• Journal of Mechanical Science and Technology
• /
• 제18권10호
• /
• pp.1869-1879
• /
• 2004

The present study has numerically investigated two-dimensional flow over three circular cylinders in an equidistant side-by-side arrangement at a low Reynolds number. For the study, numerical simulations are performed, using the immersed boundary method, in the range of g* < 5 at Re= 100, where g* is the spacing between two adjacent cylinder surfaces divided by the cylinder diameter. Results show that the flow characteristics significantly depend on the gap spacing and a total of five kinds of wake patterns are observed over the range: modulation-synchronized (g* (equation omitted) 2), inphase-synchronized (g* (equation omitted) 1.5) , flip-flopping (0.3 < g* (equation omitted) 1.2) , deflected (g* (equation omitted) 0.3), and single bluff-body patterns (g* < 0.3). Moreover, the parallel and symmetric modes are also observed depending on g* in the regime of the flip-flopping pattern. The corresponding flow fields and statistics are presented to verify the observations.

• 대한기계학회논문집A
• /
• 제30권3호
• /
• pp.302-309
• /
• 2006

Effective mixing plays a crucial role in microfluidics for biochemical applications. Owing to the small device scale and its entailing the low Reynolds number, the mixing in microchannels proceeds very slowly. In this work, we optimize the configuration of obstacles in the Y-channel mixer in order to attain maximum mixing efficiency. Before the optimum design, mixing characteristics are investigated using unstructured grid CFD method. Then, the analysis method is employed to construct the approximate analysis model to be used in the optimization procedure. The main optimization tool in the present work is sequential quadratic programming method. Using this approximate optimization procedure, we may obtain the optimum layout of obstacles in the Y-channel mixer in an efficient manner, which gives the maximum mixing efficiency.

• 대한기계학회논문집B
• /
• 제26권7호
• /
• pp.1005-1013
• /
• 2002

Spin-up is a transient flow phenomenon occurring in a container when it starts to rotate from rest or its rotational speed increases from a low to high value. However, most studies on this subject have been for two-dimensional approximation. In this study, spin-up flows in a shallow rectangular container are analysed by using three-dimensional computation. We compared our results with those obtained by others using basically two-dimensional computation. Effect of two parameters, Reynolds number and liquid depth on the flow evolution is studied. We found that 2-D result is not accurate enough, and the vertical velocity distribution should be assumed of a fourth-order polynomial function for a better comparison.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1433-1436
• /
• 2008

Flagellate bacteria such as Escherichia coli or Serratia marcescens possess a remarkable motility system based on a reversible rotary motor. We have employed S. marcescens as microactuators in low Reynolds number fluidic environments to move a larger engineering element around. Microstructures fabricated using conventional microfabrication techniques are blotted on the swarm plate, which leaves a bacterial monolayer on the surface of the microstructure. We have investigated microstructures powered by bacteria to determine how cell orientation on the microstructure surface relates to the swarming patterns as well as how the orientation is affected by the blotting process. This study will help to refine directional control of bacterial transporters by exploiting bacterial sensory mechanisms.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1997년도 추계 학술대회논문집
• /
• pp.73-80
• /
• 1997

Objective of the present study is to examine the convergence characteristics of the various multi-stage Runge-Kutta methods in solving the incompressible Navier-Stokes equations of a time-marching from casted by the artificial compressibility method. Convergence characteristics are examined over 2-stage, 4-stage and hybrid type (using 4-, 3-, 2-stages sequentially) Runge-Kutta methods for a laminar lid-driven cavity flow, and also for a turbulent bump channel flow using Chien's low-Reynolds number turbulence model. Efforts are made to establish a stable and fast convergent multi-stage Runge-Kutta method with minimal artificial dissipations.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
• /
• pp.163-166
• /
• 2006

We have introduced a new version of the 3-D lid-driven cavity problem that leads to more complicated fluid parcel trajectories and thus, enhanced mixing, but at the same time weakens corner singularities. We employed an advanced form of LES to solve this problem and presented preliminary results that show very complicated streamline structures on both large and small scales, despite a relatively low Reynolds number. Finally, we demonstrated moderate speedups via parallelization. Ongoing tests are expected to resolve the questions raised regarding possible sources of the rather poor parallel performance compared with that seen in earlier studies with the same code. Because it is expected that findings may be significant for parallel performance in general, we plan to emphasize this aspect in the oral presentation the Parrel (CFD 2006 Conference.

• 한국화재소방학회:학술대회논문집
• /
• 한국화재소방학회 2008년도 춘계학술논문발표회 논문집
• /
• pp.234-237
• /
• 2008

A direct numerical simulation (DNS) code suitable for the prediction of buoyant jet diffusion flames was developed in this study. The thermodynamic and transport properties were evaluated using CHEMKIN package to enhance the prediction performance of the developed DNS code. A two dimensional simulations were performed for the jet diffusion flames in normal and zero-gravity conditions where the Froude numbers are 5 and infinity, respectively. The simulated buoyant jet diffusion flame in normal gravity showed that the unsteady and dynamic motion although the reynolds number is low (400). It was identified that the flame in normal gravity flickered periodically. The periodic motion of the flame disappeared in zero-gravity condition. The dynamic motion of the buoyant jet diffusion flame could be well understood by comparing the flame structures obtained by the simulations of normal and zero-gravity conditions.

• 한국가시화정보학회지
• /
• 제7권2호
• /
• pp.35-41
• /
• 2010

Supersonic microjets acquire considerable research interest from a fundamental fluid dynamics perspective, in part because the combination of highly compressible flow at low-to-moderate Reynolds number is not very common, and in part due to the complex nature of the flow itself. In addition, microjets have a great variety engineering applications such as micro-propulsion, MEMS(Micro-Electro Mechanical Systems) components, microjet actuators and fine particle deposition and removal. Numerical simulations have been carried out at moderate nozzle pressure ratios and for different nozzle exit diameters to investigate and to understand in-depth of aerodynamic characteristics of supersonic microjets.

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2004년도 학술발표회
• /
• pp.376-380
• /
• 2004

측벽이 존재하는 개수로 난류흐름에 대한 DNS 자료를 이용하여 난류의 비등방성을 해석하였다. 측벽의 2등분선(sidewall bisector)에서 난류강도의 분포를 통해 바닥과 자유수면에서의 비등방성을 분석하고, AIM을 도입하여 흐름장 전반에 걸쳐 세부적인 비등방성 해석을 수행하였다. 측벽의 2등분선에서의 난류강도의 분포를 통해 바닥과 자유수면 근처에서 난류강도가 강한 비등방성을 갖는 것을 볼 수 있었다. 또한 3개의 다른 영역에서 AIM의 도입을 통해 측벽이나 바닥근처에서는 난류의 비등방성이 구형 관수로 흐름과 유사한 것으로 나타났으나, 개수로 난류흐름의 주된 특성이 velocity-dip phenomena가 존재하는 영역에서는 구형 관수로 흐름과는 달리 천이영역이 존재한다는 것을 알 수 있었다.

• EDISON SW 활용 경진대회 논문집
• /
• 제3회(2014년)
• /
• pp.568-573
• /
• 2014

본 연구에서는 원형으로 모델링 된 실린더들에 균일한 유동이 흐를 때, 실린더들의 배치에 따른 이차원 층류 유동을 분석하였다. EDISON_CFD를 이용해서 실린더간의 거리와 주기적 배열에 따라 개별 실린더들의 항력계수와 평균 항력계수의 분석을 통해 항력계수가 최대가 되는 실린더 배열을 확인하였다. 이를 위해 계산영역과 최대격자수에 따른 정확도를 분석하였다. 가로 배열(tandem position)에서의 효율적 항력 거리를 확인하였다. 세로 배열(side-by-side position)에서의 효율적 항력 거리를 확인하였다. 위의 결과들로 9개의 실린더를 3개씩 3열로 배치하고, 주기적 배열과 엇갈림 배열로 나누어 효율적 항력 배치를 확인하였다.