Date of Award

3-2005

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Mark F. Reeder, PhD

Abstract

The subsonic aerodynamic performance of a blended wing body aircraft constructed using selective laser sintering was assessed in the AFIT low-speed wind tunnel. The scaled-down model of a strike tanker aircraft consisted of a shaped fuselage and sweptback wings. The Reynolds number, based on mean wing chord, during testing was on the order of 105 while the Mach number ranged from 0.10 to 0.20. The model evaluation and analysis process included force and moment measurements acquired from a wind tunnel balance, pressure data measured with 8 taps located on the model’s upper surface, a comparison to computational fluid dynamics (CFD) solutions acquired in a parallel study conducted by AFRL/VAAC, and global pressure sensitive paint (PSP) measurements. Paint measurements were compared to pressure tap data to ensure their accuracy while lift and drag coefficients, as well as pitching and rolling moments were examined to determine performance characteristics, including stability attributes and aircraft stall. 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 with a profilometer and was found to have increased from approximately 0.3μm to 0.7μm when the paint was applied. When traditional 2-D boundary layer approaches to assessing the effect of roughness, the 0.7μm value falls well below the threshold at which one would anticipate roughness to have any effect. There is support in archival literature for the notion that roughness effects are more pronounced in a 3-D boundary layer, and the pitching moment data and the PSP data indicate that the for the painted model, there is a gradual onset of wing stall marching inward from the wingtips toward the body. By contrast, the force and, in particular, the pitching moment data suggests that the onset of wing stall is sudden across the entire wing for the unpainted case. Interestingly, the CFD data compared well with the data corresponding to the measurements of the rougher, painted model. Notably, the grid used in CFD would require at least an order of magnitude higher resolution in the boundary layer region to accurately depict the submicron roughness effects.

AFIT Designator

AFIT-GAE-ENY-05-M09

DTIC Accession Number

ADA436457

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