• Title/Summary/Keyword: Unsteady Aerodynamic Force

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Effects of oscillation parameters on aerodynamic behavior of a rectangular 5:1 cylinder near resonance frequency

  • Pengcheng Zou;Shuyang Cao;Jinxin Cao
    • Wind and Structures
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    • v.38 no.1
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    • pp.59-74
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    • 2024
  • Large Eddy Simulation (LES) is used to explore the influence of vibration frequency and amplitude on the aerodynamic performance of a rectangular cylinder with an aspect ratio of B/D=5 (B: breadth; D: depth of cylinder) at a Reynolds number of 22,000 near resonance frequency. In smooth flow conditions, the research employs a sequence of three-dimensional simulations under forced vibration with diverse frequency ratios fe / fo = 0.8-1.2 (fe : oscillation frequency; fo : Strouhal frequency when the rectangular cylinder is stationary ) and oscillation amplitudes Ah/D = 0.05 - 0.3. The individual influences of fe / fo and Ah/D on the characteristics of integrated and distributed aerodynamic forces are the focal points of discussion. For the integrated aerodynamic force, particular emphasis is placed on the analysis of the dependence of velocity-proportional component C1 and displacement-proportional component C2 of unsteady aerodynamic force on amplitude and frequency ratio. Near the resonance frequency, the dependencies of C1 and C2 on amplitude are stronger than that of frequency ratio. For the distributed aerodynamic force, the increase in frequency and amplitude promotes the position of the main vortex core and reattachment to the leading edge in the streamwise direction. In the spanwise direction, vibration enhances the spanwise correlation of aerodynamic force to weaken the three-dimensional effect of the flow field, and a lower frequency ratio and larger amplitude amplify this effect.

The effect of Local Vibration Modes on the Flutter (국부진동모드가 플러터해석에 미치는 영향연구)

  • Shin, Young-Sug;Kim, Heon-Ju;Kim, Seong-Tae;Kim, Jae-Young;Hwang, Chul-Ho
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.10
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    • pp.919-926
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    • 2011
  • The fin of high speed air vehicle is composed of skins and strong skeletons. In the flutter analysis, the eigenmodes of a fin are used for evaluating the unsteady aerodynamic force and the modal approach is applied for solving the flutter equation in both time and frequency domain. Therefore, the proper eigenmodes used for a modal flutter analysis should be chosen. For the appropriate choice of eigenmodes, when there exist local modes of a skin in the high modes, the effects of those modes on the unsteady aerodynamic force and flutter characteristics are anlalyzed.

Study of Neural Network Training Algorithm Comparison and Prediction of Unsteady Aerodynamic Forces of 2D Airfoil (신경망 학습알고리즘의 비교와 2차원 익형의 비정상 공력하중 예측기법에 관한 연구)

  • Kang, Seung-On;Jun, Sang-Ook;Park, Kyung-Hyun;Jeon, Yong-Hee;Lee, Dong-Ho
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.5
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    • pp.425-432
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    • 2009
  • In this study, the ability of neural network in modeling and predicting of the unsteady aerodynamic force coefficients of 2D airfoil with the data obtained from Euler CFD code has been confirmed. Neural network models are constructed based on supervised training process using Levenberg-Marquardt algorithm, combining this into genetic algorithm, hybrid genetic algorithm and the efficiency of the two cases are analyzed and compared. It is shown that hybrid-genetic algorithm is more efficient for neural network of complex system and the predicted properties of the unsteady aerodynamic force coefficients of 2D airfoil by the neural network models are confirmed to be similar to that of the numerical results and verified as suitable representing reduced models.

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.

How Birds and Insects Fly (곤충과 새의 비행방법)

  • Hong, Young-Sun
    • Journal of the Korea Institute of Military Science and Technology
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    • v.10 no.1
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    • pp.130-143
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    • 2007
  • Using steady state aerodynamic theories, it has been claimed that insects and birds cannot fly. To make matters worse, insects and birds fly at low Reynolds numbers. Therefore, a recurring theme in the literature is the importance of understanding unsteady aerodynamic effect and how the vortices behave when they separate from the moving surface that created them. In flapping flight, birds and insects can modify wing beat amplitude, stroke angle, wing planform area, angle of attack, and to a lesser extent flapping frequency to optimize the generation of lift force. Some birds are thought to employ two different gaits(a vortex ring gait and a continuous vortex gait) and unsteady aerodynamic effect(Clap and fling, Delayed stall, Wake capture and Rotational Circulation) in flapping flight. Leading edge vortices may produce an increase in lift. The trailing edge vortex could be an important component in gliding flight. Tip vortices in hovering support the body weight of the hummingbirds. Thus, this study investigated how insects and birds generate lift at low Reynolds numbers. This research is written to further that as yet incomplete understanding.

Analysis of Change of Contact Force in the Pantograph Pan Head of Next Generation High Speed Train (차세대 고속전철 팬터그래프 팬 헤드의 압상력 변화 해석)

  • Kang, Hyungmin;Kwon, Hyeok-bin
    • The KSFM Journal of Fluid Machinery
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    • v.20 no.1
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    • pp.35-40
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    • 2017
  • In order to investigate the change of contact force of pantograph pan head due to the change of aerodynamic force, three dimensional flow around the pan head were calculated. For this, the aerodynamic modeling of pan head of CX pantograph was performed and the standard deviation of the contact force of the simulation results were compared with those of the experimental results of wind tunnel tests. From the comparison, it was confirmed that the current grid system and the numerical methodologies can be utilized to calculate the aerodynamic characteristics of the pantograph pan head. By using these grid system and the methodologies, the standard deviations of the contact force of pan head were calculated with velocities as 200, 250, 300, 350, and 400 km/h. The maximum standard deviation of the aerodynamic contact force of pan head was 92 N at 400 km/h and statistical minimum contact force was more than 0 N. Therefore, it was confirmed that and the pan head of CX pantograph was statistically contacted with the catenary system with the train speed of 350 km/h though the aerodynamic contact force was changed.

Influence of geometric configuration on aerodynamics of streamlined bridge deck by unsteady RANS

  • Haque, Md. N.;Katsuchi, Hiroshi;Yamada, Hitoshi;Kim, Haeyoung
    • Wind and Structures
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    • v.28 no.5
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    • pp.331-345
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    • 2019
  • Long-span bridge decks are often shaped as streamlined to improve the aerodynamic performance of the deck. There are a number of important shaping parameters for a streamlined bridge deck. Their effects on aerodynamics should be well understood for shaping the bridge deck efficiently and for facilitating the bridge deck design procedure. This study examined the effect of various shaping parameters such as the bottom plate slope, width ratio and side ratio on aerodynamic responses of single box streamlined bridge decks by employing unsteady RANS simulation. Steady state responses and flow field were analyzed in detail for wide range of bottom plate slopes, width and side ratios. Then for a particular deck shape Reynolds number effect was investigated by varying its value from $1.65{\times}10^4$ to $25{\times}10^4$. The aerodynamic response showed very high sensitivity to the considered shaping parameters and exhibited high aerodynamic performance for a particular combination of shaping parameters.

Mechanism of ovalling vibrations of cylindrical shells in cross flow

  • Uematsu, Yasushi;Tsujiguchi, Noboru;Yamada, Motohiko
    • Wind and Structures
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    • v.4 no.2
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    • pp.85-100
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    • 2001
  • The mechanism of wind-induced ovalling vibrations of cylindrical shells is numerically investigated by using a vortex method. The subject of this paper is limited to a two-dimensional structure in the subcritical regime. The aerodynamic stability of the ovalling vibrations in the second to fourth circumferential modes is discussed, based on the results of a forced-vibration test. In the analysis, two modal configurations are considered; one is symmetric and the other is anti-symmetric with respect to a diameter parallel to the flow direction. The unsteady pressures acting on a vibrating cylinder are simulated and the work done by them for one cycle of a harmonic motion is computed. The effects of a splitter plate on the flow around the cylinder as well as on the aerodynamic stability of the ovalling vibrations are also discussed. The consideration on the mechanism of ovalling vibrations is verified by the results of a free-vibration test.

Aerodynamic Characteristics of Long-Span Bridges under Actively Generated Turbulences (능동 난류 생성을 통한 장대 교량의 공력 특성 비교)

  • Lee, Seungho;Kwon, Soon-Duck
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.5A
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    • pp.341-349
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    • 2011
  • The main purpose of this study is to investigate the affect of various turbulence properties on aerodynamic characteristics of twin box bridge section. To achieve this goal, active turbulence generator which successfully simulated various target turbulences was developed in the wind tunnel. From the wind tunnel tests, turbulence integral length scale did not affect on the aerodynamic forces and flutter derivatives except for the $A_1^*$ curve. Turbulence intensity gave slight effect on the unsteady aerodynamic force, but turbulence integral length scale did not affect the self-excited forces except vertical direction component.

Various Structural Approaches to Analyze an Aircraft with High Aspect Ratio Wings

  • El Arras, Anas;Chung, Chan Hoon;Na, Young-Ho;Shin, SangJoon;Jang, SeYong;Kim, SangYong;Cho, Changmin
    • International Journal of Aeronautical and Space Sciences
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    • v.13 no.4
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    • pp.446-457
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    • 2012
  • Aeroelastic analysis of an aircraft with a high aspect ratio wing for medium altitude and long endurance capability was attempted in this paper. In order to achieve such an objective, various structural models were adopted. The traditional approach has been based on a one-dimensional Euler-Bernoulli beam model. The structural analysis results of the present beam model were compared with those by the three-dimensional NASTRAN finite element model. In it, a taper ratio of 0.5 was applied; it was comprised of 21 ribs and 3 spars, and included two control surfaces. The relevant unsteady aerodynamic forces were obtained by using ZAERO, which is based on the doublet lattice method that considers flow compressibility. To obtain the unsteady aerodynamic force, the structural mode shapes and natural frequencies were transferred to ZAERO. Two types of unsteady aerodynamic forces were considered. The first was the unsteady aerodynamic forces which were based on the one-dimensional beam shape; the other was based on the three-dimensional FEM model shape. These two types of aerodynamic forces were compared, and applied to the foregoing flutter analysis. The ultimate goal of the present research is to analyze the possible interaction between the rigid-body degrees of freedom and the aeroelastic modes. This will be achieved after the development of a reliable nonlinear beam formulation that would validate the current results as well as enable a thorough investigation of the nonlinearity. Moreover, such analysis will allow for an examination of the above-mentioned interaction between the flight dynamics and aeroelastic modes with the inclusion of the rigid body degrees of freedom.