- The role of the barrel shock in controlling the secondary flow associated with gaseous injection of underexpanded air through circular and 15-degree half-angle diamond orifices into a high Reynolds number Mach 5.0 freestream was numerically investigated. The Detached-Eddy-Simulation version of Menter's two-equation SST model was used in these simulations. A discussion of the resulting flowfield with emphasis on the structure of the barrel shock and its effect on the flow is presented. A new transverse counter rotating vortex pair with the potential to act a gasdynamic flame holding mechanism was identified in the flow. The results were also post-processed to identify the salient vorticity transport processes. 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.