Corner Vortex Structures: Spanwise Imaging of a Confined, Premixed Bluff-Body-Stabilized Flame

摘要

Large-scale corner vortex structures (CVS) are observed experimentally inside the recirculation zone of a confined, turbulent, premixed, two-dimensional bluff-body-stabilized flame. These counter-rotating CVS contribute to spanwise non-uniformity of the recirculation zone velocity field under reacting conditions but are not present for non-reacting conditions. To investigate the structure and dynamics of the CVS, experiments are performed that vary the fuel type (propane vs. natural gas), inlet velocity, preheat temperature, equivalence ratio, and bluff-body aspect ratio. As equivalence ratio is decreased from stoichiometric to lean blowout (LBO), the vorticity and circulation of the CVS increase, and the combustion on the spanwise plane becomes increasingly non-uniform. During the LBO process, the CVS are the final regions to sustain reactions. Simulations or measurements of bluff body stabilized flames which neglect the vortices in the spanwise plane may fail to capture both stable and LBO combustion processes. These effects of corner vortex structures and spanwise nonuniformity should be considered in future experimental and computational studies of confined bluff body-stabilized flames.