A super-hydrophobic surface has been obtained from nanocomposite materials based on silica nanoparticles and self-assembled monolayers of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) using spin coating chemical vapor deposition methods. Scanning electron microscope images reveal the porous structure nanoparticles, which can trap small-scale air pockets. An average water contact angle 163° bouncing off incoming droplets suggest that a POTS coating. The monitored droplet icing test results...

Ice accretion is a problematic natural phenomenon that affects wide range of engineering applications including power cables, radio masts, and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously impact to form rime ice or runback as along the wing glaze ice. Most models date have ignored mixed ice, which combination glaze. A parameter we term “freezing fraction” defined fraction droplet freezes with top surface explore concept accretion....

A simple theoretical model, the Kulikovskiy–Sveshnikova–Beghin (KSB) is outlined, describing motion of a particle cloud moving down an incline. This model includes both entrainment surrounding ambient fluid and particles from slope equally valid for Boussinesq non‐Boussinesq flows. However, this can predict physically impossible densities when there significant entrainment. Modifications to are proposed which eliminate problem by including entrained snow volume. With modified realistic mean...

[1] We present a model that underscores the role played by porous snow cover in sustaining large, rapid, dilute powder avalanches over weakly cohesive snow. The attributes massive localized material injection into avalanche head to synergistic pressure gradients established within very static field this influx induces along pack surface. Treating frontal entrainment as source of fluid, we show time-histories recorded at Vallée de la Sionne (Switzerland) conform classical two-dimensional...

Granular slides are omnipresent in both natural and industrial contexts. Scale effects changes physical behaviour of a phenomenon at different geometric scales, such as between laboratory experiment corresponding larger event observed nature. These scale can be significant render models small size inaccurate by underpredicting key characteristics flow velocity or runout distance. Although highly relevant to granular due the multiplicity length time scales flow, they currently not well...

Abstract This work presents a simple two-phase flow model to analyse series of axisymmetric granular column collapse tests conducted under elevated gravitational accelerations. These columns were prepared with just-saturated condition, where the pores filled Newtonian fluid up column’s free surface. In this configuration, unlike fully submerged case, air-water-grain contact angles may be important dynamics. The interaction between phase and monodispersed inertial particle was captured by an...

Abstract Powder-snow avalanches are natural hazards which affect the way populations live in mountainous areas. Field measurements from remain one of most significant and useful sources information about their dynamics behaviour. In this paper, we consider all video data Swiss Vallée de la Sionne test site years 2003–05. General scaling laws sought for avalanche front velocity based on plume theories. Avalanche Froude numbers found, comparing three different length scales: cube root fracture...

Pyroclastic flows from volcanoes, dust storms in the desert, and submarine turbidity currents are all gravity of particles suspension occurring nature. Powder snow avalanches one such flow where density difference between suspended interstitial air is high carry a significant proportion flow's momentum. This means that Boussinesq approximation, differences considered negligible inertia terms, not valid. Aspects flows, as their internal structure transition dense to current well understood....

We analyze frontal dynamics of dilute powder snow avalanches sustained by rapid blow‐out behind the front. Such material injection arises as a weakly cohesive cover is fluidized very pore pressure gradient that particle cloud induces within snowpack. model fluid mechanics potential flow consisting traveling source denser thrust into uniform airflow. Stability analysis mass balance involving and yields relations among scouring depth, height, speed, mixed‐mean density, impact when region...

Despite their clear danger to humans, snow avalanches are hard document. They occur in inaccessible and dangerous locations, often at times of bad weather. Observation instruments frequently malfunction the harsh conditions or destroyed. Measurements powder particularly difficult, as these less usually very large. To understand air flow front inside avalanches, we have designed an pressure sensor survive conditions. It consists a differential transducer, with high‐frequency response, built...

This Letter describes an investigation of interfacial melting in ice-bearing granular flows. It is proposed that energy associated with collisions causes at ice particle's surface, which can thus occur temperatures well below freezing. A laboratory experiment has been designed allows quantification this process and its effect on the dynamics a shear flow spheres. employs rotating drum, half filled particles, situated temperature controlled laboratory. Capillary forces between wetted melted...

Scale effects are differences in physical behavior that manifest between a large event and geometrically scaled laboratory model may cause misleading predictions. This study focuses on scale granular slides, important the environment to industry. A versatile 6 m long setup has been built following Froude similarity investigate dry slides at scales varied by factor of 4, with grain Reynolds numbers Re range 10 . To provide further comparison, discrete element method simulations have also...

Abstract We contrast the frontal dynamics of dilute powder snow avalanches with behavior their tail. While former can be regarded as a fast-moving eruption current dominated by synergistic material injection into short head, latter behaves nearly arrested cloud particles expanding progressive incorporation ambient air, or entrainment snow-cover late trailing well behind front.

Abstract Köhler et al. (2018, https://doi.org/10.1002/2017JF004375 ) deploy a high spatial and temporal resolution GEODAR radar system to reveal the inside of snow avalanches over entire slope. They detect rich variety longitudinal slope normal flow structures across data set 77 recorded 6 years. Distinctive features in signatures permit definition seven regimes three distinct stopping signatures, illustrating behaviors much richer than conventional dichotomy between dense powder avalanches....

Abstract We present, analyse and discuss air-pressure data from finite-volume chute flows of dry fine snow in air. These experiments have the correct similarity criteria to model powder-snow avalanches demonstrate transition a dense suspended flow. measured dynamic air pressure at base flow, which features marked negative peak immediately behind front. This feature is also seen observations natural Russia, Japan Switzerland direct numerical simulations non-Boussinesq suspension ping-pong...

Abstract. Lobe and cleft patterns are frequently observed at the leading edge of gravity currents, including non-Boussinesq particle-laden currents such as powder snow avalanches. Despite importance instability in driving air entrainment, little is known about its origin or mechanisms behind development. In this paper we seek to gain a better understanding these from laboratory scale model avalanches using lightweight granular material. The flows appear be combination those found both...

We study the role of suspension density in eruption currents, a regime gravity-driven flow that is sustained by massive, localized blow-out particles acting as steady source heavier fluid injected into uniform at high Reynolds number. Inspired potential solution Saffman and Yuen [“Finite-amplitude interfacial waves presence current,” J. Fluid Mech. 123, 459–476 (1982)10.1017/S0022112082003152], we show relative difference between two fluids swells size current's head without changing its...

Abstract This work introduces a scaling analysis of sub-aerial axisymmetric column collapses glass beads and Newtonian glycerol-water solutions mimicking some the behaviours debris flows. The were in size range where their inertia partly decouples collapse behaviour from water column. Experiments explored viscous, surface tension particle effects through systematic variation fluid viscosity. Crucially geotechnical centrifuge was used to access elevated effective gravitational accelerations...

The wide particle size distributions, over several orders of magnitude, observed in debris flows leads to a diverse range rheological behaviours controlling flow outcomes. This study explores the influence different scale grains by conducting subaerial, fully saturated granular column collapse experiments with extreme, bimodal distributions. primary particles were where their behaviour was controlled inertia while suspension kaolin clay within fluid phase acts at spatial scales smaller than...