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首页> 外文期刊>Flow, turbulence and combustion >Thermal-drag and Transition from Quasi-steady to Highly-unsteady Combustion of a Fuel Droplet in the Presence of Upstream Velocity Oscillations
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Thermal-drag and Transition from Quasi-steady to Highly-unsteady Combustion of a Fuel Droplet in the Presence of Upstream Velocity Oscillations

机译：上游速度振荡下燃料液滴的热阻和从准稳态燃烧到高度不稳定燃烧的转变

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Numerical studies on the behaviors of combustion of 1-butanol fuel droplet at presence of upstream velocity oscillation are performed. Fuel droplet has an initial diameter of 1.25 mm and ambiance pressure and temperature are 0.4 MPa and 300 K, respectively. These conditions are those in which the microgravity experiments in literature conducted. In the excellent agreement with the experimental data, numerical results show a significant enhancement of the burning rate of droplet compared to what is predicted by quasi-steady film theory models. The mechanism of the enhancement of burning rate is clarified then by observation of a new mechanism that is named thermal-drag, TD. It is shown, depending on the amplitude and frequency of the upstream velocity oscillation, the flame in wake region of droplet can move toward the droplet surface by the force of vortex flow motions produced by the TD mechanism. It is verified that such movement of the flame is responsible for the enhancement of the burning rate and deviation of the response of the evaporation process form the predictions of the quasi-steady model. Frequency analysis of the burning rate reveals that at low frequency and amplitude the FFT diagram of the burning rate contains of only one main peak synchronies with the frequency of upstream velocity oscillation, which implies a quasi-steady response. However; at high frequency and amplitude the diagram includes of wide range of frequencies beside of the main peak that readily shows deviation from the quasi-steady conditions. In the latter, the study on the response of the combustion to the upstream velocity fluctuations in which the fluctuations contains of three wave numbers shows the amplification of the effects of low frequency fluctuations rather than that of damping of the effects of high frequency fluctuations on the evaporation processes.
机译：进行了关于1-丁醇燃料液滴在上游速度振荡的情况下燃烧行为的数值研究。燃料滴的初始直径为1.25 mm，环境压力和温度分别为0.4 MPa和300K。这些条件是文献中进行微重力实验的条件。与实验数据非常吻合，数值结果表明，与准稳态薄膜理论模型所预测的相比，液滴的燃烧速率有了显着提高。然后，通过观察一种称为热阻力TD的新机理，阐明了提高燃烧速率的机理。如图所示，取决于上游速度振荡的幅度和频率，在液滴的唤醒区域中的火焰可以在由TD机构产生的涡流运动的力的作用下朝向液滴表面移动。从准稳态模型的预测值可以证明，火焰的这种运动是导致燃烧速率提高和蒸发过程响应偏差的原因。燃烧速率的频率分析表明，在较低的频率和振幅下，燃烧速率的FFT图仅包含一个与上游速度振荡频率同步的主峰，这表明存在准稳态响应。然而;在高频和高振幅情况下，该图除了主峰外还包括宽范围的频率，很容易显示出偏离准稳态条件。在后者中，对燃烧对上游速度波动的响应的研究（其中波动包含三个波数）表明，低频波动的影响放大了，而不是高频波动的影响得到了衰减。蒸发过程。

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