Effect of the Leading-Edge Extension (LEX) Fence on the Vortex Structure over theF/A-18

摘要

The effects of the Leading Edge Extension (LEX) fence on the vortex structureover the F/A-18 at moderate to high angles of attack were studied using a 1/9 scale wind tunnel model and a 1/48 scale water tunnel model. Measurements at the tip of one of the vertical fins of the wind tunnel model confirmed that the fence reduced fin vibration caused by vortex breakdown. Flow visualisation in the water tunnel and in the wind tunnel showed that the fence caused the formation of a second LEX vortex, of the same sense as the main LEX vortex, but originating on the LEX leading edge outboard of the fence. Visualisation of the surface flow around the fence showed in detail how the fence caused the second LEX vortex. The effects on vortex breakdown and fin vibration of the interaction between the main and second LEX vortices are discussed.