Full-Field Laser Vibrometry for Combustion Diagnostics

最先进的工业燃气轮机发电技术采用精益预混燃烧，燃烧效率高，排放低。高功率密度和稀薄燃烧增加了对热声振荡的敏感性。不稳定性的建模和预测通常是通过分析火焰传递函数（FTF）来完成的，它将火焰的非定常热释放率与入射速度的扰动作为频率的函数联系起来。这种火焰的表征对于航空发动机中的涡轮机械也是必要的。由于涡轮机械领域的研究一直是与能源相关的研究，因此对社会产生了强烈的影响。在奥地利科学基金FWF资助的格拉茨工业大学（J. Woisetschläger）之前的项目中，人们发现所谓的激光测振仪——用于工程表面振动检测的干涉仪——可以直接记录密度和热释放波动。结果还表明，两个激光测振仪可以通过关联密度波动来检测火焰中的流速。热释放和速度都需要FTF记录。受通信工程调制和解调技术的启发，德累斯顿工业大学（J. Czarske， A. Fischer）的项目由德国研究基金会DFG资助，证明了另一种激光光学测量的概念，该测量使用正弦激光调频技术（也是激光测振仪技术的固有技术）结合现代高速传感器阵列和流体流动调查的时空相关技术。该项目的假设是，激光测振仪技术可以与现代高速相机传感器相结合，因此，这种基于多个激光测振仪（每个像素一个测振仪）的全场干涉测量可以记录FTF，并提供有关热释放率和速度以及火焰内时空相关性的现场信息-所有这些都不需要示踪剂颗粒或示踪剂，并且对燃烧诊断都是新颖的。在这个项目中，格拉茨工业大学和德累斯顿工业大学的专业知识将结合起来验证这一假设，并开发一种用于激光光学高速燃烧诊断的全场激光测振仪，从表征火焰所需的热声学开始，包括适当的空间/时间相关性，用于单向和双向观察。该项目包括单线激光测振仪（格拉茨工业大学）和高速记录（德累斯顿工业大学）的基准测试。除了两个主要的项目合作伙伴格拉茨工业大学（J.Woisetschläger）和德累斯顿工业大学（J. Czarske， A. Fischer）之外，三个以涡轮机械燃烧和计量专业知识而闻名的研究机构（慕尼黑工业大学，科隆DLR，布伦瑞克工业大学）将参与验证和测试过程。

State-of-the art technology in industrial gas turbines for power generation uses lean premixed combustion for high combustion efficiency and low emissions. High power densities and lean combustion increase the susceptibility to thermoacoustic oscillations. Modelling and prediction of instabilities is often accomplished by analysing the flame transfer function (FTF), which relates the unsteady heat release rate from the flame to perturbations of incoming velocity as function of frequency. Such characterization of flames is also necessary for turbomachinery in aero-engines. Since research in the field of turbomachinery always is energy related research, a strong impact on society is given. In previous projects of TU Graz (J. Woisetschläger) funded by the Austrian Science Fund FWF it was shown that so-called laser-vibrometers - interferometers used in engineering for surface vibration detection - can directly record density and heat release fluctuations. It also turned out that two laser vibrometers can detect flow velocities in flames by correlating density fluctuations. Heat release and velocity are both needed for FTF recordings. Inspired by modulation and demodulation techniques from communications engineering, projects at TU Dresden (J. Czarske, A. Fischer) funded by the German Research Foundation DFG proofed the concept of another laser-optical measurement using sinusoidal laser frequency modulation technique - also inherent to laser vibrometer technology - in combination with modern highspeed sensor arrays and spatio-temporal correlation techniques for fluid flow investigations. The hypothesis of this project is that laser vibrometer technology can be combined with modern high-speed camera sensors, so that such a proposed full-field interferometry based on numerous laser vibrometers (each pixel one vibrometer) can record FTF, and also provides field information on heat release rate and velocity as well as spatio-temporal correlations within the flame - all without the need for tracer particles or tracers and all novel to combustion diagnostics. In this project the expertise of both TU Graz and TU Dresden will be combined to verify this hypothesis and develop a full-field laser vibrometer for laseroptical high-speed combustion diagnostics, starting from the thermo-acoustics needed to characterize the flame, including appropriate spatial/temporal correlations for single and dual directional observations. This project includes a benchmarking with single line-of-sight laservibrometers (TU Graz) and high-speed velocity recordings (TU Dresden). Additional to the two main project partners TU Graz (J.Woisetschläger) and TU Dresden (J. Czarske, A. Fischer) three research institutes known for their expertise in turbomachinery combustion and metrology will participate in the verification and testing process (TU Munich, DLR Cologne, PTB Braunschweig).