Partially-premixed bluff-body flame dynamics and acoustic coupling in vitiated flows

在许多燃烧系统中，要求在速度高于火焰速度的气流中稳定火焰。钝体可以放置在流动中，以创建低速区域，从而实现火焰稳定。钝体稳定火焰应用广泛，包括飞机发动机的加力燃烧室。在加力燃烧室火焰中，几个额外的特征使对火焰稳定过程的全面了解变得复杂：(1)由于发动机内的燃烧，气流被预热，因此温度和氧气水平影响火焰；(2)燃料被添加到靠近火焰的流动中，因此没有时间完全混合；以及(3)加力燃烧室被封闭在一端(喷嘴出口)开放的管道中，因此声学共振可以引起火焰的振荡。之前的研究主要是在没有这些复杂性的情况下研究火焰稳定。拟议的工作将使用康涅狄格大学最近建造的燃烧室试验台，该试验台提供高温和低氧水平的高速流动，以模拟飞机发动机的条件。该装置能够产生钝体稳定的火焰，通过控制温度、氧气水平、燃料/空气混合和声级来分别解决这三个复杂问题。火焰被稳定在带有窗口的测试区域内，这些窗口允许对火焰进行基于激光的测量和成像。火焰和流场的测量将通过粒子成像测速仪和平面激光诱导荧光进行。此外，在普惠公司的支持下，通过设备和人员交换，将完成对不稳定火焰的高速成像。这些测量恢复了局部速度和火焰形状，从而可以定量地检查火焰不稳定的原因。这些测量将应用于飞机加力燃烧室火焰的三个选定特征的参数变化。由此产生的实验有望为钝体火焰的火焰稳定过程提供比目前可用的更完整和更定量的描述。许多案例的量化数据集将公之于众。这项研究的结果直接适用于飞机加力燃烧室，但也将广泛适用于使用替代燃料的新燃烧室设计，这可能需要增强钝体稳定性以实现燃料的灵活操作。宽体影响拟议的工作将使人们从根本上更好地理解燃料/空气混合不均匀流动中的火焰传播，包括温度升高和氧气水平降低的影响。这对飞机发动机加力燃烧室等设备的设计有直接影响，但也扩大了对流动中基本火焰行为的理解，可以广泛适用于新燃料的改进燃烧室设计。该项目每年将支持两名研究生和一名本科生，并将为这些学生提供广泛的光学测量技术培训机会。学生和PI将在测试条件的选择和加力燃烧室数据的分析方面直接与普拉特&惠特尼合作，以便在康涅狄格州大学试验台的研究结果和更大规模的全尺寸测试之间提供良好的耦合。研究生将有机会在宝洁实习。该项目中测量的数据集将被广泛分享，为未来的模型比较提供基础。

0967474RenfroIntellectual MeritIn many combustion systems, flames are required to be stabilized in flows with velocities higher than the flame speed. Bluff-bodies can be placed in the flow to create a low speed region to enable flame stabilization. Bluff-body stabilized flames are used in many applications including afterburners for aircraft engines. In afterburner flames several additional features complicate a comprehensive understanding of the flame stabilization process: (1) the flow is pre-heated due to combustion within the engine so that the temperature and oxygen levels affect the flame, (2) fuel is added to the flow close to the flame so that is does not have time to fully mix, and (3) the afterburner is enclosed in a duct open at one end (the jet exit) so that acoustic resonance can cause oscillations in the flame. Previous research has primarily studied flame stabilization without these complications.The proposed work will use a recently constructed combustor rig at the University of Connecticut that provides high speed flows with elevated temperatures and reduced oxygen levels to simulate conditions in an aircraft engine. The rig is capable of creating bluff-body stabilized flames with control over the temperature, oxygen level, fuel/air mixing, and acoustic level to address each of these three complications separately. The flames are stabilized within a test section with windows that permit laser-based measurements and imaging of the flame. Measurements of the flame and flow field will be made via particle imaging velocimetry and planar laser induced fluorescence. In addition, high-speed imaging of unsteady flames will be accomplished with the support of Pratt & Whitney through equipment and personnel exchange. These measurements recover the local velocity and flame shape so that the cause of flame de-stabilization can be quantitatively examined. These measurements will be applied as the three chosen features of aircraft afterburner flames are parametrically varied. The resulting experiments are anticipated to provide a more complete and quantitative description of the flame stabilization process for bluff-body flames than presently available. The quantitative data sets from numerous cases will be made publicly available. The results of this study are directly applicable to aircraft afterburners, but will also be broadly applicable to new combustor designs with alternative fuels, which may require enhanced bluffbody stabilization for fuel flexible operation.Broader ImpactsThe proposed work will lead to a better fundamental understanding of flame propagation in flows with non uniform fuel/air mixing including the effects of elevated temperature and reduced oxygen level. This has direct impact on the design of devices such as afterburners for aircraft engines, but also expands understanding of basic flame behavior in flows that could be broadly applicable to improved combustor design for new fuels. The project will support two graduate students and one undergraduate student each year, and will provide opportunities for these students to be trained in a broad range of optical measurement techniques. The students and PIs will collaborate directly with Pratt & Whitney on the selections of test conditions and analysis of afterburner data to provide good coupling between the results from the studies in the UConn rig and larger full scale tests. Graduate students will have the opportunity for internships at P&W. The data sets measured in this program will be shared broadly to provide a basis for future model comparisons.