Abstract: A two-dimensional particle image velocimelry (PIV) measurement experimental study is performed on a flat-plate delta wing of 82.5° sweep angle and velocimetry of the identical delta wing with a low dorsal fin. The test is conducted at a low-speed wind tunnel using a two-dimensional PIV technique at 30° angle of attack and zero sideslip. The ratio of the local fin height to the local wing semi-span is 0.6.The Reynolds number based on the root chord of the wing is 2.33×10⁶. The test results clearly indicate that the vortices over the wing-alone model are symmetric and steady. The vortices still keep steady but become asymmetric and non-conical over the model with the low fin for the same flow conditions. The results confirm that the low dorsal fin may weaken and even destroy the stability of the vortex pair of the slender delta wing, and provide for the first time experimental evidence of the theoretical predictions and depict the flow behavior at 30° angle of attack when the vortex instability onset occurs.

Key words: particle image velocimetry, vortex stability, high angle of attack, fin, slender body, delta wing