• 한국항공우주학회지
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• 제37권12호
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• pp.1173-1183
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• 2009

스마트 무인기 익형 주위의 유동 구조를 파악하고 이를 바탕으로 synthetic jet을 이용하여 정지 비행 모드에서의 수익하중 감소 여부를 파악하였다. 스마트 무인기의 실제 비행 모드에 대하여 유동 구조를 분석하여 앞전 및 뒷전에서 발생하는 와류에 의해서 수익 하중이 크게 증가함을 밝혔다. 이에 앞전과 뒷전에서 발생하는 유동의 박리를 제어하기 위하여 0.01c, $0.3c_{flap}$, $0.95c_{flap}$ 위치에 jet을 위치시켰다. 또한 무차원 주파수(F+)의 변화에 따른 유동 구조 변화와 항력 감소율을 알아보았다. 그 결과, 와류의 유동 구조를 변화시켜 앞전과 뒷전에서 발생하는 거대한 와류의 박리 주기를 짧게 하고 와류의 크기를 감소시켜 정지 비행 모드에서 수익 하중을 효과적으로 감소시킬 수 있었다.

• 대한기계학회논문집B
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• 제26권12호
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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.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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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.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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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.

• 대한기계학회논문집B
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• 제27권3호
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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.

• 대한기계학회논문집B
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• 제25권11호
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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.

• 한국가시화정보학회지
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• 제21권2호
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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.