Absolute and Convective Instability in Gas Turbine Fuel Injectors
Absolute and Convective Instability in Gas Turbine Fuel Injectors
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燃气轮机燃油喷射器的绝对和对流不稳定性
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
M. Juniper
中科院分区：
文献类型：
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作者：
M. Juniper
燃气轮机燃料喷射器中的流体动力学不稳定性有助于混合燃料和空气，但有时会锁定声振荡并导致热声不稳定。本文描述了一种线性稳定性分析，该分析可以预测流体动力学不稳定性的频率和强度，并识别导致它们的流动区域。它区分了对流不稳定性和绝对不稳定性，前者随时间增长但被流动对流带走，后者随时间增长但不被对流带走。对流不稳定的流动会放大外部扰动，而绝对不稳定的流动也会以固有频率振荡。作为输入，该分析需要速度场和密度场，它们要么来自纳维-斯托克斯方程的稳定但不稳定的解，要么来自时间平均数值模拟。在前一种情况下，分析是一种预测工具。在后一种情况下，它是一种诊断工具。该技术适用于三种流动：Re = 400 的涡流尾流、Re ∼ 106 的单流涡流燃料喷射器以及 Re ∼ 106 的具有五个涡流的稀薄预混燃气轮机喷射器。其在涡流尾流中的应用表明，该技术可以正确预测流动的频率、增长率和主波发生器区域。它还表明，从时空分析中发现的绝对不稳定区域很好地近似了造波器区域，这是通过重叠直接和伴随全局模式找到的。该近似值用于其他两个流动，因为很难计算它们的伴随全局模式。它在单流燃料喷射器中的应用表明，它可以识别负责产生 LES 和实验数据中看到的流体动力振荡的流动区域。通过该技术预测的频率与测量频率的误差在百分之几以内。该技术还解释了为什么当沿着中心线喷射中央射流时这些振荡会变得更弱。这是因为引起振荡的绝对不稳定区域变得对流不稳定。将其应用于稀薄预混燃气轮机喷射器表明，流动的几个区域在流体动力学上不稳定，每个区域具有不同的频率和不同的强度。例如，它揭示了受限旋流的中心区域是强烈绝对不稳定的，并建立了进动涡核，这可能有助于整个喷射器的混合。它还揭示了第二流和第三流之间的区域在可能与燃烧室内的声学模式一致的频率下稍微绝对不稳定。该技术与燃烧室中的声学模式相结合，可能成为混合和燃烧不稳定性被动控制的有用设计工具。版权所有 © 2012 ASME
Hydrodynamic instabilities in gas turbine fuel injectors help to mix the fuel and air but can sometimes lock into acoustic oscillations and contribute to thermoacoustic instability. This paper describes a linear stability analysis that predicts the frequencies and strengths of hydrodynamic instabilities and identifies the regions of the flow that cause them. It distinguishes between convective instabilities, which grow in time but are convected away by the flow, and absolute instabilities, which grow in time without being convected away. Convectively unstable flows amplify external perturbations, while absolutely unstable flows also oscillate at intrinsic frequencies. As an input, this analysis requires velocity and density fields, either from a steady but unstable solution to the Navier–Stokes equations, or from time-averaged numerical simulations. In the former case, the analysis is a predictive tool. In the latter case, it is a diagnostic tool. This technique is applied to three flows: a swirling wake at Re = 400, a single stream swirling fuel injector at Re ∼ 106, and a lean premixed gas turbine injector with five swirling streams at Re ∼ 106.Its application to the swirling wake demonstrates that this technique can correctly predict the frequency, growth rate and dominant wavemaker region of the flow. It also shows that the zone of absolute instability found from the spatio-temporal analysis is a good approximation to the wavemaker region, which is found by overlapping the direct and adjoint global modes. This approximation is used in the other two flows because it is difficult to calculate their adjoint global modes.Its application to the single stream fuel injector demonstrates that it can identify the regions of the flow that are responsible for generating the hydrodynamic oscillations seen in LES and experimental data. The frequencies predicted by this technique are within a few percent of the measured frequencies. The technique also explains why these oscillations become weaker when a central jet is injected along the centreline. This is because the absolutely unstable region that causes the oscillations becomes convectively unstable.Its application to the lean premixed gas turbine injector reveals that several regions of the flow are hydrodynamically unstable, each with a different frequency and a different strength. For example, it reveals that the central region of confined swirling flow is strongly absolutely unstable and sets up a precessing vortex core, which is likely to aid mixing throughout the injector. It also reveals that the region between the second and third streams is slightly absolutely unstable at a frequency that is likely to coincide with acoustic modes within the combustion chamber. This technique, coupled with knowledge of the acoustic modes in a combustion chamber, is likely to be a useful design tool for the passive control of mixing and combustion instability.Copyright © 2012 by ASME
空气旋流燃油喷射器的 URANS 和 LES CFD 方法的比较
DOI：
10.1115/gt2008-50278
发表时间：
2008
期刊：
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影响因子：
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作者：
Dunham D
通讯作者：
Dunham D