Evaluation of Nano-Scale Rotors and Motors at Static Condition

The static performance of nano-scale rotor and the mechanical efficiency of micro rotors are important factors to evaluate rotary-wing NAVs. In this paper, two pairs of nano-scale rotors, which were formed with the same airfoil section for each pair, were compared to find the influence of chord distribution and twist distribution to rotor performance. A test bench was designed with highly sensitive mechanism systems in order to be able to measure the thrust and torque of nano-rotors accurately. The static performance of nano-scale rotors was evaluated experimentally with the test bench at ultra-low Re. And computations based on 3D unsteady incompressible Navier-Stokes solver with artificial compressibility were carried out as well to obtain the detailed flow field of nano rotor. It was found that the rotor figure of merit degraded a lot with size reduction. And the rotor solidity determined by chord distribution has a positive effect on the rotor thrust coefficient while pitch angle distribution influences the power coefficient. Flow field analysis indicated that the state of leading edge vortex might be the inherent reason of the difference of performance between rotors. The mechanical efficiency of several small motors were also compared which showed that the performance of small rotors decline with the reduction of size.