Analysis of Flow Structure in Microturbine Operating at Low Reynolds Number

In this paper, three-dimensional flows in laminar subsonic cascades at relatively low Reynolds numbers (Re < 2500) are presented, based on numerical calculations. The stator and rotor blade designs are those for a MEMS-based Rankine microturbine power-plant-on-a-chip with 109micron chord blades. Blade passage calculations in 3D were done for different Reynolds numbers, tip clearances (from 0 to 20%) and incidences (0 degrees to 15 degrees) to determine the impact of aerodynamic conditions on the flow patterns. These conditions are applied to a blade passage for a stationary outer casing. The 3D blade passage without tip clearance indicates the presence of two large symmetric vortices due to the interaction between hub/casing boundary layers and the blade. Opening the tip clearance introduces the tip vortex, which tends to become dominant above a tip clearance of 10%. In addition to providing a description and understanding of the 3D flow in a MEMS microturbine, these results suggest the importance of considering 3D flows in the design of microturbomachinery, even though the geometry is dominantly 2D.