• Advances in aircraft and spacecraft science
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• 제6권6호
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• pp.497-513
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• 2019

A wind tunnel test was conducted that measured surface fluctuating pressures aft of a ramp at transonic speeds. Dynamic pressure test data was used to perform a study to determine best locations for streamwise sensor pairs for shocked and unshocked runs based on minimizing the error in root-mean-square acceleration response of the panel. For unshocked conditions, the upstream sensor is best placed at least 6.5 ramp heights downstream of the ramp, and the downstream sensor should be within 2 ramp heights from the upstream sensor. For shocked conditions, the upstream sensor should be between 1 and 7 ramp heights downstream of the shock, with the downstream sensor 2 to 3 ramp heights of the upstream sensor. The shock was found to prevent the passage coherent flow structures; therefore, it may be desired to use the shock to define the boundary of subzones for the purpose of loads definition. These recommendations should be generally applicable to a range of expansion corner geometries in transonic flow provided similar flow structures exist. The recommendations for shocked runs is more limited, relying on data from a single dataset with the shock located near the forward end of the region of interest.

• 한국항공우주학회지
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• 제31권5호
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• pp.93-99
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• 2003

극초음속 추진기관의 설계 및 평가에 있어 추력의 측정은 매우 중요하다. 일반적인 추력 측정방법으로는 추력 측정기를 사용하고 있지만 이러한 방법으론 엔진의 자유제트 실험이나 모델 연소기 같은 실험에는 적용이 부적절하다. 이 때문에 피토압력을 이용한 새로운 추력 계산 방법을 고려하였고 검증하였다. 피토 압력을 통해 계산된 추력의 검증은 추력측정기를 통해 측정된 실제 추력값과의 비료를 통해 이루어질 수 있으며 이를 위해 추력측정기 위에 소형 초음속 풍동을 장착하였다. 추력이 측정되는 동안 충동 후방의 피토압력을 동시에 측정하였다. 측정된 피토 압력을 이용하여 구한 추력값을 검증하기 위해서, 추력측정기로 측정한 추력을 완정팽창 노즐이론 및 추력계수를 이용한 이론적인 계산에 의해 구해진 추력값과 비료, 분석하였다.

• 한국항공우주학회지
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• 제39권9호
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• pp.816-822
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• 2011

본 연구에서는 프로펠러의 형상 및 환경 요소의 영향에 따른 추력값을 빠르게 계산할 수 있는 프로그램을 개발하였다. 여기서 유도 요소를 계산하기 위해서, 카와다에 의해 소개된 준-무한 나선와류 모델을 이용하였다. 본 code의 구조는 Wrench의 프로펠러 양력선 이론에 기초하여 제작되었으며, 프로펠러의 추력, 파워 및 효율 등의 공력값을 계산할 수 있다. 1차적인 프로그램의 신뢰성 있는 검증을 위해 NACA 보고서의 시험 결과와 비교 및 검증을 시행하였다. 2차적인 프로그램의 검증을 위해서는, 프로펠러 회전속도와 전진 속도에 변화를 주면서 아음속 풍동 시험을 수행하였다.

• International Journal of Railway
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• 제7권4호
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• pp.100-108
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• 2014

A numerical analysis method for predicting aerodynamic noise at inter-coach space of high-speed trains, validated by wind-tunnel experiments for limited speed range, is proposed. The wind-tunnel testing measurements of the train aerodynamic sound pressure level for the new generation Korean high-speed train have suggested that the inter-coach space aerodynamic noise varies approximately to the 7.7th power of the train speed. The observed high sensitivity serves as a motivation for the present investigation on elucidating the characteristics of noise emission at inter-coach space. As train speed increases, the effect of turbulent flows and vortex shedding is amplified, with concomitant increase in the aerodynamic noise. The turbulent flow field analysis demonstrates that vortex formation indeed causes generation of aerodynamic sound. For validation, numerical simulation and wind tunnel measurements are performed under identical conditions. The results show close correlation between the numerically derived and measured values, and with some adjustment, the results are found to be in good agreement. Thus validated, the numerical analysis procedure is applied to predict the aerodynamic noise level at inter-coach space. As the train gains speed, numerical simulation predicts increase in the overall aerodynamic sound emission level accompanied by an upward shift in the main frequency components of the sound. A contour mapping of the aerodynamic sound for the region enclosing the inter-coach space is presented.

• 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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• 제14권5호
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• pp.383-411
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• 2011

Roof is an integral part of building envelope. It protects occupants from environmental forces such as wind, rain, snow and others. Among those environmental forces, wind is a major factor that can cause structural roof damages. Roof due to wind actions can exhibit either flexible or rigid system responses. At present, a dynamic test procedure available is CSA A123.21-04 for the wind uplift resistance evaluation of flexible membrane-roofing systems and there is no dynamic test procedure available in North America for wind uplift resistance evaluation of rigid membrane-roofing system. In order to incorporate rigid membrane-roofing systems into the CSA A123.21-04 testing procedure, this paper presents the development of a load cycle. For this process, the present study compared the wind performance of rigid systems with the flexible systems. Analysis of the pressure time histories data using probability distribution function and power spectral density verified that these two roofs types exhibit different system responses under wind forces. Rain flow counting method was applied on the wind tunnel time histories data. Calculated wind load cycles were compared with the existing load cycle of CSA A123.21-04. With the input from the roof manufacturers and roofing associations, the developed load cycles had been generalized and extended to evaluate the ultimate wind uplift resistance capacity of rigid roofs. This new knowledge is integrated into the new edition of CSA A123.21-10 so that the standard can be used to evaluate wind uplift resistance capacity of membrane roofing systems.

• 한국항공우주학회지
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• 제40권6호
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• pp.475-484
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• 2012

익형 풍동시험 시 모델의 제작오차에 의해 시험 익형과 지지대 익형의 두께에서 차이가 있을 경우 시험 익형의 공력특성에 주는 영향을 양력, 항력 및 모멘트 값의 변화를 수치 해석하여 비교 및 분석하였다. 이를 위해 익형모델을 세 부분으로 나누어 제작하는 경우 가운데 위치하는 시험 익형을 기준 형상으로 하여 시험 익형 양쪽에 부착하여 지지대 역할을 하는 익형의 최대두께를 가운데 익형에 비해 작게 설정하였다. 익형모델은 NACA64- 418을 사용하였으며, 난류모델은 천이현상을 잘 예측할 수 있는 Transition SST를 사용하였다. 다양한 받음각과 레이놀즈 수에서 지지대 역할을 하는 익형모델과 두께 차이가 매우 큰 경우에도 가운데 위치한 시험 익형의 공력특성에 미치는 영향이 매우 작음을 확인하였다.

• 한국항공우주학회지
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• 제37권3호
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• pp.232-239
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• 2009

군용항공기에 탑재된 외부무장은 필요시 투하되기 위해서는 무엇보다도 먼저 안전한 분리가 이루어져야한다. 따라서 이러한 외부 장착물의 안전한 분리는 여러 가지 실험을 통해 사전에 반드시 검증이 이루어져야 한다. 본 논문은 전투기에 장착한 외부 장착물이 전투기로부터 분리 될 때 안전한 분리가 이루어지는가를 풍동실험을 통해 검증하기 위한 연구를 수행하였다. 이러한 무장분리문제와 관련된 풍동실험 기법으로 널리 활용되고 있는 자유낙하실험과 Grid test 기법을 사용되었다. 본 논문에서는 이러한 각 풍동실험 기법의 수행절차를 기술하고 각 기법의 실험결과로써 얻어진 데이터를 통해 무장투하가 사출기의 작동 여부와 관계없이 안전하게 분리됨을 확인하였으며, 각 기법에서 얻어진 결과가 모두 안전 제한치 내에 있음을 확인할 수 있었다.

• Wind and Structures
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• 제2권4호
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• pp.253-266
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• 1999

This paper presents the effects of free-stream turbulence on streamwise surface pressure fluctuations on two-dimensional rectangular cylinders. Particular attention is given to possible effects of turbulence integral scale on fluctuation and peak pressures. The mean, standard deviation, peak pressure coefficients, spectra and cross-correlation of fluctuating pressures were measured to investigate the nature of the separation and reattachment phenomenon in turbulent flows over a wide range of turbulence intensity and integral scale.

• Wind and Structures
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• 제23권4호
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• pp.313-350
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• 2016

Taipei 101 Tower, which has 101 stories with height of 508 m, is located in Taipei where typhoons and earthquakes commonly occur. It is currently the second tallest building in the world. Therefore, the dynamic performance of the super-tall building under strong wind actions requires particular attentions. In this study, Large Eddy Simulation (LES) integrated with a new inflow turbulence generator and a new sub-grid scale (SGS) model was conducted to simulate the wind loads on the super-tall building. Three-dimensional finite element model of Taipei 101 Tower was established and used to evaluate the wind-induced responses of the high-rise structure based on the simulated wind forces. The numerical results were found to be consistent with those measured from a vibration monitoring system installed in the building. Furthermore, the equivalent static wind loads on the building, which were computed by the time-domain and frequency-domain analysis, respectively, were in satisfactory agreement with available wind tunnel testing results. It has been demonstrated through the validation studies that the numerical framework presented in this paper, including the recommended SGS model, the inflow turbulence generation technique and associated numerical treatments, is a useful tool for evaluation of the wind loads and wind-induced responses of tall buildings.