• Title/Summary/Keyword: Resonant Convection

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Enhancement of Mass Transfer of an Enclosed Fluid by Time-periodic Thermal Forcing (간헐 열전달을 이용한 밀폐용기내의 물질전달 향상)

  • Kwak H. S.
    • Journal of computational fluids engineering
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    • v.7 no.1
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    • pp.36-43
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    • 2002
  • A numerical investigation is made of unsteady double-diffusive convection of a Boussinesq fluid in a rectangular cavity subject to time-periodic thermal excitations. The fluid is initially stratified between the top endwall of low solute concentration and the bottom endwall of high solute concentration. A time-dependent heat flux varying in a square wave fashion, is applied on one sidewall to induce buoyant convection. The influences of the imposed periodicity on double-diffusive convection are examined. A special concern is on the occurrence of resonance that the fluctuations of flow and attendant heat and mass transfers are mostly amplified at certain eigenmodes of the fluid system. Numerical solutions illustrate that resonant convection results in a conspicuous enhancement of time-mean mass transfer rate.

Double-Diffusive Convection in a Rectangular Cavity Responding to Time-Periodic Sidewall Heating (주기적인 측벽가열에 반응하는 사각공동내의 이중확산 대류)

  • Kwak H. S.
    • 한국전산유체공학회:학술대회논문집
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    • 2001.10a
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    • pp.112-117
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    • 2001
  • A numerical investigation is made of unsteady double-diffusive convection of a Boussinesq fluid in a rectangular cavity subject to time-periodic thermal excitations. The fluid is initially stratified between the top endwall of low solute concentration and the bottom endwall of high solute concentration. A time-dependent heat flux varying in a square wave fashion, is applied on one sidewall to induce buoyant convection. The influences of the imposed periodicity on double-diffusive convection are scrutinized. A special concern is on the occurrence of resonance that the fluctuations of flow and attendant heat and mass transfers are mostly amplified at certain eigenmodes of the fluid system. Numerical solutions are analyzed to illustrate the characteristic features of resonant convection.

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An Experimental Study on Resonance of Temperature Field by Low-Frequency Oscillating Wall in a Side Heated Enclosure (저 주파수 벽면 가진에 의한 밀폐공간 내부 온도장의 공진 특성 실험)

  • Kim, Seo-Yeong;Kim, Seong-Gi;Choe, Yeong-Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.9
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    • pp.1272-1280
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    • 2001
  • An experimental study has been conducted to elucidate the resonance of natural convection in a side-heated square enclosure having a mechanically oscillating bottom wall. Under consideration is the impact of the imposed oscillating frequency, amplitude and the system Rayleigh number on the fluctuation of air temperatures. The experimental results show that the magnitude of the fluctuation of air temperature is substantially augmented at a specific forcing frequency of the oscillating bottom wall. The resonant frequency is increased with the increase of the Rayleigh number and it is little affected by the amplitude of the oscillating wall. It is also found that the resonant frequency is relevant to the Brunt- V$\"{a}$iS$\"{a}$l$\"{a}$ frequency which represents the stratification degree of the system.

Numerical Analysis of Nonlinear Combustion Instability Using Pressure-Sensitive Time Lag Hypothesis (시간지연 모델을 이용한 비선형 연소불안정 해석기법 연구)

  • Park Tae-Seon;Kim Seong-Ku
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.7 s.250
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    • pp.671-681
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    • 2006
  • This study focuses on the development of numerical procedure to analyze the nonlinear combustion instabilities in liquid rocket engine. Nonlinear behaviors of acoustic instabilities are characterized by the existence of limit cycle in linearly unstable engines and nonlinear or triggering instability in linearly stable engines. To discretize convective fluxes with high accuracy and robustness, approximated Riemann solver based on characteristics and Euler-characteristic boundary conditions are employed. The present procedure predicts well the transition processes from initial harmonic pressure disturbance to N-like steep-fronted shock wave in a resonant pipe. Longitudinal pressure oscillations within the SSME(Space Shuttle Main Engine) engine have been analyzed using the pressure-sensitive time lag model to account for unsteady combustion response. It is observed that the pressure oscillations reach a limit cycle which is independent of the characteristics of the initial disturbances and depends only on combustion parameters and operating conditions.