Effect of thickness-to-chord ratio on flow structure of a low swept delta wing

Gülsaçan, Burak
Low swept delta wings, which are the simplified planforms of Unmanned Air Vehicles (UAVs), Unmanned Combat Air Vehicles (UCAVs) and Micro Air Vehicles (MAVs), have drawn considerable attention in recent years. In order to characterize and improve the operational parameters of these vehicles, the flow physics over low swept delta wings and its control should be well understood. In literature, the effect of thickness-to-chord ratio (t/C) on aerodynamic performance of a delta wing was studied on high and moderate swept delta wings, whereas no attention has been paid on the effect of t/C ratio on global flow structure of low swept delta wings. In the present study, the effect of t/C ratio on flow structure of a delta wing with sweep angle of 35 degree is characterized in a low speed wind tunnel using laser illuminated smoke visualization, near surface and cross-flow particle image velocimetry, and surface pressure measurements. Four delta wing models with t/C ratio varying from 4.75 % to 19 % are tested at angles of attack varying from 4 to 10 degrees for Reynolds numbers Re=10,000 and 35,000. The results indicate that the effect of thickness-to-chord ratio on flow structure is quite substantial, such that, as the wing thickness increases, the flow structure transforms from leading edge vortex to three-dimensional separated flow regime. The wing with low t/C ratio of 4.75 % experiences pronounced surface separation at significantly higher angle of attack compared to the wing with high t/C ratio. The results might explain some of the discrepancies reported in previously conducted studies related to delta wings. In addition, it is observed that the thickness of the shear layer separated from windward side of the wing is directly correlated with the thickness of the wing. To conclude, the flow structure on low swept delta wing is highly affected by t/C ratio, which in turn might indicate the potential usage of wing thickness as an effective flow control parameter. 
Citation Formats
B. Gülsaçan, “Effect of thickness-to-chord ratio on flow structure of a low swept delta wing,” M.S. - Master of Science, Middle East Technical University, 2017.