A wind tunnel study of the effect of intermediate density ratio on saltation threshold

[Display omitted] •The Titan Wind Tunnel (TWT) is used to collect new freestream threshold data.•We convert the data to dimensionless values as a function of density ratio, A(ρp/ρ).•This unique dataset confirms the slope of A(ρp/ρ) in the transitional region.•It also gives higher values of A(ρp/ρ) i...

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Veröffentlicht in:Aeolian research 2020-08, Vol.45, p.100601, Article 100601
Hauptverfasser: Burr, Devon M., Sutton, Stephen L.F., Emery, Joshua P., Nield, Emily V., Kok, Jasper F., Smith, James K., Bridges, Nathan T.
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Sprache:eng
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Zusammenfassung:[Display omitted] •The Titan Wind Tunnel (TWT) is used to collect new freestream threshold data.•We convert the data to dimensionless values as a function of density ratio, A(ρp/ρ).•This unique dataset confirms the slope of A(ρp/ρ) in the transitional region.•It also gives higher values of A(ρp/ρ) in this region outside of error bars.•The scatter in these transitional density ratio data invites continued investigation. An expression for saltation threshold – the minimum wind speed required to initially saltate particles – is necessary for modeling aeolian processes on Earth and other bodies. Analysis of a compilation of experimental data led to the conclusion that this threshold is a function of the ratio of the density of the particle to that of the entraining fluid (ρp/ρ), and to a curve for the dimensionless threshold parameter, A(ρp/ρ). Whereas data of low-density ratio and of high-density ratio conditions show constant A values, the single dataset used to define the transitional region of the curve shows a range of values. To revisit this transitional region, we collect new freestream threshold data at 1–20 bars (1–20 × 105 Pa) with particles 150–1000 µm in diameter and having densities 400–3300 kg/m3 using the Titan Wind Tunnel. From these new data spanning a range of intermediate density ratios, we calculate friction wind speeds and values for A(ρp/ρ). We filter our threshold data for the same conditions (particle diameter > 200 µm, particle Reynolds number > 10) as in previous work and combine them with previously published data to derive a new density ratio curve with the same form as the previous expression. This new curve of A(ρp/ρ), with different parameter values and including uncertainties, confirms the slope in the transitional region between low- and high-density ratios, though giving slightly higher values for A. This work offers improved prediction of threshold wind speeds under thicker-than-terrestrial atmospheres on other solar or extrasolar planets, while also suggesting current challenges to accurate experimental simulation of aeolian transport under such conditions.
ISSN:1875-9637
2212-1684
DOI:10.1016/j.aeolia.2020.100601