Masaru Usami

Rarefied gas flow through a circular orifice and short tubes

Rarefied gas flow through a circular orifice and short tubes has been investigated experimentally, and the conductance of the aperture has been calculated for Knudsen number between 2 x 10/sup -4/ and 50. The unsteady approach was adopted, in which the decay of pressure in an upstream chamber was measured as a function of time. For flow with high pressure ratio, empirical equations of the conductance are proposed as a function of Reynolds number, or Knudsen number, and length-todiameter ratio of the apertures.

Automatic Production of a Cell Network on a Flow Field with Large Variation of Density in the Monte Carlo Direct Simulation.

The double structure of cells is a very flexible, powerful tool to find the cell in which a particular molecule is located using the Monte Carlo Direct Simulation. The flow field is first divided into very small rectangular grid cells (small cells). Since the macrocell in which intermolecular collisions are counted and macroscopic properties are sampled is constructed of many grid cells, the simulated region of physical space can be divided freely into a network of macrocells. Although a table indicating the macrocell to which each grid cell belongs is essential in the double-cell structure, it is troublesome work to obtain a reasonable table, especially for complicated flow fields. A computer program for assembling grid cells and constructing a network of macrocells is generated by both a common computational method and a method utilizing a neural net. Cell networks calculated with these methods are shown and discussed.