Abstract: In the design of a transport fuselage afterbody with a large upswept angle, four primary parameters, i.e., the upswept angle, fineness, contraction ratio and flatness, are currently used as the main design criteria. In this article, three fuselage models with large upswept afterbodies are constructed based on three typical transport aircraft. The flows over these fuselage models are investigated by computational fluid dynamics (CFD) in order to study the effect of geometric parameters of the afterbody on the drag and fluid performance of the fuselage and the applicability of these parameters in describing the effect of afterbody shape on drag. The results show that the pressure drag which accounts for 15% to 20% of total drag dominates the quantum of the total drag of the fuselage, and that reducing fuselage drag should start with the reduction of the pressure drag. The shape of the afterbody section is the key factor affecting the pressure drag, while its flatness cannot describe accurately and extensively the effect of the afterbody section on the pressure drag. The parameter of near-roundness should be adopted to describe this effect. Finally, the five parameters of upswept angle, fineness, contraction ratio, near-roundness and near-roundness change ratio along the fuselage axis are provided which may be regarded as the design principle of large upswept afterbody for transport fuselage.

Key words: transport aircraft, upswept fuselage, pressure drag, afterbody parameter, design principle