• 제목/요약/키워드: Aerodynamic Coefficient

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고속열차 주위의 점성 압축성 2차원 유동해석 (Numerical Analysis of 2-Dimensional Viscous Compressible Flow around the High Speed Train)

  • 하성도;김유일
    • 연구논문집
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    • 통권25호
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    • pp.13-22
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    • 1995
  • At the running speed higher than 250 km/h, several aerodynamic problems such as the increase of aerodynamic resistance, aerodynamic noise, pressure fluctuation at the tunnel entry, impulsive wave at the tunnel exit bring about the power consumption, deterioration of riding quality, and severe environmental noise. To solve these aerodynamic problems, the flow phenomena around the high speed train have to be analyzed in detail. In this study, the flow around the train is modelled as the 2-dimensional viscous compressible flow and the flow field is calculated numerically for the three different types of geometry and running speed. The aerodynamic drag coefficient and the pressure coefficient are evaluated each case.

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끝틈새가 선회각이 큰 터빈 동익 익렬 후류영역에서의 3차원유동 및 압력손실에 미치는 영향 (The Effect of Tip Clearance Height on the Three-Dimensional Flow and Aerodynamic Loss in the Wake Region of a High-Turning Turbine Rotor Cascade)

  • 권현구;박진재;이상우
    • 한국유체기계학회 논문집
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    • 제7권5호
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    • pp.36-42
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    • 2004
  • The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

에어포일 공력 성능 예측을 위한 딥러닝 기반 방법론 연구 (Deep learning-based Approach for Prediction of Airfoil Aerodynamic Performance)

  • 천성우;정호진;박민규;정인호;조해성;기영중
    • 항공우주시스템공학회지
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    • 제16권4호
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    • pp.17-27
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    • 2022
  • 본 논문에서는 에어포일의 좌표 데이터에 대해 공력 특성을 예측할 수 있는 합성곱 신경망 기반 네트워크 프레임 워크를 설계하였으며 Xfoil을 이용한 공력 데이터를 적용하여 네트워크의 가능성을 확인하였다. 이 때 에어포일의 두께 변화에 따른 공력 특성 예측을 수행하였다. 부호화 거리 함수를 이용하여 에어포일의 좌표 데이터를 이미지 데이터로 변환하였으며 받음각 정보를 반영하였다. 또한 에어포일의 압력 계수 분포를 축소 모델 기법 중 하나인 적합 직교 분해를 이용하여 축소된 데이터로 표현하였으며 이를 네트워크의 출력 데이터로 사용하였다. 제시하는 네트워크의 내삽과 외삽 성능을 평가하기 위하여 시험 데이터를 구성하였고, 결과적으로 내삽 데이터에 대한 예측 성능이 외삽에 비해 우수함을 확인하였다.

전산유체역학 해석에 의한 교량 단면의 공력 특성값 추정 (Prediction of Aerodynamic Coefficients of Bridges Using Computational Fluid Dynamics)

  • 홍영길
    • 한국안전학회지
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    • 제28권1호
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    • pp.57-62
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    • 2013
  • Aerodynamic characteristics of cross section shape is an important parameter for the wind response and structural stability of long span bridges. Numerical simulation methods have been introduced to estimate the aerodynamic characteristics for more detailed flow analysis and cost saving in place of existing wind tunnel experiment. In this study, the computational fluid dynamics(CFD) simulation and large eddy simulation( LES) technique were used to estimate lift, drag and moment coefficients of four cross sections. The Strouhal numbers were also determined by the fast Fourier transform of time series of the lift coefficient. The values from simulations and references were in a good agreement with average difference of 16.7% in coefficients and 8.5% in the Strouhal numbers. The success of the simulations is expected to attribute to the practical use of numerical estimation in construction engineering and wind load analysis.

가변속도-가변피치 풍력터빈의 공기역학적 토크의 비선형 특성에 관한 고찰 (An Investigation on Nonlinear Characteristics of Aerodynamic Torque for Variable-Speed Variable-Pitch Wind Turbine)

  • 임채욱
    • 한국유체기계학회 논문집
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    • 제14권2호
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    • pp.29-34
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    • 2011
  • Aerodynamic torque of wind turbine is highly nonlinear due to the nonlinear interactions between wind and blade. The aerodynamic nonlinearity is represented by nonlinear power and torque coefficients which are functions of wind speed, rotational speed of rotor, and pitch angle of blade. It is essential from the viewpoint of understanding and analysis of dynamic characteristics for wind turbine to linearize the aerodynamic torque and define aerodynamic nonlinear parameters as derivatives of aerodynamic torque with respect to the three parameters. In this paper, a linearization method of the aerodynamic torque from power coefficient is presented through differentiating it by the three parameters. And steady-state values of three aerodynamic nonlinear parameters according to wind speed are obtained and their nonlinear characteristics are investigated.

리어가이더 선단각도에 따른 룸에어콘용 관류홴의 공력성능에 관한 실험적 연구 (Experimental Study on the Aerodynamic Performance of a Cross-Flow Fan for the Various Leading Angles of a Rear-Guider for a Room Air-Conditioner)

  • 김장권;오석형
    • 동력기계공학회지
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    • 제17권3호
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    • pp.35-43
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    • 2013
  • Generally, the chassis of an indoor RAC is composed of a rear-guider and a stabilizer. The aerodynamic performance of a cross-flow fan is strongly influenced by the various design factors of the chassis of an indoor RAC. The purpose of this paper is to select the optimum design factors through the aerodynamic performance of a cross-flow fan. The design factors are the leading angle of a rear-guider (${\theta}_1$), a stabilizer setup angle(${\theta}_2$), a rear-guider clearance(${\epsilon}_1$), and a stabilizer clearance(${\epsilon}_2$), respectively. As a result, the optimum design factors of an indoor RAC can be presented as a combination of ${\theta}_1=33^{\circ}$, ${\theta}_2=55^{\circ}$, ${\epsilon}_1=6{\sim}8mm$, and ${\epsilon}_2=7mm$ through the analysis of a static pressure coefficient and a static pressure efficiency.

룸에어콘 실내기의 설계인자 변화에 따른 관류홴의 공력성능 연구 (Study on the Aerodynamic Performance of a Cross-Flow Fan for the Various Design Factors of an Indoor Room Air-Conditioner)

  • 김장권;정규조
    • 동력기계공학회지
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    • 제9권3호
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    • pp.33-38
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    • 2005
  • The aerodynamic performance of a cross-flow fan is strongly influenced by the various design factors of a rear-guider and a stabilizer. The purpose of this paper is to investigate the effects of a rear-guider and a stabilizer on the aerodynamic performance of a cross-flow fan. The design factors considered in this paper are a rear-guider clearance, a stabilizer clearance, and a stabilizer setup angle, respectively. This experiment was carried out with a constant revolution number of 700 rpm in a cross-flow fan installed in the fan tester. The static pressure, flowrate, torque, and revolution number were measured in this paper. Also, the pressure coefficient and the efficiency were analysed according to the various assembly conditions using a stabilizer setup angle, a stabilizer clearance, and a rear-guider clearance in the indoor room air-conditioner.

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Aerodynamic effects of subgrade-tunnel transition on high-speed railway by wind tunnel tests

  • Zhang, Jingyu;Zhang, Mingjin;Li, Yongle;Fang, Chen
    • Wind and Structures
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    • 제28권4호
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    • pp.203-213
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    • 2019
  • The topography and geomorphology are complex and changeable in western China, so the railway transition section is common. To investigate the aerodynamic effect of the subgrade-tunnel transition section, including a cutting-tunnel transition section, an embankment-tunnel transition section and two typical scenarios for rail infrastructures, is selected as research objects. In this paper, models of standard cutting, embankment and CRH2 high-speed train with the scale of 1:20 were established in wind tunnel tests. The wind speed profiles above the railway and the aerodynamic forces of the vehicles at different positions along the railway were measured by using Cobra probe and dynamometric balance respectively. The test results show: The influence range of cutting-tunnel transition section is larger than that of the embankment-tunnel transition section, and the maximum impact height exceeds 320mm (corresponding to 6.4m in full scale). The wind speed profile at the railway junction is greatly affected by the tunnel. Under the condition of the double track, the side force coefficient on the leeward side is negative. For embankment-tunnel transition section, the lift force coefficient of the vehicle is positive which is unsafe for operation when the vehicle is at the railway line junction.

봅슬레이의 형상변화가 공력성능에 미치는 영향 (Effects of Geometric Parameters of a Bobsleigh on Aerodynamic Performance)

  • 심현석;정효연;김준희;김광용
    • 대한기계학회논문집 C: 기술과 교육
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    • 제3권3호
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    • pp.233-240
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    • 2015
  • 본 연구에서는 다양한 형상변수들이 봅슬레이의 공력성능에 미치는 영향을 평가하기 위하여 삼차원 Reynolds-averaged Navier-Stoke 해석을 수행하였으며, 난류모델로는 표준 k-${\varepsilon}$ 모델이 사용하였다. 격자계로는 비정렬 사면체 격자를 사용하였다. 성능 평가를 위한 형상변수로는 전방범퍼의 장축의 길이, 범퍼의 높이, 그리고, 카울링 측면과 정면 각각에서의 곡률반경 등 네가지 변수를 설정하였으며. 이들이 공력성능으로 선정된 항력계수에 미치는 영향을 평가하였다. 해석결과, 범퍼의 높이와 카울링 측면의 곡률반경이 항력계수에 민감한 영향을 미침을 알 수 있었다.

풍동실험을 통한 방풍용 서양측백나무와 농업용방풍망의 공기역학계수 평가 (Wind Tunnel Evaluation of Aerodynamic Coefficients of Thuja occidentalis and Mesh Net)

  • 이소진;하태환;서시영;송호성;우샘이;장유나;정민웅;조광곤;한덕우;황옥화
    • 한국농공학회논문집
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    • 제63권5호
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    • pp.63-71
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    • 2021
  • Windbreak forests, which have a windproof effect against strong winds, are known to be effective in reducing the spread of odors and dust emitted from livestock farms. The effect of reducing the spread of odors and dust can be estimated through numerical models such as computational fluid dynamics, which require aerodynamic coefficients of the windbreaks for accurate prediction of their performance. In this study, we aimed to evaluate the aerodynamic coefficients, Co, C1, C2, and α, of two windbreaks, Thuja occidentalis and a mesh net, through wind tunnel experiments. The aerodynamic coefficients were derived by the relation between the incoming wind speed and the pressure loss due to the windbreaks which was measured by differential pressure sensors. In order to estimate the change in the aerodynamic coefficient concerning various leaf density, the experiments were conducted repeatedly by removing the leaves gradually in various stages. The results showed that the power law regression model more suitable for coefficient evaluation compared to the Darcy-Forchheimer model.