I. Estermann

At sufficiently high altitudes, the earths atmosphere becomes so rarefied that its flow characteristics can no longer be described by the equations of continuum fluid mechanics. This is due to the fact that with decreasing density, the mean free path k of the molecules in the atmosphere increases until it becomes equal to or larger than a characteristic dimension d of the flow field. The ratio of these quantities, designated as the Knudsen number K = k/d, divides gas dynamics into various flow regimes, with K < 0.01 representing continuum flow, K > 10 free molecular flow, and intermediate values the regimes commonly called slip and transition flows. For the simulation of high altitude flight conditions which may be characterized by K > 0.01, new facilities and measuring techniques have been developed in the last decade. The first group includes wind tunnels designed for operation at static pressures between 0.001 and 0.1 mm Hg, the second rotating arms, discs or cylinders operating under various degrees of vacuum conditions, and apparatus for the investigation of energy and momentum exchange between individual molecules and solid surfaces. More recently, attempts have been made to simulate not only the density, but also the temperature and ionization conditions in the uper atmosphere, as well as the speeds relative to molecular velocities encountered by satellites and vehicles re-entering the atmosphere from outer space. The section on techniques of measurement will deal with various methods for flow visualization in rarefied gases, with instruments for the measurement of density, force, and pressure in rarefied gases, and with free molecule probes.

WGL-Tagung 1961, Freiburg im Breisgau

Conference Paper

englisch

A4, 9 Seiten

Jahrbuch der Wissenschaftlichen Gesellschaft für Luftfahrt, 1961, Jahrbuch der Wissenschaftlichen Gesellschaft für Luftfahrt; S.122-130; 1962; Braunschweig : Vieweg

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Bestellbar

1962