Showing papers by "James D. Iversen published in 1976"
TL;DR: In this article, the threshold speeds of particles with different densities were determined as a function of particle diameter and in terms of threshold parameter vs. particle friction Reynolds number in wind-tunnel experiments performed to determine the threshold friction speed of particles.
207 citations
01 Nov 1976
197 citations
TL;DR: In this paper, a correlation function, derived on the basis of self similar variable eddy viscosity decay, is introduced and utilized to correlate aircraft trailing vortex velocity data from ground and flight experiments.
Abstract: A correlation function, derived on the basis of self similar variable eddy viscosity decay, is introduced and utilized to correlate aircraft trailing vortex velocity data from ground and flight experiments. The correlation function collapses maximum tangential velocity data from scale model and flight tests to a single curve. The resulting curve clearly shows both the inviscid plateau and the downstream decay regions. A comparison between experimental data and numerical solution shows closer agreement with the variable eddy viscosity solution than the constant viscosity analytical solution.
114 citations
TL;DR: In this article, the effects of both Reynolds number and interparticle forces of cohesion were used to predict threshold speeds for windblown dust and sand on Mars and Venus, and an optimum particle size was found for which threshold speed is a minimum.
Abstract: Attempts to predict threshold speeds for windblown dust and sand on Mars and Venus have raised new questions about the mechanism of soil and sand transport by wind. Estimates of threshold speeds on Mars and Venus are made including the effects of both Reynolds number and interparticle forces of cohesion. The current estimates show lower threshold speeds for small particles than previous estimates by Hess, who assumed that Reynolds number is the only important parameter. These estimates, on the other hand, show somewhat higher threshold speeds than those of Sagan and Bagnold, who assumed that the particles are cohesionless. An optimum particle size results, for which threshold speed is a minimum, contrary to Sagan and Bagnold's prediction.
88 citations
TL;DR: In this paper, the threshold wind speeds for setting particles into motion on Mars were estimated by evaluating experimentally observed threshold friction velocities and determining the ratio of this velocity to the threshold speed at the top of earth's atmospheric boundary layer (ABL).
63 citations
TL;DR: In this article, both experimental investigation in an atmospheric wind tunnel and numerical solutions of the equations of motion of a single grain under Martian surface conditions were conducted to study the eolian mechanics of saltating grains.
Abstract: Mariner 9 spacecraft images showing evidence of variable surface features and surface erosion resulting from atmospheric wind on Mars have caused a renewed interest in the eolian mechanics of saltating grains. To study this phenomenon, both experimental investigation in an atmospheric wind tunnel and numerical solutions of the equations of motion of a single grain under Martian surface conditions were conducted. The numerical solutions for earth were used and empirically adjusted to correlate with existing experimental data for Mars. These modified equations were then solved to estimate grain motion for Mars. These calculations show the importance of a lifting force on the grain to initiate motion in both earth and Mars calculations. Major findings include a comparison of earth and Mars grain trajectories that show Mars length scales to be longer and to fall with a higher terminal grain velocity. The grains in the Mars calculation also made a smaller collision angle with the surface on rebound.
59 citations