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Experimental studies of base pressure manipulation for an axisymmetric model at Mach 3 with cold gas injection and burning are described. Air, nitrogen, helium, and hydrogen are used for cold gas injection tests. Burning tests use hydrogen subsonically injected either radially upstream of the base plane or axially through a porous base plate. These modes of injection yielded base burning that is efficient for base drag reduction. Base burning is also combined with external compression, simulating external burning to show that the separate effects are additive. NomenclatureA b = model base area 7 = injection mass flow parameter, Fig. 7 sp = specific impulse, Fig. 8 M = Mach number M = molecular weight M a = air molecular weight bieed = injection mass flow Pj = freestream static pressure p b-base pressure p b0 = undisturbed base pressure V l = freestream velocity P 1 = freestream density

Progress is described on a model of the turbulent axisymmetric base flow behind bluff-base bodies. The purpose of the model is to provide an analytical basis for incorporation of external burning and base injection effects upon the base flow. An integral technique is used for solution of the problem. At the current time , however , extreme difficulties are being encountered in the choi ce of field variable profiles to insert in the integral technique. Several choices of profiles and governing moment equations are yiel ding a singulari ty before the rear stagnation point is reached in a downstream, integration of the equation .