• Title, Summary, Keyword: lift coefficient

Search Result 334, Processing Time 0.224 seconds

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
    • /
    • v.14 no.2
    • /
    • pp.1-8
    • /
    • 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.

  • PDF

Application of Vortex Generators on Smart Un-manned Aerial Vehicle(SUAV) (스마트 무인기에 부착한 Vortex Generator 효과)

  • Chung, Jin-Deog;Choi, Sung-Wook;Cho, Tae-Whan
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.31 no.8
    • /
    • pp.688-693
    • /
    • 2007
  • To improve aerodynamic efficiency of the Smart Un-manned Aerial Vehicle(SUAV), vortex generator was applied along the wing upper surface during SUAV tests. Vortex generator, initially used in TR-S2 configuration to enhance lift characteristic, increased lift coefficient. Meanwhile vortex generator produced excessive drag and eventually reduced lift-to-drag ratio. To examine the effect of vortex generator's height, three different heights of vortex generator were used for various SUAV configuration. Vortex generator of 3mm height used in TR-S4 configuration produced 3.1% increase in maximum lift coefficient and 1.5% reduction in lift-to-drag ratio.

Aerodynamic Performance Improvement by Divergent Trailing Edge Modification to a Supercritical Airfoil

  • Yoo, Neung-Soo
    • Journal of Mechanical Science and Technology
    • /
    • v.15 no.10
    • /
    • pp.1434-1441
    • /
    • 2001
  • A computational study has been performed to determine the effects of divergent trailing edge (DTE) modification to a supercritical airfoil in transonic flow field. For this, the computational result with the original DLBA 186 supercritical airfoil was compared to that of the modified DLBA 283. A wavier-Stokes code, Fluent 5. 1, was used with Spalart-Allmaras's one-equation turbulence model. Results in this study showed that the reduction in drag due to the DTE modification is associated with weakened shock and delayed shock appearance. The decrease in drag due to the DTE modification is greater than the increase in base drag. The effect of the recirculating flow region on lift increase was also observed. An airfoil with DTE modification achieved the same lift coefficient at a lower angle of attack while giving a lower drag coefficient. Thus, the lift-to-drag ratio increases in transonic flow conditions compared to the original airfoil. The lift coefficient increases considerably whereas the lift slope increases just a little due to DTE modification.

  • PDF

Drag and Lift Forces of a Circular Cylinder Located Parallel to a Planar Jet (평면 제트내의 평행하게 놓인 원형 실린더가 받는 항력과 양력)

  • Gang, Sin-Hyeong;Hong, Sun-Sam
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.20 no.1
    • /
    • pp.369-376
    • /
    • 1996
  • Variations of the drag and lift forces of a circular cylinder in a planar turbulent jet were experimentally investigated. The force was directly measured using the load cell and estimated by integrating the pressure distribution on the cylinder. As the cylinder moves outward from the center of the jet, the direction of lift force changes and the drag force decreases. Reynolds number, the ratio of cylinder's diameter to half width of jet had effect on maximum drag coefficient and the location where the direction of lift changes.

Numerical Investigation of Drag and Lift Characteristics of Cavitator of Supercavitating Underwater Vehicle (초공동 수중운동체 캐비테이터의 항력과 양력특성에 관한 수치해석적 연구)

  • Kang, Byung Yun;Jang, Seyeon;Kang, Shin-Hyoung
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.38 no.10
    • /
    • pp.797-805
    • /
    • 2014
  • The purpose of this study was to investigate the drag and lift characteristics of the cavitator of a supercavitating underwater vehicle and the pressure loss due to water intake. These investigations were performed by changing the diameter, velocity, radius of curvature of the intake, and angle of attack of the cavitator. With increasing ratio of the intake diameter to the cavitator diameter ratio($d/D_1$), the drag coefficient and the pressure loss coefficient of the water intake decreased. The greater the increase in the ratio of the intake velocity-to-free stream velocity ratio(S), the smaller was the decrease in the drag coefficient and the lift coefficient. When the intake had a radius of curvature(c), the pressure loss coefficient decreased. On the contrary, the effect of the radius of curvature on the drag coefficient was imperceptible. For angles of attack (${\alpha}$) of the caviatator in the range of $0^{\circ}$ to $10^{\circ}$, the drag coefficient and the pressure loss coefficient changed slightly, whereas the lift coefficient increased linearly with increasing angle of attack.

The effect of aerodynamic characteristics on the insect wing tip trajectory in hovering flight (정지 비행에서의 곤충 날개 궤적에 따른 공기역학적 특성)

  • Cho, Hun-Kee;Joo, Won-Gu
    • Proceedings of the KSME Conference
    • /
    • /
    • pp.1441-1445
    • /
    • 2008
  • Insect flight is adapted to cope with each circumstance by controlling a variety of the parameters of wing motion in nature. Many researchers have struggled to solve the fundamental concept of insect flight, but it has not been solved yet clearly. In this study, to find the most effective flapping wing kinematics, we conducted to analyze CFD data on fixing some of the optimal parameters of wing motion such as stoke amplitude, flip duration and wing rotation type and then controlled the deviation angle by fabricating wing tip motion. Although all patterns have the similar value of lift coefficient and drag coefficient, pattern A(pear-shape type) indicates the highest lift coefficient and pattern H(pear-shape type) has the lowest lift coefficient among four wing tip motions and three deviation angles. This result suggest that the lift and drag coefficient depends on the angle of attack and the deviation angle combined, and it could be explained by delayed stall effect.

  • PDF

The Aerodynamic Characteristics by the Insect Wing Tip Trajectory in Hovering Flight (정지 비행에서의 곤충 날개 궤적에 따른 공기역학적 특성)

  • Cho, Hun-Kee;Joo, Won-Gu
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.33 no.7
    • /
    • pp.506-511
    • /
    • 2009
  • Insect flight is adapted to cope with each circumstance by controlling a variety of the parameters of wing motion in nature. Many researchers have struggled to solve the fundamental concept of insect flight, but it has not been solved yet clearly. In this study, to find the most effective flapping wing dynamics, we conducted to analyze CFD data on fixing some of the optimal parameters of wing motion such as stoke amplitude, flip duration and wing rotation type and then controlled the deviation angle by fabricating wing tip motion. Although all patterns have the similar value of lift coefficient and drag coefficient, pattern A(pear-shape type) indicates the highest lift coefficient and pattern H(pear-shape type) has the lowest lift coefficient among four wing tip motions and three deviation angles. This result suggest that the lift and drag coefficient depends on the angle of attack and the deviation angle combined, and it could be explained by delayed stall and wake capture effect.

Characteristics of Flow Coefficients in an Engine Cylinder Head with a Quasi-steady Flow Condition by Continuous Variation of the Valve Lift (밸브 양정의 연속 변화에 의한 준정상 유동 조건에서의 엔진 실린더헤드 유량계수 특성)

  • Oh, Dae-San;Lee, Choong-Hoon
    • Journal of the Korean Society of Safety
    • /
    • v.25 no.6
    • /
    • pp.22-27
    • /
    • 2010
  • Flow Coefficients of intake port in an engine cylinder head were measured by a newly designed flow rig. In measuring the flow coefficient with traditional method, the valve lift was manually varied by technician with adjusting a micrometer which is directly connected to the intake valve of the cylinder head. The cam shaft of the cylinder head is directly rotated by a step motor and the valve lift was automatically varied with cam shaft profile in the newly designed flow rig. The measurement of the flow coefficient was automated by rotating the cam shaft with the step motor. Automatic measurement of the flow coefficient could be safely measured by separating a technician from the noise and vibration of the traditional flow rig. Also, the automatic measurement of the flow coefficient reduce the measurement time and provide meaningful statistical data.

Development of a Lift Correction Method for Shear Flow Effects in BEM Theory (BEM 이론을 위한 전단유동 효과 보정 기법 개발)

  • Lee, Kyung Seh;Jung, Chin Hwa;Park, Hyun Chul
    • 한국신재생에너지학회:학술대회논문집
    • /
    • /
    • pp.57.2-57.2
    • /
    • 2011
  • In this study, the effects of shear flows around a 2-dimensional airfoil, S809 on its aerodynamic characteristics were analyzed by CFD simulations. Various parameters including reference inflow velocity, shear rate, angle of attack, and cord length of the airfoil were examined. From the simulation results, several important characteristics were found. Shear rate in a flow makes some changes in the lift coefficient depending on its sign and magnitude but angle of attack does not have a distinguishable influence. Cord length and reference inflow also cause proportional and inversely proportional changes in lift coefficient, respectively. We adopted an analytic expression for the lift coefficient from the thin airfoil theory and proposed a modified form applicable to the traditional load analysis procedure based on the blade element momentum theory. Some preliminary results applied to an well known load simulation software, FAST, are presented.

  • PDF

Transonic flow past a Whitcomb airfoil with a deflected aileron

  • Kuzmin, Alexander
    • International Journal of Aeronautical and Space Sciences
    • /
    • v.14 no.3
    • /
    • pp.210-214
    • /
    • 2013
  • The sensitivity of transonic flow past a Whitcomb airfoil to deflections of an aileron is studied at free-stream Mach numbers from 0.81 to 0.86 and vanishing or negative angles of attack. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver using the $k-{\omega}$ SST turbulence model. The numerical study demonstrates the existence of narrow bands of the Mach number and aileron deflection angles that admit abrupt changes of the lift coefficient at small perturbations. In addition, computations reveal free-stream conditions in which the lift coefficient is independent of aileron deflections of up to 5 degrees. The anomalous behavior of the lift is explained by interplay of local supersonic regions on the airfoil. Both stationary and impulse changes of the aileron position are considered.