Formation of sand ripples under a turbulent liquid flow

Franklin, Erick de Moraes

doi:10.1016/j.apm.2015.03.021

Cited by 4 publications

(2 citation statements)

References 35 publications

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“…Based on the mechanism of the formation of periodic structures by other scholars, ,− we believe that the formation of the periodic HS-s/sS is related to two main factors: one surface shock wave and one interference between SPP and the incident laser. For surface shock wave, it is a type of discontinuous peak propagation in the medium, which will make the physical properties of the medium such as pressure, temperature, and density change by leaps …”

Section: Resultsmentioning

confidence: 88%

“…Figure a shows the sand ripples that often appear in the desert. The physical mechanism for the formation of sand ripples can be attributed to the action of wind on loose sand. − When the strength of wind is large enough, individual sand grains are lifted by the direct action of the shear stress exerted by the wind on the sand surface. The wind-accelerated sand grains will hit other particles, creating a cascade effect similar to avalanche ionization.…”

Section: Resultsmentioning

confidence: 99%

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Periodic Heterogeneous Surface with Superhydrophilic/Superhydrophobic Stripes Processed by a Picosecond Laser

Liang

Zhou

et al. 2022

Langmuir

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Heterogeneous surface with superhydrophilic/ superhydrophobic stripes (HS-s/sS) has great practical significance, which can be used in fuel cell water management, condensation heat transfer enhancement, underwater drag reduction. Herein, a fast and simple method for uniform HS-s/ sS on several mesh materials, including copper, stainless steel, and nickel, is achieved by using picosecond (ps) laser line-by-line scanning. Note that the scanning period between the lines is kept constant during processing, the HS-s/sS is formed by selforganized, while the similar structure cannot be processed on solid metal surfaces using the same parameters. The processing parameters, including scanning speed, defocus amount (DA), scanning period, and single pulse energy are systematically investigated to optimize HS-s/sS fabrication. It is found that the period of processed stripe on the mesh material is ∼1 mm, which is much larger than the scanning period. Interestingly, the as-prepared mesh surface show superhydrophobicity in the convex striped surface and superhydrophilicity in concave striped parts. The scanning electron microscopy results show that the structures on convex stripe are mainly composed of disordered hill-like structures, while the structures on the concave stripe mainly consist of periodic nanostripe structures. Moreover, the proportion of oxygen on the convex stripe is obviously higher than that on the concave stripe. The underlying mechanism of the HS-s/sS formation can be attributed to the interference between surface phonon polaritons (SPP) and the incident picosecond laser, as well as surface shock wave caused by the picosecond laser. We believe that such functional surfaces will be promising candidates for controlling liquid motion and fluid diversion processes.

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Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Periodic Heterogeneous Surface with Superhydrophilic/Superhydrophobic Stripes Processed by a Picosecond Laser

Liang

Zhou

et al. 2022

Langmuir

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Turbulent channel flow perturbed by triangular ripples

Cúñez

Rodrigues

Franklin

2018

J Braz. Soc. Mech. Sci. Eng.

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This paper presents an experimental investigation of the perturbation of a turbulent closed-conduit flow by two-dimensional triangular ripples. Two ripple configurations were employed: one single asymmetric triangular ripple, and two consecutive asymmetric triangular ripples, all of them with the same geometry. Different water flows were imposed over either one or two ripples fixed to the bottom wall of a closed conduit, and the flow field was measured by PIV (particle image velocimetry). Reynolds numbers based on the channel height were moderate, varying between 27500 and 34700. The regime was hydraulically smooth, and the blockage ratio was significant. Experimental data for this specific case remain scarce, and the physics involved has yet to be fully elucidated. Using the instantaneous flow fields, the mean velocities and fluctuations were computed, and the shear stresses over the ripples were determined. The velocities and stresses obtained in this way for the single ripple and for the pair of ripples are compared, and the surface shear stress is discussed in terms of bed stability. Our results show that for the single and upstream ripples the shear stress increases at the leading edge and decreases toward the crest, while for the downstream ripple it decreases monotonically between the reattachment point and the crest. The stress distribution over the downstream ripple, which is different This is a pre-print of an article published in Journal of the Brazilian Society of Mechanical Sciences and Engineering, 40:138, 2018. The final authenticated version is available online at: http://dx.

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A Comprehensive Picture for Binary Interactions of Subaqueous Barchans

Franklin

2020

Geophysical Research Letters

100

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We investigate experimentally the short-range interactions occurring between two subaqueous barchans. The experiments were conducted in a water channel of transparent material where controlled grains were poured inside, and a camera placed on the top acquired images of the bedforms. We varied the grain types (diameter, density, and roundness), pile masses, transverse distances, water flow rates, and initial conditions. As a result, five different patterns were identified for both aligned and off-centered configurations, and we propose interaction maps that depend basically on the ratio between the number of grains of each dune, Shields number, and alignment of barchans. In addition, we show experimental indications that an ejected barchan has roughly the same mass of the impacting one in some cases and that in wake-dominated processes the asymmetry of the downstream dune is large. The present results shed light on the size regulation of barchans found on Earth and other planets. Plain Language Summary Barchans are crescent-shaped dunes that are often organized in dune fields, where binary interactions and collisions play a significant role in regulating their dynamics and sizes. Barchan collisions are frequent in many environments, such as Earth's deserts and on the surface of Mars, but their large time scales (the decade and the millennium for aeolian and Martian collisions, respectively) compared to the aquatic case (of the order of the minute) make subaqueous barchans the ideal object of study. Taking advantage of that, we performed experiments in a water channel of transparent material, where pairs of barchans were transported by the water flow while a camera acquired images of them. We found five different types of barchan-barchan interaction and propose maps that provide a comprehensive classification for the short-range interactions of subaqueous barchans. In addition, we show that, in some cases, an ejected barchan has roughly the same mass of the impacting one and that the perturbation of the flow caused by the upstream barchan generates large asymmetries in the downstream one. Our results represent a significant step toward understanding the barcanoid forms and size regulation of barchans found in water, air, and other planetary environments.

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Formation of sand ripples under a turbulent liquid flow

Cited by 4 publications

References 35 publications

Periodic Heterogeneous Surface with Superhydrophilic/Superhydrophobic Stripes Processed by a Picosecond Laser

Periodic Heterogeneous Surface with Superhydrophilic/Superhydrophobic Stripes Processed by a Picosecond Laser

Turbulent channel flow perturbed by triangular ripples

A Comprehensive Picture for Binary Interactions of Subaqueous Barchans

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