C-17 Low Speed Wind Tunnel Wake-Vortex Study

This wind tunnel research, sponsored by the Natick Soldier Research, Development and Engineering Center (NSRDEC), investigates the flow behind a 1/84 scale model of the C-17 Globemaster III in a clean configuration with troop and cargo doors closed. A pressure rake swept through a region perpendicular to the aircraft’s line of flight generated two-dimensional maps of the aircraft wake at fixed distances away from the cargo door. Recirculation and separation in this region can adversely influence airdrop operations, and a detailed understanding of the flow-field is essential to developing engineering and operational approaches to mitigate their effects and increase mission success and safety. The tests covered several angles of attack and Mach numbers. The results demonstrated that the size and intensity of the wake near the cargo door were directly affected by the angle of attack of the aircraft, but the aircraft airspeed had a much smaller affect on the pressure recovery fraction data. At higher angles of attack, the aft section of the aircraft experienced more uniform free-stream flow that was less turbulent than at lower angles of attack. The lift and drag force data obtained, in conjunction with the pressure flow-field surveys will be used to validate future Computational Fluid Dynamics (CFD) studies. A statistical analysis of the velocity field near the body of the aircraft suggests the presence of vortices; however, the results are inclusive and will be investigated further with the aid of CFD analyses. The uncertainty in the wake measurements was less than 2%.