Flow field and local burning velocity affected by stretch in swirl flow of turbulent premixed flames

Abstract

In this study, we have investigated turbulent premixed flames affected by local stretch in a swirl flow, measured by the simultaneous OH-PLIF/SPIV system. Evaluating the transient of burning velocity and stretch rate, the flow and the flame dynamics in a cyclone-jet combustor were discussed. The flame front was determined by the OH fluorescence signal. Results show that the axial mean velocity becomes the maximum around the center axis, whereas the axial or the radial rms velocity takes the maximum at the position far from the center axis. These could be caused by the velocity fluctuation due to the flame and flow interactions. According to the local burning velocity and the stretch rate, the estimated Markstein number (Ma) roughly matches the value of the laminar flame. With an increase of the swirl number (Sw), the rms velocity is enlarged. Interestingly, the probability of higher burning velocity increases at larger Sw. At the same time, the flame extinction occurs more frequently. Thus, it is derived that the swirl flow has a positive effect to increase the local burning velocity, but it simultaneously has a negative effect which causes the local flame extinction.

Keywords

• stretch rate
• swirl
• laser diagnostics
• burning velocity
• extinction