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Tuesday, July 28, 2020 | History

3 edition of Saltation thresholds and entrainment of fine particles at Earth and Martian pressures found in the catalog.

Saltation thresholds and entrainment of fine particles at Earth and Martian pressures

Rodman Leach

# Saltation thresholds and entrainment of fine particles at Earth and Martian pressures

## by Rodman Leach

Subjects:
• Eolian processes.,
• Mars (Planet) -- Surface.

• Edition Notes

The Physical Object ID Numbers Statement Rodman Leach and Ronald Greeley, James Pollack. Series NASA technical memorandum -- 102103. Contributions Greeley, Ronald., Pollack, James B., Ames Research Center. Format Microform Pagination 1 v. Open Library OL14664427M

Phoreman, J () Wind tunnel studies of aeolian saltation threshold and dust storm triggering mechanisms with the use of high-speed video and specialized boundary-layer wind tunnels at atmospheric and Martian mean surface pressures. Masters Thesis, University of . m/sec, well below experimentally predicted particle saltation thresholds for Martian conditions[1]. These results are con-sistent with the observed stability of fine-particle deposits at the landing site all during mision operations: wind produced no perceived changes to fine particle deposits or artificially disturbed surface materials.

Traction- transportation process in moving water that drags,rolls, or slides heavy particles along in continuous contact with bed what is the difference between Traction and Saltation Saltation- transportation of running water or wind of particles running too large to be carried in suppension, the particles are bounced along on the surface or. particle orientation occurs during saltation of particles, some degree of orientation may also reflect orientation to flow conditions below the fluid threshold. The detection of preferred occurs almost instantaneously after entrainment of ~ µm grains by saltation into.

The transport of particles by wind can occur in several modes, which depend predominantly on particle size and wind speed (figure 1).As wind speed increases, sand particles of ~ µm diameter are the first to be moved by fluid drag (see section ).After lifting, these particles hop along the surface in a process known as saltation (Bagnold , Shao ), from the Latin . Sediment transport in which heavier sand particles move forward by skipping and bouncing along the surface. Suspended sediment materials carried in the wind consists primarily of silt or clay size particles and if highly concentration can result in dust storms.

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### Saltation thresholds and entrainment of fine particles at Earth and Martian pressures by Rodman Leach Download PDF EPUB FB2

Saltation Thresholds and Entrainment of Fine Particles at Earth and Martian Pressures Rodman Leach and Ronald Greeley, Dept. of Geology, Arizona State University, Tempe, Arizona James Pollack, Ames Research Center, Moffett Field, California November I_I/kSA National Aeronautics and Space Administration Ames Research Center.

Get this from a library. Saltation thresholds and entrainment of fine particles at Earth and Martian pressures. [Rodman Leach; Ronald Greeley; James B Pollack; Ames Research Center.]. Saltation thresholds and entrainment of fine particles at Earth and Martian pressures.

Ames to investigate saltation threshold, flux, deflation rates, and other aeolian phenomena on the planet. The threshold shear velocity required to move sand grains with a diameter of ∼ µm in diameter by saltation under martian atmospheric conditions is ∼ m s −1 compared to m s −1.

Saltation (flux of sand particles) is a function of threshold shear velocity and is affected by soil moisture, relative humidity, aggregate stability of soil, cover of biological soil crusts, density and cover of vegetation, vegetation height, and porosity of vegetation cover.

Plants redistribute rainfall by stem-flow, throughfall, and canopy. Saltation thresholds and entrainment of fine particles at Earth and Martian pressures. of gravity on saltation threshold and the interparticle force at 0-g, is also described and test data.

Threshold curves relating the minimum wind speeds needed to raise particles of different sizes on Mars were derived from extrapolations to Mars from values derived for Earth (Sagan and Pollack, ; Hess, ) and from laboratory simulations of the Martian environment (GreeleyGreeley ; Iversen and White, ).In these curves, wind speeds are given in terms of the.

This mechanistic approach using a set of force equilibrium equations to assess the potential entrainment of particles was first suggested in by Phillips and was later () applied by Toma and a research team from ARC and PETRONAS to explain the aging of wall-deposit layer occurring during waxy crude transportation as an effect of size.

The literature states that the experiments under these low-fluid-density conditions were considered to involve fluid (“static”) threshold only (Greeley et al.,p. 10), in which entrainment is only a function of fluid r, numerical modeling has shown that under low-fluid-density conditions, impact threshold, with the impact force of upwind grains contributing to entrainment.

Rodman N. Leach's 9 research works with citations and reads, including: Radar-aeolian roughness project. Recently, and in the Mars context, there has been further effort to perform wind tunnel experiments on threshold velocities (Greeley et al., ).

The present paper is an attempt to use experiments on the aqueous transport of fine grains on Earth to scale the problem of atmospheric transport of fine particles on Mars.

Wind tunnel testing with particles of different density and with atmospheric pressure down to the level of the Martian surface ( Pa), has led to improved formulations for threshold prediction, including better understanding of the effects of particle cohesion. Using buoyance as the similitude parameter for Martian atmospheric conditions is required because we cannot recreate Mars' gravity in the MARSWIT facility, but sand particles with a density reduced to the proportion between Earth and Mars gravity (where Mar's gravity is of Earth's gravity) can be used to simulate the force required to.

Typical saltation trajectory heights are of the order of centimeters, much less than for fine particles in suspension, which can reach heights of kilometers [White et al., ]. These larger. Results for Earth atmospheric pressure show a linear trend between threshold velocity and Φ for sand‐size particles (particle size > 60 μm and therefore Φ greater than ∼ m/s), and an increase in velocity for smaller particles, similar to the relation seen for simple boundary layer conditions.

The results from three experiments with. The wind tunnel was run with Mojave Mars Simulant and air at 3, 6, and 9mbar, to cover most of the pressure range at Martian surface levels.

Our first measurements imply that the insolation of the Martian surface can reduce the entrainment threshold velocity between 4% and 19% for the conditions sampled with our experiments. dust in a Mars simulant soil.

The experiments were carried out under Martian gravity in a parabolic ﬂight. The reduced gravity was provided by a centrifuge under external microgravity.

The onset of saltation was measured for a ﬂuid threshold shear velocity of ± m/s. This is considerably lower than found under Earth gravity. Venusian surface pressures measured by Venera 9 and 10 averaged about 90 bar (equivalent to ∼ m, or ∼10 m per 1 bar, in the terrestrial ocean) with measured wind speeds – m s −1 (Keldysh, ).Surface images from the Venera landers (9, 10, 13, 14) showed fine-grained material at some of the sites suggesting the presence of material potentially capable of being moved.

dence on the impact-entrainment processes has been obtained from few and simplified studies of the splash (e.g. Willetts & Rice, Mitha et al. ), from investigating the vertical intensity and distribution of the saltation cloud including the wind profile within the saltation layer (e.g.

Williams. In geology, saltation (from Latin saltus, "leap") is a specific type of particle transport by fluids such as wind or occurs when loose materials are removed from a bed and carried by the fluid, before being transported back to the surface.

Examples include pebble transport by rivers, sand drift over desert surfaces, soil blowing over fields, and snow drift over smooth surfaces such as. [10] Particles are lifted if this ratio is >1.

Table 1 gives values used in the model. Figure 1a shows that, except for sand‐grade particles on Mars, the lift force dominates the gravity force. Thus if the top layer of a soil bed were perfectly sealed, or if a pressure change were applied instantaneously without giving the soil time to equilibrate, particles would be removed due to the.

The onset of saltation was measured for a fluid threshold shear velocity of $\pm$ m/s. This is considerably lower than found under Earth gravity. In addition to a reduction in weight, this low threshold can be attributed to gravity dependent cohesive forces within the sand bed, which drop by 2/3 under Martian gravity.Wind-blown dust models use input data, including soil conditions and meteorology, to interpret the multi-step wind erosion process and predict the quantity of dust emission.

Therefore, the accuracy of the wind-blown dust models is dependent on the accuracy of each input condition and the robustness of the model schemes for each elemental step of wind erosion.