Numerical Simulation of an Expanding Pulsed Flow in a Laval Nozzle for the Molecular Laser Isotope Separation

Abstract

The unsteady flow in Laval nozzle for the molecular laser isotope separation (MLIS) of uranium is numerically simulated by solving the Euler equation through Harten-Yee TVD method, in order to clarify the characteristics of the pulsed flow in the cases when the flow is impulsively started and stopped. The former corresponds to the case when the pulsed valve is instantly opened and the latter corresponds to the case when the pulsed valve is instantly closed. The calculated results show the propagation behavior of the primary shock, the secondary shock and the unsteady expansion wave. It is shown that the temperature in the nozzle is decreased at a relatively short time after the flow is impulsively started, whereas it takes long time to converge towards the quasi-steady flow. After the steady flow is impulsively stopped at nozzle inlet, the flow at each measuring point remains unchanged until the expansion wave reaches there. And then, the flow characteristics such as pressure and temperature are gradually changed.The ratio of the width of pulsed nozzle to that of continuous nozzle is calculated under typical MLIS conditions. This ratio is closely related to the time to converge towards the quasi-steady flow from the valve opening for a given repetition rate of pulsed flow. It has been shown that this time is largely determined by the flow oscillation upstream of the nozzle throat.