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High‐Speed Drag Measurements of Aluminum Particles in Free Molecular Flow
Author(s) -
DeLuca Michael,
Sternovsky Zoltan
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja026583
Subject(s) - drag , drag coefficient , parasitic drag , free molecular flow , radius , aerodynamic drag , spheres , physics , atmosphere (unit) , mechanics , flow (mathematics) , materials science , thermodynamics , computer security , astronomy , computer science
High‐speed drag in a free molecular flow is still poorly understood despite playing an important role in a variety of physical situations, including meteor ablation in the upper atmosphere, the orbits of satellites, and the dynamics of cosmic dust grains. To measure drag at high speeds, small aluminum spheres 0.1–2.1 μ m in radius were shot at 1–10 km/s into air, N 2 , Ar, and CO 2 using an electrostatic dust accelerator. The measured drag coefficient in air is Γ = 1.29 ± 0.13 , with similar values for the other gases. The measurement constrains the heating coefficient to Λ = 0.58 ± 0.37 in air assuming the gas molecules reflect diffusely from the particles' surfaces. The drag appears to be independent of the molecular structures of the four gases tested but has a slight dependence on molecular mass. The drag is also higher than frequently assumed, which has implications for the modeling of high‐speed objects in free molecular flows.