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.

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The report reviews both theoretical and experimental investigations of the Magnus effect on arbitrary bodies of revolution. The main emphasis is on spinning projectiles at angle of attack, both with and without fins. Flow visualization measurements are used to assess the accuracy of the existing theories. Laminar, turbulent, and mixed boundary layers are considered. (Author).

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.