• 제목/요약/키워드: Leading Edge Vortex

검색결과 136건 처리시간 0.028초

고받음각 2차원 에어포일 주위의 비정상 유동의 진동 특성에 관한 연구 (ANALYSIS OF UNSTEADY OSCILLATING FLOW AROUND TWO DIMENSIONAL AIRFOIL AT HIGH ANGLE OF ATTACK)

  • 유재경;김재수
    • 한국전산유체공학회지
    • /
    • 제18권1호
    • /
    • pp.1-6
    • /
    • 2013
  • Missile and fighter aircraft have been challenged by low restoring nose-down pitching moment at high angle of attach. The consequence of weak nose-down pitching moment can be resulting in a deep stall condition. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance and safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed at high angle of attack up to 50 degrees around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.3 and Reynolds number of $10^5$. The lift, drag, pressure, entropy distribution, etc. are analyzed according to the angle of attack. The results of average lift coefficients are compared with other results according to the angle of attack. From a certain high angle of attack, the strong vortex formed by the leading edge are flowing downstream as like Karman vortex around a circular cylinder. The primary and secondary oscillating frequencies are analyzed by the effects of these unsteady aerodynamic characteristics.

특이점분포방식(特異點分布方式)에 의한 비정상수중익문제(非正常水中翼問題)의 해석(解析) -제2보(第2報) 3차원(次元) 문제(問題)로의 확장(擴張)- (Solution of Unsteady Hydrofoil Problems by Discrete Vortex Method with Application to Fish Propulsion -2nd Report; Expension to 3-Dimensonal Problems-)

  • 김형태;이창섭
    • 대한조선학회지
    • /
    • 제20권3호
    • /
    • pp.1-16
    • /
    • 1983
  • In this paper a discrete-vortex-method(DVM) is presented for investigating the hydromechanics of the planar hydrofoils performing the undulatory motion which can be related to fish propulsion with carangiform mode. This is an extention of the authors previous work(1981) on the 2-dimensional hydrofoil. The applicability and accuracy of the present method are shown by means of comparing the calculated lifts and moments, and their distributions over the planforms with those in available references, for aspect ratio 1.0 and 2.0 rectangular hydrofoils and a swept-back hydrofoil of aspect ratio 2.0 from reduced frequency 0.1 to 0.5. The agreement is considered good. To assure the applicability of the DVM to the study of the propulsive performance of the oscillating planar hydrofoils, the convergence tests are performed. The mean thrust(in pure heave, this is wholly due to leading-edge suction), the mean power to maintain the motion and the hydromechanical efficiency are calculated for the rectangular hydrofoil of aspect ratio 8.0 and these are compared with the calculations by Chopra & Kambe(1977) and Lan(1979) for the same cases.

  • PDF

유전자 알고리즘을 이용한 컨테이너선을 위한 침식예방용 최적방향타 단면 설계 (Study on Optimization of Anti-erosion Rudder Section of Large Container Ship by Genetic Algorithm)

  • 김문찬;이언식;변태영
    • 대한조선학회논문집
    • /
    • 제45권4호
    • /
    • pp.403-410
    • /
    • 2008
  • This paper describes the optimization of the rudder section by the genetic algorism based on VLM(Vortex Lattice Method) and panel method. The developed propeller-rudder analysis program has been validated by comparing with experimental data. The research extends to optimize the anti-erosion rudder section of the large container ship. The object function is the amount of pressure at leading edge of rudder which is closely related with erosion phenomena. The optimized rudder has been compared with conventional rudder with NACA 0021 section by analyzing with the developed program. The finally optimized section has low and mild pressure distribution in comparison with the NACA rudder. The experiments is expected to be carried out for the validation of the present optimization and more parametric study of section geometry is also expected to be conducted in the near future.

Experimental investigation on flow field around a flapping plate with single degree of freedom

  • Hanyu Wang;Chuan Lu;Wenhai Qu;Jinbiao Xiong
    • Nuclear Engineering and Technology
    • /
    • 제55권6호
    • /
    • pp.1999-2010
    • /
    • 2023
  • Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 104 to 3.95 × 104. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 104 with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.

Effects of Combustor-Level High Inlet Turbulence on the Endwall Flow and Heat/Mass Transfer of a High-Turning Turbine Rotor Cascade

  • Lee, Sang-Woo;Jun, Sang-Bae;Park, Byung-Kyu;Lee, Joon-Sik
    • Journal of Mechanical Science and Technology
    • /
    • 제18권8호
    • /
    • pp.1435-1450
    • /
    • 2004
  • Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

Detached Splitter를 이용한 원형 단면 실린더의 항력제어 (Control of Drag Force on a Circular Cylinder using a Detached Splitter)

  • 선승한;황종연;양경수
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2001년도 춘계학술대회논문집E
    • /
    • pp.253-258
    • /
    • 2001
  • Control of drag force on a circular cylinder using a detached splitter plate is numerically studied for laminar flow. A splitter plate with the same length as the cylinder diameter(d) is placed horizontally in the wake region. Its position is described by the gap ratio(G/d), where G represents the gap between the cylinder base point and the leading edge of the plate. The drag varies with the gap ratio; it has the minimum value at a certain gap ratio for each Reynolds number. The drag sharply increases past the optimum gap ratio; this seems to be related to the sudden change in the bubble size in the wake region. This trend is consistent with the experimental observation currently available in case of turbulent flow. It is also found that the net drag coefficient significantly depends on the variation of base suction coefficient.

  • PDF

탈설계점에서의 선형 터빈 익열 끝벽 열(물질)전달 특성 (Endwall Heat (Mass) Transfer Characteristics of a Linear Turbine Cascade at Off-Design Conditions)

  • 이상우;박진재
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2004년도 추계학술대회
    • /
    • pp.1092-1097
    • /
    • 2004
  • The heat (mass) transfer characteristics on the endwall surface of a first-stage linear turbine rotor cascade at off-design conditions has been investigated by employing the naphthalene sublimation technique. The experiments are carried out at the Reynolds number of $2.78{\times}10^{5}$ for two incidence angles of -5% and +5%. The positive incidence angle results in intensification of the pressure-side leg of a leading-edge horseshoe vortex, which delivers higher heat transfer along its trace. On the other hand, the negative incidence angle show an opposite tendency.

  • PDF

고성능 엇회전식 축류팬의 공력특성에 대한 전산해석 (Numerical analyses on the Aerodynamic Characteristics of a Counter-rotating Axial Flow Fan)

  • 조이상;조진수
    • 융복합기술연구소 논문집
    • /
    • 제5권1호
    • /
    • pp.37-40
    • /
    • 2015
  • Numerical analyses on the aerodynamic characteristics of a counter rotating axial flow fan is carried out using the frequency domain panel method. Front rotor and rear rotor blades of a counter rotating axial fan are designed by using the simplified meridional flow analysis method with the radial equilibrium equation and the free vortex design condition, according to design requirements. Performance characteristics of a counter rotating axial flow fan are estimated for the variation of design parameters such as the hub to tip ratio, the taper ratio and the solidity. Pressure losses were higher at leading edge and hub region of rotor blades. Characteristic curve of the counter rotating fan was overpredicted without consideration of viscous effect.

글라이딩하는 제비나비 날개형상의 공력특성연구 (Aerodynamic Property of Swallowtail Butterfly Wing in Gliding)

  • 이병도;박형민;최해천
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2007년도 춘계학술대회A
    • /
    • pp.395-398
    • /
    • 2007
  • In nature, the swallowtail butterfly is known to be a versatile flyer using gliding and flapping efficiently. Furthermore, it has long tails on the hind-wing that may be associated with the enhancement of the gliding performance. In the present study, we investigate the aerodynamic property of swallowtail butterfly wing in gliding. We use an immersed boundary method and conduct a numerical simulation at the Reynolds numbers of 1,000 - 3,000 based on the free-stream velocity and the averaged chord length for seven different attack angles. As a result, we clearly identify the existence of the wing-tip and leading-edge vortices, and a pair of the streamwise vortices generated along the hind-wing tails. Interestingly, at the attack angle of $10^{\circ},$ hairpin vortices are generated above the center of the body and travel downstream.

  • PDF

축류팬의 비정상 유동장 및 유동소음의 수치 해석 (NUMERICAL ANALYSIS OF UNSTEADY FLOW FIELD AND AEROACOUSTIC NOISE OF AN AXIAL FLOW FAN)

  • 김욱;허남건;전완호
    • 한국전산유체공학회지
    • /
    • 제15권4호
    • /
    • pp.60-66
    • /
    • 2010
  • Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.