Rarefied Flows of the Monatomic Gas in an Axi-Symmetric Expansion Nozzle

Abstract

Rarefied transition flows in a nozzle with the form of an asymptotic cone are calculated for the throat Knudsen-number K_n less than 0.3 by using the direct simulation Monte Carlo method. The properties near the nozzle axis are as follows: (1) as K_n increases, conversion of the thermal energy into the kinetic energy becomes less efficient, and hence the overall temperature increases whereas the mean velocity decreases, (2) the number density is barely affected by K_n, (3) the rate of divergence of the parallel temperature T_x and the perpendicular temperature T_p increases with K_n; as the nozzle area-ratio increases, T_x gradually rises above the equilibrium temperature to approach the frozen limit, whereas T_p drops below the equilibrium temperature. These behaviors of T_x, T_p in the nozzle flow are similar to those in the spherical expansion flow because of the analogy of the flow field between the two.