Effects of Doors and Cavities on a Slanted Afterbody

Cargo aircraft often feature a highly upswept afterbody to prevent tail strikes during takeoff and landing and to accommodate rear ramp doors. While functional, this geometry induces a strong counter-rotating vortex pair in the fuselage wake, significantly contributing to form drag, disturbing cargo drop trajectories and posing risks to paratroopers. To investigate this complex bluff body aerodynamics, a simplified model having a sharp-edge slanted afterbody consisting of an axisymmetric forebody and a slanted afterbody at a fixed angle Φ = 45° was employed. This study explores the wake dynamics and transitional behavior of this Baseline configuration and its variations, including the addition of a rear door and cavity modifications. A combination

of stereo and planar PIV techniques was used to capture detailed flow fields, revealing how wake states evolve with Reynolds number. Drag measurements are correlated with observed transitions, and vortex dynamics including spacing, vertical location, and peak vorticity were analyzed to further understand vortex behavior. Key findings highlight the reattachment of shear layers post-transition in both the Baseline and Cavity configurations, with the shear layer notably tucking into the cavity in the latter case. Additionally, notable changes in flow structure are observed with the addition of a rear door to both the Baseline and Cavity geometries, suggesting a strong geometric influence on the wake without necessarily inducing a transition in flow state. These insights reinforce the critical role of aft-body design in managing vortex dynamics and drag for bluff body flows representative of cargo aircraft fuselages.