• Title/Summary/Keyword: diffusive instability

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Turing, Turing Instability, Computational Biology and Combustion (Turing, Turing 불안정성 그리고 수리생물학과 연소)

  • Kim, J.S.
    • Journal of the Korean Society of Combustion
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    • v.8 no.1
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    • pp.46-56
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    • 2003
  • The present paper is concerned with the development of the computational biology in the past half century and its relationship with combustion. The modem computational biology is considered to be initiated by the work of Alan Turing on the morphogenesis in 1952. This paper first touches the life and scientific achievement of Alan Turing and his theory on the morphogenesis based on the reactive-diffusive instability, called the Turing instability. The theory of Turing instability was later extended to the nonlinear realm of the reactive-diffusive systems, which is discussed in the framework of the excitable media by using the Oregonator model. Then, combustion analogies of the Turing instability and excitable media are discussed for the cellular instability, pattern forming combustion phenomena and flame edge. Finally, the recent efforts on numerical simulations of biological systems, employing the detailed bio-chemical knietic mechanism is discussed along with the possibility of applying the numerical combustion techniques to the computational cell biology.

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Influence of Flame Instabilities on Propagation Characteristics of Stagnating Turbulent Premixed Flames (화염 불안정성이 난류 예혼합 화염의 전파 특성에 미치는 영향에 관한 연구)

  • Kwon, Jaesung;Huh, Kang Y.
    • 한국연소학회:학술대회논문집
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    • 2012.04a
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    • pp.287-288
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    • 2012
  • DNS is performed to examine the propagation characteristics of stagnating turbulent premixed flames. Results show good agreement with the recently proposed relationship for turbulent burning velocity, $S_T$. It is shown that $S_T$ increases through a thinner flamelet, turbulence production and correlation between fluctuating velocity and buoyancy force respectively for diffusive-thermal, hydrodynamic and Rayleigh-Taylor instability. The mean curvature doesn't have significant effect on $S_T$ at the leading edge.

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Investigation of Premixed Flame Instability with Heat and Momentum Losses (열 및 운동량 손실이 예혼합화염의 연소불안정성에 미치는 영향에 관한 연구)

  • Kang Sang Hun;Baek Seung Wook;Im Hong Geun
    • Journal of the Korean Society of Propulsion Engineers
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    • v.9 no.3
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    • pp.101-119
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    • 2005
  • For MEMS applications, the effects of the momentum and heat loss on the stability of laminar premixed flames in a narrow channel are investigated by high-fidelity numerical simulations. A general finding is that momentum loss promotes the Saffman-Taylor (S-T) instability which is additive to the Darrieus-Landau (D-L) instabilities, while the heat loss effects result in an enhancement of the diffusive-thermal (D-T) instability. These effects are also valid in nonlinear behavior of the premixed flame. The simulations of multiple cell interactions are also conducted with heat and momentum loss effects.

A Numerical Study on Nonlinear Dynamic Behavior of Diffusive-Thermal Instability in Diluted CH4/O2 Conterflow Diffusion Flames (희석된 메탄/산소 대향류 확산화염에서 확산-열 불안정으로 인한 화염의 비선형 동적 거동에 관한 수치해석)

  • Sohn, Chae-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.6
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    • pp.688-696
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    • 2004
  • Nonlinear dynamic behavior of diffusive-thermal instability in diluted CH$_4$/O$_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution, which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is net observed in this study, which is attributed to both convective flow and preferential diffusion effects.

Numerical Study on Dynamic Behavior of Diffusive-Thermal Instability in $CH_4/O_2$ Conterflow Diffusion Flames (메탄/산소 대향류 확산화염에서 확산-열 불안정으로 인한 화염의 거동에 관한 수치적 연구)

  • Sohn, Chae-Hoon
    • 한국연소학회:학술대회논문집
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    • 2004.06a
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    • pp.95-101
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    • 2004
  • Dynamic behavior of diffusive-thermal instability in diluted $CH_4/O_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate. transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed Oil the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution. which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is not observed in this study, which is attributed to both convective flow and preferential diffusion effects.

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HOPF BIFURCATION PROPERTIES OF HOLLING TYPE PREDATOR-PREY SYSTEMS

  • Shin, Seong-A
    • The Pure and Applied Mathematics
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    • v.15 no.3
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    • pp.329-342
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    • 2008
  • There have been many experimental and observational evidences which indicate the predator response to prey density needs not always monotone increasing as in the classical predator-prey models in population dynamics. Holling type functional response depicts situations in which sufficiently large number of the prey species increases their ability to defend or disguise themselves from the predator. In this paper we investigated the stability and instability property for a Holling type predator-prey system of a generalized form. Hopf type bifurcation properties of the non-diffusive system and the diffusion effects on instability and bifurcation values are studied.

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Diffusive-Thermal Instability and Buoyancy-Driven Instability in Laminar Attached Free-jet Flames with DC Electric Fields (직류 전기장을 인가한 층류부착화염에서 물질-열 확산 및 부력에 의한 화염진동 비교에 관한 연구)

  • Han, Jong-Kyu;Yoon, Sung-Hwan;Park, Jeong;Yun, Jin-Han;Gil, Sang-In;Seo, Sang-Il;Kim, Young-Ju
    • Journal of the Korean Society of Combustion
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    • v.16 no.3
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    • pp.41-51
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    • 2011
  • In this paper, we describe the behavior of two self-excitations in laminar attached free-jet flames under the influence of DC electric fields, one of buoyancy-driven and the other of diffusion-thermal instability, established from the horizontal and vertical injection. In the horizontal injection with removed buoyancy effect, oscillating flames with the frequency of 1.3 - 7.4 Hz were observed in a certain condition with Lewis number more than unity. On the other hand, it was appeared Lewis number induced self-excitation as well as buoyancy-driven self-excitation in the vertical upward injection with DC electric fields. This behavior had frequency range of 1.6 - 9.4 Hz and was exhibited to attribute the buoyancy effect. Finally, a well-defined division about two self-excitations having similar frequency range is briefly discussed.

Vibration Characteristics of Lean Premixed Flame Anchored by a Hydrogen Pilot Flame in a Tube (파일롯 화엄에 의해 고정된 관내 예혼합 화염의 진동 특성)

  • Guahk, Young-Tae;Oh, Kwang-Chul;Shin, Hyun-Dong
    • 한국연소학회:학술대회논문집
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    • 2004.06a
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    • pp.42-48
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    • 2004
  • Lean laminar premixed propane and methane flames which were anchored by a hydrogen-pilot flame in a tube were investigated experimentally. The flame shapes were observed by varying mean velocity from 10cm/s to 140cm/s and equivalence ratio from 0.45 to 0.8. In this study, behaviors of flames are divided into five regions such as tail-out, flash-back, flickering, stable and vibrating flames with respect to the mean velocity and the equivalence ratio. Although the flames are unstable in both the flickering and the vibrating region, they have different characteristics such as the frequency, sound generation and creation process of flame curvature. The flickering region exists near the flammability limit and the flame flickers in a frequency of about 10Hz. When flame front is bended, the propane flame front is straightened and the methane flame front is bended more by thermo-diffusive instability. In the vibrating region, the flame vibrates emitting audible sound in a frequency of about 100Hz. In the boundary of vibrating region, the vibration of flame changes between two modes such as single frequency vibration and dual frequency vibration. Increase and decrease of vibration in each mode are determined by thermo-acoustic instability.

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STABILITY AND BIFURCATION IN A DIFFUSIVE PREY-PREDATOR SYSTEM : NON-LINEAR BIFURCATION ANALYSIS

  • Bhattacharya, Rakhi;Bandyopadhyay, Malay;Banerjee, Sandip
    • Journal of applied mathematics & informatics
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    • v.10 no.1_2
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    • pp.17-26
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    • 2002
  • A stability analysis of a non-linear prey-predator system under the influence of one dimensional diffusion has been investigated to determine the nature of the bifurcation point of the system. The non-linear bifurcation analysis determining the steady state solution beyond the critical point enables us to determine characteristic features of the spatial inhomogeneous pattern arising out of the bifurcation of the state of the system.

A Numerical Study of the Flame Cell Dynamics in Opposed Nonpremixed Tubular Configuration (비예혼합 튜브형상내 화염셀의 거동에 대한 수치 해석적 연구)

  • Park, Hyunsu;Yoo, Chun Sang
    • 한국연소학회:학술대회논문집
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    • 2014.11a
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    • pp.175-178
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    • 2014
  • The flame cell dynamics in 2-D opposed nonpremixed tubular configuration was investigated using high-fidelity numerical simulations. The diffusive-thermal instability occurs as the $Damk{\ddot{o}}hler$ number, Da, approaches the 1-D extinction limit of the tubular flames and several flame cells are generated depending on Da, and flame radius. In general, the number of flame cells are found close to the largest wave number from the linear stability analysis. It was also found from the displacement speed analysis that during the local flame extinction and cell formation, negative edge flame speed is observed due to small gain from reaction compared to large loss from diffusion.

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