Side Forces on Ogive-Cylinder Bodies at High Angles of Attack in Transonic Flow

Abstract

Flow characteristics about slender axisymmetric bodies of revolution at high angles of attack in the high subsonic and transonic speed range are poorly understood. This may be ascribed to several extremely complex interactions involving inviscid mixed subsonic and supersonic flows, viscous attached and separated boundary-layer flow, and the resulting vortex flow. It was reported in Ref. 1 that at high subsonic and transonic flows and at angles of attack above 20°, with zero side-slip, ogive-cylinder bodies of revolution exhibited rather large steady side forces. The direction and magnitude of these side forces were unpredictable. Pressure distribution measurements and schlieren photographs in Ref. 2 indicated that an unsymmetric vortex buildup was causing these forces. In spite of reported failures in various research programs due to unexpected side forces, no systematic data exist which deal with physical causes or effects. Consequently, the objective of the present investigation was to obtain systematic information about the effects of Mach number, nose geometry, angle of attack, and boundary layer conditions on the measured side forces. The experiments were conducted in the NSRDC 18-in. indraft tunnel using a slotted test section. Unit Reynolds numbers varied between 2.7 x 10/ft and 4.3 x 10/ft for the speed range of M = 0.5-M=1.1 (0.5, 0.6, 0.7, 0.8, 0.9, and 1.1). Tangent ogive noses of fineness ratios (F.R.) 2, 3, and 4 were tested with bluntness ratios (B.R.) of 0 to 50% (100 nose tip radius/base radius) using a cylindrical afterbody of 1.1 in. base diameter and 8.688 in. length. Schematic diagram of the tested configurations are shown in Fig. 1. Aerodynamic forces were obtained by a six component internal balance. Schlieren photography and oil flow techniques provided both external and surface flow visualization. At several speeds, roll angles were changed from 0-90° and 180° to check the flow sensitivity to small geometric changes. At M = 0.5, 0.7, and 0.9, both laminar and turbulent boundary layers were examined. Turbulent boundary layers were generated by a i in. wide strip of No. 54 Grit placed from the nose to the base of the models along the windward meridian. The flow model which can be reconstructed from the schlieren photographs, oil flow experiments and aerodynamic