The millimeter size turbomachine is a new concept that may find applications in the field of micro propulsion (UAVs) or small sized batteries (portable computers). The manufacturing methods used in the semi-conductor industry today provide low cost production for technologies of the MEMS (Micro Electro Mechanical System) type. Onera is carrying out a feasibility study for a thermal micro-machine. In collaboration with other departments (DEFA), the Turbomachinery team is performing an aerodynamic simulation of a centripetal micro-turbine.
This turbine, based on MEMS technology, was designed and studied using a 3D Navier-Stokes computing code (elsA code). Due to the dimensions in question (about 20 mm), the machine operates at low Reynolds numbers (between 5,000 and 50,000). This type of configuration causes a large amount of friction on the walls and higher heat transfers than in a conventional turbine. Furthermore, the technology used restricts the geometry to 2D (fig. 1). In order to optimize the performances, a better understanding of the low Reynolds number effects is needed. In particular, a study was made to analyze the aerothermodynamic effects according to the different rotor/stator configurations (fig. 2) and showed that the turbine is capable of reaching a power of 100W, which corresponded to the objective set.
Figure 1 : view of the turbine geometry and streamlines
Figure 2 : absolute velocity (left) and entropy (right) fields
at test section mid-height at the rotor leading edge
