Drag Force on Objects in the Nearly Free Molecular Flow Regime as a Function of Speed Ratio
Final rept. 15 Feb 1973-14 Feb 1974
MARYLAND UNIV COLLEGE PARK INST FOR MOLECULAR PHYSICS
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The drag coefficient of an object moving in a rarefied gas can be expanded in terms of the inverse Knudsen number. In the reported equation one term represents the drag coefficient in the free molecular flow limit. It is shown that a second coefficient is determined by a set of well defined collision integrals associated with sequences of successive collisions among two molecules and the object. These collision integrals are evaluated for a disc and a sphere assuming that the gas molecules are reflected diffusively by the object. The molecules are treated as hard spheres and the drag coefficient is studied as a function of the velocity of the object.
- Fluid Mechanics