• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.8
• /
• pp.899-906
• /
• 2005

It is known that an oscillating airfoil can Produce a driving force through the generation of a reversed $K\'{a}rm\'{a}n$ vortex street, and this can be expected to be a new highly effective propulsion system. The wake formation behind the heaving airfoil was visualized and was measured using PIV systems We have been examined various conditions such as frequency number, amplitude in NACA 0010. As Strouhal number is greater than 0.08. wake profile with velocity deficit can be transformed into the wake with velocity excess After evaluating vortex center flow patterns in the wake investigated using tracking trajectories in temporal evaluation of the shedding vortices. We also Presented the experimental results on the unsteady vortices structure of the heaving airfoil at various parameters.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.2E
• /
• pp.85-88
• /
• 2006

Blade-vortex interaction (BVI) is one of the most important phenomena in rotor flow since it causes undesirable intense vibration and noise. Since three dimensional Euler or Navier-Stokes solutions to BVI require very high computational cost, BVI has been approximated by airfoil-vortex interaction (AVI) in chordwise planes. To describe more realistic situations with AVI, three dimensional vortex informations such as position, core size and strength are embedded artificially to Computational Aeroacoustics (CAA) calculation at each computational time step. To implement this requirement, in this paper, a technique called free vortex embedded method was used. And the solution by this method was compared with the solution by conventional method for interaction between freely convected vortex and airfoil. For the application to three dimensional free vortex embedded CAA, two dimensional free vortex embedded CAA method was validated in advance.

• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.358-361
• /
• 2010

A Reynolds-Averaged Navier-Stokes (RANS) code with transition prediction model is developed and the computational results on an oscillating airfoil are compared with the experimental data for OA209 airfoil. An approximated eN method that can predict transition onset points and the length of transition region is directly applied to the RANS code. The hysteresis loop in dynamic stall is compared for the computational results using transition prediction and fully turbulent models with the experimental data. Results with transition prediction show more correlation with the experimental data than the fully turbulent computation.

• Journal of computational fluids engineering
• /
• v.19 no.1
• /
• pp.80-86
• /
• 2014

Numerical investigation on the dynamic stall over an oscillating airfoil is presented. A Reynolds-Averaged Navier-Stokes (RANS) equations are coupled with transition transport equations for the natural transition. Computational results considering the turbulent transition are compared with the fully turbulent computations and the experimental data. Results with transition prediction show closer correlation with the experimental data than those with the fully turbulent assumption, especially in the reattachment region.

• Journal of computational fluids engineering
• /
• v.14 no.2
• /
• pp.25-31
• /
• 2009

Numerical optimization of rotor blade airfoils is performed with a response surface method for helicopter rotor. For the baseline airfoils, OA 312, OA 309, and OA 407 airfoils are selected and optimized to improve aerodynamic performance. Aerodynamic coefficients required for the response surface method are obtained by using Navier-Stokes solver with k-$\omega$ Shear Stress Transport turbulence model. An optimized airfoil has increased drag divergence Mach number. The present design optimization method can generate an optimized airfoil with multiple design constraints, whenever it is designed from different baseline airfoils at the same design condition.

• Proceeding of EDISON Challenge
• /
• 2013.04a
• /
• pp.415-420
• /
• 2013

천음속 영역에서 비행하는 에어포일 주위의 유동은 아음속 영역과는 달리 충격파(Shockwave)를 동반하고 이에 따라 복잡한 유동 현상이 발생한다. 본 연구는 천음속 영역에서 설계된 에어포일 주위의 유동에서 충격파 발생에 따른 유동변화의 특징들을 관찰하였다. 특히, 충격파에 의해서 발생하는 진동(Buffeting)과 경계층 유동 박리(Shock-induced boundary layer separation)현상에 대한 관찰과 일반적인 에어포일과 초임계 에어포일(Supercritical airfoil)간의 유동 특성의 차이점을 분석하였다. 본 연구를 위해서 EDISON CFD코드가 사용되었다.

• Proceeding of EDISON Challenge
• /
• 2013.04a
• /
• pp.365-370
• /
• 2013

현대에 이르러 초음속 운영 영역에서의 항공기에 대한 많은 연구가 진행되고 있으나, 음속 폭음 현상과 충격파 현상에서 야기된 높은 항력 및 연료 효율성 저하로 인하여 그 한계에 부딪치고 있다. Busemann 복엽 익형은 이와 같은 문제를 해결하기 위한 형상이며, 상하 형상에 의한 파동 상쇄효과 및 파동 감소효과를 통해 충격파의 강도와 음속 폭음 효과를 감소시키는 형상이다. 하지만 본 익형은 탈설계 조건에서 항력 계수가 급격하게 증가하는 등의 문제점을 가지고 있다. 본 연구에서는 EDISON_CFD를 이용하여 Busemann 복엽 익형의 주변 유동 특성에 대하여 면밀한 고찰을 수행하였다. 우선 Busemann 복엽 익형의 초기 형상에 대한 유동 조건별 해석을 통하여 탈설계 조건에서의 항력 성능 저하 문제에 대한 고찰을 하였다. 이후 3개의 형상 변수에 대한 매개 변수 연구를 통하여 익형의 각 형상 변수가 탈설계 영역 및 해당 영역에서의 최대 항력 계수에 미치는 영향에 대한 고찰을 수행하였으며, 이를 통하여 기존 형상보다 좁은 탈설계 구간을 가지고, 최대 항력 계수가 약 34.8% 감소한 부스만 복엽 익형을 설계하였다.

• Wind and Structures
• /
• v.32 no.1
• /
• pp.47-53
• /
• 2021

This paper proposes a novel diffuser design for Diffuser Augmented Wind Turbines (DAWT) based on the blunt trailing edge airfoil AF300. Computational Fluid Dynamics (CFD) simulations are carried out to measure the performance of the AF300 diffuser against diffusers made with the shape of other high performance low wind speed airfoils. The results show that the proposed diffuser produces a greater air mass flow increase through the plane of the turbine than the other diffusers and it can be used to increase the performance of a horizontal axis wind turbine.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.3
• /
• pp.212-216
• /
• 2017

Aerodynamic analysis for the airfoil, KARI-11-180 having 18% thickness ratio, was performed with CFD techniques. The boundary layer grid was generated by projecting the wall grid normally and fine grid was placed behind the trailing edge to capture the wake accurately. The distance to the far boundary is 100 chords and the flow condition is same as the wind tunnel test condition. Transition SST and DES turbulence models were utilized for accurate prediction of the transiton point. The predicted lift is higher but the drag is predicted lower than the wind tunnel test. 3-dimensional results with airfoil models of which aspect ratio were 2 and 5 were compared with 2-dimensional results.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.1795-1800
• /
• 2003

An experimental study was carried out to investigate near-wake characteristics of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched about the half chord point between $-5^{\circ}C$ and $+25^{\circ}C$ angles of attack at the freestream velocities of 3.4 and 23.1 m/s The corresponding Reynolds numbers based on the chord length were $3.3{\times}10^4$ and $2.2{\times}10^5$, respectively. A hot-wire anemometer was used to measure the near-wake flow variable at the reduced frequency of 0.1. Ensemble-averaged velocity and turbulence intensity profile were presented to examine the near-wake characteristics depending on the Reynolds number. The axial velocity deficit in the near-wake region tend to decrease with the increase in the Reynolds number a found in many stationary airfoil test . Turbulence intensity in the near-wake region have a tendency to decrease with the increase in the Reynolds number during the pitch-up motion, whereas it shows different feature during the pitch-down motion either the laminar boundary layer or turbulent boundary layer separation.