Full-Field Laser Vibrometry for Combustion Diagnostics

• Applicant: Professor Dr.-Ing. Jürgen W. Czarske
• Subject Area: Measurement Systems
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282277522

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).

• DFG Programme: Research Grants
• International Connection: Austria
• Co-Investigators: Professor Dr.-Ing. Andreas Fischer; Professor Dr.-Ing. Jakob Woisetschläger