• 한국연소학회지
• /
• 제13권4호
• /
• pp.8-15
• /
• 2008

When a circular cylinder is placed at the center of a slot burner nozzle, once stable Woflhard-Parker type laminar lean premixed flame is changed to an oscillating flame with self-induced noise. The wrinkled flame surface showed the same pattern and frequency of the Karman vortex street at the downstream of a circular cylinder. The interaction of flame with Karman vortex street is observed to be responsible for flame oscillation. The measured flame oscillation frequency is very similar to the estimated Karman vortex shedding frequency based on the St-Re relationship of the flow past circular cylinder, which could be considered as a strong evidence for the interaction between laminar pre-mixed flame and a Karman vortex street. As Reynolds number increases oscillation frequency decreases and the self-induced noise level increases as well as the flame front is more severly wrinkled. This result suggests that the flame/vortex interaction becomes more active at higher Re.

• Journal of Mechanical Science and Technology
• /
• 제15권5호
• /
• pp.623-629
• /
• 2001

The PSC (Propagation of Surfaces under Curvature) algorithm is adapted to the simulation of a flame propagation in a premixed medium including the effect of volume expansion across the flame front due to exothermicity. The algorithm is further developed to incorporate the flame anchoring scheme. This methodology is successfully applied to numerically simulate the response of an anchored V-flame to two strong free stream vortices, in accord with experimental observations of a passage of Karman vortex street through a flame. The simulation predicts flame cusping when a strong vortex pair interacts with flame front. In other words, this algorithm handles merging and breaking of the flame front and provides an accurate calculation of the flame curvature which is needed for flame propagation computation and estimation of curvature-dependent flame speeds.

• 대한기계학회논문집B
• /
• 제22권12호
• /
• pp.1669-1680
• /
• 1998

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength assigned by the density difference between the burned and the unburned region. The present model provides good agreement with the experimental results. Including volume expansion, the flow field is adjusted to accommodate the increased volume flow rate which crossing the flame front and the result predicts the same behavior of measured velocity field qualitatively. The effect of increasing volume expansion does not change the initial growth rate of flame area but increase the residence time. Consequently this effect increases the maximum area of flame front. The flame propagation in varying flow field due to volume expansion provides a promising way to represent the wrinkled turbulent premixed flames in a numerically efficient manner.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 춘계학술대회논문집
• /
• pp.170-175
• /
• 2005

The focus of this paper is to observe the aerodynamic and vibration characteristics of the NACA0012 blade(AR=16.6) fixed on the lower surface of the wind tunnel, by changing air speed and the blade's angle of attack. After fixing a slit-typed vortex generator on the front of the blade, it could be observed that the vibrational characteristics caused by interactions between vortex and blade through the 5-hole pilot tubes. And, also, two different blades in stiffness had been prepared for observing those characteristics above in this experiment. The results were compared with the given stiffness of blade, as well. According to the results, it is clear to recognize that the vibration spectrum increases while air speed and angle of attack increase, and, also, less stiffness means bigger vibration spectrum.

• Wind and Structures
• /
• 제29권1호
• /
• pp.55-64
• /
• 2019

The effect of vortex impingement on the fluid dynamics around a cylinder submerged in the wake of another of different diameters is numerically investigated at a Reynolds number Re = 200. While the diameter (D) of the downstream cylinder is fixed, impinging vortices are produced from the upstream cylinder diameter (d) varied as d/D = 0.24, 0.4, 0.6, 0.8 and 1.0, with a spacing ratio L=5.5d, where L is the distance between the center of the upstream cylinder to the front stagnation point of the downstream cylinder. Two-dimensional simulations are carried out using the finite volume method. Fluid forces acting on the two cylinders are correlated with impinging vortices, vortex shedding, and wake structure. Different facets of wake formation, wake structure, and flow separation and their connections to fluid forces are discussed.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1998년도 추계 학술대회논문집
• /
• pp.204-210
• /
• 1998

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength determined by the density difference between the burned and the unburned region. Volume expansion adjusts the flow field to accommodate the increased volume flow rate crossing the flame front. Test result predicted the measured velocity field qualitatively. The method was applied to study the interaction of vortex and premixed flame. Increased volume expansion did not change the initial growth rate of flame area. However, the residence time and flame surface area increased with higher expansion ratios.

• 융합신호처리학회논문지
• /
• 제20권4호
• /
• pp.199-204
• /
• 2019

경계층 내 측정된 유속은 변동 성분을 활용한 표준편차 혹은 배경 유속을 포함한 평균 속도로 해석되어 왔다. 하지만, 각각의 결과로 유동 상호작용을 설명하는데 한계가 있어 본 논문에서는 시간 영역의 유속을 퓨리에 변환하여 주파수 분석으로 유동 현상을 규명하는 방법을 제안한다. 이를 위해 경계층 내 평판 위에 부착된 반구 내부로 염료를 주입시켜 후류 영역에서 생성되는 머리핀 와류를 가시화하여 발생 빈도를 계측하였다. 또한 반구 전방의 평판을 뚫어 흡입함으로써 후류 영역 내 유속 변화를 열선 유속계로 측정하였다. 제안된 주파수 분석의 평가를 위해 기존의 통계 해석법과 비교하였으며, 유동의 정성적인 결과에 부합하는 주파수 분석과정을 제시한다.

• Wind and Structures
• /
• 제26권5호
• /
• pp.293-304
• /
• 2018

A numerical study is conducted on the flow characteristics of a rectangular cylinder (chord-to-width ratio C/W = 2 - 10) mounted close to a rigid wall at gap-to-width ratios G/W = 0.25 - 6.25. The effects of G/W and C/W on the Strouhal number, vortex structure, and time-mean drag and lift forces are examined. The results reveal that both G/W and C/W have strong influences on vortex structure, which significantly affects the forces on the cylinder. An increase in G/W leads to four different flow regimes, namely no vortex street flow (G/W < 0.75), single-row vortex street flow ($0.75{\leq}G/W{\leq}1.25$), inverted two-row vortex street flow ($1.25<G/W{\leq}2.5$), and two-row vortex street flow (G/W > 2.5). Both Strouhal number and time-mean drag are more sensitive to C/W than to G/W. For a given G/W, Strouhal number grows with C/W while time-mean drag decays with C/W, the growth and decay being large between C/W = 2 and 4. The time-mean drag is largest in the single-row vortex street regime, contributed by a large pressure on the front surface, regardless of C/W. A higher C/W, in general, leads to a higher time-mean lift. The maximum time-mean lift occurs for C/W = 10 at G/W = 0.75, while the minimum time-mean lift appears for C/W = 2 at the same G/W. The impact of C/W on the time-mean lift is more substantial in single-row vortex regime. The effect of G/W on the time-mean lift is larger at a larger C/W.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2011년도 추계학술대회 초록집
• /
• pp.40.2-40.2
• /
• 2011

A Counter-rotating wind turbine is one of the new concepts that are proposed to increase the performance of a wind turbine. It has two rotors rotating in the same axis, and it is known that its power coefficient can reach to 0.64 in the ideal case. While the BEMT is widely used to analyze the aerodynamic performance of wind turbines, the analysis of the counter-rotating wind turbine by using it is limited due to the aerodynamic interaction between the two rotors. In this study, the vortex lattice method is used to consider the effect of the front rotor on the rear rotor of the counter-rotating wind turbine and calculate the aerodynamic performance of it. The power and thrust sharing in the two rotors of the counter-rotating wind turbine are predicted and the total power and thrust are compared with that of a single rotor. Moreover, the wake convection and expansion rate is also compared with that of a single rotor.

• 한국해양환경ㆍ에너지학회지
• /
• 제3권2호
• /
• pp.18-24
• /
• 2000

성질이 다른 두가지 유체가 복잡한 상호작용을 하는 경우의 유동을 살펴 보기 위하여 2차원 비점성 수치해법을 개발하고, 이를 감압된 수중 파이프에서의 기름 유출 문제에 적용하였다. 두 유체의 경계면은 보오텍스 쉬트로 모델링하고 보오텍스격자법 (vortex-in-cell method)을 적용하여 유동을 해석하며, 장시간의 유동 모사를 위하여 경계면의 분할과 접합이 가능하도록 하였다. Boussinesq 가정에서 외부유체의 관내로의 유입 속도가 기존의 수학모델과 거의 동일함을 확인하였고, 경계면에서의 복잡한 상호 유입과 보오텍스 유동에도 불구하고 Lock Exchange가 발생함을 보였다. 개발된 수치해법은 다양한 해양환경의 2상유체 문제에 효과적으로 이용될 수 있다고 사료된다.