High‐speed photography of water drop impacts on sand and soil

Abstract

Summary The way that water drops impact on soil is of widespread importance for soil science, particularly in the context of irrigation and erosion. With modern high‐speed photography techniques, impacts on granular materials are becoming more widely studied, but the variation in particle‐size distribution of soil presents particular challenges. Here, the impacts of individual water drops on two contrasting soil textures (pure sand and a loamy soil) have been studied with high‐speed photography, and compared at Weber numbers between 50 and 750. Granular samples with wider distributions of particle sizes produce larger variations in experimental outcomes. For the sand, which contained >98% particles between 60 μm and 2 mm in size, the typical outcome involved spreading and retraction of the drop to a circular profile with a raised rim. The loamy soil had greater surface roughness than the sand, with a wider distribution of particle sizes, so that the spread of the drop was more anisotropic, involved more movement of target particles and often involved droplet breakup into satellite drops. Overall outcomes were best described by a gravity‐dominated cratering mechanism, and the scaling exponent for the crater diameter with respect to impact energy was 0.22 ± 0.03. Dynamic penetration studies enabled visualization of granular motion below the surface, and both static and dynamic penetration results illustrated a transition between inertial and viscous regimes over time. As the water content of the soil was increased, droplet breakup was initially encouraged before capillary imbibition dominated at water contents close to 10%v/v. This research is useful for understanding how rain and irrigation, which comprise many millimetre‐scale drops, influence large‐scale hydraulic properties in soil, including surface sealing. Highlights Drop impact on to soil is important, but its systematic study is difficult because of variation in soil particle sizes. High‐speed photography was used to study drop impacts on to a pure sand and loamy soil, and analysed quantitatively. Results show how granular samples with wider distributions of particle sizes produce more variation in experimental outcomes. The maximum extent of drop spreading was best described by a scaling model developed for planetary cratering.

Soil Deformation after Water Drop Impact—A Review of the Measurement Methods

“…Based on recordings from high-speed cameras, it is possible to obtain data on the dynamics and course of the cratering phenomenon [ 40 , 44 , 53 , 56 ]. Some works used single images or short sequences of images taken by the method of high-speed photography as an independent object of analysis or a way of presenting successive stages of the studied process [ 42 , 43 , 45 , 49 , 54 ]. The quantities determined based on the films include, among others, the time of crater formation and the change in its diameter over time, which was considered in the work of Delon et al [ 43 ], Nefzaoui and Skurtys [ 44 ], Zhao et al [ 53 ], and Mazur et al [ 58 ].…”

“…The quantities determined based on the films include, among others, the time of crater formation and the change in its diameter over time, which was considered in the work of Delon et al [ 43 ], Nefzaoui and Skurtys [ 44 ], Zhao et al [ 53 ], and Mazur et al [ 58 ]. The course of the wetting of deposit material by drops can also be the subject of research [ 36 , 38 , 50 , 54 ]. Camera measurements provide insight into the movement of bed material [ 42 , 48 ] and the formation of the rim [ 39 , 44 , 49 ].…”

Dynamic Behavior of Droplet Impact on Laminar Superheated Particles

“…The impact of liquid droplets on particles is commonly encountered in both natural and industrial applications, such as the immersion, splashing, and erosion of water droplets when impacting the soil during natural rainfall, − the preparation of liquid marbles, , and the wet deposition of polluted particles from industrial emissions. , When considering the contact collision between droplets and superheated particles, the interaction and dynamic behavior play very important roles in changes in boiling regime and heat transfer efficiency between solid and liquid. Despite the high thermal resistance of the contact of particles compared to the planar structure, , the droplet will still enter the film boiling regime when the temperature of the particles is much higher than the saturation temperature of the droplet .…”

Influence of rheology and micropatterns on spreading, retraction and fingering of an impacting drop

“…[3][4][5][6] Drop impact is also involved in applications related to atomization of liquids, ice accretion on airplanes, solder-drop dispensing to produce microelectronics and blood pattern analysis. 7,8 Other aspects of drop impacts are important in agriculture, such as during irrigation 9 or when pesticide is applied and may scatter because of drop bouncing and splashing. [10][11][12] Knowledge of drop impact dynamics is essential to effectively control drop deposition on different surfaces in applications, but aspects of our basic understanding are still lacking.…”