| 30 Oct 2026
Experimental and numerical study on the impact force of water droplets in the medium speed regime
Abstract. This study investigated the impact force exerted by a water droplet colliding with a solid surface at medium velocities. Raindrop impacts on wind turbine blades can cause erosion damage, reducing the power efficiency. Addressing this issue is of practical importance for wind energy. Previous studies have revealed that the droplet impacts can be scaled with inertial force, expressed as ρD2V2 , where ρ, D, and V are water density, droplet diameter, and impact velocity, respectively. This study examined whether this scaling can be applied under conditions representative of raindrop impacts on wind turbine blades, where the impact velocity is relatively high, ranging from 35 to 126 m/s. To this end, the impact force of millimeter-sized droplets was measured using a whirling arm rain erosion tester and a pressure sensor. Computational fluid dynamics simulations were conducted to model the experimental conditions. The simulation results, assuming an ideal spherical droplet, showed the scaling of ρD2V2 for the impact force. The experimental data generally followed the scaling law; however, the peak impact forces tended to be slightly higher. Images of the droplets before impact indicate that the droplets were significantly deformed by the high-speed airflow in the vicinity of the rapidly rotating blade. To accurately evaluate impact forces at moderate-to-high velocities, it is necessary to account for aerodynamic effects on the droplets rather than assuming a spherical shape.
Competing interests: As discussed previously with the Editorial Office, we would like to respectfully request that the researcher identified below be excluded from both the peer-review process and the open discussion process for this manuscript due to a conflict of interest. This manuscript was previously submitted to another journal in the field of wind energy. During the review process, we received comments from an anonymous reviewer that we considered excessively critical, and the manuscript was subsequently rejected. Because the review was anonymous, we have no means of confirming the reviewer’s identity. Nevertheless, based on the circumstances, we have concerns that the reviewer may have been the researcher identified below. Considering this background, we respectfully request that this researcher not be invited to review the present manuscript. We also request that any comments submitted by this researcher during the open discussion process not be considered as part of the evaluation of the manuscript. The individual with whom we have a conflict of interest is Prof. Nobuyuki Fujisawa at Shinshu University and Niigata University (e-mail address: fujisawa@eng.niigata-u.ac.jp). We make this request solely to ensure a fair and impartial evaluation of the manuscript and would appreciate the confidential handling of this information.
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