• 동력기계공학회지
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• 제22권1호
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• pp.11-17
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• 2018

The steady-state, incompressible and three-dimensional numerical analysis was carried out to evaluate the internal flow fields characteristics of wind tunnel contractions made by Morel's curve equations. The turbulence model used in this study is a realizable ${\kappa}-{\varepsilon}$ well known to be excellent for predicting the performance of the flow separation and recirculation flow as well as the boundary layer with rotation and strong back pressure gradient. As a results, when the flow passes through the interior space of the analytical models, the flow resistance at the inlet of the plenum chamber is the largest at $Z_m=300$, 400 mm, but the smallest at $Z_m=700mm$. The maximum turbulence intensity in the test section is about 2.5% when calculated by the homogeneous flow, so it is improved by about 75% compared to the 10% turbulence intensity at the inlet of the plenum chamber due to the contraction.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.391-394
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• 2011

이 논문은 전투기나 미사일 등의 전면부에서 음속이상의 속도로 날아갈 때 발생하는 충격파의 각도와 영향을 수치데이터와 비교한 논문이다. 서울대학교 초음속풍동을 이용하여 원뿔형 모델에 대해서 마하수를 다르게 하여 충격파의 위치와 크기를 측정하여 보았다. 마하수 2.0, 3.0, 그리고 3.8에 대해서 실험을 수행했다. 그 결과 충격파의 위치와 크기는 실험의 속도, 받음각, 사이드 슬립각에 따라서 다르고 때에 따라 blockage effect가 발생한다는 것을 확인했다.

• 한국전산유체공학회지
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• 제10권2호
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• pp.60-68
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• 2005

For study on the unsteady wall interference effect, flows around a forced oscillating airfoil in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The Spalart-Allmaras one-equation model is employed for the turbulence effect. The computed results of the oscillating airfoil having a thin wake showed that the lift curve slope is increased and the magnitude of hysteresis loop is reduced by the interference effects. Since the vortex around the airfoil is generated and convected downstream faster than the free-air condition, the phase of lift, drag and pitching moment coefficients was shifted. The pressure on the test section wall shows harmonic terms having the oscillating frequency contained in the wail effect.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.35.1-35.1
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• 2011

When the wind speed is measured by the met-mast sensor it is distorted due to the shadow effect of tower. In this paper the tower shadow effect is analyzed by a computational fluid dynamics code. First three dimensional modeling and flow analysis of the met-mast system were performed. The results were compared with the available experimental wind-tunnel test data to confirm the validity of the meshes and turbulence model. Two-dimensional model was then developed based on the three-dimensional works and experimental data. 2D analysis for various Reynolds numbers and turbulence strengths were then performed to establish the tower shadow effect database, which can be utilized as correction factors for the measured wind energy.

• Wind and Structures
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• 제22권4호
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• pp.477-501
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• 2016

Though hilly topography influences both wind speeds and directions aloft, only the influence on wind speeds, i.e. the speed-up effect, has been thoroughly investigated. Due to the importance of a model showing the spatial variations of wind directions above hilly terrains, it is worthwhile to systematically assess the applicability and limitations of the model describing the influence of hilly topographies on wind directions. Based on wind-tunnel test results, a model, which describes the horizontal and vertical variations of the wind directions separately, has been proposed in a companion paper. CFD (Computational Fluid Dynamics) techniques were employed in the present paper to evaluate the applicability of the proposed model. From the investigation, it has been found that the model is acceptable for describing the vertical variation of wind directions by a shallow hill whose primary-to-secondary axis ratio (aspect ratio) is larger than 1. When the overall hill slope exceeds $20^{\circ}$, the proposed model should be used with caution. When the aspect ratio is less than 1, the proposed model is less accurate in predicting the spatial variation of wind directions in the wake zone in a separated flow. In addition, it has been found that local slope of a hill has significant impact on the applicability of the proposed model. Specifically, the proposed model is only applicable when local slope of a hill varies gradually from 0 (at the hill foot) to the maximum value (at the mid-slope point) and then to 0 (at the hill top).

• Wind and Structures
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• 제34권2호
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• pp.185-197
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• 2022

This study aimed to analyze the wind-induced mechanical energy (WME) of a proposed super high-rise and long-span transmission tower-line system (SHLTTS), which, in 2021, is the tallest tower-line system with the longest span. Anew index - the WME, accounting for the wind-induced vibration behavior of the whole system rather than the local part, was first proposed. The occurrence of the maximum WME for a transmission tower, with or without conductors, under synoptic winds, was analyzed, and the corresponding formulae were derived based on stochastic vibration theory. Some calculation data, such as the drag coefficient, dynamic parameters, windshielding areas, mass, calculation point coordinates, mode shape and influence function, derived from wind tunnel testing on reducedscale models and finite element software were used in calculating the maximum WME of the transmission tower under three cases. Then, the influence of conductors, wind speed, gradient wind height and wind yaw angle on WME components and the energy transfer relationship between substructures (transmission tower and conductor) were analyzed. The study showed that the presence of conductors increases the WME of transmission towers and changes the proportion of the mean component (MC), background component (BC) and resonant component (RC) for WME; The RC of WME is more susceptible to the wind speed change. Affected by the gradient wind height, the WME components decrease. With the RC decreasing the fastest and the MC decreasing the slowest; The WME reaches the its maximum value at the wind yaw angle of 30°. Due to the influence of three factors, namely: the long span of the conductors, the gradient wind height and the complex geometrical profile, it is important that the tower-line coupling effect, the potential for fatigue damage and the most unfavorable wind yaw angle should be given particular attention in the wind-resistant design of SHLTTSs

• Wind and Structures
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• 제30권2호
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• pp.181-198
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• 2020

In the traditional buffeting response analysis method, the spanwise incomplete correlation of buffeting forces is always assumed to be same as that of the incident wind turbulence and the action of the signature turbulence is ignored. In this paper, three typical bridge decks usually adopted in the real bridge engineering, a single flat box deck, a central slotted box deck and a two-separated paralleled box deck, were employed as the investigated objects. The wind induced pressure on these bridge decks were measured via a series of wind tunnel pressure tests of the sectional models. The influences of the wind speed in the tests, the angle of attack, the turbulence intensity and the characteristic distance were taken into account and discussed. The spanwise root coherence of buffeting forces was also compared with that of the incidence turbulence. The signature turbulence effect on the spanwise root coherence function was decomposed and explained by a new empirical method with a double-variable model. Finally, the formula of a sum of rational fractions that accounted for the signature turbulence effect was proposed in order to fit the results of the spanwise root coherence function. The results show that, the spanwise root coherence of the drag force agrees with that of incidence turbulence in some range of the reduced frequency but disagree in the mostly reduced frequency. The spanwise root coherence of the lift force and the torsional moment is much larger than that of the incidence turbulence. The influences of the wind speed and the angle of attack are slight, and they can be ignored in the wind tunnel test. The spanwise coherence function often involves several narrow peaks due to the signature turbulence effect in the high reduced frequency zone. The spanwise coherence function is related to the spanwise separation distance and the spanwise integral length scales, and the signature turbulence effect is related to the deck-width-related reduced frequency.

• 한국항공우주학회지
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• 제35권11호
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• pp.964-972
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• 2007

공기역학적으로 최대동력계수를 얻을 수 있도록 최적화된 블레이드를 장착한 수평축 풍력터빈 모델을 아음속 풍동에 장착하여 공력특성을 실험하였다. Upwind 방식과 downwind방식의 풍력 터빈 로터의 공력 특성을 비교하였을 때, 후자가 전자에 비해 측정토크의 교란이 더 크게 나타났으며, 이는 지지대에서 발생된 후류와 블레이드의 상호간섭이 원인으로 작용한다고 여겨진다. 블레이드 설치각이 0o인 경우에 설계 속도비 6에 해당하는 위치에서 최대 동력계수를 보여주고 있어 설계 조건을 잘 만족함을 알 수 있었다. 또한 음의 피치각 변화가 같은 값의 양의 피치각 변화에 비해 더 커다란 동력 감소가 발생되는 결과를 보여주었다.

• 한국강구조학회 논문집
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• 제9권2호통권31호
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• pp.259-267
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• 1997

본 연구에서는 주 케이블에 횡방향 새그를 가진 자정식 현수교의 내풍안정성을 검토하기 위하여 풍동실험을 수행하고, 주형의 거동을 중심으로 그 결과를 분석하였다. 등류와 난류하에서 수행한 부분 모형 실험에서 가장 내풍안정성이 뛰어난 단면을 최종단면으로 선정하고, 전교 모형 실험을 통하여 검증하였다. 또한 차후 연구를 위한 플러터 계수를 측정하여 제시하였다. 교량의 사용성과 피로문제를 검토하기 위하여 버페팅 응답을 조사하였지만, 공학적 관점에서 만족할 만한 수준인 것으로 나타났다. 주형의 항력계수가 상당히 큼에도 불구하고 횡방향 변위가 매우 작게 나타났는데, 이는 주 케이블의 횡방향 새그가 주형의 변위를 구속하기 때문인 것으로 판단된다.

• 한국강구조학회 논문집
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• 제21권3호
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• pp.245-255
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• 2009

산업용 건축물은 일반적으로 박공지붕형 저층의 형태로 많이 건설된다. 본 연구는 박공지붕형 저층건물의 풍압분포와 특성을 알아보기 위하여 풍동실험을 수행하였다. 풍동실험은 경사각 변화에 따른 외장재용 피크외압계수 분포양상을 알아보기 위하여 동일한 폭과 높이, 길이를 가지지만 지붕 경사각이 서로 다른 7가지의 모형을 제작하여 실험하였다. 실험결과 지붕과 벽면의 모서리 부분에서 최대 피크외압계수가 나타났으며, 이를 KBC-2005 및 각국의 기준과 비교하여 보았다. 실험에 의한 피크외압계수는 AIJ-2004와 매우 유사하게 나타났지만 KBC -2005보다는 다소 크게 나타났다.