No abstract

The flame curvature and the lift-off height of a triple flame under acoustic oscillations are investigated. The multi-slot burner, which can make uniform streamwise flow velocity and stabilize the triple flame two-dimensionally is employed. The triple flame is formed at the anti-node of velocity oscillations. The flame curvature and the lift-off height of the triple flame are measured from images that are taken by a high speed camera. The fuel concentration gradient of the mixing layer which flows into the flame surface with acoustic oscillations is calculated by using the model of the meandering mixing layer. As a result, the flame curvature changes periodically and its period of change corresponds with that of acoustic oscillations approximately. When the triple flame moves in the direction of the air flow, the flame curvature increases. When the triple flame moves in the direction of the mixture flow, the flame curvature decreases. It is estimated that the fuel concentration gradient changes in the half-period of acoustic oscillations. However, the flame curvature changes in the same period of acoustic oscillations.

No abstract

Lift-off height and flame curvature of triple flame with various sound pressures has been investigated. The triple flame was formed by multi-slot burner which can make the triple flame in a mixing layer two dimensionally without vortex interference in a shear layer. The mixing layer was observed by Schlieren system. The standing acoustic waves whose sound pressure is up to 0.12 kPa with 0.5 kHz were generated in a stainless resonance tube. As a result, the lift-off height significantly decreased with increase in the sound pressure, whereas the significant change of the flame curvature were not observed. The meandering of the mixing layer due to fluid displacement caused by velocity oscillation was observed by Schlieren images. From the above, the mechanism of lift-off height reduction can be explained that the fuel concentration gradient is made to gentle by meandering of mixing layer and the flame moves to the new position where the fuel concentration gradient is equal to the original fuel concentration gradient without sound.