UC San Diego

This thesis addresses the aerodynamics of Tsuji burners, involving a flame developing from the forward stagnation region of a cylindrical porous fuel injector placed in an air stream. Attention is focused on cases when the fuel-injection velocity is comparable to the outer air velocity, so that the boundary layer is blown off from the cylinder surface. In the resulting flow, the flame is embedded in the thin mixing layer that forms about the stream surface separating the outer air stream from the fuel stream, both having in general different density. The flow structure, nearly inviscid outside the mixing layer, is investigated here for cases where the porous fuel injector is placed in a uniform air stream or at the center of a symmetrical planar counterflow configuration. In both cases the velocity on the air side of the mixing layer is potential, while the velocity found on the fuel side is rotational, because fuel injection generates vorticity through the requirement that fuel emerges normal to the cylinder surface. It is shown that introduction of a density-weighted streamfunction reduces the problem to the case of constant-density flow, with the density-square-root-weighted ratio of injection velocity to free-stream velocity Lambda emerging as the only controlling parameter. The numerical solution, involving the determination of the vorticity distribution through an iterative scheme, provides the structure of the flow, including the location of the flame and associated strain-rate distribution. Numerical results are presented for values of Lambda ranging from small injection velocities Lambda << 1 to large injection velocities Lambda >> 1. The inviscid results reported here in the limit of vanishingly small injection velocities Lambda << 1 indicate that the outer air velocity never approaches the classical solution corresponding to potential flow with Lambda=0, a result with important implications for the analysis of flames stabilized in Tsuji burners.