Full-Field Laser Vibrometry for Combustion Diagnostics

最先进的工业燃气轮机发电技术使用稀薄预混燃烧，以实现高燃烧效率和低排放。高功率密度和稀薄燃烧增加了热声振荡的敏感性。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，该函数将火焰的非稳态热释放速率与作为频率函数的入射速度的摄动联系起来。这种对火焰的描述对于航空发动机中的涡轮机械也是必要的。由于透平机械领域的研究一直是与能源相关的研究，因此在社会上产生了很大的影响。在由奥地利科学基金FWF资助的TU Graz(J.Woisetschläger)之前的项目中，已证明所谓的激光振动计--工程上用于表面振动检测的干涉仪--可以直接记录密度和热释放的波动。结果还表明，两台激光振动仪可以通过关联密度波动来检测火焰中的流动速度。FTF记录既需要放热又需要速度。受通信工程调制和解调技术的启发，德累斯顿理工大学(J.查尔斯克，A.费舍尔)由德国研究基金会DFG资助的项目证明了另一种激光光学测量的概念，即使用正弦激光频率调制技术-也是激光测振仪技术固有的-与现代高速传感器阵列和用于流体流动研究的时空相关技术相结合。该项目的假设是，激光测振仪技术可以与现代高速摄像传感器相结合，从而使这种基于大量激光测振仪(每个像素一个测振仪)的全场干涉测量可以记录FTF，并提供关于火焰中热释放速率和速度以及时空相关性的现场信息-所有这些都不需要示踪粒子或示踪剂，这对燃烧诊断来说都是新的。在这个项目中，TU Graz和TU Dresden的专业知识将结合起来验证这一假设，并开发用于激光光学高速燃烧诊断的全场激光振动仪，从表征火焰所需的热声学开始，包括用于单向和双向观测的适当的空间/时间相关性。该项目包括使用单视线激光测振仪(TU Graz)和高速速度记录仪(TU Dresden)进行基准测试。除了两个主要项目合作伙伴TU Graz(J.Woisetschläger)和TU Dresden(J.查尔斯克，A.Fischer)外，三家在透平机械燃烧和计量方面拥有专业知识的研究机构将参与验证和测试过程(德国慕尼黑大学、德国科隆大学、PTB Braunschweig)。

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).