EGU2020-2040
https://doi.org/10.5194/egusphere-egu2020-2040
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Conditions for the emergence and growth of aeolian sand structures

Elena Malinovskaya and Otto Chkhetiani
Elena Malinovskaya and Otto Chkhetiani
  • A.M. Obukhov Institute of Atmospheric Physics Russian Academy of Sciences, Laboratory of geophysical hydrodynamics, Moscow, Russian Federation (elen_am@inbox.ru)

One of the important characteristics of the wind process of dust removal is a critical or threshold wind velocity [1]. Saltating flow grows with increasing of the effective roughness [2] that affecting shear stress and friction velocity [3]. The drag coefficient increases depending on the density of the coating by particles of the surface [4]. The location of particles in the aeolian structure, their size and relative position determine their resistance to wind influence. Aeolian structures change the structure of flows and the balance of mass transfer of particles deposited and rising from the surface [5]. The surface microstructures and ripples significantly affect of sand removal.
The flow of particles with a size of 100 μm on the surface has been considered using the OPEN FOAM with LES model. The calculation area has sizes of 5x5x2 mm. For the velocity at the upper boundary, 2.8 m/s select in accordance with the experimental data [6]. It should be noted that with a relative increase in the distance between pairs of particles and a change in the level of the upper surface, the pressure difference between the base and top of the particle increases by 10-30 percents. Depending on the distance between the particles, the buoyant force acting from the side of the air flow, the critical velocity, and the departure velocity of the particle also change. When the distances between the surfaces of the particles are close to its size, the buoyant force is greater than the adhesion and gravity forces. As a result, areas with different probability for the sand removal by wind, due to which, in particular, the occurrence of aeolian ripples occurs.
The average critical velocity increases when moving up the windward slope of the dune [7, 8]. This phenomenon is possibly associated with the influence of ripples on the air flow. The flow around of the micro-ripples with a height of 0.1-1 mm was considered for air flow velocity of 2-4 m/s at a height of 1-2 cm. The addition of supplementary elements of heterogeneity at the apex near the rough surface of the streamlined aeolian structure leads to a displacement of the separation point of the ascending flows. Also we have a change in the length of the recirculation zone and the time intervals of the strengthening of the wind at the apex, which was observed in [6].
The study was supported by the RFBR project 19-05-50110 and partial support of the program of the Presidium of the Russian Academy of Sciences No. 12.
1. Shao Y. Physics and modeling of wind erosion. Springer.2008.p.452.
2. Martin R.L., Kok J.F. J.Geophys.Res.2018.123(7).1546-1565.
3. Turpin C et al. Earth Surf. Proc. and Land.2010.35(12). 1418-1429.
4. Yang X.I.A. et al. J. Fluid Mech.2019.880. 992-1019.
5. Luna M.C.M.M. et al. Geomorph.2011.129(3-4). 215-224.
6. Semenov O.E. Introduction to experimental meteorology and climatology of the sand storms. Almaty. 2011. p.580 (in Russian).
7. Neuman C.M.K et al. Sediment. 2000. 47(1). 211-226.
8. Malinovskaya E.A. Izv. Atmos. Oceanic Phys. 2019. 55(2). 86-92.

How to cite: Malinovskaya, E. and Chkhetiani, O.: Conditions for the emergence and growth of aeolian sand structures , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2040, https://doi.org/10.5194/egusphere-egu2020-2040, 2020

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Presentation version 1 – uploaded on 25 Apr 2020
  • CC1: Comment on EGU2020-2040, Nathalie Vriend, 04 May 2020

    Dear Elena,

     

    Thank you for your uploaded slides.

    It seems to be that your OPENFOAM simulation is done using particles on a rigid flat surface underneath (or are the particles shown actually rigidly attached to the bed?). What is the role of the bottom boundary condition? If you replace this with an undulating bed (at the wavelength of the particle diameter), or an erodible bed, would the results change drastically?

     

    Thank you,

    Nathalie

    • AC1: Reply to CC1, Elena Malinovskaya, 04 May 2020

      Hello, Natali!
      Thank for your interest!

      It was was a uniform object depicting particles on the surface, built by 3D modeling. The boundary condition u=0 is used on the surface of the lower surface. The significant computing power is required for distances between particles smaller than the diameter. The task was to determine the aerodynamics of nearby particles, depending on the distance between them. 
      The effects of superposition of the topographic influence on the flow will be lost, as in the case of the arrangement of particles on surface.
      Such (undulating)  bed is more relevant when taking into account larger effects such as microrippels. It is possible to use models with periodic cavities (pits) physically as simplring the case of particles. We partially use such a representation (in obtaining estimates).
      A wavy doubly periodic surface does not sufficiently determine the geometry of the particles.

      Thank you, Elena.