Direct simulation of reentry flows with ionization
The Direct Simulation Monte Carlo (DSMC) method is applied in this paper to the study of rarefied, hypersonic, reentry flows. The assumptions and simplifications involved with the treatment of ionization, free electrons and the electric field are investigated. A new method is presented for the calculation of the electric field and handling of charged particles with DSMC. In addition, a two-step model for electron impact ionization is implemented. The flow field representing a 10 km/sec shock at an altitude of 65 km is calculated. The effects of the new modeling techniques on the calculation results are presented and discussed.
CONTACT POTENTIAL MEASUREMENTS WITH ADSORBED FILMS
Measurements have been made of the contact potential differences between a clean unheated tungsten filament, and the same filament coated with an adsorbed film of thorium, caesium, oxygen, or a mixture of caesium and oxygen. The method used is well adapted to prevent accidental contamination of the filament surfaces. The values found for the contact potentials between cold surfaces are The surface on the left is positive to that on the right. These values of contact potential do not agree with those calculated from the thermionic emission constants. An example is given of the application of the method to the measurement of the changes in work function produced by heating a tungsten filament to various temperatures in presence of caesium vapor, thus changing the amount of adsorbed caesium.
Calculation of and Errors in the Susceptibility
The measurement of the susceptibility requires three measurements, two of which have to be performed with a substance of known susceptibility. The difference of these last two measurements furnishes the proportionality constant of the apparatus, always employing the same volume, while the difference with the unknown substance gives the required susceptibility.