Performance of Isolated UAV Rotors at Low Reynolds Number 2020-01-0046

Vertical takeoff and landing vehicle platforms with many small rotors are gaining importance for small UAVs as well as distributed electric propulsion for larger vehicles. To predict vehicle performance, it must be possible to gauge interaction effects. These rotors operate in the less-known regime of low Reynolds number, with different blade geometry. As a first step, two identical commercial UAV rotors from a flight test program are studied in isolation, experimentally and computationally. Load measurements were performed in Georgia Tech’s 2.13 m × 2.74 m wind tunnel. Simulations were done using the RotCFD solver which uses a Navier-Stokes wake computation along with rotor-disc loads calculation using low-Reynolds number blade section data. It is found that in hover, small rotors available in the market vary noticeably in performance at low rotor speeds, the data converging at higher RPM and Reynolds number. This is indicative of the high sensitivity of low-Re rotor flows to minor geometrical differences/imperfections in the rotors. It requires proper handling in computations. CFD results show a higher deviation from the experimental thrust data at low rotor speeds. While thrust prediction comes close to the experiments at high rotor speed, matching torque prediction values within reasonable bounds is still a challenge.