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首页> 外文期刊>Experiments in Fluids >Residence time measurement of an isothermal combustor flow field
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Residence time measurement of an isothermal combustor flow field

机译：等温燃烧器流场的停留时间测量

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Residence times of combustors have commonly been used to help understand NOx emissions and flame blowout. Both the time mean velocity and turbulence fields are important to the residence time, but determining the residence time via analysis of a measured velocity field is difficult due to the inherent unsteadiness and the three-dimensional nature of a high-Re swirling flow. A more direct approach to measure residence time is reported here that examines the dynamic response of fuel concentration to a sudden cutoff in the fuel injection. Residence time measurement was mainly taken using a time-resolved planar laser-induced fluorescence (PLIF) technique, but a second camera for particle image velocimetry (PIV) was added to check that the step change does not alter the velocity field and the spectral content of the coherent structures. Characteristic timescales evaluated from the measurements are referred to as convection and half-life times: The former describes the time delay from a fuel injector exit reference point to a downstream point of interest, and the latter describes the rate of decay once the effect of the reduced scalar concentration at the injection source has been transported to the point of interest. Residence time is often defined as the time taken for a conserved scalar to reduce to half its initial value after injection is stopped: this equivalent to the sum of the convection time and the half-life values. The technique was applied to a high-swirl fuel injector typical of that found in combustor applications. Two test cases have been studied: with central jet (with-jet) and without central jet (no-jet). It was found that the relatively unstable central recirculation zone of the no-jet case resulted in increased transport of fuel into the central region that is dominated by a precessing vortex core, where long half-life times are also found. Based on this, it was inferred that the no-jet case may be more prone to NOx production. The technique is described here for a single-phase isothermal flow field, but with consideration, it could be extended to studying reacting flows to provide more insight into important mixing phenomena and relevant timescales.
机译：燃烧器的停留时间通常被用来帮助理解NO x 的排放和火焰的爆破。时间平均速度场和湍流场都对停留时间很重要，但是由于固有的不稳定性和高Re旋流的三维特性，很难通过分析测得的速度场来确定停留时间。这里报道了一种更直接的测量停留时间的方法，该方法检查了燃料浓度对燃料喷射突然中断的动态响应。停留时间的测量主要使用时间分辨平面激光诱导荧光（PLIF）技术进行，但是增加了第二台用于颗粒图像测速（PIV）的相机，以检查阶跃变化不会改变速度场和光谱含量相干结构。通过测量评估的特征时标称为对流和半衰期：前者描述了从喷油嘴出口参考点到下游关注点的时间延迟，后者描述了一旦受到燃油影响，衰减率。降低了注射源处标量浓度的浓度，已将其转移到关注点。停留时间通常被定义为在注入停止后守恒标量减少到其初始值的一半所花费的时间：这等于对流时间和半衰期值的总和。该技术已应用于燃烧室应用中常见的高旋流喷油器。研究了两个测试案例：使用中央喷射（有喷射）和没有中央喷射（无喷射）。已经发现，没有喷气机的情况的相对不稳定的中央再循环区域导致燃料向中央区域的运输增加，该中央区域由进动的旋涡芯支配，在那里还具有长的半衰期。据此推断，无喷箱可能更容易产生NO x 。本文中针对单相等温流场描述了该技术，但考虑到这一点，它可以扩展到研究反应流，以提供对重要混合现象和相关时间尺度的更多了解。

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