Model to predict water droplet trajectories in the flow past an airfoil

A theoretical model is presented to predict water droplet trajectories in the flow past an airfoil. The model considers droplet deformation and includes a drag coefficient that accounts for the influence of flow acceleration. This is because, as seen from the reference frame of the droplet, the flow accelerates as the airfoil approaches, even if the airfoil moves at constant velocity. To validate the theoretical model, a series of experimental tests have been carried out in a rotating arm facility. Three parameters were changed in the experiments: 1) the size of the model airfoil (radius of curvature 0.103 m, 0.070 m, and 0.030 m), 2) its velocity (50 m/s, 60 m/s, 70 m/s, 80 m/s, and 90 m/s), and 3) the droplets' initial diameters (in the range from 550 μm to 1050 μm). Comparison between the results obtained using the theoretical model and those collected in the experimental tests (droplet tracking was carried out using a high speed imaging system) showed a good agreement. This suggests that, within the range of parameters that has been tested, the proposed theoretical model could be confidently used for trajectory prediction purposes.