For millimeter-scale microturbines, the principal challenge is to achieve a design scheme to meet the aerothermodynamics, geometry restriction, structural strength, and component functionality requirements while in consideration of the applicable materials, realizable manufacturing, and installation technology. This paper mainly presents numerical investigations on the aerothermodynamic design, geometrical design, and overall performance prediction of a millimeter-scale radial turbine with a rotor diameter of 10 mm. Four kinds of turbine rotor profiles were designed, and they were compared with one another in order to select the suitable profile for the microradial turbine. The leaving velocity loss in microgas turbines was found to be a large source of inefficiency. The approach of refining the geometric structure of rotor blades and the profile of diffuser were adopted to reduce the exit Mach number, thus improving the total-static efficiency. Different from general gas turbines, microgas turbines are operated in low Reynolds numbers (104–105), which has significant effect on flow separation, heat transfer, and laminar to turbulent flow transition. Based on the selected rotor profile, several microgas turbine configurations with different tip clearances of 0.1 mm, 0.2 mm, and 0.3 mm, two different isothermal wall conditions, and two laminar-turbulent transition models were investigated to understand the particular influences of low Reynolds numbers. These influences on the overall performance of the microgas turbine were analyzed in detail. The results indicate that these configurations should be included and emphasized during the design process of the millimeter-scale microradial turbines.
