Some effects of shock/wake and shock/flame interaction

The effect of disturbances interacting with the near wake of axisymmetric afterbodies at Mach 2 has been studied experimentally. The disturbance flowfields were generated by cowls of convergent-divergent internal section or by over-expanding the airflow at the lip of an open-jet wind tunnel. In the latter case, the effect of combustion of hydrogen fuel in the near wake and the effect of varying stagnation temperature has also been examined. It is shown that there is an optimal position for the cowl which maximizes the base pressure, that 'wake buzz' may prove detrimental to performance, that the base pressure with shock/wake and shock/flame interaction is only weakly dependent on stagnation temperature and that incipient separation on the afterbody may prove to be a limiting factor in achieving high base pressures. This notwithstanding it is demonstrated that shock/wake or shock/flame interaction can give rise to substantial base thrust.