• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.467-470
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• 2002

The offects of a small control rod (d=3mm) located near a main circular cylinder on the drag reduction and wake structure modification were investigated. The location of the small control rod mounted on a rod-like spring is self-adjusting according to the wake structure far optimal control of the flow around the main cylinder. The experiments were carried out at the Reynolds numbers based on the cylinder diameter (D=50mm) in the range $Re_{D}=1{\times}10^4{\~}6{\times}10^4$. Mean velocity and turbulent statistics were measured with varying the angle along the cylinder circumference ${\Theta}=15^{\circ},\;30^{\circ},\;45^{\circ}$ and the distance between the main and control rods L =0.7, 1. Compared with the bare cylinder, the main circular cylinder with the fixed and self-adjusting rods reduced drag coefficient by $10{\%}$ at the angle of ${\Theta}=45^{\circ}$. For the main cylinder with self-adjusting rot as the Reynolds numbers increase, the streamwise mean velocity is increased, however, the turbulence intensity is decreased. In addition, the control rods tested in this study are effective at higher Reynolds number than at lower Reynolds number.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.825-830
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• 2004

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc (DCA) compressor cascades. Two types of double-circular-arc cascades were used in this analysis. The appropriate turbulence model for compressor analysis was selected among the conventional turbulence models such as Baldwin-Lomax, k-$\varepsilon$ and k-$\varepsilon$ models. The results of current study were compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE/PWIM algorithm for collocated grid and hybrid scheme for the convective terms were the main features of numerical tools. As commonly known, turbulence modeling is very important for the prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. For selection of turbulence model, 2-D analysis was performed. And then, k-$\varepsilon$ turbulence model with wall function chosen as the reasonable turbulence model for 3-D calculation was used to increase the efficiency of computation times. A reasonable result of 3-D flow pattern passing through the double-circular-arc cascade was obtained.

• 대한조선학회논문집
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• 제28권2호
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• pp.146-158
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• 1991

2차원 날개 단면 주위의 유동을 레이저 유속계측장치(LDV)를 이용하여 계측하였다. 레이저 유속계측장치는 주위 유동에 영향을 주지 않으면서 물체 주위의 유속을 정밀하게 계측할 수 있는 장비로서 본 논문에서는 2W Ar-Ion 레이져 광선을 이용한 2색 3선형 레이저 시스템을 사용하여 2방향 속도를 동시에 계측하였다. 레이저유속 계측장치를 사용하여 NACA0012 단면 주위의 유동을 계측한 후 난류경계층, 박리현상(Separation) 및 날개 뒷날에서의 유동 현상등에 대한 해석을 수행하였다. 계측된 유동장의 해석 결과를 Head의 운동량 적분법에 의한 계산결과와 비교하였다. 입사각이 작고 레이놀드수가 비교적 큰 경우에는 계측결과에 의한 경계층 특성과 운동량 적분법에 의한 계산결과가 잘 일치함을 보였다. 2차원 날개단면 주위 유동을 정밀 계측하여 수치계산 방법에 의한 결과와의 비교를 위한 유동계측 자료를 확보하였으며 캐비테이션 특징 및 양력특성이 우수한 새로운 날개단면 개발에 응용될 수 있는 2차원 단면시험법을 개발하였다.

• EDISON SW 활용 경진대회 논문집
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• 제1회(2012년)
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• pp.81-84
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• 2012

항공기 설계에서 중요한 해석 대상중의 하나인 에어포일 NACA 4412 형상을 2차원 난류 점성유동으로 접근하여 일정 받음각에 따른 유동 현상을 실험 결과와 비교해 보았다. 또한, 역압력구배, 유동 박리, 와류 등의 현상이 어디에서 어떻게 생성되는지 해석을 통하여 분석해 보았다.

• Journal of Mechanical Science and Technology
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• 제17권8호
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• pp.1234-1245
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• 2003

An experimental study was carried out to investigate the reduced frequency effect on the near-wake of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched around the center of the chord between -5$^{\circ}$and ＋25$^{\circ}$angles of attack at an airspeed of 3.4 m/s. The chord Reynolds number and reduced frequencies were 3.3 ${\times}$10$^4$, and 0.1, 0.7, respectively Phase-averaged axial velocity and turbulent intensity profiles are presented to show the reduced frequency effects on the near-wake behind the airfoil oscillating In pitch. Axial velocity defects in the near-wake region have a tendency to increase in response to a reduced frequency during pitch up motion, whereas it tends to decrease during pitch down motion at a positive angle of attack. Turbulent intensity at positive angles of attack during the pitch up motion decreased in response to a reduced frequency, whereas turbulent intensity during the pitch down motion varies considerably with downstream stations. Although the true instantaneous angle of attack compensated for a phase-lag is large, the wake thickness of an oscillating airfoil is not always large because of laminar or turbulent separation.

• 항공우주기술
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• 제8권1호
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• pp.197-206
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• 2009

스마트 무인기의 공력특성을 향상시키기 위하여 주익에는 와류생성기(vortex generator), 주익의 끝단에는 유동펜스(flow fence)를 적용하였다. 와류생성기는 SUAV의 최대양력계수와 실속각을 지연시키는 효과가 있었지만 높은 항력증가를 초래하여, 결국에는 양항비가 줄어들었다. 이를 개선하기 위하여 L-형태와 높이가 3mm와 5mm인 와류생성기를 적용하였다. 유동펜스는 나셀 틸팅각이 증가함에 따라 나셀에서 발생하는 박리에 의하여 주익성능이 감소하는 현상을 방지하기 위하여 사용하였다. 두 가지 유동제어 장치를 사용함에 따라 스마트 무인기의 공력특성들이 어떻게 변화하였는지를 정리하였다.

• 한국자동차공학회논문집
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• 제15권5호
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• pp.63-71
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• 2007

The conversion efficiency, durability and pressure drop of the automotive exhaust catalysts are dependent on the flow distribution within the substrate. Conventional porous medium approaches assuming monolith resistance based on the one-dimensional laminar flow for simulating the flow through the automotive exhaust catalysts over-predict the flow uniformity in the monolith. In this study, additional pressure loss is also considered by accounting for entrance effects due to the oblique flow incident on the front face of monolith as a consequence of flow separation and recirculation within the diffuser. The incorporation of an additional pressure loss improves the predictions for the maximum flow velocity within the substrate. An numerical study has also been conducted for the three-dimensional unsteady incompressible non-reacting flow inside various dual-monolith catalytic converters for the rapid acceleration/deceleration driving.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.60-60
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• 2021

Investigating Backward-Facing Step(BFS) flow is important in that it is a representative case for separation flows in various engineering flow systems. There have been a wide range of experimental, theoretical, and numerical studies to investigate the flow characteristics over BFS, such as flow separation, reattachment length and recirculation zone. However, most of such previous studies were concentrated only on the perpendicular step angle. In this study, several numerical investigations on the flow pattern over BFS with various step angles (10° ~ 90°) and expansion ratios (1.48, 2 and 3.27) under different Reynolds numbers (5000 ~ 64000) were carried out, mainly focused on the reattachment length. The numerical simulations were performed using an open source 3D CFD software, OpenFOAM, in which the velocity profiles and turbulence intensities are calculated by RANS (Reynolds Averaged Navier-Stokes equation) and 3D LES (Large Eddy Simulation) turbulence models. Overall, it shows a good agreement between simulations and the experimental data by Ruck and Makiola (1993). In comparison with the results obtained from RANS and 3D LES, it was shown that 3D LES model can capture much better and more details on the velocity profiles, turbulence intensities, and reattachment length behind the step for relatively low Reynolds number(Re < 11000) cases. However, the simulation results by both of RANS and 3D LES showed very good agreement with the experimental data for the high Reynolds number cases(Re > 11000). For Re > 11000, the reattachment length is no longer dependent on the Reynolds number, and it tends to be nearly constant for the step angles larger than 30°.) Based on the calibrated and validated numerical simulations, several additional numerical simulations were also conducted with higher Reynolds number and another expansion ratio which were not considered in the experiments by Ruck and Makiola (1993).

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2001년도 Proceedings of 2001 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.151-163
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• 2001

A two color PIV technique has been developed for visualization of complex and high speed flow in a ramjet combustor. Two color PIV has the advantages that velocity distributions in high speed flowfields can be measured simply by varying the time interval between two different laser beams and a directional ambiguity problem can be solved by color separation, and then a signal-to-noise ratio can be increased through nearly perfect cross-correlation. As a basic research of the ramjet engine, a 2-D shaped combustor with two symmetric air intakes has been manufactured and an experimental study has been conducted using a two color PIV technique. The flow characteristics such as recirculation zones, intake air mixing and turbulent kinetic energy have been investigated varying inlet angles and dome heights. It was found that the primary recirculation zone is affected mainly by the dome height, whereas the secondary recirculation zone is influenced by the air inlet angle.

• 대한기계학회논문집B
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• 제28권7호
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• pp.800-808
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• 2004

Wind tunnel test of an airplane model with forward swept wing was done in KARI LSWT to evaluate and measure the aerodynamic characteristics of initially designed configuration. Since the given wing planform did not fully satisfy the design requirements, local flow control devices such as vortilon, vortex generator and flow fence were used to delay separation and to enhance aerodynamic characteristics. Also decision making processes of design parameters such as vertical tail boom length, the location, size and the incidence angle of horizontal tail were discussed. The general aerodynamic characteristics of forward swept wing for various control surface deflection conditions of flap, aileron and elevator were also given.