Icing poses significant hazards to aviation safety. Superhydrophobic surfaces have gained widespread attention for their capability to induce rebounding and detachment of impacting water droplets from surfaces, thereby achieving anti-icing. When icing occurs on equipment such as wind turbines and aircraft, the droplet diameter typically ranges from micrometers to tens of micrometers, and the surface is often in motion. However, experimental research on the characteristics of micrometer-scale water droplets impacting moving superhydrophobic surfaces remains vacant. Consequently, in this paper, we developed an experimental platform to investigate the impact of micron-sized water droplets on moving superhydrophobic surfaces. High-speed photography revealed that, contrary to observations with millimeter-scale droplets, the contact time of micrometer-scale water droplets impacting superhydrophobic surfaces increases significantly (by 78%) at high surface tangential velocities. Furthermore, numerical simulations were conducted to gain deeper insights into the impact process, particularly focusing on the influence of surface motion on the impact characteristics of water droplets. This influence mainly manifests in three aspects: it prolongs the centroid descent process, redirects water droplets from the expansion direction to the flow direction, and changes the expansion and retraction characteristics of water droplets. The extension of the contact time of micrometer-scale water droplets due to the high-speed motion of superhydrophobic surfaces is attributed to the intense stretching of the water droplets' front edge. Subsequently, by applying dual synthetic jets to water droplets, the tangential relative impact velocity between the droplets and the surface is decreased, resulting in a 28% reduction in the contact time. This research deepens the understanding of the impact dynamics of micron-sized droplets on moving walls and provides new insights for developing active and efficient anti-icing/de-icing technologies based on superhydrophobic surfaces.

Large Eddy Simulation (LES) is first used to investigate the drag reduction effect of an array-based configuration of Plasma Synthetic Jet Actuators (PSJAs) on a hemisphere in supersonic inflow, and analyze the effect of energy allocation and array angle on the drag reduction performance of opposing Plasma Synthetic Jet (PSJ) in this paper. Numerical simulation results have been compared with experimental data, confirming the validity of the simulation method. The results show that different energy allocations have a significant effect on the drag of the hemisphere. However, the effect of the change in array angle on the drag of the hemisphere is not as noticeable as the effect caused by energy allocation. Interference regions between the two PSJAs occur, which undermine the effectiveness of drag reduction. High Turbulent Kinetic Energy (TKE) regions primarily concentrate on the core region of the jet and downstream of the bow shock. The influence of the array angle on TKE is most evident in the downstream region of the exits of the PSJs on both sides. Temporal evolution of the coherent structures reveals that as the PSJ intensity decreases, the large-scale vortices progressively break up into smaller-scale vortices, and energy is also transferred from large-scale structures to small-scale structures.

The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.