Liquid Droplets Research Articles

Electrically switched asymmetric interfaces for liquid manipulation.

External field driven fluid manipulation, in particular electric field, offers the advantages of real-time control and exceptional flexibility, rendering it highly promising for applications in microfluidic devices, liquid separation and energy catalysis. However, it is still challenging for controlled liquid transport and fine control of droplet splitting. Herein, we demonstrate a strategy to achieve direction-controlled liquid transport and fine droplet splitting on an anisotropic groove-microstructured electrode surface via an electrically switched asymmetric interface. The balance of asymmetric capillary force generated by microstructures and electro-capillary force is critical in determining directional liquid transport and fine droplet splitting. Asymmetric bubbles generated by liquid electrolysis form an asymmetric liquid-gas-solid interface and result in gradient liquid wetting behavior on the two neighboring electrode surfaces. The electric field further enhances the asymmetric wetting of a liquid droplet on the electrode surface, exhibiting electric field direction-dependent motion. Moreover, the groove-microstructured electrode surface can strengthen the liquid droplet anisotropic wetting and correspondingly refine the volume range of the splitting sub-droplet. Even unidirectional/bidirectional liquid droplet transport can be controlled in collaboration with the asymmetric groove-microstructure and electric field. Thus, this work provides a new route for liquid transport and droplet splitting, showing great potential in controllable separation, microreaction and microfluidic devices.

Formulation and Physicochemical Evaluation of Spray Gel Containing Cordyline fruticosa L. Leaf Extract for Topical Delivery

Spray gel is a gel system applied through a spray pump, producing small or large liquid droplets. Cordyline fruticosa (L.) A. Cheval, commonly known as Andong Merah, is a plant with various medicinal properties, including wound healing activity attributed to its flavonoid content. This research aimed to formulate and evaluate the physicochemical properties of a spray gel containing Cordyline fruticosa leaf extract for topical delivery, focusing on the effects of different concentrations of Carbopol 940 as a gelling agent and sorbitol as a humectant. Cordyline fruticosa leaf extract was obtained by maceration using 96% ethanol. Three spray gel formulations were prepared, varying the concentrations of Carbopol 940 (0.4 g, 0.6 g, and 0.8 g) and sorbitol (5 ml, 7.5 ml, and 10 ml). The prepared spray gels were then subjected to physicochemical evaluation, including organoleptic tests (color, odor, and consistency), homogeneity tests, pH measurements, viscosity measurements, spray pattern analysis, and adhesion tests. All spray gel formulations exhibited acceptable physicochemical properties. The formulations were homogeneous, with a pH within the acceptable range for topical applications. The viscosity and adhesion properties varied with the concentrations of Carbopol 940 and sorbitol. The spray pattern analysis revealed a circular spread pattern, with the pressure required for spraying influenced by the viscosity of the formulation. The spray gel formulations containing Cordyline fruticosa leaf extract demonstrated good physicochemical qualities, indicating their potential suitability for topical delivery. Further studies are recommended to optimize the formulation for enhanced stability and therapeutic efficacy.

Wetting phenomena of droplets and gas bubbles: Contact angle hysteresis based on varying liquid-solid and solid-gas interfacial tensions.

Wetting phenomena have been widely observed in our daily lives, such as dew on lotus leaf, and applied in technical applications, e.g., ink-jet printing. In contrast to constant liquid-solid and solid-gas interfacial tensions in Young's law, we here focus on the wetting phenomena by considering varying fluid-solid interfacial tensions. We analyze the energy landscape, the map of Young's contact angle, the number and corresponding contact angle of local energy minima, and the contact angle hysteresis for a liquid droplet on a solid substrate in a gas phase. In addition, a gas bubble on a solid substrate in a liquid phase has been scrutinized from the aspect of surface energy minimization. The wetting effect has been regarded, where the liquid and gas species penetrate into the solid phase on the microscopic scale [F. Wang and B. Nestler, Phys. Rev. Lett. 132, 126202 (2024)]. We assume the liquid-solid and the solid-gas interfacial tensions to be a function dependent on the volume fraction of the liquid and the gas species and investigate the impact of the size ratio of the droplet to the solid surface that is overlooked in existing theories on the wetting phenomena. Our finding sheds light on the microscopic origin of the contact angle hysteresis and the droplet size effect on the wetting phenomena.

Mitigation Strategies against Antibody Aggregation Induced by Oleic Acid in Liquid Formulations.

Polysorbates 20 and 80 (PS20 and PS80) are commonly used in the formulations of biologics to protect against interfacial stresses. However, these surfactants can degrade over time, releasing free fatty acids, which assemble into solid particles or liquid droplets. Here, we apply a droplet microfluidic platform to analyze the interactions between antibodies and oleic acid, the primary free fatty acid resulting from the hydrolysis of PS80. We show that antibodies adsorb within seconds to the polar oleic acid-water interface, forming a viscoelastic protein layer that leads to particle formation upon mechanical rupture. By testing two different monoclonal antibodies of pharmaceutical origin, we show that the propensity to form a rigid viscoelastic layer is protein-specific. We further demonstrate that intact PS80 is effective in preventing antibody adsorption at the oleic acid-water interface only at low antibody concentrations and low pH, where oleic acid is fully protonated. Importantly, introduction of the amino acid l-arginine prevents the formation of the interfacial layer and protein particles even at high antibody concentrations (180 mg mL-1). Overall, our findings indicate that oleic acid droplets in antibody formulations can lead to the formation of protein particles via an interface-mediated mechanism. Depending on the conditions, intact PS80 alone might not be sufficient to protect against antibody aggregation. Additional mitigation strategies include the optimization of protein physicochemical properties, pH, and the addition of arginine.

High-speed tracking of coalescence and mixing of optically controlled droplets

We are presenting an all-optical platform for on-demand and nonintrusive studies of coalescence of micron-sized liquid droplets in air. The platform has the purpose to mimic the airborne conditions occurring in typical environments where droplet interactions are involved. By means of the Förster resonance energy transfer mechanism, we have been able to track the dynamics of two coalescing glycerol droplets, with a radius of ∼10µm and a temporal resolution of 86µs. At the onset of coalescence, a fast mixing is observed. Such an effect depletes the fluorescence of the donor fluorophore to half its initial intensity on a timescale below the temporal resolution of our platform, whereas a complete mixing is observed to occur on a timescale of seconds. The experimental platform design and findings facilitate an increased understanding of the microphysics of collisions, coalescence, and the subsequent mixing/diffusion of droplets on the micrometer lengthscale and the microsecond timescale. Published by the American Physical Society 2024

Controlled Assembly of Lipid Molecules via Regulating Transient Spatial Confinement

The constructs of lipid molecules follow self-assembly, driven by intermolecular interactions, forming stacking of lipid bilayer films. Achieving designed geometry at nano- to micro-levels with packing deviating from the near-equilibrium structure is difficult to achieve due to the strong tendency of lipid molecules to self-assemble. Using ultrasmall (<fL) droplets containing designed molecules, our prior work has demonstrated that molecular assembly, in principle, is governed mainly by transient inter-molecular interactions under their dynamic spatial confinement, i.e., tri-phase boundaries during drying. As a result, the assemblies can deviate, sometimes significantly, from the near-equilibrium structures of self-assembly. The present work applies the approach and concept to lipid molecules using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Taking advantage of the high spatial precision and the minute size of the delivery probe in our combined atomic force microscopy and microfluidic delivery, the transient shape of each liquid droplet is regulated. In doing so, the final geometry of the POPC assemblies has been regulated to the designed geometry with nanometer precision. The results extend the concept of controlled assembly of molecules to amphiphilic systems. The outcomes exhibit high potential in lipid-based biomaterial science and biodevice engineering.

Multitwinned Ice Nanocrystals.

Multitwinned nanocrystals are commonly found in substances that preferentially adopt tetrahedral local arrangements, but not yet in water crystals. Ice nanocrystals are pivotal in cloud microphysics, and their surfaces become increasingly prominent in determining structure as crystal size decreases. Nevertheless, discussions on nanocrystal structures have predominantly centered on ice polymorphs observed in bulk: hexagonal (Ih), cubic (Ic), and stacking-disordered (Isd) ices. Here, we demonstrate, through molecular dynamics (MD) simulations, that decahedral and icosahedral nanocrystals form from liquid water droplets of a few nanometers in size without violating the ice rule. The brute force spontaneous crystallization is conducted using the mW model, and the thermodynamic stability is examined using the TIP4P/Ice model. During the crystallization process, the formation of twin boundaries precedes the emergence of centers exhibiting 5-fold and icosahedral symmetry. The free energy calculation suggests the icosahedron has comparable stability with ice Ih nanocrystal. The frequent occurrence of these unreported ice nanocrystals aligns with the fact that natural polycrystalline snow crystals predominantly display a 70.5-degree angle between the Ih c-axes of adjacent branches. Moreover, we show that the formation of multitwinned ice nanocrystals is enhanced within a fullerene, providing a potential avenue for experimental observations.

De novo designed YK peptides forming reversible amyloid for synthetic protein condensates in mammalian cells

In mammalian cells, protein condensates underlie diverse cell functions. Intensive synthetic biological research has been devoted to fabricating liquid droplets using de novo peptides/proteins designed from scratch in test tubes or bacterial cells. However, the development of de novo sequences for synthetic droplets forming in eukaryotes is challenging. Here, we report YK peptides, comprising 9–15 residues of alternating repeats of tyrosine and lysine, which form reversible amyloid-like fibrils accompanied by binding with poly-anion species such as ATP. By genetically tagging the YK peptide, superfolder GFPs assemble into artificial liquid-like droplets in living cells. Rational design of the YK system allows fine-tuning of the fluidity and construction of multi-component droplets. The YK system not only facilitates intracellular reconstitution of simplified models for natural protein condensates, but it also provides a toolbox for the systematic creation of droplets with different dynamics and composition for in situ evaluation.

Spatio-temporal reconstruction of droplet impingement dynamics by means of color-coded glare points and deep learning

Abstract The present work introduces a deep learning approach for the three-dimensional reconstruction of the spatio-temporal dynamics of the gas-liquid interface on the basis of monocular images obtained via optical measurement techniques.
The method is tested an evaluated at the example of liquid droplets impacting on structured solid substrates.
The droplet dynamics are captured through high-speed imaging in an extended shadowgraphy setup with additional glare points from lateral light sources that encode further three-dimensional information of the gas-liquid interface in the images.
A neural network is trained for the physically correct reconstruction of the droplet dynamics on a labelled dataset generated by synthetic image rendering on the basis of gas-liquid interface shapes obtained from direct numerical simulation.
The employment of synthetic image rendering allows for the efficient generation of training data and circumvents the introduction of errors resulting from the inherent discrepancy of the droplet shapes between experiment and simulation. 
The accurate reconstruction of the three-dimensional shape of the gas-liquid interface during droplet impingement on the basis of images obtained in the experiment demonstrates the practicality of the presented approach.
The introduction of glare points from lateral light sources in the experiments is shown to improve the reconstruction accuracy, which indicates that the neural network learns to leverage the additional three-dimensional information encoded in the images for a more accurate depth estimation.
By the successful reconstruction of obscured areas in the input images, it is demonstrated that the neural network has the capability to learn a physically correct interpolation of missing data from the numerical simulation.
Furthermore, the physically reasonable reconstruction of unknown gas-liquid interface shapes for drop impact regimes that were not contained in the training dataset indicates that the neural network learned a versatile model of the involved two-phase flow phenomena during droplet impingement.

Nucleic Acid-Rich Stress Granules Are Not Merely Crowded Condensates: A Quantitative Raman Imaging Study.

Liquid droplets, formed by intracellular liquid-liquid phase separation (LLPS), are called membraneless organelles. They provide transient enzymatic reaction fields for maintaining cellular homeostasis, although they might transform into aggregates, leading to neurodegenerative diseases. To understand the nature of intracellular droplets, it is crucial to quantify the liquid droplets inside a living cell as well as to elucidate the underlying biological mechanism. In this study, we performed near-infrared fluorescence and Raman imaging to quantify chemical components inside stress granules (SGs) formed by LLPS in living cells. The Raman images reveal that the nucleic acid concentration inside the SGs was more than 20% higher than the surrounding cytoplasm, whereas the lipid concentration was lower. Quantitative Raman intensity analysis using a water Raman band as an internal standard enables in situ concentration determination of nucleic acids in the SGs and other organelles. The intensity of the biomolecular C-H bands relative to the water band indicates that the crowding environment inside the SGs depends on the stress type; under oxidative stress, the inside of the SGs was nearly identical to the outside, whereas it was sparser in hyperosmotic stressed cells, suggesting that the high concentrations of nucleic acids play a pivotal role in maintaining the environments inside the SGs. These results demonstrate that intracellular droplets are not always highly condensed.

Long range self-transport of liquid droplets driven by electric field and roughness gradient

It is well known that roughness and charge gradients could be used for droplet self-transport. The key issue is how to synergize the two effects. The uniform density charge can form linearly increasing charge gradient on a roughness gradient surface. Under this condition, the influence on the droplet self-transport under the synergy of these two effects was obtained by statics analysis, and the driving function was presented. An energy equation was constructed to study the conditions for crossing periodic boundaries, and the problem of distance limitation on periodic surfaces due to energy dissipation was solved by converting electric potential into droplet kinetic energy. A periodic roughness gradient surface with K = 0.07 was designed and prepared via 3D printing. Water droplets can be transported over long distances and the maximum velocity increases with charge density up to 46 mm/s. Finally, the effect of different structures on the maximum charge density in the Cassie state was investigated by simulation. The biomimetic structures exhibit great compressive stability, which can increase the surface charge density of droplets in the Cassie state by 3.6 times compared to pillar structures. It can be widely used in the fields of materials science and interface chemistry, etc.

Influence of Emulsion Lipid Droplet Crystallinity on Postprandial Endotoxin Transporters and Atherogenic And Inflammatory Profiles in Healthy Men - A Randomized Double-Blind Crossover Acute Meal Study.

Consumption of high-fat meals is associated with increased endotoxemia, inflammation, and atherogenic profiles, with repeated postprandial responses suggested as contributors to chronically elevated risk factors. However, effects of lipid solid versus liquid state specifically have not been investigated. This exploratory randomized crossover study tests the impact of lipid crystallinity on plasma levels of endotoxin transporters (lipopolysaccharide [LPS] binding protein [LBP] and soluble cluster of differentiation 14 [sCD14]) and select proinflammatory and atherogenic markers (tumor necrosis factor-alpha [TNF-α], C-reactive protein [CRP], interleukin-1-beta [IL-1β], interferon-gamma [IFN-γ], interleukin-6 [IL-6], soluble intercellular adhesion molecule [sICAM], soluble vascular cell adhesion molecule [sVCAM], monocyte chemoattractant protein-1 [MCP-1/CCL2], plasminogen activator inhibitor-1 [PAI-1], and fibrinogen). Fasted healthy men (n = 14, 28 ± 5.5 years, 24.1 ± 2.6kgm-2) consumed two 50g palm stearin oil-in-water emulsions tempered to contain either liquid or crystalline lipid droplets at 37°C on separate occasions with blood sampling at 0, 2-, 4-, and 6-h post-meal. Timepoint data, area under the curve, and peak concentration values are compared. Overall, no treatment effects are seen (p > 0.05). There are significant effects of time, with values decreasing from baseline, for TNF-α, MCP-1/CCL2, PAI-1, and fibrinogen (p < 0.05). Responder analysis pointed to differential treatment effects associated with some participant baseline characteristics but, overall, palm-stearin emulsion droplet crystallinity does not acutely affect plasma endotoxin transporters nor select inflammatory and atherogenic markers.

A numerical framework for modeling evaporation and combustion of isolated, spherically-symmetric, multi-component fuel droplets

This paper presents a comprehensive numerical framework for simulating the evaporation and combustion of isolated, spherically-symmetric, multi-component fuel droplets. The framework incorporates a detailed description of chemical reactions in the gaseous phase and is capable of modeling pure evaporation, autoignition, and hot-wire ignition scenarios.The transport equations for mass, species, and energy are solved in both the liquid (droplet) and gaseous (surrounding atmosphere) phases. Diffusion in the liquid phase is described using the Stefan–Maxwell theory, while in the gaseous phase, both molecular and thermal diffusion are considered. The model also includes the thermophoretic effect for carbonaceous particles and accounts for gas radiation through various models, ranging from optically-thin approximations to more complex methods like the P1 and discrete ordinate methods. Non-gray radiative effects are handled using the Weighted-Sum-of-Gray-Gases Model (WSGGM). Liquid/gas interface conditions are evaluated by imposing flux continuity of mass and energy, along with thermodynamic equilibrium for species. Deviations from ideal thermodynamic behavior in the liquid droplet are managed by incorporating a suitable activity coefficient or by using a proper cubic equation of state. Additionally, the presence of supporting fibers is modeled using a simplified one-dimensional approach. The transport equations are solved using the method of lines, with spatial discretization performed via the finite difference method on a body-fitted grid. The resulting system of Differential–Algebraic Equations (DAEs) is then solved using a fully-coupled approach.Thanks to its generality in terms of kinetic and thermodynamic descriptions and the reduced computational time, the proposed framework offers significant potential for advancing our understanding of the complex combustion processes of multi-component liquid fuels and for enhancing the planning and execution of experiments involving isolated fuel droplets.

Thermodynamic and economic analysis of a novel compressed air energy storage system coupled with solar energy and liquid piston energy storage and release

Compressed air energy storage (CAES) is one of the important means to solve the instability of power generation in renewable energy systems. To further improve the output power of the CAES system and the stability of the double-chamber liquid piston expansion module (LPEM) a new CAES coupled with liquid piston energy storage and release (LPSR-CAES) is proposed. The coupled LPEM conducts suction stage B at the end of the expansion stage, ensuring stable exhaust pressure and temperature for the module. By establishing the thermodynamic and economic models of LPSR-CAES, the effect laws of key node parameters on the system performance are investigated. The results show that the heat transfer between liquid droplets and air dominates the heat transfer in LPEM. The proposed LPEM exhibits excellent isothermal performance and stability, with a maximum temperature difference of about 20 K during the cycle, and stable exhaust temperature changes within 10 K. Under the design conditions, the converted electrical efficiency, round-trip efficiency, exergy efficiency and net present value of the system are 68.31 %, 58.86 %, 66.99 % and 12.25 M$ respectively. The higher the solar supplement temperature, the more outstanding the thermal and economic performance of the system. The short-term energy storage system performance of the proposed system is more prominent. Based on the actual light data, the system can achieve 72.09 % and 69.41 % of converted electrical efficiency and exergy efficiency, respectively, at the 219th day. The results of this study provide theoretical support for the engineering application of the proposed system.

Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

The diffusiophoresis of charged hydrophobic nanoparticles (NPs) governed by an imposed ionic concentration gradient is analysed. The main objective is to elucidate the impact of the laterally mobile adsorbed surface ions at the interface on the propulsion of the hydrophobic NPs in diffusiophoresis. In addition, the dielectric polarization due to the difference in dielectric constant between the NPs and the suspension medium is also considered. The mobile surface ions create a friction as well as an electric force at the hydrophobic surface, which leads to a modification of the slip velocity condition and the slip length. We obtain an exact numerical solution of the governing electrokinetic equations in their full form by adopting a control volume formulation. The numerical model is supplemented by analytical solutions derived based on the Debye–Hückel linearization. We find that the lateral mobility of the surface ions obstruct the coions to diffuse from the higher concentration side to the lower concentration side, which results in a repulsive force to the particle leading to the occurrence of a negative mobility. Based on the numerical results and analytical solutions, we have shown that for a fully mobile surface charge, the diffusiophoresis of a hydrophobic NP is identical to the diffusiophoresis of a liquid droplet whose viscosity is related to the slip length of the hydrophobic particle. We establish that the dielectric polarization enhances the velocity of a hydrophobic particle, which has potential applications in the practical context.

Damage evolution simulation and lifetime prediction for composite blades under continuous droplet impacts

Offshore wind power generation is a promising technology in renewable energy applications due to its high reserves of wind energy in sea areas. To improve the energy transformation efficiency, the blade length of the offshore wind turbines has become larger and larger, and it has made rain erosion be one of the most frequent failures during the turbine operation. As the natural rainfall is stochastic in spatial and time domains, it is difficult to depict the damage evolution process caused by rain impact exactly. Therefore, regular and continuous droplet impact simulation and experiments present an alternative methodology for this issue. With the composite structure of the blade and deformability of the liquid droplet in consideration, a fluid solid interaction model will be established to investigate the impact response and subsequent damage evolution. In which, the Smooth Particle Hydrodynamics (SPH) model is utilized to depict the constitutive relationship within the droplet, and Finite Element Method (FEM) is used to construct the Representative Volume Element (RVE) model of the blade leading edge. The impact process is simulated first to obtain the impact pressure distribution at the contact center and velocity field in the droplet. Furthermore, the stress wave propagation in the blade multilayer structure can be analyzed. Owing to the multiaxial fatigue feature of the continuous droplet impact, the continuum damage mechanics is integrated with the fatigue criterion and the Jump-in-Cycle procedure is used to simulate the high-cycle fatigue process. The damage factor distribution on the blade coating surface and its influence on mechanical properties are analyzed. Thereafter, the droplet impact fatigue life can be accumulated based on Miner’s linear rules. The theoretical achievements are validated by experimental data provided by Rain Erosion Testing (RET), which shows a good agreement between each other. As a result, V-N curves and D-N curves, i.e. quantitative relationship between droplet falling conditions and impact fatigue life, are established. The achievements in this study can provide an effective tool for rain erosion mechanism analysis and life prediction in industrial applications.

Investigation on supersonic jet noise reduction by water injection: Effects of water injection parameters

In order to protect the payload and the rocket structure from severe vibrations, water injection is commonly used on launch pads to reduce the high noise level radiated by supersonic plumes at lift-off. Even if this technique is widely used, the mechanisms behind sound reduction remain unclear. Sound reduction occurs due to multiple phenomena, each of them having different effects on the jet noise. Experiments based on acoustic measurements have been carried out on a hot supersonic jet on MARTEL facility (Mach number of 3 and a total temperature of 1700 K) to deeper identify the effect of evaporation and water injection parameters. Water flow rate, water injection speed and injection distance to the nozzle have been tested independently to identify the most important water injection parameters. It appears that water flow rate is the most important parameter to decrease noise level and that injecting water at high speed results in noise increase in the downstream direction. Results also highlight the importance of having liquid droplets at the end of the potential core to reduce noise.

Gas–Liquid Two-Phase Stirring Dynamics and Droplet Splashing Characteristics in Top-Blown Process

Gas–Liquid Two-Phase Stirring Dynamics and Droplet Splashing Characteristics in Top-Blown Process

Binary imidazolium based aqueous ionic liquid droplet on a rough surface: a molecular dynamics study

Ionic liquids (ILs) have garnered immense attention due to their tunable physicochemical properties. In this study, we delve into the wetting behaviour and interfacial properties of aqueous binary IL mixtures containing [EMIM] [BF4] and [HMIM] [BF4] on both smooth and rough graphite surfaces. Employing classical molecular dynamics simulations, we systematically explored the effects of IL concentration and surface morphology on wetting phenomena. To ensure the equilibrium of the systems, we began by calculating the interaction energies between the components. Subsequently, contact angles were computed, shedding light on the wetting characteristics of the aqueous binary IL mixtures. We meticulously examined the density profiles of the IL systems from the substrate to unravel the dominance of one IL over the other, exploiting the hydrophilic nature of [EMIM] [BF4] and the hydrophobic nature of [HMIM] [BF4]. A comprehensive analysis of hydrogen bond distribution allowed us to discern the intricate nature of these aqueous binary IL droplets. We probed the changes in intermolecular forces within the aqueous IL solution by investigating surface tensions. The tunability of these ILs emerges as a significant aspect of our study, paving the way for their tailored application in engineering and scientific domains. Schematic diagram showing the density distribution of hydrophilic and hydrophobic ILs ([EMIM] [BF4] and [HMIM] [BF4]) in water and also the hydrogen bond (HB) distribution of anion ([BF4]−) water inside the droplet on a pillared surface with a surface fraction ( f ) of 0.4 and pillar height of H = 4 .

Computational fluid dynamics investigation of pesticide spraying by agricultural drones

Precise control over pesticide spraying by agricultural drones requires fundamental research of multiphase flow, heat and mass transfer of liquid droplets in downwash flow. In this study, water was used as a carrier agent in pesticide formulations, in which the liquid droplets exhibit a Newtonian fluid behavior. A general computational fluid dynamics (CFD) model that characterizes propeller motion coupled with droplet evaporation and deposition was developed. The downwash flow generated by the propeller rotation was simulated using a multiple reference frame method along with the SST-k-ω turbulence model. Spraying of liquid droplets was simulated using a discrete phase model. The flow model validation was conducted by comparing the simulated velocities with experimental data, and the spray model validation was completed by a comparison of droplet depositions from CFD predictions and experiments. The results indicated that the droplet deposition fluctuates with an increase of propeller speed, and that both temperature and relative humidity affect the droplet deposition. In addition, the relation between the number of particles and the impact velocity was identified quantitatively, impact velocity with respect to particle diameter was predicted, and the effects of surface inclination, surface roughness, and crosswind speed on droplet deposition were analyzed. Moreover, an in-depth discussion about the intrinsic relation between downwash flow and droplet spraying was conducted.