ACCELERATION OF A FLAME BY FLAME VORTEX INTERACTIONS

The acceleration of a premixed flame propagating in a planar channel past stationary obstacles is investigated using a computer model based on combining the discrete vortex method with a flame interface algorithm. Results presented in this article show that the initial acceleration of the flame is caused by the sudden contraction of the flow due to the presence of the obstacles. Because the burning speed SL remains constant, it is the increase in surface area that is responsible for the apparent acceleration. This combustion-generated flow also causes turbulent recirculation regions to form downstream of the obstacles. When the flame interacts with these turbulent eddies, the burning rate increases, producing a stronger velocity field in the channel that further accelerates the flame. In geometries containing a series of obstacles, the higher flow velocities caused by the distorted flame result in stronger turbulent eddies behind subsequent obstacles. Numerical results for these geometries demonstrate the positive feedback mechanism of acceleration as the flame encounters these increasingly stronger turbulent regions. In this article, results are presented for different locations of the series of obstacles, as well as a clustering of obstacles near the ignition source. The effects of blockage ratio, ignition shape, and fuel concentration are also investigated with the computer model. © 1990.