• 한국추진공학회지
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• 제18권3호
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• pp.8-16
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• 2014

본 논문은 옆미끄럼각에 따른 초음속 흡입구 버즈마진의 영향도에 대해 분석하였다. 버즈마진은 비행체 종축면에서 획득한 측정 물리량 기반으로 제어 명령을 산출하는 제어기에 의해 안정화 된다고 가정하였다. 해당 분석은 3차원 CFD를 통해 획득한 결과를 기반으로 수행되었으며, 3차원 CFD 해석 데이터는 종축면의 센서 측정 물리량을 모사하기 위해 사용되었다. 종축면 측정치 기반의 제어시스템에서는 기대하지 않은 횡방향 유동 섭동이 총 받음각의 증가의 결과로 나타나며, 이는 엔진 흡입구 성능의 감소를 의미한다. 결과적으로, 제어 안정성 또한 줄어들게 되어 보다 큰 제어 마진이 요구됨을 확인할 수 있었다.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.285-295
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• 2016

A contact strip shape of a high speed train pantograph system was optimized with CFD to increase the aerodynamic performance and stability of contact force, and the results were validated by a wind tunnel test. For design of the optimal contact strip shape, a Kriging model and genetic algorithm were used to ensure the global search of the optimal point and reduce the computational cost. To enhance the performance and robustness of the contact strip for high speed pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack were selected as design objectives. Aerodynamic forces were measured by a load cell and HWA (Hot Wire Anemometer) was used to measure the Strouhal number of wake flow. PIV (Particle Image Velocimetry) was adopted to visualize the flow fields. The optimized contact strip shape was shown a lower drag with smaller fluctuation of vertical lift force than the general shaped contact strip. And the acoustic noise source strength of the optimized contact strip was also reduced. Finally, the reduction amount of drag and noise was assessed when the optimized contact strip was applied to three dimensional pantograph system.

• Journal of Advanced Marine Engineering and Technology
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• 제31권7호
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• pp.842-851
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• 2007

Oscillating foil propulsion, the engineering application of fish-like movement of a hydrofoil, has received in recent decades as a possible competitor for propellers. The oscillating foil produces an effective angle of attack, resulting in a normal force vector with thrust and lift components, and it can be expected to be a new highly effective propulsion system. We have explored propulsion hydrodynamics as a concept in wake flow pattern. The present study has been examined various conditions such as oscillating frequencies and amplitudes in NACA0010 profile. Flow visualizations showed that high thrust was associated with the generation of moderately strong vortices, which subsequently combine with trailing-edge vorticity leading to the formation of a reverse $K\acute{a}rm\acute{a}n$ vortex street. Vortex generation was inherent to jet production and playeda fundamental role in the wake dynamics. And it was shown that the strong thrust coefficient obtained as the Strouhal number was larger.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.303-308
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• 2006

HyShot 스크램제트 엔진의 연소 특성을 살펴보기 위해 수치해석을 수행하였다. 고도, 받음각, 당량비는 각각 28km, $0^{\circ}$, 0.426으로 주어졌다. $H_2$ 및 OH 질량 분율로부터 분사기 상류 재순환 영역의 화염지지기구 역할 및 주된 연소가 카울로부터 15cm 후방에서 시작됨을 알 수 있었다. 2차원 해석은 HyShot 스크램제트 엔진의 연소기 내부 압력을 비교적 잘 모사하고 있으며, 또한 주기적 연소 특성을 보여준다.

• 한국전산유체공학회지
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• 제12권2호
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• pp.37-45
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• 2007

The hybrid Cartesian/immersed boundary method is applied to simulate fluid-structure interaction of a two-dimensional orbiting flexible foil. The elastic deformation of the flexible foil is modelled based on the dynamic equation of a thin-plate. At each time step, the locations and velocities of the Lagrangian control points on the flexible foil are used to reconstruct the boundary conditions for the flow solver based on the hybrid staggered/non-staggered grid. To test the developed code, the flow fields around a flapping elliptical wing are calculated. The time history of the vertical force component and the evolution of the vorticity fields are compared with recent other computations and good agreement is achieved. For the orbiting flexible foil, the vorticity fields are compared with those of the case without the deformation. The combined effects of the angle of attack and the orbit on the deformation are investigated. The grid independency study is carried out for the computed time history of the deformation at the tip.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.388-393
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• 2001

An experimental study is conducted to investigate the interaction of vortices over a delta wing with leading edge extension(LEX) through the off-surface flow visualization and the 5-hole probe measurements of the wing wake region. Especially, the application of a new visualization technique is employed by ultrasonic humidifier water droplet and laser beam sheet. The results, both the off-surface visualization and the 5-hole probe, show that LEX tends to stabilize the vortices of the delta wing up to the high angle of attack even though the model is yawed. With increasing yaw, the windward leading edge vortex moves inward, and closer to the wing surface, while the leeward vortex moves outwards and away from the wing surface. The vortex interaction is promoted in the windward side, and is delayed in the leeward side.

• 한국항공우주학회지
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• 제34권4호
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• pp.1-10
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• 2006

비정상 공기역학적 해석코드와 동역학적 해석 프로그램이 연계된 코드를 이용하여 단분리 시스템의 유동해석과 함께 분리과정의 거동을 해석하였다. 본 연구는 일단 추진 모터를 가진 장거리 미사일 단분리과정 만을 연구대상으로 하였다. 연구의 목적은 이러한 단분리 시스템의 안전성과 신뢰도를 검증하기 위해 단분리 과정에 대한 비정상 동역학 시뮬레이션을 수행하였다. 특히 비행 중 받음각 요란에 의한 자유흐름 조건의 변화에 대해서도 시뮬레이션을 수행하여, 받음각 요란이 단분리의 안정성과 신뢰도에 미치는 영향을 알아보고자 하였다. 해석코드는 병렬화 된 중첩 정열격자계를 사용하여 비정상 초음속 오일러 코드로 공기역학적 해석을 한 후, 이 결과를 6자유도를 갖는 운동방정식의 입력 데이터로 하여 동역학적 시물레이션을 수행하였다.

• 한국해양공학회지
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• 제26권6호
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• pp.39-45
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• 2012

Underwater robots are generally used for the construction of seabed structures, deep-sea ecosystem research, ocean energy development, etc. A ducted marine propulsor is widely used for the thruster of an underwater robot because of its collision protection, efficiency increase, cavitation reduction, etc. However, the flow of a ducted propeller is very complex because it involves strong flow interactions between the blade impeller and duct. The present work aimed to design a ducted propeller using 2-D strip theory and CFD analysis. The hydrodynamic forces (i.e. and ) were computed to set the local angle of attack in a spanwise direction of the propeller blade. After the propeller design, performance coefficients such as the thrust, torque, and efficiency were computed to check whether the designed performance was achieved. To validate the present analysis, the thrust was compared with experimental data and good agreement was obtained.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.266-267
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• 2017

본 연구에서는 중첩된 두 비행물체에서 단분리 시 일어나는 주위 유동장 해석에 초점을 맞춰 해석을 수행하였다. 수치적인 해석을 위하여 정지된 비행체에서 분리되는 실린더 형태의 부스터를 중첩격자를 이용하여 모델링 하였으며 상용해석코드인 CFD-FASTRAN$^{TM}$을 사용하여 계산하였다. 실제 현상을 모사하기 위하여 경계조건 및 외력을 도출하였으며 각 비행조건에 따른 부스터 분리 시 주위 유동장 해석을 수행하였다. 단분리 시의 비행속도와 받음각 조건에 대한 해석결과를 이용하여 실제 분리 현상을 모사할 수 있는 수치적인 경계조건을 파악하고 안전한 단분리 예측에 본 연구결과를 활용하고자 한다.

• 한국가시화정보학회지
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• 제18권1호
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• pp.59-66
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• 2020

In the present study, we experimentally investigated the flow around a circular cylinder with axially arranged holes (AAH). The wind-tunnel experiment was performed at Re = 3.2 × 10⁴ while varying the angle of attack (α) from 0° to 90°. At low α, the passive jet from the AAH pushes near wake to the downstream, increasing the wake formation length. On the other hand, at high α, blowing and suction through AAH occurs alternatively, rather decreasing the wake formation length. The passive jet generated by AAH can effectively control not only the wake where AAH is located, but also the wake between holes. As a result, the AAH reduce the drag on the cylinder up to 23.8% at low α but rather increase the drag at high α, as compared to that on a smooth cylinder.