Numerical Simulation of Wake Flowfield Behind the C-130 with Cargo Ramp Open

Abstract

Simulation results are presented for a C-130 aircraft configured to perform cargo airdrop operations. Flight operations with the cargo ramp open lead to strong vortical flow structures and unsteady flows, which can adversely affect airdrop operations and parachute deployments. The results document complex wake structures formed behind the C-130 with the cargo ramp open at 0 and 50% flap settings. In particular, the wake contains two asymmetric counter-rotating vortices formed between the open ramp and the upsweep section of the aircraft and near the rear edges of the ramp. The flow separates along these edges because of the sharp turn that flow makes as it enters the cargo compartment. The separated flow then rolls up into two vortices. These vortices move outward and upward, and then they pass very near the lower surface of the horizontal stabilizer. These vortical flows lead to unsteady airloads on the horizontal stabilizer, and thus the aircraft. The wake effects are larger behind the upper upsweep section and are minimum at the lower positions. Grid and time sensitivity studies are performed for several geometries to ensure numerical simulations are accurate for the separated and vortical flows. The results show that, as the grid becomes more refined in the region behind the upsweep section of the aircraft, the localized wake structures and unsteady effects are better captured by the flow solver.