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When a droplet impacts a fabric mesh at a sufficiently high impact velocity, it not only spreads over the fabric but also penetrates its pores. To determine the influence of this liquid penetration of the fabric on droplet spreading on thin fabric meshes, we measured the droplet spreading ratio on fabric with and without an underlying substrate using a high-speed camera. For fabrics without a substrate, the droplet spreading ratio is reduced as the fabric penetration by the liquid reduces the droplet volume spreading on top of the fabric. Using entropic lattice Boltzmann simulations, we find that the lower droplet spreading ratio on fabrics, both with and without a substrate, is due to an increase in viscous losses inside the droplet during spreading. Comparing droplet impact of blood with its Newtonian counterpart, we show that for spreading on fabrics, just like on smooth surfaces, blood can be approximated as a Newtonian fluid. [ABSTRACT FROM AUTHOR]

In liquid spray applications, the sprays are often created by the formation and destabilization of a liquid sheet or jet. The disadvantage of such atomization processes is that the breakup is often highly irregular, causing a broad distribution of droplet sizes. As these sizes are controlled by the ligament corrugation and size, a monodisperse spray should consist of ligaments that are both smooth and of equal size. A straightforward way of creating smooth and equally sized ligaments is by droplet impact on a mesh. In this work we show that this approach does however not produce monodisperse droplets, but instead the droplet size distribution is very broad, with a large number of small satellite drops. We demonstrate that the fragmentation is controlled by a jet instability, where initial perturbations caused by the injection process result in long-wavelength disturbances that determine the final ligament breakup. During destabilization the crests of these disturbances are connected by thin ligaments which are the leading cause of the large number of small droplets. A secondary coalescence process, due to small relative velocities between droplets, partly masks this effect by reducing the amount of small droplets. Of the many parameters in this system, we describe the effect of varying the mesh size, mesh rigidity, impact velocity and wetting properties, keeping the liquid properties the same by focusing on water droplets only. We further perform lattice Boltzmann modelling of the impact process that reproduces key features seen in the experimental data. [ABSTRACT FROM AUTHOR]

Time-resolved wind-driven rain (WDR) load is investigated on an array of low-rise cubic buildings using an Eulerian multiphase (EM) model together with large eddy simulation (LES). The influence of wind-flow unsteadiness on the unsteady behavior of raindrops and the WDR intensity is discussed in detail. The wind-flow field predicted with LES has been validated with wind-tunnel measurements. The mean WDR intensity values obtained using the EM model are found to be in agreement with in-situ WDR measurements. The time-resolved simulations show that the instantaneous specific catch ratio values of smaller droplets fluctuate a lot around their mean values due to higher influence of turbulence. Instantaneous specific catch ratios for the smallest raindrops are mainly dictated by local turbulent structures present in the shear layer or below the rooftop level. On the other hand, the motion of larger raindrops is mainly influenced by the larger-scale motions above the cubes. It is also shown that, running means of the specific catch ratio over a time window of 100–300 s of physical time stabilize to a constant value. [ABSTRACT FROM AUTHOR]

The article presents a study on the influence of the wettability of a liquid on a surface to the maximum spreading of drops at low impact velocity. Topics discussed include the dynamic contact angle at maximum spreading, the relation between the capillary energy at zero impact velocity and spreading ratio at zero impact velocity, and the rescaling of the influence of the liquid and the nature and roughness of the surface with the spreading ratio at zero velocity.