• Title/Summary/Keyword: Vortex distribution

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Wind pressure on a solar updraft tower in a simulated stationary thunderstorm downburst

  • Zhou, Xinping;Wang, Fang;Liu, Chi
    • Wind and Structures
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    • v.15 no.4
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    • pp.331-343
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    • 2012
  • Thunderstorm downbursts are responsible for numerous structural failures around the world. The wind characteristics in thunderstorm downbursts containing vortex rings differ with those in 'traditional' boundary layer winds (BLW). This paper initially performs an unsteady-state simulation of the flow structure in a downburst (modelled as a impinging jet with its diameter being $D_{jet}$) using a computational fluid dynamics (CFD) method, and then analyses the pressure distribution on a solar updraft tower (SUT) in the downburst. The pressure field shows agreement with other previous studies. An additional pair of low-pressure region and high-pressure region is observed due to a second vortex ring, besides a foregoing pair caused by a primary vortex ring. The evolutions of pressure coefficients at five orientations of two representative heights of the SUT in the downburst with time are investigated. Results show that pressure distribution changes over a wide range when the vortices are close to the SUT. Furthermore, the fluctuations of external static pressure distribution for the SUT case 1 (i.e., radial distance from a location to jet center x=$D_{jet}$) with height are more intense due to the down striking of the vortex flow compared to those for the SUT case 2 (x=$2D_{jet}$). The static wind loads at heights z/H higher than 0.3 will be negligible when the vortex ring is far away from the SUT. The inverted wind load cases will occur when vortex is passing through the SUT except on the side faces. This can induce complex dynamic response of the SUT.

Axial-Compressor Design with Mean-line Analysis and Vortex Method (평균유속법과 Vortex 방법을 사용한 축류압축기 설계)

  • Choi, Min-Suk;Yoon, Sugn-Ho;Baek, Je-Hyun
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.795-800
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    • 2001
  • In this study, a program to design a multi-stage axial compressor is developed wi th mean-line analysis and vortex methods. In a preliminary design stage, a method. to design in a short time is needed and mean-line analysis is usually used for this purpose. Arbitrary pressure ratio and reaction can be assigned to generate overall geometry and several vortex methods are adopted to consider the radial distribution of velocity and reaction. The variation of performance, when we use free vortex, forced vortex, and exponential method, is compared and discussed.

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The Effect of Serrated Fins on the Flow Around a Circular Cylinder

  • Boo, Jung-Sook;Ryu, Byong-Nam;Kim, Kyung-Chun
    • Journal of Mechanical Science and Technology
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    • v.17 no.6
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    • pp.925-934
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    • 2003
  • An experimental study is performed to investigate the characteristics of near wake flow behind a circular cylinder with serrated fins using a constant temperature anemometer and flow visualization. Various vortex shedding modes are observed. Fin height and pitch are closely related to the vortex shedding frequency after a certain transient Reynolds number. The through velocity across the fins decreases with increasing fin height and decreasing fin pitch. Vortex shedding is affected strongly by the velocity distribution just on top of the finned tube. The weaker gradient of velocity distribution is shown as increasing the freestream velocity and the fin height, while decreasing the fin pitch. The weaker velocity gradient delays the entrainment flow and weakens its strength. As a result of this phenomenon, vortex shedding is decreased. The effective diameter is defined as a virtual circular cylinder diameter taking into account the volume of fins, while the hydraulic diameter is proposed to cover the effect of friction by the fin surfaces. The Strouhal number based upon the effective diameters seems to correlate well with that of a circular cylinder without fins. After a certain transient Reynolds number, the trend of the Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter. The normalized velocity and turbulent intensity distributions with the hydraulic diameter exhibit the best correlation with the circular cylinder's data.

NUMERICAL ANALYSIS OF PRESSURE PERTURBATION OF DELTA WING VORTEX FLOW AT A HIGH ANGLE OF ATTACK (고 받음각 ONERA 70도 삼각날개 와류 유동의 압력 섭동 분석)

  • Son, M.S.;Sa, J.H.;Park, S.H.;Byun, Y.H.
    • Journal of computational fluids engineering
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    • v.20 no.2
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    • pp.73-80
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    • 2015
  • Delayed Detached-Eddy Simulation was conducted to investigate surface pressure coefficient distribution and surface pressure fluctuation over an ONERA 70-degree delta wing at a high angle of attack. Time-averaged surface pressure distribution is directly affected by the primary vortices, whereas the pressure fluctuation is influenced by the unsteady fluctuating boundary layer over the surface. And pressure coefficient, velocity, pressure fluctuation, and turbulent kinetic energy were analyzed along the vortex core in order to investigate the process of vortex breakdown. Consequently, strong pressure fluctuations were found where the vortex breakdown was occurred at x~620 mm. The turbulent kinetic energy abruptly increased and followed after the vortex breakdown.

Distribution of the Reynolds Stress Tensor Inside Tip Leakage Vortex of a Linear Compressor Cascade (I) - Effect of Inlet Flow Angle - (선형 압축기 익렬에서 발생하는 익단 누설 와류내의 레이놀즈 응력 분포 (I) -입구 유동각 변화의 영향-)

  • Lee, Gong-Hee;Park, Jong-Il;Baek, Je-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.8 s.227
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    • pp.902-909
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    • 2004
  • A steady-state Reynolds averaged Navier-Stokes simulation was conducted to investigate the distribution of the Reynolds stress tensor inside tip leakage vortex of a linear compressor cascade. Two different inlet flow angles ${\beta}=29.3^{\circ}$(design condition) and $36.5^{\circ}$(off-design condition) at a constant tip clearance size of $1\%$ blade span were considered. Classical methods of solid mechanics, applied to view the Reynolds stress tensor in the principal direction system, clearly showed that the high anisotropic feature of turbulent flow field was dominant at the outer part of tip leakage vortex near the suction side of the blade and endwall flow separation region, whereas a nearly isotropic turbulence was found at the center of tip leakage vortex. There was no significant difference in the anisotropy of the Reynolds normal stresses inside tip leakage vortex between the design and off-design condition.

Characteristics of Near Wake Behind a Circular Cylinder with Serrated Fins (I) - Mechanism of Vortex Shedding - (톱니형 휜이 부착된 원주의 근접후류특성 연구 (I) - 와유출 메카니즘의 특성변화 규명 -)

  • Ryu, Byeong-Nam;Kim, Gyeong-Cheon;Bu, Jeong-Suk
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.8
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    • pp.1183-1190
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    • 2002
  • An experimental study is performed to investigate the characteristics of near wake behind a circular cylinder with serrated fins using the constant temperature anemometer and through flow visualization. Previous report(Boo et al., 2001) shows that there are three different modes in vortex shedding behavior. This paper is focused on the identification of the physical reasons why the difference iss occured in vortex shedding. The through flow velocity crossing fins decreases as increasing fin height and decreasing fin pitch mainly due to the flow resistence. Vortex shedding is affected strongly by velocity distribution around fin tube, especially by the velocity gradient. The velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. Those differences in velocity gradients generate different vortex shedding mechanism.

A simplified vortex model for the mechanism of vortex-induced vibrations in a streamlined closed-box girder

  • Hu, Chuanxin;Zhao, Lin;Ge, Yaojun
    • Wind and Structures
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    • v.32 no.4
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    • pp.309-319
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    • 2021
  • The vortex-drift pattern over a girder surface, actually demonstrating the complex fluid-structure interactions between the structure and surrounding flow, is strongly correlated with the VIVs but has still not been elucidated and may be useful for modeling VIVs. The complex fluid-structure interactions between the structure and surrounding flow are considerably simplified in constructing a vortex model to describe the vortex-drift pattern characterized by the ratio of the vortex-drift velocity to the oncoming flow velocity, considering the aerodynamic work. A spring-suspended sectional model (SSSM) is used to measure the pressure in wind tunnel tests, and the aerodynamic parameters for a typical streamlined closed-box girder are obtained from the spatial distribution of the phase lags between the distributed aerodynamic forces at each pressure point and the vortex-excited forces (VEFs). The results show that the ratio of the vortex-drift velocity to the oncoming flow velocity is inversely proportional to the vibration amplitude in the lock-in region and therefore attributed to the "lock-in" phenomena of the VIVs. Installing spoilers on handrails can destroy the regular vortex-drift pattern along the girder surface and thus suppress vertical VIVs.

Numerical Studies on the Variation of Flow Structure Due to Sea Surface Temperature at the Lee Side of Jeju Island in the Korean Peninsula (해수면 온도변화에 따른 제주도 후면 흐름구조 변화에 관한 수치연구)

  • Lee, Soon-Hwan;Park, Gwang-Soon
    • Journal of the Korean earth science society
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    • v.27 no.1
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    • pp.61-72
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    • 2006
  • Numerical studies on the influence of interaction between atmosphere and ocean on the variation of Karman vortex at the lee side of Jeju Island were carried out. Karman vortex tends to be occurred at limited height associated with Hanla mountain. And we can find clear Karman vortex at 900 hPa height in this study. One big vortex cell occurred at lee side of Jeju Island in the begging stage of its development and the cell was divided into three small cells as time goes by. And the strength and lifetime of small vortexes depend on the distribution of SST (Sea Surface Temperature). Weak gradient of SST makes long-lasting Karman vortex but produces weak potential vorticity at lee side of Jeju-do in comparison with the vortex under strong SST gradient. Strong SST gradient also increases not only the mixing depth but also the mixing ratio at lower level of troposphere. And the increased atmospheric mixing decreases the mechanical forcing due to isolated topography. Then the strength of Karman vortex at the lee side of Jeju Island becomes weak under strong gradient of SST. Thus the evolution of Karman vortex is closely related to distribution of SST around the isolated island.

Inverse Airfoil Design for Wind Turbine (역설계 기법을 이용한 풍력터빈 에어포일 형상 설계)

  • Ryu, Ki-Wahn;Park, Myoung-Ho
    • Journal of Wind Energy
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    • v.4 no.2
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    • pp.55-60
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    • 2013
  • The mathematical implementation for inverse airfoil design of wind turbines is presented using vortex panel method based on assumptions of the two-dimensional incompressible potential flow. The vortex panel method employs linear distribution of the vortex strength to obtain the well converged solution. Stream function is adopted to get the basic formula for the inverse airfoil design, and a symmetric seed airfoil is given for initial data of the iteration approach. The final airfoil shape has been compared with the original airfoil shape for validation of the mathematical procedure.

Characteristics of Tip Vortex by Blade Loading (Blade Loading에 의한 팁와류의 특성)

  • Yoon, Yong Sang;Song, Seung Jin
    • 유체기계공업학회:학술대회논문집
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    • 2002.12a
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    • pp.273-278
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    • 2002
  • The characteristics of tip vortex within a blade tip region were examined experimentally in various flow coefficients by the way of changing tip clearance and blade stagger angle in an axial Low Speed Research Compressor(LSRC). The objective was to identify the unsteady pressure distribution in the blade passage by ensemble average technique acquired from high-frequency response pressure transducers and the tip vortex by root mean square value(RMS value). Data were reduced statistically using phase-lock technique for detailed pressure distributions.

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