| The objective of this study is the numerical analysis of gas flow rarefaction phenomena with application to a number of aerospace-related problems. The understanding and accurate numerical prediction of rarefied flow regime is important both for aerospace systems that operate in this regime, and for the development of new generation of gasdriven nano- and micro-scale devices, for which the gas mean free path is comparable with the reference flow scale and rarefaction effects are essential. The main tool for the present analysis is the direct simulations Monte Carlo (DSMC) method.; The first topic is the study of rarefied flows in the CHAFF-IV facility. A test particle method was used to analyse the pumping efficiency of CHAFF-IV, and determine optimum geometrical configuration of the chamber. The second topic under consideration is the influence of the surface roughness on nozzle plume flow and plume impingement for different flow regimes from free molecular to near-continuum. Surface roughness effects in rocket nozzles are found to be significant only in very rarefied flows where Reynolds number is about unity.; The third topic is the effect of rarefaction on radiometric forces. This effect is shown to be an important factor affecting the radiometric forces. The maximum radiometric forces for all gases under consideration are observed at a Knudsen number of about 0.1. For a radiometer vane placed in a finite size chamber, the maximum force was found to be roughly proportional to the surface area of the vane. This is an indication that the collision-less area force, and not thermal transpiration edge force, dominates the radiometric phenomena in that regime. The role of molecular diameter, viscosity and chamber size on radiometric forces have been found to be significant.; The forth topic is the numerical study of the interaction between optical lattices created by two counter-propagating laser beams and initially stagnant gases, in the entire flow regime from free molecular to continuum. It has been shown that in a weekly collisional regime optical lattices can trap and accelerate neutral molecules from room temperature level to tens of kilometers over a single laser pulse. In the collisional regime, the optical lattice---gas interaction was found to result in strong energy and momentum deposition to the gas.; Two types of optical lattice-based micropropulsion devices have been proposed for low and high density regimes. For the high density microthruster, an optical lattice is used to deposit energy and momentum to the region near the nozzle throat with subsequent increase in propulsion efficiency. In the low density microthruster, a multiple orifice flow is considered, and thrust is produced by molecules accelerated to high velocities by a chirped lattice potential. |
