선체 표면에서의 유동 패턴을 정성적으로 조사하기 위하여 유막법을 이용한 유동가시화도 수행하였다. 선미와 근접 후류영역은 매우 복잡한 3차원의 유동특성을 가지고 있으며, 특히 종방향 와류영역에서 고리 모양의 후류 구조를 볼 수 있었다. 그리고 중앙평행부에서의 얇은 경계층은 선미 영역을 지나며 점차 두꺼워지고 복잡한 3차원 난류후류로 발전하였다.

• 대한조선학회논문집
• /
• 제36권3호
• /
• pp.8-14
• /
• 1999

KRISO 3600TEU 콘테이너 이중모형선 주위 유동의 평균속도와 난류성분들을 풍동실험을 통해 실험적으로 연구하였다. 선미와 후류의 여러 단면에서의 속도분포를 x형의 열선 프로우브로 측정하여 평균속도와 레이놀즈 응력, 그리고 난류 운동에너지 등을 구하였다. 선미영역과 후류영역에서의 유동은 매우 복잡한 3차원 유동특성을 보여주고 있다. 측정 결과로부터 주유동 방향의 와 구조의 형성과 이러한 와 유동이 후류의 유동에 미치는 영향을 알 수 있었으며, 하류로 나아감에 따라 전단층 영역이 점차 확장되어짐을 확인하였다. 이와 같은 선체주위 유동의 난류 성분들의 측정은 향후 수치계산 및 정확한 난류모델의 개발에 비교자료로 사용되어질 것이다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2009년도 제33회 추계학술대회논문집
• /
• pp.395-398
• /
• 2009

Currently, a new generation of ducted fan UAVs (Unmanned Aerial Vehicles) is under development for a wide range of inspection, investigation and combat missions as well as for a variety of civil roles like traffic monitoring, meteorological studies, hazard mitigation etc. The current study presents extensive results obtained experimentally in order to investigate the tip clearance effects on performance characteristics of a ducted fan for small UAV systems. Three ducted fans having different tip clearance gap and with same rotor size were examined under three different yawed conditions of calibrated slanted hot-wire probe. Three dimensional velocity flow fields were measured from hub to tip at outlet of the ducted fan. The analysis of data were done by PLEAT (Phase locked Ensemble Averaging Technique) and three non-linear differential equations were solved simultaneously by using Newton -Rhapson numerical method. Flow field characteristics such as tip vortex and secondary flow were confirmed through axial, radial and tangential velocity contour plots. At the same time, the effects of tip clearance on axial thrust and input power were also investigated by using wind tunnel measurement system. For enhancing the performance of ducted fan, tip clearance level should be as small as possible.

• 한국분무공학회지
• /
• 제21권2호
• /
• pp.111-115
• /
• 2016

This paper experimentally reports the effect of suspension stability on the thermal conductivity of water-based Au nanofluids. For this purpose, the water-based Au nanofluids are prepared by the one-step method called electro-chemical method with volume fraction of 0.0005%. The thermal conductivity of water-based Au nanofluids is measured from $22^{\circ}C$ to $42^{\circ}C$ using the transient hot wire method. To quantify the suspension stability of Au nanofluids, the suspension stability of nanofluids is evaluated using the in-house developed laser scattering system at a fixed wavelength of 632.8nm with the elapsed time. Based on the experimental results, the both thermal conductivity and suspension stability of water-based Au nanofluids are gradually decreased according to the time. These results experimentally show that the suspension stability of water-based Au nanofluids is the one of the important factor of thermal conductivity.

• 대한기계학회논문집B
• /
• 제23권2호
• /
• pp.218-225
• /
• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.

• 한국유체기계학회 논문집
• /
• 제12권5호
• /
• pp.25-32
• /
• 2009

A study is conducted to improve the suction performance on suction devices which are used to remove polluted air generated by welding or machining process in a spacious working place of industry. Air-curtain is applied around the inlet of suction duct to interrupt the inflow of fresh air from the downstream region where is located opposite to the polluted air source. Two different air-curtain devices, such as a $45^{\circ}$ backward and a fully backward, are adopted. Suction region is experimentally investigated by measuring the suction velocities using a hot-wire anemometer. Contours of the suction velocity are compared with the computed results. The suction condition is selected to 110,000 Reynolds number which is widely used on typical suction devices, and a width of blowing passage for creating the air-curtain is chosen to 9.38% of the suction duct diameter. The experimental results show that the suction performance obtained with the $45^{\circ}$ backward air-curtain was better than that obtained with the fully backward air-curtain. On the suction duct using the $45^{\circ}$ backward air-curtain, the suction region estimated on basis of the 0.4m/sec is improved by 66% at the same input power.

• International Journal of Fluid Machinery and Systems
• /
• 제5권3호
• /
• pp.117-125
• /
• 2012

In the present experimental study, the authors try to clarify the characteristics of the flow around and inside a cross-flow impeller in a typical geometry, over a wide parameter range of an aspect ratio $L/D_2$. In order to eliminate the complicated casing factors, the impeller rotates in open space without any casings. As a result, by using hot wire anemometer measurements and by conventional flow visualisations with a particle image velocimetry technique, the authors show that both the outflow rate and the maximum vorticity attain the maximum for $L/D_2$ = 0.6. In order to investigate the aspect-ratio effect, we further reveal minute fluctuating pressures on an impeller end wall for a singular $L/D_2$ = 0.6. Especially in these pressure measurements, the eccentric vortex is prevented to revolute by the insertion of a tongue, in order to consider the spatial structure of flow more precisely.

• International Journal of Fluid Machinery and Systems
• /
• 제1권1호
• /
• pp.10-23
• /
• 2008

The development of pre-set wavelength G$\ddot{o}$rtler vortices are studied in the boundary-layer flows on concave surfaces of 1.0 and 2.0 m radius of curvature. The wavelengths of the vortices were pre-set by thin wires of 0.2 mm diameter placed 10 mm upstream and perpendicular to the concave surface leading edge. Velocity contours were obtained from velocity measurements using a single hot-wire anemometer probe. The most amplified or dominant wavelength is found to be 15 mm for free-stream velocity of 2.1 m/s and 3.0 m/s on the concave surface of R = 1 m and 2 m, respectively. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on the growth rate of the vortices. The occurrence of a secondary instability mode is also shown in the form of mushroom-like structures as a consequence of the non-linear growth of the G$\ddot{o}$rtler vortices. By pre-setting the vortex wavelength to be much larger and much smaller than the most amplified one, the splitting and merging of G$\ddot{o}$rtler vortices can be respectively observed.

• 대한기계학회논문집
• /
• 제12권3호
• /
• pp.534-540
• /
• 1988

본 연구에서는 디이젤분무 주위기체의 유동특성중에서 유동속도에 관하여 보 고 하였다. 본모에서는 분무기간중 분사압력의 시간경과특성이 상이한 두 종류의 분 사계를 사용하여 생성된 분무와 주위 기체와의 유동방향의 시간경과 및 유입시기, 정 상유입속도 도달시간등을 분무의 축방향과 반경방향에 대하여 상세한 측정결과를 얻었 기에 보고한다.