Flame Stabilization in Small Cavities

摘要

This research is motivated by the necessity to improve the performance of ultracompact combustors, whichnrequires flame stabilization in small cavities. An extensive computational investigation on the characteristics ofncavity-stabilized flames is presented. A high-fidelity, time-accurate, implicit algorithm that uses a global chemicalnmechanism for JP8-air combustion and includes detailed thermodynamic and transport properties as well asnradiation effects is used for simulation. Calculations are performed using both direct numerical simulation andnstandard k-" Reynolds-averaged Navier–Stokes model. The flow unsteadiness is first examined in large axi-nsymmetric and small planar cavities with nonreactive flows. As with previous investigations on axisymmetricncavities,multiple flowregimeswere obtained by varying cavity length (x=Do):wake backflowregime, unsteady cavitynvortex regime, steady cavity vortex regime, and compressed cavity vortex regime. However, planar cavities onlynexhibit steady cavity vortex and compressed cavity vortex regimes. Two opposed nonaligned air jets were positionednin this planar cavity: the outermost air jet in coflowwith themainstreamflow(i.e., normal injection). The fuel jet wasninjected either in coflow, crossflow, or counterflow with respect to the mainstream flow. Flow unsteadiness wasnobserved to be relatively small for coflow- and crossflow-fuel-jet injection. By reversing the air jet positionsn(i.e., reverse injection), the flow unsteadiness is promoted regardless of fuel jet positioning. Finally, the effect ofncombustion and cavity equivalence ratio (u0001CAV)on flame unsteadiness is addressed.With normal injection (reverseninjection), low and high u0001CAV leads to low (high) and high (low) flame unsteadiness, respectively. Based on thesenresults recommendations are provided to designers/engineers to reduce flame unsteadiness in these cavities.