• Title, Summary, Keyword: Unsteady lift coefficient

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Unsteady Lift Measurements of the Dragonfly-type Wing (잠자리 유형 날개의 비정상 양력 측정)

  • Kim, Song-Hak;Jang, Jo-Won
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.14 no.2
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    • pp.1-8
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    • 2006
  • Unsteady lift measurements were carried out in order to investigate the effects of phase difference and reduced frequency of a dragonfly-type model with two pairs of wing. A load-cell was employed to measure the lift generated by a plunging motion of the dragonfly-type model with the incidence angles of 0$^{circ}$. Experimental conditions are as follows: phase differences between fore- and hind-wings are 0$^{circ}$, 90$^{circ}$, 180$^{circ}$, and 270$^{circ}$, and reduced frequencies are 0.075, 0.15 and 0.225, respectively. The freestream velocity was 143 m/sec and corresponding chord Reynolds number was $3.4{\times}10^3$. The variation of phase-averaged lift coefficients during one cycle of the wing motion is presented. Results show that the total value of the positive lift coefficient during one cycle of the wing motion is the largest at the phase difference of 90$^{circ}$, and that the maximum lift coefficient and lift coefficient per unit of time increases with reduced frequency.

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Unsteady Aerodynamics of Flat Plate with Porous Trailing-edge (다공성 표면 평판 끝 단 위의 비정상 공력 특성에 대한 연구)

  • Jeong, Ye-Eun;Moon, Young-J.
    • 한국전산유체공학회:학술대회논문집
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    • pp.134-137
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    • 2008
  • In this study, a computational analysis is conducted to investigate the effects of porous surfaces on the lift and drag forces of the flat plate. With the porous treatment, it is found that the strength of the Karman vortex as well as its influences over the trailing-edge surface are much weakened, resulting in significant reduction of the pressure fluctuations over the flat plate. The drag and lift coefficients are decreased by 85% and 18%, respectively, compared to the solid surface. The computed results also indicate that the size of the porous surface area does not have much influences but the back side of the flat plate has non-negligible effects on the interaction between the wall and the Karman vortex. As a result, the lift coefficient for the solid back side case is decreased only by 50.5% compared to the solid case and the drag coefficient is even increased by 65%.

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Study on Unsteady Forces Acting on a Heaving Foil (히빙운동익에 작용하는 비정상 유체력 특성)

  • Yang, Chang-Jo;Kim, Beom-Seok;Choi, Min-Seon;Lee, Young-Ho
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • pp.222-227
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    • 2005
  • A Flapping foil produces an effective angle of attack, resulting in a normal force vector with thrust and lift components, and it can be expected to be a new highly effective propulsion system. A heaving foil model was made and it was operated within a circulating water channel at low Reynolds numbers. The unsteady thrust and lift acting on the heaving foil were measured simultaneously using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as heaving frequency and amplitude in NACA 0010 profile. The results showed that thrust coefficient and efficiency increased with reduced frequency and amplitude. We also presented the experimental results on the unsteady fluid forces of a heaving foil at various parameters.

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A Study on the Unsteady Fluid Forces Acting on a Heaving Foil (히빙운동익에 작용하는 비정상 유체력 특성)

  • Yang Chang-Jo
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.1
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    • pp.150-156
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    • 2006
  • A Flapping foil Produces an effective angle of attack, resulting in a normal force vector with thrust and lift components, and it can be expected to be a new highly effective propulsion system. A heaving foil model was made and it was operated within a circulating water channel at low Reynolds numbers. The unsteady thrust and lift acting on the heaving foil were measured simultaneously using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as heaving frequency and amplitude in NACA 0010 Profile. The results showed that thrust coefficient and efficiency increased with reduced frequency and amplitude. We also Presented the experimental results on the unsteady fluid forces of a heaving foil at various Parameters.

Numerical study on the effect of three-dimensional unsteady tunnel entry flow characteristics on the aerodynamic performance of high-speed train (터널진입시 비정상 유동특성이 고속전철의 공력성능에 미치는 영향에 관한 수치해석적 연구)

  • 정수진;김태훈;성기안
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.5
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    • pp.596-606
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    • 2002
  • The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10% of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.

Numerical Analysis for Flowfield of a Circular Arc Type Sea Anchor by Discrete Vortex Method (이산와법에 의한 원호형 Sea Anchor의 유동장 수치해석)

  • Ro, Ki-Deok;Kwon, Byeong-Guk;An, Heui-Chun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.8
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    • pp.1041-1051
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    • 1998
  • The fluid dynamic properties of a circular arc type sea anchor were calculated by a discrete vortex method. The flow for the surface of the sea anchor was represented by arranging bound vortices at adequate intervals. The simulations were performed by assuming that the separations occur at edges. With time, the drag coefficient was almost constant but the lift coefficient oscillated in a cycle by von Karman's vortex street. As the camber ratios increase, the drag coefficient and Strouhal number were almost constant but the oscillating amplitude of the lift coefficient increased largely.

Numerical Calculation of Flow Pattern and Fluid Force on a Circular Arc-type Sea Anchor

  • Ro, Ki-Deok;Oh, Se-Kyung
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.8
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    • pp.1258-1269
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    • 2004
  • The fluid dynamic characteristics of a circular arc type sea anchor were calculated by a discrete vortex method. The flow for the surface of the sea anchor was represented by arranging bound vortices at adequate intervals. The simulations were performed by assuming that the separations occur at edges. With time, the drag coefficient was almost constant but the lift coefficient oscillated in a cycle due to von Karman's vortex street. As the camber ratios increase, the drag coefficient and Strouhal number were almost constant but the oscillating amplitude of the lift coefficient increased largely.

Aerodynamic Characteristics of 2-D, Unsteady Flow Past a Square Cylinder (Revaluation of SOLA Scheme) (2차원각주의 비정상 공력특성(SOLA스킴의 재평가))

  • 이영호
    • Journal of Advanced Marine Engineering and Technology
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    • v.14 no.2
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    • pp.48-65
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    • 1990
  • Numerical solutions of the Navier-Stokes equations, governing 2-dimensional, time-dependent, viscous, incompressible fluid flow past a square cylinde in an infinite region, are presented for Reynolds numbers $10^2$, $10^3$and $10^4$. Finite-difference scheme, based on SOLA-VOF is adopted and a discretization of the convection term for irregular grid is newly suggested by altering the original nonconservation form into conservation one. Distribution of finer grids around the body reveals fairly reasonable consistency with the experimental variables : drag coefficient, lift coefficient, Strouhal number, fluctuating pressure coefficient, etc.

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Unsteady Subsonic Aerodynamic Characteristics of Wing in Fold Motion

  • Jung, Yoo-Yeon;Kim, Ji-Hwan
    • International Journal of Aeronautical and Space Sciences
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    • v.12 no.1
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    • pp.63-68
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    • 2011
  • Aerodynamic characteristics of a wing during fold motion were investigated in order to understand how variations or changes in such characteristics increase aircraft performance. Numerical simulations were conducted, and the results were obtained using the unsteady vortex lattice method to estimate the lift, drag and the moment coefficient in subsonic flow during fold motion. Parameters such as the fold angle and the fold angular velocity were summarized in detail. Generally, the lift and pitching moment coefficients decreased as the angle increased. In contrast, the coefficients increased as the angular velocity increased.

Numerical Study on the Effects of Corrugation of the Gliding Dragonfly Wing (글라이딩 하는 잠자리 날개 주름의 영향에 대한 수치해석적 연구)

  • Kim, Won-Kap;Byun, Do-Young;Park, Hoon-Cheol
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.9
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    • pp.835-840
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    • 2008
  • We investigate the aerodynamic performance of the dragonfly wing which has the cross-sectional corrugation by using the static 2-dimensional unsteady simulation. Computational condition is at Re=150, 1400 and 10,000 with the angles of attack from 0 to 40 degrees. As computational results, the increment of the lift coefficient by corrugation is nearly constant over the critical angle of attack. Also, upper side corrugation of the wing have very little influence on increase of the lift coefficient.