ANALYSIS OF FORCED COMBUSTING JETS

The ability to induce vortex formations and roll up in jet diffusion flames by means of fuel-jet forcing is studied for a range of conditions. Numerical experiments at large Froude and Reynolds numbers demonstrate that a diffusion flame is much less responsive than an isothermal jet suggesting that there is little prospect for controlling a diffusion flame in this manner. This trend is verified by stability calculations. As the jet velocity is reduced and the Froude number becomes smaller, buoyancy begins to become significant, and the flame responds more strongly to forcing. At even lower velocities, buoyancy becomes so dominant that the jet becomes inherently unstable, and large vortices are seen to appear and grow even without forcing. Indeed, it appears that the steady solution is unstable to infinitesimal perturbations. These pulsations at low Froude numbers occur at frequencies associated with the well-known flickering phenomena in flames. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.