The Effect Of Propulsive Jet Specific Heat Ratio On Base Pressure At A Freestream Mach Number Of 218

The report documents studies to determine experimentally the effect of thrusting-jet specific heat ratios on missile model base pressure. The tests were conducted at a freestream Mach number of 2.18 over a wide range of jet static to freestream static pressure ratios. Variation of the specific heat ratios was obtained by the use of different jet gases. Jet static pressure ratios up to 40 have been covered. Flow interference effects were held to a minimum by mounting the model on a support attached to a strut in the plenum chamber of the wind tunnel and reaching through the wind tunnel nozzle throat into the test section. The effects of molecular weight (at gamma = 1.66) on base pressure were briefly investigated. A molecular weight shift from 40 to 29 showed only a slight effect on base pressure, however, a shift from 29 to 4 increased the base pressure coefficient an average of 0.04 or approximately 20% of the minimum value. It was observed in this investigation that the base pressure reached its minimum value at a freestream-to-jet molecular weight ratio of unity for all jet static pressure ratios tested. Extension areas recommended for further investigation include the determination of jet-specific-heat ratio, jet temperature and molecular-weight effects on base pressure when freestream conditions and model afterbody geometry are systematically varied. (Author).