首页> 外文期刊>Combustion Science and Technology >INTRINSIC INSTABILITY OF THREE-DIMENSIONAL PREMIXED FLAMES UNDER LOW- AND HIGH-TEMPERATURE CONDITIONS: EFFECTS OF UNBURNED-GAS TEMPERATURE ON HYDRODYNAMIC AND DIFFUSIVE-THERMAL INSTABILITIES
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INTRINSIC INSTABILITY OF THREE-DIMENSIONAL PREMIXED FLAMES UNDER LOW- AND HIGH-TEMPERATURE CONDITIONS: EFFECTS OF UNBURNED-GAS TEMPERATURE ON HYDRODYNAMIC AND DIFFUSIVE-THERMAL INSTABILITIES

机译:低温和高温条件下三维预混合火焰的内在不稳定性:未燃烧气体温度对水动力和扩散热不稳定性的影响

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The intrinsic instability of three-dimensional (3D) premixed flames under low-and high-temperature conditions was numerically treated to study the effects of unburned-gas temperature on hydrodynamic and diffusive-thermal instabilities. Superimposing a sinusoidal disturbance with sufficiently small amplitude on a planar flame, we obtained the relation between the growth rate and wave number, i.e., the dispersion relation. As the unburned-gas temperature became lower, the growth rate decreased and the unstable range narrowed due to the decrease of the burning velocity of a planar flame. At sufficiently small wave numbers, the obtained numerical results were consistent with the theoretical solutions. When the Lewis number was small, we obtained a large growth rate and wide unstable range due to diffusive-thermal effects. The growth rate and wave number were normalized by the burning velocity of a planar flame and preheat zone thickness. The normalized growth rate increased and the normalized unstable range widened with a decrease of unburned-gas temperature. This was because thermal-expansion effects became stronger owing to the increase of the temperature ratio of burned and unburned gases. To elucidate the characteristics of cellular flames generated by intrinsic instability, we superimposed a disturbance with the critical wave number corresponding to the maximum growth rate, i.e., the linearly most unstable wave number. The superimposed disturbance evolved, and a hexagonal cellular flame formed. The behavior of cellular flames became stronger as the unburned-gas temperature became lower, even though the growth rate decreased. The burning velocity of a cellular flame normalized by that of a planar flame increased due to the strength of thermal-expansion effects.
机译:对三维(3D)预混火焰在低温和高温下的固有不稳定性进行了数值处理,以研究未燃烧气体温度对流体动力和扩散热不稳定性的影响。在平面火焰上叠加振幅足够小的正弦波扰动,我们得到了增长率和波数之间的关系,即色散关系。随着未燃气体的温度降低,由于平面火焰的燃烧速度的降低,生长速率降低并且不稳定范围变窄。在足够小的波数下,得到的数值结果与理论解是一致的。当Lewis数小时,由于扩散热效应,我们获得了较大的生长速率和较宽的不稳定范围。生长速度和波数通过平面火焰的燃烧速度和预热区厚度进行归一化。随着未燃烧气体温度的降低,归一化的增长率增加,归一化的不稳定范围扩大。这是因为由于燃烧气体和未燃烧气体的温度比的增加,热膨胀作用变得更强。为了阐明由内在不稳定性产生的蜂窝状火焰的特性,我们在扰动上叠加了临界波数,该临界波数对应于最大增长率,即线性最不稳定的波数。产生了叠加的扰动,并形成了六角形的蜂窝状火焰。即使生长速度降低,但随着未燃气体温度的降低,蜂窝状火焰的行为会变得更强。由于热膨胀效应的强度,通过平面火焰归一化的蜂窝状火焰的燃烧速度增加了。

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