PSP-Based Experimental Investigation of a Blended Wing Body Aircraft

Abstract

The aerodynamic characteristics of a blended wing body aircraft, constructed using selective laser sintering (SLS), were assessed in the AFIT low-speed wind tunnel. The scaled- down model (Rec ~ 10 5 and M = 0.10 to 0.20) of a strike tanker consisted of a shaped fuselage and sweptback wings. The model evaluation and analysis process included force and moment measurements acquired from a wind tunnel balance, pressure sensitive paint (PSP) measurements, and a comparison to computational fluid dynamics (CFD) solutions. One of the most interesting results was the striking difference in the force and moment measurements before and after the paint was applied to the surface. The average surface roughness, Ra, was measured and was found to have increased from approximately 0.3μm to 0.7μm when the paint was applied. Although this value is well below the roughness threshold suggested by 2-D boundary layer theory, the effect was clear and repeatable. Force and moment coefficient data suggest that the onset of wing stall was sudden across the entire wing for sufficiently smooth cases but occurs gradually for rougher surfaces. Interestingly, the CFD results compared well with the experimental data corresponding to the measurements of the rougher, painted model. Both the PSP data and the CFD results indicated that the primary mechanism of lift transitioned from leading-edge suction along the wing to vortex lift near the wing-body junction as angle of attack increased. Taken as a whole, the data suggests that, for the range of conditions tested, submicron roughness has a pronounced effect on the transition to the vortex lift mechanism for increasing angle of attack.