Using dual laser vibrometry to monitor the stability of gas turbine combustion

Laser vibrometry (LV) is originally a laser-based measurement technique dedicated to the analysis of surface vibrations. This technique wasadapted at TU Graz as a line-of-sight measurement technique for the observation of coherent vortices in a turbulent flow, and then lately as a technique for monitoring the stability of an air-methane flame using two instruments (Dual Laser Vibrometry - DLV). This paper reports on measurements realised on a resonant flame (premixed air-methane, quarter-wave resonator, amplification with a siren). A remarkable relation between the flame dynamics, and phase-defined DLV measurements can be observed. Signal processing will be shortly described. In order to support the observations, and correlate the results with data from other measurement techniques, high-speed schlieren visualisations and stereoscopic Particle-Image-Velocimetry (PIV) were used. The paper eventually addresses issues regarding quantification (from line-of-sight to local measurement, amplitude analysis of the density fluctuations rho' and comparison with the local thermoacoustic couplings). One recommended application of DLV is its ability to perform precise and low-cost combustor benchmark stability tests (time-resolved measurement, broad frequency spectrum, no need for seeding, very high sensitivity, measurement possible over the whole combustion volume).