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APPLICATION OF STATISTICAL MOMENTS IN THE REDUCTION OF SUPERSONIC-MOLECULAR-BEAM DATA.
CALIFORNIA UNIV BERKELEY DIV OF AERONAUTICAL SCIENCES
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A statistical method of inverting T-O-F data from supersonic molecular beam systems is described. The effect of the modulator waveform on the T-O-A curve was studied to find a suitable approximation to this function along with the optimum conditions for securing data. The idealized shutter function was used and a data processing method was developed by applying the method of statistical moments to the governing integral equation. This permits the distribution of velocities in the molecular source to be determined when its form is known beforehand from the physics of the flow field. A nozzle-beam system with an extremely high pumping speed was used to secure T-O-F data from along the axis of a nitrogen free-jet expansion at points for which the measured beam intensities were 70 to 85 percent of the predicted values and the gas was only moderately rarefied. These data were reduced by applying to T-O-F analysis for the ellipsoidal distribution function predicted by the Willis-Hamel theory. The theory of Ashkenas and Sherman was used to estimate the viscous effects and arrive at a quasi-isentropic theory which fit the data quite well over most of the jet axis. Finally, the results of the study were compared to those of previous investigators to illustrate that the Berkeley system is capable of coming much closer to ideal operation than other existing facilities. Author
APPROVED FOR PUBLIC RELEASE