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

Devon M. Burr, Stephen L.F. Sutton, Joshua P. Emery, Emily V. Nield, Jasper F. Kok, James K. Smith, Nathan T. Bridges

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


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.

Original languageEnglish (US)
Article number100601
JournalAeolian Research
StatePublished - Aug 2020


  • Density ratio
  • Laboratory wind tunnel experiments
  • Planetary processes
  • Saltation threshold

ASJC Scopus subject areas

  • Geology
  • Earth-Surface Processes


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