• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1674-1680
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• 2002

An experimental study was made of a large-scale vortical structure over a backward-facing step. The Reynolds number based on the step height was R $e_{H}$ =33,000. To recognize the large-scale vortex, three components of velocity were measured. The measurements were performed in the recirculation zone (x/H=4.0) and the reattachment zone(x/H=7.5). To measure the wall pressure fluctuations in a turbulent flow over a backward-facing step, a 32-channel microphone array was installed beneath the wall in the streamwise and spanwise directions. From the measured pressure field, the size of large-scale vortex was obtained. As a detailed study, a conditionally-averaging technique was employed to characterize the coherent structure of the large-scale vortex. To see the relationship between the flow field and the relevant spatial mode of the pressure field, the spatial box filtering (SBF) was examined. A cross-correlation between velocity and pressure fluctuations was performed to identify the structure and the length scale of the large-scale vortex.x.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.628-631
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• 2016

본 연구에서는 플라잉디스크의 윗면 곡률과 끝단두께에 따른 공력특성의 변화 및 유동 흐름을 EDISON_CFD를 통해 해석하고자 한다. 플라잉디스크는 받음각이 증가할수록 윗면 표면에서는 박리 거품이 발생하게 되고 아랫면에서 윗면으로 올라 갈려는 유동의 흐름이 발생하게 되어 뒷전과 후류에서 거대한 박리 거품이 발생하게 되어 공력특성 및 유동흐름에 큰 변화를 주게 된다. 총 5가지의 형상에 대해서 받음각을 $0^{\circ}{\sim}25^{\circ}$까지 마하수 0.0588, 해석모델은 KFLOW에서 k-w SST를 레이놀즈수 $3.78{\times}10^5$을 조건으로 각 형상의 공력특성과 유동의 흐름의 비교를 분석하였다. 그 결과 윗면의 곡률이 증가 할수록 앞전박리가 활발해지고, 끝단두께가 두꺼워 질수록 뒷전박리가 활발해진다. 이로 인해 곡률은 완만할수록 두께는 얇을수록 양력계수와 실속각을 증가 시킬 수 있다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.117-121
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• 2001

A numerical simulation was conducted to investigate the effect of height position of Rushton type Impeller in the fermentation. The computational method was based on the CFX code. The simulation was performed for 3 height differences(25, 30, 35mm) between Rushton type impeller and bottom of fermentation. The instantaneous flow fields showed that the bulk flow consisted of large scale vortices. However the main flow results showed that the formation of ring vortices above and below the impeller depended on the height of the impeller.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.275-285
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• 2003

A visualization study on the effect of forcing amplitude in tone-excited jet diffusion flames has been conducted. Visualization techniques are employed using optical schemes. which are a light scattering photography. Flame stability curve is attained according to Reynolds number and forcing amplitude at a fuel tube resonant frequency. Flame behavior is globally grouped into two from attached flame to blown-out flame according to forcing amplitude: one sticks the tradition flame behavior which has been observed in general jet diffusion flames and the other shows a variety of flame modes such as the flame of a feeble forcing amplitude where traditionally well-organized vortex motion evolves, a fat flame. an elongated flame. and an in-burning flame. Particular attention is focused on an elongation flame. which is associated with a turnabout phenomenon of vortex motion and on a reversal of the direction of vortex roll-up. It is found that the flame length with forcing amplitude is the direct outcome of the evolution process of the formed inner flow structure. Especially the negative part of the acoustic cycle under the influence of a strong negative pressure gradient causes the shapes of the fuel stem and fuel branch part and even the direction of vortex roll-up to dramatically change.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1543-1551
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• 2001

The characteristics of starting flow of a six-blade Rushton turbine mixer were investigated by using a cinematic Particle Image Velocimetry technique. The flows were quantified by measurements of velocity fields with a 4 ms time interval for a blade rotational speed of 100 r.p.m, so that the turbine Reynolds number(ND$^2$/ ν) was fixed to 6,960. The radial shedding of the trailing vortices starts from passing four blades after the beginning of rotation. It clearly shows that the vortex pairing phenomena caused by the interactions between trailing cortices firm consequtive blades. The average convection velocity of the radial flow is found to be 28 % of the tip velocity. The starting flow seems to arrive at a steady state after 8 revolutions in this study, which corresponds nearly one circulation through the bulk flow trajectory with the average radial convection velocity.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.24-33
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• 2023

This work is to observe the wake flow generated behind a ramp. We have conducted a large eddy simulation with two ramp models having different heights with two different inflow conditions. Reynolds number based on the height of the large ramp (LR) and small ramp (SR) are Re_h = 2.8×10⁴ and 1.4×10⁴ respectively. The wake flow visualization shows the formation of streamwise counter-rotating vortices pairs at the downstream of the obstacle. These primary vortices are stretched and lifted up when moving downstream. In order to observe the effect of the inflow condition on the wake transition, two different inlet flow conditions are given on the inlet section as an inlet boundary condition. Induced counter-rotating vortices pairs due to sharp-edged triangular ramp obstacles are developed and propagated downstream. In the result, the large ramp shows a more complicated wake structure of the boundary layer than the small ramp.