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Pulsating Hydrodynamic Instability in a Dynamic Model of Liquid-Propellant Combustion

机译:液体推进剂燃烧动力学模型中的脉动水动力不稳定性

摘要

Hydrodynamic (Landau) instability in combustion is typically associated with the onset of wrinkling of a flame surface, corresponding to the formation of steady cellular structures as the stability threshold is crossed. In the context of liquid-propellant combustion, such instability has recently been shown to occur for critical values of the pressure sensitivity of the burning rate and the disturbance wavenumber, significantly generalizing previous classical results for this problem that assumed a constant normal burning rate. Additionally, however, a pulsating form of hydrodynamic instability has been shown to occur as well, corresponding to the onset of temporal oscillations in the location of the liquid/gas interface. In the present work, we consider the realistic influence of a nonzero temperature sensitivity in the local burning rate on both types of stability thresholds. It is found that for sufficiently small values of this parameter, there exists a stable range of pressure sensitivities for steady, planar burning such that the classical cellular form of hydrodynamic instability and the more recent pulsating form of hydrodynamic instability can each occur as the corresponding stability threshold is crossed. For larger thermal sensitivities, however, the pulsating stability boundary evolves into a C-shaped curve in the disturbance-wavenumber/ pressure-sensitivity plane, indicating loss of stability to pulsating perturbations for all sufficiently large disturbance wavelengths. It is thus concluded, based on characteristic parameter values, that an equally likely form of hydrodynamic instability in liquid-propellant combustion is of a nonsteady, long-wave nature, distinct from the steady, cellular form originally predicted by Landau.
机译:燃烧中的流体动力学(兰道)不稳定性通常与火焰表面起皱有关,这与超过稳定性阈值时形成稳定的蜂窝状结构相对应。在液体推进剂燃烧的背景下,近来已经显示出这种不稳定性发生在燃烧速率的压力敏感性和干扰波数的临界值上,从而极大地推广了以前的经典结果,假定该问题假定了恒定的正常燃烧速率。然而,另外,已经显示出也发生了脉动形式的流体动力学不稳定性,这对应于在液体/气体界面的位置中的时间振荡的开始。在目前的工作中,我们考虑了非零温度敏感性在局部燃烧率上对两种稳定性阈值的现实影响。已经发现,对于该参数的足够小的值,对于稳定的平面燃烧存在稳定的压力敏感度范围,使得相应的稳定性可以分别出现经典的细胞形式的水动力不稳定性和最近的脉动形式的水动力不稳定性。超过阈值。然而,对于较大的热敏性,脉动稳定性边界在干扰波数/压力敏感度平面内演变为C形曲线,表明对于所有足够大的干扰波长,脉动微扰的稳定性都会下降。因此,基于特征参数值可以得出结论,液体推进剂燃烧中流体动力不稳定性的同等可能形式具有不稳定的长波性质,与Landau最初预测的稳定的细胞形式不同。

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