Cylinder Drag in the Transition from Continuum to Free-Molecule Flow

Abstract

The drag coefficients for cylinders normal to the flow have been determined experimentally at Mach ∼2, Mach ∼4, and Mach ∼6 with Knudsen numbers extending from continuum conditions to free-molecule-flow conditions. The results indicate a smooth transition from inviscid values at low Knudsen numbers to free-molecule-flow predictions for diffuse reflection at high Knudsen number. Small departure theories which are applicable to the ``near free molecule flow'' regime are compared to the experimental data.