• Title/Summary/Keyword: Vortical structure

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Large-Scale Vortical Structure of Turbulent Separation Bubble Affected by Unsteady Wake (비정상 후류가 난류박리기포의 응집구조에 미치는 영향)

  • Jeon, Se-Jong;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.9
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    • pp.1218-1225
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    • 2002
  • Large-scale vortical structure of a turbulent separation bubble affected by unsteady wake is essential to understand flow mechanisms in various fluid devices. A spoked-wheel type of wake generator provides unsteady wake, which modifies the turbulent separation bubble significantly by changing rotation directions and passing frequencies. A detailed mechanism of vortex shedding from the separation bubble with unsteady wake is analyzed by taking a conditional average with spatial box filtering, which spatially integrates measured signals at pre-determined wavelength. A convecting nature of the large-scale vortical structure is analyzed carefully. Spatial evolution of the large-scale vortical structure with frequency variance is also exemplified.

Large-Scale Vortical Structures in The Developing Plane Mixing Layer Using LES

  • Seo, Taewon;Kim, Yeung-Chan;Keum, Kihyun
    • International Journal of Aeronautical and Space Sciences
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    • v.2 no.1
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    • pp.12-19
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    • 2001
  • Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.

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Noise and flow analysis of lift-type disk wind power System (양력형 디스크 풍력 발전기의 유동 및 소음 해석)

  • Ko, Seungchul;Na, Jisung;Lee, Joon Sang
    • Journal of the Korean Society of Visualization
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    • v.15 no.3
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    • pp.52-56
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    • 2017
  • In this study, we investigate the flow characteristics of lift-type disk which behaves the up-down motion using the large eddy simulation (LES) and immersed boundary method (IBM). Also, we perform the noise analysis using pressure field at 1.35 m distance and reveal the cause of noise to observe the vortical structure analysis of flow result. It is observed that vortical structure and wind shear were generated at leading edge and tower with high velocity deficit and flow separation. High magnitude of flow noise was observed in low frequency range which is from 30 Hz to 60 Hz. It was observed that vortical structure at leading edge was generated in frequency range from 33.3 Hz to 41.6 Hz. Temporal characteristic in vortical structure at leading edge was similar to noise characteristics, having the similar frequency ranges.

Numerical Study on Vortex Structures in a Two-dimensional Bluff-Body Burner in the Transitional Flow Regime

  • Kawahara, Hideo;Nishimura, Tatsuo
    • Journal of the Korean Society of Combustion
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    • v.7 no.1
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    • pp.31-36
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    • 2002
  • Vortical structures are investigated numerically for both cold and combusting flows from a two-dimensional bluff-body burner in the transitional flow regime from steady to unsteady state. The Reynolds number of the central fuel flow is varied from 10 to 230 at a fixed air Reynolds number of 400. The flame sheet model of infinite chemical reaction and unit Lewis number are assumed in the simulation. The temperature dependence of the viscosity and diffusivity of the gas mixture is also considered. The vortex shedding is observed depending on the fuel flow. For cold flow, four different types of vortical structure are identified. However, for combusting flow of methane-air system the vortical structures change significantly due to a large amount of heat release during the combustion process, in contract to cold flow.

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NUMERICAL STUDY ON THE CHARACTERISTICS OF VORTEX FREQUENCY AND LAMINAR MIXING OF A PASSIVE SCALAR IN COAXIAL JET FLOWS (동축제트의 와류주파수 및 혼합특성에 대한 수치해석 연구)

  • Kim, Won-Hyun;Park, Tae-Seon
    • 한국전산유체공학회:학술대회논문집
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    • 2007.10a
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    • pp.21-26
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    • 2007
  • This study focuses on the near-field vortical structure and dynamics of coaxial jets. The characteristics of laminar flow and mixing in coaxial jets are investigated using a unsteady flow simulation. In order to analyze the geometic effects on the vortical structure, several cases of different configurations are selected for various values of the velocity ratio of inner jet to outer jet. From the result, it is confirmed that mixing is promoted by the development of vortical structure and the interaction between inner jet and outer jet. This feature is strongly related to the vortex frequency in the shear-layers. The vortex frequency depends on the velocity ratio and the lip thickness of inner nozzle, but the outer pipe length has no effect on the frequency variation.

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NUMERICAL STUDY ON THE CHARACTERISTICS OF VORTEX FREQUENCY AND LAMINAR MIXING OF A PASSIVE SCALAR IN COAXIAL JET FLOWS (동축제트의 와류주파수 및 혼합특성에 대한 수치해석)

  • Kim, Won-Hyun;Park, Tae-Seon
    • Journal of computational fluids engineering
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    • v.14 no.3
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    • pp.49-55
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    • 2009
  • This study focuses on the near-field vortical structure and dynamics of coaxial jets. The characteristics of laminar flow and mixing in coaxial jets are investigated using a unsteady flow simulation. In order to analyze the geometric effects on the vortical structure, several cases of different configurations are selected for various values of the velocity ratio of inner jet to outer jet. From the result, it is confirmed that the flow mixing is promoted by the development of vortical structure and the interaction between inner jet and outer jet. This feature is strongly related to the vortex frequency in the shear-layers. The vortex frequency depends on the velocity ratio and the lip thickness of inner nozzle, but the outer pipe length has no effect on the frequency variation.

Numerical study of Particle Motion in a Developing Mixing Layer using Large-eddy Simulation (LES를 이용한 발전하는 혼합층에서의 입자 운동에 관한 수치 해석 연구)

  • Kim, Tae-Jin;Seo, Tae-Won
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.94-99
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    • 2001
  • The numerical simulation of the particle dispersion in the vortical flows provides insight into the mechanism of particle-fluid interaction. The simulation results show that the mixing layers are characterized by the large-scale vortical structures undergoing pairing process. The particle dispersion is strongly influenced by the large-scale structures and the particle sizes. The analysis shows that the mixing layers grows like a step-function.

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Design of Sidewall Ribs for Suppressing Vortex Structures and Reducing Evaporation Rate in Liquid Hydrogen Storage Tank (액체수소 저장용기의 와류 구조 억제 및 증발률 저감을 위한 측벽 rib 설계)

  • Byeonggeon Kim;Hyungi Kim;Yunjeong Park;Mingyu Im;Sungwoo Park;Jinyul Hwang
    • Journal of the Korean Society of Visualization
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    • v.22 no.2
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    • pp.11-19
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    • 2024
  • We performed numerical simulations on a C-type liquid hydrogen (LH2) storage tank for commercial vehicles to reduce evaporation rates by manipulating vortical structures. Owing to external heat, natural convection occurs inside the tank, leading to the enhanced evaporation of LH2. We observed that the regions of high magnitude vorticity correlate with those of high evaporation rates. Specifically, vortical structures in the side section area show higher vorticity magnitude and evaporation rates compared to those in the midsection area. To suppress these vortical motions, we installed an array of ribs at intervals corresponding to the mean diameter of the vortical structures. As a result, the area occupied by vortical structures in the side section area decreased, leading to a reduction in evaporation speed by approximately 2.3 times. This study elucidates the internal evaporation mechanism in storage tanks from the perspective of flow structures and potentially contributes to minimizing the boil-off rate in cryogenic storage tanks.

An experimental study on the structure of the jet flame in cross flow (균일 유동장에 수직으로 분사된 제트화염의 구조에 대한 실험적 연구)

  • 유영돈
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
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    • 1994.11a
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    • pp.84-89
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    • 1994
  • 주유동에 수직으로 분사된 제트 화염의 구조는 이해하기 위하여 화염 길이와 온도를 측정하고 reactive mie scattering 방법을 이용하여 단면 가시화를 실시하였다. 주유동 속도와 제트 분사 속도의 증가에 따라 화염 길이도 함께 증가함을 알 수 있고, 단면 가시화 결과 화염 내부에 존재하는 inner vortical structure는 일반적인 동축제트 화염과 같은 대칭 구조를 갖지 앉고 유동 조건에 따라 inner vortical motion 의 생성 위치가 변화함을 알 수 있다 이는 본 유동장의 특성 중의 하나인 bound vortex와 제트와 주유동이 접하는 상류 면에서 발생하는 rolling-up 의 강도에 좌우됨을 알 수 있다.

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Numerical Simulation of the Evolution and Structure of a Single Vortex in Reacting and Non-reacting Jet Flow Fields (반응 및 비반응 제트 유동장에서 단일 와동의 전개 및 구조에 대한 수치모사)

  • Hwang, Chul-Hong;Oh, Chang-Bo;Lee, Chang-Eon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.10
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    • pp.28-37
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    • 2004
  • A two-dimensional direct numerical simulation was performed to investigate the evolution and vortical structure of a single vortex in reacting and non-reacting jet flow fields. A predictor-corrector-type numerical scheme with a low Mach number approximation was used, and a two-step global reaction mechanism was adopted as the combustion model. Through the comparisons of single vortex behaviors in reacting and non-reacting jet flow fields, it was found that the evolution characteristics and vortical structure of the single vortex were significantly influenced by a outer vortex that was generated from the buoyance effect as well as the chemical heat release. Furthermore, it was also identified that the differences of the vortical structure in reacting and non-reacting jet flow fields were mainly attributed to the thermal expansion, Baroclinic torque and buoyance effect.