Droplet impact on a spinning surface has been observed in different industries and plays an important role in the performance of industrial systems. In the current study, the dynamics of water droplet impact on a hydrophilic spinning disk is investigated. An experimental setup is designed in a way that droplet diameter, impact velocity, disk rotational speed, and location of impact are precisely controlled. While the droplet diameter is fixed in the present study, other mentioned parameters are changed and their effects on the droplet behavior are discussed. High-speed imaging is used to record the droplet dynamics under various operating conditions. It is demonstrated that after impact, droplet spreads on the surface due to a high adhesion between water and the hydrophilic substrate. It is indicated that the wetted area is a function of time, impact velocity, disk rotational speed, and centrifugal acceleration. Furthermore, depending on the mentioned parameters, different phenomena such as rivulet formation, fingering, and detachment of secondary droplet(s) are observed. In the angular direction, in general, the wetted length increases as time passes. However, in the radial direction, the droplet first spreads on the surface and reaches a maximum value, and then recedes until a plateau is attained. At this instant, a bulk of liquid, which is called wave in this study, moves radially outward from the inner boundary of the droplet toward its outer boundary due to the effect of centrifugal force. Once the wave reaches the outer boundary, depending on its size and momentum, fingers or rivulets are formed, and small droplet(s) may detach. The process is analyzed comprehensively, and different empirical correlations for wetted lengths in radial and angular directions, secondary droplet formation, number of fingers, the onset of fingering, and wave velocity are developed.

Suspension plasma spraying (SPS) is an effective technique to enhance the quality of the thermal barrier, wear-resistant, corrosion-resistant, and superhydrophobic coatings. To create the suspension in the SPS technique, nano and sub-micron solid particles are added to a base liquid (typically water or ethanol). Subsequently, by using either a mechanical injection system with a plain orifice or a twin-fluid atomizer (e.g., air-blast or effervescent), the suspension is injected into the high-velocity high-temperature plasma flow. In the present work, we simulate the interactions between the air-blast suspension spray and the plasma crossflow by using a three-dimensional two-way coupled Eulerian–Lagrangian model. Here, the suspension consists of ethanol (85 wt.%) and nickel (15 wt.%). Furthermore, at the standoff distance of 40 mm, a flat substrate is placed. To model the turbulence and the droplet breakup, Reynolds Stress Model (RSM) and Kelvin-Helmholtz Rayleigh-Taylor breakup model are used, respectively. Tracking of the fine particles is continued after suspension’s fragmentation and evaporation, until their deposition on the substrate. In addition, the effects of several parameters such as suspension mass flow rate, spray angle, and injector location on the in-flight behavior of droplets/particles as well as the particle velocity and temperature upon impact are investigated. It is shown that the injector location and the spray angle have a significant influence on the droplet/particle in-flight behavior. If the injector is far from the plasma or the spray angle is too wide, the particle temperature and velocity upon impact decrease considerably.

The goal of this study is to explore and analyze the concurrent shear-driven droplet shedding and coalescence under the effect of various parameters, such as droplet size, and distance, as well as airflow velocity, and surface wettability. To investigate and capture different aspects of droplet dynamics, both experimental and numerical modeling are conducted. The Volume of Fluid (VOF) coupled with the Large Eddy Simulation (LES) turbulent model in conjunction with the dynamic contact angle is implemented to model droplet shedding on different surface wettabilities. Analysis revealed a great match between the numerical and experimental outcomes. It is shown that in addition to surface wettability and airflow speed, droplet sizes, and the distance between them are crucial factors in controlling droplet dynamics during the shedding and coalescence. It is illustrated that on the Aluminum (hydrophilic) surface, the $2^{nd}$ droplet (the one further from the airflow inlet) tends to move toward the $1^{st}$ droplet. On the superhydrophobic surface, on the other hand, droplets behaved differently, which is mainly related to initial droplet shape and dynamic contact angles. When the $1^{st}$ droplet is larger between the two, the $2^{nd}$ droplet tends to move towards the first one in contrast to the case where the $1^{st}$ droplet is the smaller one. To better interpret the droplet dynamics, and the effect of different parameters on their behavior, further details on aerodynamic forces including the drag and lift forces before and after the coalescence are presented in this work.

An experimental study is performed to investigate the effect of tangential velocity on the dynamics of a water droplet impacting a spinning superhydrophobic surface. It is revealed that an increase in the tangential velocity, results in droplets spreading from symmetrical to asymmetrical shapes on the superhydrophobic surface. Moreover, depending on the impact and tangential velocities, three behaviors are observed: bouncing, symmetrical splashing, and asymmetrical splashing. In the bouncing regime, it is found that the droplet contact time is independent of impact velocity and decreases as the tangential velocity increases. However, the maximum spreading diameter in this regime is a function of both the impact and the tangential velocities. Furthermore, a splashing threshold is introduced to estimate the transition between the bouncing, symmetrical splashing, and asymmetrical splashing regimes. It is revealed that the value of K in the present work (i.e. superhydrophobic spinning disk) is approximately 60% less than the K value obtained by other researchers for the case of aluminum spinning disk. Moreover, two values are found for k to define the boundaries between these three observed regimes.

Selection of process parameters is an important step in Powder-Based Additive Manufacturing (PBAM) of metals. In order to achieve an optimal parameter set, current literature is mainly focused on the understanding of powder dynamics by analysing the aerodynamic forces. In this letter, however, we show the importance of the laser induced force (radiation pressure) on the powder dynamics. Generalised Lorenz-Mie theory has been employed to accurately estimate the radiation pressure and it is shown that its magnitude is significant in comparison to various aerodynamic forces and the grains weight, hence, can significantly contribute to denudation and spatter observed in the manufacturing process. Furthermore, the importance of compressibility and rarefaction effects on the magnitude of drag and lift forces that a particle experiences is identified by estimating the Ma and Kn numbers under process conditions, which directly impact the powder dynamics.