Visualization of flow past a model of the CF-18 aircraft in a water tunnel.

Abstract

Incompressible flow past a 1:48 scale model of the CF-18 fighter aircraft was studied in a water tunnel at the University of Ottawa. Flow visualization records were obtained for flow around different stores, the Leading Edge Extension (LEX) vortex, and the forebody vortex, at various angles of attack. The stores were mostly studied in the low angle of attack range between $\alpha$ = $-$1$\sp\circ$ and $\alpha$ = 5$\sp\circ$. At these angles, their effect on the flow was local. Decreasing the spacing between stores caused the flow to slow down considerably because of the interaction of the separated flow on the wing with the boundary layers of the individual stores. The LEX vortex became stronger as the angle of attack was increased, and the location of its breakdown moved upstream. The breakdown location showed good correlation with results of other model and full-scale studies. The forebody vortex was weaker than the LEX vortex, and was consistently drawn towards the LEX until the two vortices began interacting. The variation of the LEX vortex bursting location with angle of attack is only weakly sensitive to Reynolds number and, therefore, the water tunnel tests can provide a good simulation of full-scale flow characteristics. On the other hand, flow characteristics near surfaces change substantially with increasing Reynolds number, so that the water tunnel results in such regions must be viewed with reservation, when considering their relevance to the high Reynolds number flow around the aircraft. (Abstract shortened by UMI.)