Investigation of co-rotating vortex merger in ground proximity

The experiments were conducted in a water tunnel facility and were aimed at investigating the merging process of co-rotating wake vortices in ground effect. A corresponding two-dimensional analytical model was also introduced based on experimental results. The two like-sign vortices were generated with equal size and strength above the ground plane. The evolution of vortex pair was attained by using particle image velocimetry at a series of downstream locations. The main finding is that the ground effect promotes the merging process and accelerates the vortices' rotation around one another. Vertical movements, known as vortex rebound, and lateral movements are observed. The ground effect also leads to the emergence of a secondary vortex (SV), which adds to the complexity of the vortex system. Prediction of the modified potential model, which takes vortex decay, viscous drag and the evolution of the SV into account, is compared with the experimental data. The results show that the vortex merging and rebound of a co-rotating vortex pair is successfully predicted and the prediction of vortex orientation and lateral motion are also improved by this model.