Viscous drag in the transonic regime over an axi-symmetric body with a unique aft contour surface is investigated. The forebody is composed of an arbitrary ellipsoid. The unique aft contour surface has been obtained by an exact solution of the small perturbation transonic equation, using guidelines and tools developed at the Naval Postgraduate School. This unique contour allows the delay of shock formation in the aft portion, hence delaying the onset of wave drag which results in a reduction of the overall transonic pressure drag on the body. The drag coefficient thus computed is compared with another axisymmetric body with the same ellipsoid forebody but a simple boat-tailed conical afterbody. Computational Fluid Dynamics (CFD) has been used to compute the viscous flow over the two bodies at zero incidence using a Navier-Stokes flow-solver. Results obtained confirm the advantage of the special shaped afterbody over the conical afterbody by showing the delayed formation of shock waves at the aft portion in transonic flow, consequently achieving a lower maximum drag coefficient of approximately 5.5%. These results can be used in the design low pressure-drag surfaces for shapes such as missiles, projectiles, aircraft external ferry tanks and aircraft engine nacelles for improved performance within the transonic flight regime.
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