Effect of Thickness-to-Chord Ratio on Flow Structure of Nonslender Delta Wing

The effects of thickness-to-chord (t/C) ratio on flow structures of nonslender delta wings with sweep angles of 35 and 45 degrees are characterized in a low-speed wind tunnel using velocity, pressure, and force measurements. The delta wings with t/C ratios varying from 2 % to 19 % are tested at broad ranges of attack angles and Reynolds numbers. The results indicate that the effect of t/C ratio on flow structure is quite substantial. Considering the low angles of attack where the wings experience leading edge vortex structure, the strength of the vortex structure increases as the t/C ratio increases. However, the wing with lowest t/C ratio has pronounced surface separation at significantly higher angle of attack compared to the wing with highest t/C ratio, which indicates that lowest t/C ratio wing might be more resistive to the stall condition. These results are well supported by the force measurements such that high t/C ratio induces higher lift coefficient, C_L, at low attack angles, whereas maximum C_L values that can be reached are significantly higher and appears at significantly higher angle of attack for low t/C ratio wings. Considering the C_L/C_D ratio, increase in t/C ratio induces remarkable drop in C_L/C_D values.