• 제목/요약/키워드: Vortical Structure

검색결과 124건 처리시간 0.029초

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

  • 전세종;성형진
    • 대한기계학회논문집B
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    • 제26권9호
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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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    • 제2권1호
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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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양력형 디스크 풍력 발전기의 유동 및 소음 해석 (Noise and flow analysis of lift-type disk wind power System)

  • 고승철;나지성;이준상
    • 한국가시화정보학회지
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    • 제15권3호
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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
    • 한국연소학회지
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    • 제7권1호
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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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동축제트의 와류주파수 및 혼합특성에 대한 수치해석 연구 (NUMERICAL STUDY ON THE CHARACTERISTICS OF VORTEX FREQUENCY AND LAMINAR MIXING OF A PASSIVE SCALAR IN COAXIAL JET FLOWS)

  • 김원현;박태선
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2007년도 추계 학술대회논문집
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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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동축제트의 와류주파수 및 혼합특성에 대한 수치해석 (NUMERICAL STUDY ON THE CHARACTERISTICS OF VORTEX FREQUENCY AND LAMINAR MIXING OF A PASSIVE SCALAR IN COAXIAL JET FLOWS)

  • 김원현;박태선
    • 한국전산유체공학회지
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    • 제14권3호
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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.

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

  • 김태진;서태원
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집E
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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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균일 유동장에 수직으로 분사된 제트화염의 구조에 대한 실험적 연구 (An experimental study on the structure of the jet flame in cross flow)

  • 유영돈
    • 한국에너지공학회:학술대회논문집
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    • 한국에너지공학회 1994년도 추계학술발표회 초록집
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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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반응 및 비반응 제트 유동장에서 단일 와동의 전개 및 구조에 대한 수치모사 (Numerical Simulation of the Evolution and Structure of a Single Vortex in Reacting and Non-reacting Jet Flow Fields)

  • 황철홍;오창보;이창언
    • 한국항공우주학회지
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    • 제32권10호
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    • pp.28-37
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    • 2004
  • 반응 및 비반응 유동장에서 단일와동의 전개 및 와(渦) 구조 검토를 위해 2 차원 직접 수치모사를 수행하였다. 수치기법으로는 낮은 마하수 근사법이 적용된 예측-교정자법이 적용되었으며, 연소모텔로는 2단계 총괄 반응식이 사용되었다. 반응 및 비반응 유동장에서 단일와동의 거동 비교를 통해, 와동의 전개특성 및 구조는 화학반응으로부터 생성된 열 뿐만 아니라 부력에 의해 생성된 외부 와동에 크게 영향을 받음을 확인하였다. 또한 반응장의 경우에 부피 팽창항, Baroclinic torque항 및 부력항에 의해 와동의 구조가 크게 변화될 수 있음을 알았다.

진동하는 구 주위의 유동에 관한 수치적 연구 (Numerical Study of Flow Around an Oscillating Sphere)

  • 이진욱;이대성;하만영;윤현식
    • 설비공학논문집
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    • 제22권11호
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    • pp.767-772
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    • 2010
  • The incompressible viscous flow past a sphere under forced oscillation is numerically investigated at a Reynolds number of 300. The immersed boundary method is used to handle the sphere oscillating vertically to the streamwise direction. There are two important variables to characterize the oscillating state of a sphere. One is an oscillating amplitude normalized by the sphere diameter is set as a fixed number of 0.2. Another is the frequency ratio which is defined by $f_e/f_o$, where fe and fo are the excited frequency and the natural frequency of vortex shedding for the stationary sphere. In this study, three different frequency ratios of 0.8, 1.0 and 1.2 are considered. The results show a periodic flow with hairpin vortices shedding from upper and lower positions as well as vortical legs obliquely extended by oscillating motion of sphere. The enveloping vortical structure experience rupture twice in one period of oscillation. As the frequency of oscillation is increased, the vortical legs are getting shorter and eventually the hairpin vortices are much closer to the adjacent one.