Investigation of Bioinspired Flow for a Nano Coaxial Rotor in Hover

A computational study of a nano coaxial rotor with bioinspired blade motion was conducted at an ultralow Reynolds number to determine the principle of improving rotor performance via an induced unsteady mechanism. A flow solver was established based on the preconditioned compressible Navier-Stokes equations, a lower-upper Symmetric-Gauss-Seidel with pseudo time sub-iteration (LUSGS-Its) dual-time marching method, and an overset grid technique. The effect of different pitching rotors on the nano coaxial rotor performance was investigated. A pitching upper rotor slightly impacted the nonpitching lower rotor, whereas it significantly affected the pitching lower rotor. Four blade pitching frequencies were applied successively to the upper rotor to investigate the effect of pitching frequency on rotor performance. The results indicated that the greatest improvement in figure of merit occurred at a blade pitching frequency of 4/revolution. The figure of merit values for the upper rotor and lower rotor were 7.2% and 6.7%, respectively. The generation and evolution of the leading-edge vortex and trailing-edge vortex led to reattachment of flow in cases in which the rotor performance was improved. (C) 2021 American Society of Civil Engineers.