Abstract:

ESDU Aero B.S.02.03.01 introduces the concept of dividing the drag into inviscid wave drag, skin friction drag, viscous form drag and base drag. ESDU data for estimating skin friction and base drags are available and are referenced. For viscous form drag, calculation of the inviscid flow about a body shape that includes the displacement thickness of the boundary layer is recommended. For wave drag reference is made to the exact solutions that exist for a right-circular cone and are given in the ESDU data. For more general body shapes, three principal theories are referenced: linearised theory, van Dyke's second-order theory and the method of characteristics. A parameter involving the maximum slope of the profile in an axial plane is introduced for assessing the accuracy of results obtained using those theories. The contributions of the forebody, the afterbody and due to interference of the forebody with the afterbody are treated separately in the ESDU data; the data for forebodies and afterbodies are expected to be accurate over a greater range than would be obtained with linearised theory, but the interference drag is based on linearised theory. The supersonic-hypersonic similarity law, which is useful for generalising limited data, is explained. Brief consideration is given to bodies of non-circular cross section. All the theories mentioned assume supersonic flow everywhere, that is a sharp nose with attached shock wave. When the bodies have blunt noses the shock is detached and the theories do not apply; semi-empirical ESDU data are referenced for various nose blunting shapes. A bibliography is included.