Viscous effects on performance of two-dimensional supersonic linear micronozzles

A comprehensive numerical investigation of a steady viscous How through a two-dimensional supersonic linear micronozzle has been performed. The baseline model for the study is derived from the NASA Goddard Space Flight Center microelectromechanical systems-based hydrogen peroxide prototype microthruster. On the microscale, substantial viscous subsonic layers may form on the nozzle expander walls, which reduce thrust and efficiency. One approach to compensate for the presence of these layers has been to design micronozzles with expansion angles larger than traditional macroscale nozzles. Numerical simulations have been conducted for a range of Reynolds numbers (Re = 15-800) and for expander half-angles of 10-50 deg. Two different monopropellant fuels have been considered: decomposed 85% pure hydrogen peroxide and decomposed hydrazine. It is found that an inherent tradeoff exists between the viscous losses and the losses resulting from the nonaxial exit How at larger expansion angles. Our simulations indicate that the maximum nozzle efficiency occurs for both monopropellants at a nozzle expansion half-angle of approximately 30 deg, which is significantly larger than that of traditional conical nozzle designs.