This report contains the results of an experimental investigation to determine the effects of support interference on the base drag and fore drage of two bodies of revolution. The results show that the rear supports affect the drag of a body of revolution through the immediate influence on the pressures acting over the rear portions of the body and thus the magnitude of the interference depends on the afterbody shape of the model, the Reynolds number of flow, and the condition of the boundary layer.
Summary: Tests were conducted to determine the effects of viscosity on the drag and base pressure characteristics of various bodies of revolution at a Mach number of 1.5. The models were tested both with smooth surfaces and with roughness added to evaluate the effects of Reynolds number for both laminar and turbulent boundary layers. The principal geometric variables investigated were after-body shape and length-diameter ratio. For most models, force tests and base pressure measurements were made over a range of Reynolds numbers, based on model length, from 0.6 million to 5.0 millions. Schlieren photographs were used to analyze the effects of viscosity on flow separation and shock-wave configuration near the base and to verify the condition of the boundary layer as deduced from force tests. The results are discussed and compared with theoretical calculations.
Base bleed is a technique whereby all or part of the boundary layer is 'bled' from the rear portion of a projectile to the base region. Passage from the model's surface to the base region is by means of concentric cylindrical passageways. The purpose of base bleed is to reduce the Magnus moment on overlong spinning bodies of revolution and to reduce the base drag. Both analytic and experimental results are presented. The boundary layer is represented by means of the momentum thickness.
Wind tunnel tests were conducted to provide support interference information for planning and directing wind tunnel tests at supersonic and hypersonic Mach numbers. Sting-length and sting-diameter effects on base and surface pressures of a blunt 6-deg cone with a sliced base were investigated at Mach numbers 2, 3, 5, and 8. Dynamic stability tests on a blunt 7-deg cone were also conducted at Mach numbers 2, 5, and 8. The objectives of the 7-deg cone tests were to define critical sting lengths as determined by the measurement of dynamic stability derivatives, static pitching moment, and base pressure. Two frequencies of oscillation were investigated, and data were obtained for laminar, transitional, and turbulent boundary-layer conditions at the model base. The data from the 6- and 7-deg cone tests showed that the critical sting length depended on the interference indicator, Mach number, angle of attack, state of the model boundary layer, and frequency of oscillation. The critical sting length was generally less for models with turbulent boundary layers than for those with laminar boundary layers. A critical sting length of 2.5 model diameters was determined to be suitable for all test conditions that produced a turbulent boundary layer at or ahead of the model base.
