Rounded Edge Effects on the Slanted Afterbody Aerodynamics

Modern cargo aircraft such as the Boeing C-17 possess a large upswept angle on the fuselage afterbody. This angle,

designed in part to prevent tail strikes on takeoff and landing, produces a pair of counter rotating vortices within the

fuselage wake. This vortex wake state can present significant, sometimes dangerous, challenges for cargo and personnel

drops as well as undesirable aerodynamic effects, such as added drag and negative lift. Previous work has explored the

fundamental dynamics of the vortex wake state through a representative bluff body geometry consisting of a cylindrical

forebody with an angled sharp edge cut ending on the afterbody trailing edge; dubbed the slanted afterbody. The present

work examines the slanted afterbody with the addition of an edge radius, i.e. the rounded afterbody, allowing the

model to more closely resemble cargo aircraft. Techniques such as oil flow visualization and pressure sensitive paint

for surface flow topology measurements as well as spanwise shadowgraph for wake-field visualization were used to

understand the physics of this wake field. The model was tested for two slant angles, 32° and 45°, and compared to

the sharp edge model over two Mach numbers (??∞ = 0.3 and ??∞ = 0.6) and two Reynolds numbers (??????=0.832E6

and ??????=1.47E6), i.e. four cases per condition. The 45° rounded afterbody displays flow structures consistent with

the vortex wake state, with notable variations due to the variable separation location imposed by the rounded edge. In

contrast, the 32° rounded edge model presents differences when compared to the vortex wake state of the sharp edge

model and suggests the existence of a vortex state without a separation bubble at the center plane, previously unseen and

in need of further examination.