• Title/Summary/Keyword: Aerodynamic center

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Spatial correlation of aerodynamic forces on 5:1 rectangular cylinder in different VIV stages

  • Lei, Yongfu;Sun, Yanguo;Zhang, Tianyi;Yang, Xiongwei;Li, Mingshui
    • Wind and Structures
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    • v.34 no.1
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    • pp.81-90
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    • 2022
  • To better understand the vortex-induced vibration (VIV) characteristics of a 5:1 rectangular cylinder, the distribution of aerodynamic force and the non-dimensional power spectral density (PSD) of fluctuating pressure on the side surface were studied in different VIV development stages, and their differences in the stationary state and vibration stages were analyzed. The spanwise and streamwise correlations of surface pressures were studied, and the flow field structure partitions on the side surface were defined based on the streamwise correlation analysis. The results show that the variation tendencies of mean and root mean square (RMS) pressure coefficients are similar in different VIV development stages. The RMS values during amplitude growth are larger than those at peak amplitude, and the smallest RMS values are observed in the stationary state. The spanwise correlation coefficients of aerodynamic lifts increase with increase of the peak amplitude. However, for the lock-in region, the maximum spanwise correlation coefficient for aerodynamic lifts occurs in the VIV rising stage rather than in the peak amplitude stage, probably due to the interaction of vortex shedding force (VSF) and self-excited force (SEF). The streamwise correlation results show that the demarcation point positions between the recirculation region and the main vortex region remain almost constant in different VIV development stages, and the reattachment points gradually move to the tailing edge with increasing amplitude. This study provides a reference to estimate the demarcation point and reattachment point positions through streamwise correlation and phase angle analysis from wind tunnel tests.

Optimization Study of a Helicopter Rotor Blade Section Using EDISON Ksec2D and Grid Search Method (EDISON Ksec2D와 Grid Search 법을 이용한 헬리콥터 블레이드 단면의 형상 최적화)

  • Na, Deok-Hwan;Hahm, Jae-Joon;Bae, Jae-Seong
    • Proceeding of EDISON Challenge
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    • 2016.03a
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    • pp.183-189
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    • 2016
  • In this paper, an optimization study on a helicopter rotor blade cross-section was made. Generalization was made to the baseline cross-section to simplify the analysis. To have better performance in aeroelastic response, with the aerodynamic center being the origin of the baseline, the distance between aerodynamic center and shear center, and the distance between mass center and shear center of the blade were minimized. For efficient searching of optimum solutions over the design space, grid search method, which is a method of graphical search was used. Two design variables, radius of balancing weight at leading edge, and offset of the spar from leading edge were selected for the study. Cubic spline interpolation method was used to accommodate searching of the optimum solution. 2-Leveled searching system was devised in accordance with the interpolation method. Optimum solution was found to show 6% decrease in both distance between aerodynamic center and shear center, and mass center and shear center to the baseline.

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Investigation on Aerodynamic Performance of a Highly-Loaded Axial Fan with Active/Passive Flow Control Using FSI Analysis (유체-구조 연성해석을 이용한 능동/수동 유동제어방식이 결합된 고하중 축류 팬의 성능특성 연구)

  • Ma, Sang-Bum;Kim, Kwang-Yong;Choi, Jaeho;Lee, Wonsuk
    • Journal of Hydrogen and New Energy
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    • v.28 no.1
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    • pp.113-119
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    • 2017
  • An investigation on aerodynamic performance of a highly-loaded axial fan has been conducted to find the effects of tip injection and casing groove on aerodynamic performance in this study. Three-dimensional Reynolds-averaged Navier-Stokes equations with $k-{\varepsilon}$ turbulence model were used to analyze the fluid flow in the fan with Fluid-Structure Interaction (FSI) analysis. The hexahedral grid was used to construct computational domain, and the grid dependency test drew the optimal grid system. FSI analysis was also carried out to predict the deformation of rotor and stator blades, and the effect of deformation on the aerodynamic performance of axial fan was analyzed compared to the performance predicted without FSI analysis.

Dynamic response of railway vehicles under unsteady aerodynamic forces caused by local landforms

  • Chen, Zhengwei;Liu, Tanghong;Li, Ming;Yu, Miao;Lu, Zhaijun;Liu, Dongrun
    • Wind and Structures
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    • v.29 no.3
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    • pp.149-161
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    • 2019
  • When a railway vehicle runs in crosswinds, the unsteady aerodynamic forces acting on the train induced by the vehicle speed, crosswind velocity and local landforms are a common problem. To investigate the dynamic performance of a railway vehicle due to the influence of unsteady aerodynamic forces caused by local landforms, a vehicle aerodynamic model and vehicle dynamic model were established. Then, a wind-loaded vehicle system model was presented and validated. Based on the wind-loaded vehicle system model, the dynamic response performance of the vehicle, including safety indexes and vibration characteristics, was examined in detail. Finally, the effects of the crosswind velocity and vehicle speed on the dynamic response performance of the vehicle system were analyzed and compared.

Numerical Study on the Aerodynamic Performance of Asymmetric Vertical Folding Rotor Sail (비대칭 수직 접이식 로터세일의 성능 평가에 관한 수치해석 연구)

  • Jung Yoon Park;Janghoon Seo;Dong-Woo Park
    • Journal of the Society of Naval Architects of Korea
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    • v.61 no.2
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    • pp.68-76
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    • 2024
  • The rotor sail is one of the representative devices in eco-friendly wind-assisted propulsion systems that have been practically applied to commercial ships. The present study proposes an asymmetric vertical folding rotor sail (AFRS) designed for small ships, featuring asymmetric geometry along the vertical direction and the function of vertical folding. To evaluate the aerodynamic performance of rotor sail, the drag, lift and lift-to-drag ratio were derived using computational fluid dynamics. The aerodynamic performance of AFRS was compared with that of normal rotor sail with different aspect ratios and spin ratios. The effect of geometric parameters on the aerodynamic performance of AFRS was assessed by varying the asymmetric diameter ratio. The maximum improvement in lift-to-drag ratio for AFRS was approximately 12% in the considered case. Additionally, the resistance is decreased when AFRS is vertically folded without rotating. Throughout the present study, improved aerodynamic and resistance performances for AFRS were confirmed, which will successfully provide additional propulsion to small ships.

Longitudinal static stability requirements for wing in ground effect vehicle

  • Yang, Wei;Yang, Zhigang;Collu, Maurizio
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.7 no.2
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    • pp.259-269
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    • 2015
  • The issue of the longitudinal stability of a WIG vehicle has been a very critical design factor since the first experimental WIG vehicle has been built. A series of studies had been performed and focused on the longitudinal stability analysis. However, most studies focused on the longitudinal stability of WIG vehicle in cruise phase, and less is available on the longitudinal static stability requirement of WIG vehicle when hydrodynamics are considered: WIG vehicle usually take off from water. The present work focuses on stability requirement for longitudinal motion from taking off to landing. The model of dynamics for a WIG vehicle was developed taking into account the aerodynamic, hydrostatic and hydrodynamic forces, and then was analyzed. Following with the longitudinal static stability analysis, effect of hydrofoil was discussed. Locations of CG, aerodynamic center in pitch, aerodynamic center in height and hydrodynamic center in heave were illustrated for a stabilized WIG vehicle. The present work will further improve the longitudinal static stability theory for WIG vehicle.

Study on aerodynamic coefficients and responses of the integrated catwalk of Halogaland Bridge

  • Wan, Jia-wei;Wang, Qi;Liao, Hai-li;Li, Ming-shui
    • Wind and Structures
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    • v.25 no.3
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    • pp.215-232
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    • 2017
  • Wind tunnel tests and numerical aerodynamic analyses were conducted for an integrated catwalk structure under strong winds. From the wind tunnel tests, it is found that the aerodynamic coefficients were different from those of the typical type. The drag coefficient was larger than typical and was sensitive to number of vertical meshes installed rather than the solidity ratio. Comparing with typical catwalk, the integrated one showed larger deformation under strong wind, and the large torsional deformation are mainly caused by drag force. It did not show aerodynamic divergence even the torsional deformation reaching $20^{\circ}$. The reason could be that the stiffness is smaller and thus the catwalk is able to deform to the shape compactable with higher loading. Considering safety for construction, storm rope system is introduced to the catwalk to reduce the deformation to acceptable level.

The Numerical Assessment with Modified Vehicle Rear Body Shape on the Aerodynamic Crosswind Stability Improvement (차량 후미부 형상 변경에 따른 공력 횡풍 안정성 개선에 관한 수치해석 연구)

  • Choi, Sang-Yeol;Kim, Yonung-Tae;Chang, Youn-Hyuck;Ha, Jong-Paek;Kim, Eun-Seok
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.51-53
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    • 2008
  • The vehicle aerodynamic crosswind characteristics are mainly governed by the coefficient of side force and yawing moment. These performances affect not only the driving comfort which can be felt by driver but also the safety due to the instability of vehicle. The aims of this investigation are to improve the aerodynamic crosswind performance of sedan vehicle under the crosswind conditions. In order to improve the crosswind stability, numerical analysis has been performed by modifying the rear body shape of vehicle. As the results, we observed about 20% reduction of yawing moment coefficient relative to the base vehicle.

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Numerical studies of unsteady flow field and aerodynamic forces on an oscillating 5:1 rectangular cylinder in a sinusoidal streamwise flow

  • Ma, Ruwei;Zhou, Qiang;Wang, Peiyuan;Yang, Yang;Li, Mingshui
    • Wind and Structures
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    • v.34 no.1
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    • pp.91-100
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    • 2022
  • Numerical simulations are conducted to investigate the uniform flow (UF) and sinusoidal streamwise flow (SSF) over an oscillating 5:1 rectangular cylinder with harmonic heaving motion at initial angles of attack of α = 0° and 3° using two-dimensional, unsteady Reynolds-averaged Navier-Stokes (URANS) equations. First, the aerodynamic parameters of a stationary 5:1 rectangular cylinder in UF are compared with the previous experimental and numerical data to validate the capability of the computationally efficient two-dimensional URANS simulations. Then, the unsteady flow field and aerodynamic forces of the oscillating 5:1 rectangular cylinder in SSF are analysed and compared with those in UF to explore the effect of SSF on the rectangular cylinder. Results show that the alternative vortex shedding is disturbed by SSF both at α = 0° and 3°, resulting in a considerable decrease in the vortex-induced force, whereas the unsteady lift component induced by cylinder motion remains almost unchanged in the SSF comparing with that in UF. Notably, the strong buffeting forces are observed at α = 3° and the energy associated with unsteady lift is primarily because of the oscillations of SSF. In addition, the components of unsteady lift induced by the coupling effects of SSF and cylinder motion are discussed in detail.

A study on the Aerodynamic Characteristics of a Flat plat Variable Wing by Combined Swept Back and Forward (평판 가변날개에서 앞-뒤젖힘이 동시에 변할 때의 공력특성에 관한 연구)

  • Lee, B.J.;Oh, S.D.
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.5 no.1
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    • pp.31-50
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    • 1997
  • A new variable wing that can be swept back and forward synchronously were developed to enhance the aerodynamic and stability characteristics of a high speed airplane. The configuration of the new variable wing changes in such a way that inner part of the wing sweeps forward and outer part of the wing sweeps backward, the shift of aerodynamic center of the wing is small, therfore the static margin that is required for the stability of a airplane is not affected. In this study, various configurations of wing models by combined swept back and forward were designed and a wind tunnel tests were conducted to investigate the aerodynamic characteristics of these variable wings. The experimental results showed that the variable wing by combined swept back and forward has no effect on the pitching moment coefficient affecting on an aircraft stability margin and enhance the aerodynamic characteristics for a given approach angle of attack.

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