Impact of surface discontinuities on flowfield structure of a micronozzle array

Abstract

This work carries out two-dimensional numerical simulations of rarefied gas flow in convergent–divergent micronozzles. Such a device is considered part of a micronozzle array. Although previous studies have investigated micronozzles with continuous divergent surfaces, the present work evaluates the impact of the surface smoothness on the flowfield structure by including discontinuities on the divergent contour. Such a scenario was not previously investigated. As a secondary goal, detailed physical explanations are given for those flow features reported but not extensively discussed in previous micronozzle studies. A direct simulation Monte Carlo method is employed to describe these flows due to the moderate rarefaction degree typically observed in microdevices. The results pointed out the sensitivity of the macroscopic properties—velocity, pressure, and temperature—due to the geometric variations on the divergent surface. In addition, Knudsen number distributions are computed to map nonequilibrium flow regions. The results indicated that the proposed surface discontinuities do not play the main role in the investigated micronozzle flows. This finding was not previously reported for micronozzle flows and contradicts the expected behavior in macroflows, where shock waves and/or expansion waves arise in supersonic flows experiencing abrupt changes in the flow direction.