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

在许多燃烧系统中，火焰需要在速度高于火焰速度的流动中稳定。崖体可以放置在流动中，以创建一个低速区域，以实现火焰稳定。崖体稳定火焰用于许多应用，包括飞机发动机的加力燃烧室。在加力燃烧室火焰几个附加功能复杂化全面了解火焰稳定过程:(1)流得预热是由于发动机内的燃烧,温度和含氧量影响火焰,(2)燃料添加到流靠近火焰,这是没有时间充分融合,和(3)开了加力燃烧室一端封装在一个管开放(喷气出口),这样声共振会引起振荡的火焰。以前的研究主要是研究没有这些并发症的火焰稳定。这项工作将使用康涅狄格大学最近建造的燃烧室装置，该装置可以在高温和低氧水平下提供高速流动，以模拟飞机发动机的情况。该钻机能够通过控制温度、氧气水平、燃料/空气混合和声学水平来产生崖体稳定火焰，分别解决这三个复杂问题。火焰在一个带有窗口的测试区域内稳定下来，该窗口允许基于激光的火焰测量和成像。火焰和流场的测量将通过粒子成像测速和平面激光诱导荧光进行。此外，在普惠公司的支持下，通过设备和人员交流，将完成非定常火焰的高速成像。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失稳的原因。这些测量将应用于飞机加力火焰的三个选择特征是参数变化的。由此产生的实验预计将提供比目前可用的更完整和定量的描述崖体火焰稳定过程。将向公众提供来自许多案例的定量数据集。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型燃烧室设计，这些燃烧室可能需要增强崖体稳定性以实现燃料灵活运行。更广泛的影响所提出的工作将导致对火焰在非均匀燃料/空气混合流动中传播的更好的基本理解，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，但也扩展了对流动中基本火焰行为的理解，可以广泛应用于改进新燃料的燃烧室设计。该项目每年将资助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的机会。学生和专业人员将直接与普惠公司合作，选择测试条件和分析加力燃烧室数据，以便在康涅狄格大学钻井平台的研究结果与更大规模的全尺寸测试结果之间提供良好的耦合。研究生将有机会在宝洁实习。该计划测量的数据集将广泛共享，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.