PRESSURE ON AXISYMMERTIC BASE IN A TRANSONIC OR SUPERSONIC FREE STREAM IN THE PRESENCE OF A JET

摘要

A series of tests were carried out on a model fitted with a set of interchangeable nozzles giving base-to-jet diameter ratios of 3, 5, 7 and 9 jet design Mach numbers of 1, 1.5, 2 and 3, at free stream Mach numbers of 0.9, 1.1, 1.5 and 2. Two different boundary layer thicknesses were available.nThe results are presented and are compared with those of other workers [Refs. 2,4-9] and are correlated by the method of Brazzel and Henderson [Ref. 3]. It is shown that for a given value of diameter ratio, base pressure is a function of mass flow, but is independent of the jet Mach number, and some progress is made towards predicting the point at which Brazzel and Henderson's correlation ceases to apply—the minimum of base pressure.nThe unsteady flow reported by Reid and Hastings [Ref. 2] and by Craven, Chester, and Graham [Ref. 9] was found to occur for one or two of the sonic nozzles (which had zero divergence angle) depending on the external Mach number and the jet total pressure. A set of photographs of the phenomenon is included (Fig. 19).nThe minimum base pressure appears to decrease with increase of free stream Mach number, independently of base-to-jet diameter ratio and probably of nozzle design Mach number; the ratio of jet total pressure to base pressure at minimum base pressure appears to be a constant for any given nozzle.