Use of the Pitot Tube in Very Low Density Flows
Final rept. Feb 1964-Jan 1981
CALSPAN FIELD SERVICES INC ARNOLD AFS TN AEDC DIV
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The cryogenically pumped vacuum chamber has made it possible to generate gas dynamic flows of much lower density than conventional wind tunnels. In the process of calibrating these flows since 1964, pitot tube data have been obtained in a regime that corresponds to very high altitude flight, low Reynolds numbers 100cm, or high Knudsen numbers mean-free-path 40X pitot diameter . Under these conditions, pitot pressures may be four times the inviscid stagnation pressure. Therefore, a substantial correction must be applied to the measured pitot tube data to use it for gas stream calibrations. The available pitot data are correlated in concise form with Reynolds number evaluated behind a normal shock, Re2, and total temperature as a parameter. The physical variables are combined in a form of presentation that permits direct determination of stream properties in nozzle or free-jet expansions without the usual successive approximations. The data are presented in a form that permits selection of pitot tube size, transducer range, and applicability of the instrument in specific flow conditions. The use of the pitot tube to survey the rarefied flow of jet from a rocket motor in a space chamber is discussed. The low density nozzles used in Aerospace Chamber 10V are probably unique in the low density limit, and the pitot pressure data provide an insight into the gas dynamics of rarefied flows.
- Test Facilities, Equipment and Methods
- Fluid Mechanics