Analysis of shock-plugs in quasi-one-dimensional compressible flow.

摘要

At small length scales, such as in micro-nozzles, the assumption that a shock wave is infinitesimally thin breaks-down due to the thickness of the shock being non-negligible compared to the dimensions of the nozzle. In this thesis, shock waves of finite thickness, or "shock-plugs," are modeled using the same methods and assumptions as a standard shock wave analysis. Due to the finite thickness of shock-plugs, however, two additional parameters are required in order to account for the differing inlet and exit areas, as well as the pressure on the side walls of the channel. A "typical" micro-nozzle with appropriate dimensions is considered to investigate the effects of these new parameters. It is found that the assumptions made in this model do not constrain shock thickness, and that a shock-plug of any thickness can exist inside of a nozzle for given values of inlet total properties and back pressure. Furthermore, analysis of the pressure on the side walls in the shock-plug model suggests that entropy generation within both shock-plugs and shock waves is best thought of as being due to unrestrained expansion as opposed to internal friction or temperature gradients, as it is more commonly held.