Investigation on Surface Roughness of PolyJet-Printed Airfoil Geometries for Small UAV Applications

The present study focuses on producibility and surface roughness characteristics of airfoil geometries and their effect on aerodynamic performance for different velocities, surface roughness values and angles of attack. Two different tray orientations (along X and Y axis), two different build directions (vertical and horizontal) and two different surface finish settings (matte and glossy) were used to evaluate the effect of these parameters on the surface roughness of both up- and down-facing surfaces of airfoils produced by PolyJet. On both surfaces, surface roughness measurements were performed on two crossing directions. The results showed that horizontal build direction where surfaces of airfoils were parallel to the build platform experienced lower surface roughness than the vertical build direction. Vertically oriented specimens showed a considerable degree of distortions especially in trailing edges along with very high surface irregularities on side walls. In general, glossy or matte finish settings resulted in similar surface roughness values and specimens located along X direction showed better surface quality than specimens located along Y direction with an inconsiderable difference. Besides this, CFD analysis revealed that surface roughness caused by printing strategies directly influences the aerodynamic performance of the fixed-wing UAVs (Unmanned Aerial Vehicles) to considerable degrees. The increase in the drag force coefficient, due to surface roughness, reached almost 7.5% for high cruise velocity at 0 degrees angle of attack and 13% at 10 degrees angle of attack in which stall commences.