Overview of Rotary Flow Visualization Results on the F/a-18 Aircraft

To understand the physics of the complex vortex flow field of the F/A-18 aircraft during maneuvering at high incidences, a series of flow visualizations were conducted in the IAR 0.38 x 0.51m water tunnel. A 1/72-scale model was tested on the new orbital-platform rotary apparatus at angles of attack from 20o to 65o with sideslip angles in the range 10 . It was found that the aerodynamic behaviour of the F/A-18 aircraft is dominated by forebody/LEX vortex interactions. Strong or weak leeward vortex interactions occur at different rotation rates and sideslip angles, causing non-linear lateral-directional aerodynamic behaviour. The boundaries of the threshold rotation rates at post-stall angles of attack and non-zero sideslip have been defined by the flow visualization results. Asymmetric forebody vortex shedding occurred at 57.5o 65o under static conditions. The rotary vortex flow field exhibits hysteretic behaviour over the range of steady rotation rates.