• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.638-642
• /
• 2016

현재 양력발생의 원리는 긴 경로 이론과 동시 통과 이론 등으로 알려져 있으며, 이 이론들은 간단히 설명하려는 목적으로 인해 양력발생의 원리가 와전되어왔다. 본 연구에서는 여러 양력발생의 원리 중 Kutta-Joukowski의 이론을 이용하여 순환을 통한 양력발생의 관계에 대해 연구를 수행하였다. 해석 모델은 대칭형 에어포일인 NACA0012를 이용하였다. 해석 프로그램으로는 EDISON을 이용하였으며 시간에 따른 와도를 확인하기 위해 비정상상태 해석을 진행하였다. 그 결과 유동이 시간의 경과에 따라 에어포일 뒷전으로 밀려나면서 Kutta-Joukowski의 이론에 중요한 논점인 출발 와류가 생성됨을 확인할 수 있었다. 이로 인해 순환이 형성되어 양력이 발생함을 추측할 수 있다. 추가적으로 받음각과 출발 와류 사이의 영향성을 연구하였다. 받음각이 커짐에 따라 출발 와류가 에어포일 뒷전에서 더 크게 발생하였고, 받음각이 낮아질수록 출발 와류의 진행이 가속화됨을 확인할 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.8
• /
• pp.729-736
• /
• 2009

In order to understand flow characteristics and flight mechanism of hummingbird's flapping flight, two-dimensional numerical analysis is carried out on the flapping motion of hummingbird, Selasphorus rufus. Hummingbird's flapping wing motion is realistically modeled from wind tunnel experimental data to perform numerical analysis. Numerical simulation shows that, as freestream velocity changes, wing trajectory is also adjusted and it substantially affects lift and thrust generation mechanism. According to this tendency, flight domain is separated as "low speed" and "high speed" regime, and each flight domain is studied for physical understanding. As a result, the lift generation during downstroke can be explained by the well-known effects, such as leading edge vortex effect, delayed stall, wake capture and so on. In addition, the lift generation during upstroke, the unique character of hummingbird, is also examined by detailed flow analysis. The thrust generation mechanism is investigated by examining the hummingbird's wing bone structure, vortex generation pattern and the resulting pressure gradient.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2009.05a
• /
• pp.919-923
• /
• 2009

케이블 교량에서 발생하는 사장케이블의 진동현상에 대한 현상학적 특성을 명확히 이해해야, 사장케이블의 적합한 제진설계가 가능하다. 본 연구에서는 ADINA CFD 코드를 이용하여, 이중원형실린더에서 발생하는 와류방출현상과 실린더에 작용하는 외력을 해석함으로써, 사장케이블에서 발생하는 진동현상의 원인을 규명하고자 하였다. 이를 위하여 본 연구에서는 흐름의 레이놀즈수, 실린더간 간격과 이중원형실린더에 대한 바람의 입사각을 변화시키며 이중원형실린더에서 발생하는 와류방출현상과 이로 인해 실린더에 작용하는 항력, 양력과 같은 외력을 분석하였다. 분석 결과, 풍상측 케이블에는 일방향의 항력이 주로 작용하므로 케이블 진동이 제한적으로 발생하나, 풍하측 케이블에는 항력과 같은 규모의 진동하는 양력이 작용하는 것으로 나타났으며 이로 인해 풍하측 케이블에서 진동이 크게 발생하는 것으로 나타났다.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.21 no.2
• /
• pp.200-206
• /
• 2015

In order to verify the lift enhancement of the 2D hydrofoil with trailing edge rotor and check the ability of its practical use, experimental studies were conducted in the caviation tunnel using the test model with NACA0020 section. The three-component forces acting on the model could be measured by exclusively designed sting type multi-component load cell. The trailing edge of the model has been replaced with rotor which could be controlled by DC servo motor installed at the exterior of the tunnel. A typical effect of the trailing edge rotor has been introduced among the systematic experiments on various angular deviation of the model and the rotational velocity of the trailing edge rotor. It is appeared that the circulation control effect could be easily adjusted by selecting the rotational velocity of the trailing edge rotor and the lift force was augmented more than two times. Thus the proposed lifting device could be utilized as a novel high lifting device which has adjustability of lift force.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.1
• /
• pp.1-9
• /
• 2007

Numerical simulation is conducted to investigate aerodynamic force generation mechanism for the "figure-of-eight" motion of Dipteran fly, Phormia-Regina. Wing trajectory is referred to experimental result, which was observed from the tethered flight under freestream condition. Numerical simulation shows that the lift is mainly generated during downstroke motion and the large amount of thrust is generated abruptly at the end of upstroke motion. In the present work, vortical structure in the wake and the pressure field around the airfoil are examined to understand the generation of lift and thrust. Consequently, the lift generation is related with the leading edge vortex which is developed by an effective angle of attack. And the thrust generation can be explained by vortex pairing in the flow field and by vortex staying in the pressure field.

• Journal of Aerospace System Engineering
• /
• v.17 no.6
• /
• pp.63-71
• /
• 2023

In the present study, the effect of pitch amplitude on the unsteady aerodynamics of a NACA 0012 airfoil is numerically investigated. When the frequency ratio is equal to 1.0, airfoil pitching with 20 and 30 degrees of pitch amplitude shows almost small lift generation, but the lift is significantly increased in case of 10-degree pitch amplitude. When the frequency is 0.5, the lift coefficients have large values, and the lift increases with a decrease in pitch amplitude. When the frequency ratio is 1.0, the airfoil generates large thrust. The thrust decreases as the pitch amplitude decreases. When the frequency ratio is 0.5, drag is generated for the 30-degree pitch amplitude, but the thrust is generated for 10-degree pitch amplitude. In future, the effect of heave amplitude on the unsteady aerodynamics of the airfoil will be studied.

• Proceedings of the Korean Information Science Society Conference
• /
• 2004.04a
• /
• pp.907-909
• /
• 2004

에어포일(airfoil)이 공기속을 지날 때 양력이 발생한다. 공간상을 비행하는 물체에는 중력, 추력, 양력, 항력의 네 가지 힘이 작용한다. 본 논문에서는 항공역학의 연구결과를 바탕으로 차이니즈탑이란 물체가 회전하면서 수직상승과 호버링 그리고 하강하는 동안의 운동형태를 사실적이면서도 실시간으로 구현한다. 그 결과는 게임이나 비행 시뮬레이션에 응용할 수 있다.

• Journal of the Society of Naval Architects of Korea
• /
• v.36 no.1
• /
• pp.22-29
• /
• 1999

In the development of high speed marine vehicle, lilting devices became important in sharing the pay load or controlling the attitude. The devices are also important to meet the IMO regulation to prevent the marine pollution by keeping the high rudder force for VLCC even in low speed operation. The high lift devices such as the Coanda device have been introduced to the aircraft as a common practice for a long time among the aero-engineers. If the Coanda device can be utilized to the flapped rudder, the severe requirement of rudder force could be provided for the VLCC in low speed operation. The performance of the rudder system has been investigated at the towing tank of Seoul National University.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.6
• /
• pp.653-663
• /
• 2012

The study considers the high maneuverability flight and path optimization is conducted to investigate the appropriate generation of the lift and thrust considering the angle of the stroke plane. The path optimization problem is defined according to the various purposes of the high maneuverability flight. The flying purposes are to maximize thrust force, lift force and both lift and thrust forces. The flapping motion of the airfoil is made by a combined sinusoidal plunging and pitching motion in each problem. The optimization process is carried out by using well-defined surrogate models. The surrogate model is determined by the results of two-dimensional computational fluid dynamics analysis. The Kriging method is used to make the surrogate model and a genetic algorithm is utilized to optimize the surrogate model. The optimization results show the flapping motions for the high maneuverable flight. The effects on the generation of lift and thrust forces are confirmed by analyzing the vortex.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.6
• /
• pp.10-17
• /
• 2006

NACA23012익형에 대하여 synthetic jet을 이용하여 박리 제어를 수행하였다. 공력특성의 향상을 위해 앞전 droop과 plain flap의 박리 부근에 synthetic jet을 위치시켰다. 고 받음각에서 앞전 박리의 발생으로 인한 실속을 앞전 droop의 작동과 이때 발생하는 앞전 박리를 synthetic jet으로 효과적으로 지연시킬 수 있고, 또한 실속 특성을 개선 할 수 있음을 확인하였다. 양력의 향상을 위하여 plain flap을 장착하였고, 이때 발생하는 박리를 synthetic jet으로 지연시켜 제어면의 작동 효율을 증가 시킬 수 있음을 확인하였다. 앞전 droop과 plain flap으로 구성된 간단한 고양력 장치에 발생하는 박리를 synthetic jet으로 제어함으로 실속을 지연시킴과 동시에 실속 특성을 향상시키고, 최대 양력의 증가로 fowler flap에 버금가는 공력특성을 확보할 수 있음을 확인하였다.