Aerodynamics of Non-lifting Bodies

Abstract

This chapter presents the sources of drag that are encountered by a nonlifting body that is moving at transonic Mach numbers. In inviscid conditions drag can be produced if the integrated pressure over a body has a component in the opposite direction to the flow (pressure drag). First, the reader is introduced to the relation between the geometry of a body and the pressure distribution over the body. Subsequently, a method for the calculation of the pressure drag over axisymmetric bodies is presented based on the linear potential flow equation. It is shown how the pressure drag is a function of the cross-sectional area distribution of the body. The concept of area ruling is presented and examples are shown of practical implementations of the area rule. If the flow is assumed viscous, other drag sources arise: friction drag and drag due to boundary-layer separation. A qualitative characterization of laminar and turbulent boundary layers is presented along with the concepts of transition and separation. Also, the interaction between shock and boundary layer (both weak and strong) is further detailed and it is shown how this influences drag divergence in transonic conditions. In addition, calculation methods are presented to estimate the boundary-layer properties of laminar and turbulent boundary layers along with their transition region for bodies subjected to an external pressure and velocity distribution. This chapter contains 8 examples and concludes with 29 practice problems.