Masters Theses

Date of Award

8-2018

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Devon M. Burr

Committee Members

Joshua P. Emery, Christopher M. Fedo, Jasper Kok

Abstract

The aeolian saltation threshold is the minimum wind speed required to entrain sediment into saltation. An expression for saltation threshold is needed for Earth and other planetary bodies with aeolian activity. The saltation threshold has been inferred to be a function of the density ratio, the ratio of the density of the sediment being entrained to the density of the entraining fluid (ρp/ρ). Previous work, including experiments in the Venus Wind Tunnel (VWT), resulted in a curve for the dimensionless threshold parameter, A, as a function of the density ratio [Iversen et al. 1987]. However, that curve does not fit threshold data from the Titan Wind Tunnel (TWT) [Burr et al., 2015]. In this work, I investigate the derived curve of the density ratio term [Iversen et al., 1987] by running new threshold experiments in the TWT under a range of density ratios conditions. I convert these new threshold wind speeds to A values and compare these new values to the density ratio curve of Iversen et al. [1987]. These new results with uncertainty estimates do not overlie the previous density ratio curve. Consequently, I derive new density ratio curves to fit the expanded data set using the same format as the previous expression but with new values for the two exponential parameters. The different curves are based on varying roughness heights, representing different ways that the boundary layer profile data could be fit and different definitions of threshold. These new curves have exponent parameters that increase the value of A in the transitional portion of the curve previously defined by the VWT data. Multiple factors might explain why the TWT data do not lie on the density ratio curve derived from VWT data. This mismatch could be due to 1) grain size effects, 2) lack of sediment transport during boundary layer profile collection, 3) boundary layer depth in the small TWT test section, 4) different similitude parameters, 5) grain shape, and 6) grain sorting. This work raises important questions about the aerodynamics and sediment entrainment processes that occur at intermediate density ratios and impels future work.

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