Simultaneous three-component velocity measurements in a swirl-stabilized flame

Modern gas turbines are operated with lean fuel mixtures causing instabilities of the heat release and, by means of a thermoacoustic coupling, oscillations of the flow velocity within the flame. Since these oscillations can reduce the combustion efficiency, a better understanding of their formation mechanism and spatial origin is necessary. Therefore, simultaneous, three-component (3C) velocity measurements with high measurement rate are required. The Doppler global velocimetry with laser frequency modulation (FM-DGV) achieves measurement rates up to 100 kHz and was successfully applied for measurements in flames, but does not provide simultaneous 3C velocity data. In order to overcome this drawback, the FM-DGV is extended to allow simultaneous 3C measurements. The functionality is demonstrated by measurements within a swirl-stabilized flame. In combination with time-resolved measurements of the sound pressure and chemiluminescence emission, the spatial origin of the sound pressure emission in the acoustic far-field is identified as flow velocity and heat release oscillations in the acoustic near-field of the flame. Hence, a deeper insight into the thermoacoustic coupling can be achieved.