This study focused on the in-hover aerodynamics of a small rotor with a thin circular-arc airfoil and a convex structure at a low Reynolds number. The method combined computational fluid dynamics (CFD) with the blade element momentum theory (BEMT). The former was used for studying the two-dimensional parametric aerodynamics of the airfoil at a low Reynolds number and the latter was used for the prediction of the rotor’s hover performance. A novel thin circular-arc airfoil with a convex structure with a high aerodynamic performance, high structural strength, light weight and easy manufacturing process is presented in this paper. A convex curve on the upper surface was adopted to increase the thickness of the airfoil at partial chord, and a stiffener in the airfoil was installed to improve the structural strength of rotor span-wise. The aerodynamic performance of the airfoil was numerically simulated by the two-dimensional steady and incompressible Navier–Stokes equations. The in-hover performance of the rotor for small-scale vehicles was predicted by an improved version of the blade element momentum theory (BEMT). Finally, a carbon-fiber rotor with the presented airfoil was manufactured that had a diameter of 40 cm and a pitch of 6.2 inches. The analysis results were verified by experiments. It was shown that the maximum calculation errors were below 6%. The improved BEMT can be used in the analysis of in-hover micro-rotor aerodynamics at low Reynolds numbers.

In this paper, the aerodynamic performance of an orthogonal octorotor UAV considering horizontal wind disturbances is investigated with numerical simulations and experiments. To obtian the effect of horizontal wind on the flight efficiency of the orthogonal octorotor UAV, the power consumption and thrust with different wind speeds (0–4 m/s) and rotational speeds (1500–2300 RPM) are measured in a low-speed wind tunnel. Also, the velocity distribution of downwash flow, blade tip vortex distribution, streamline distribution and rotor blade tip pressure distribution of the orthogonal octorotor UAV were simulated by the computational fluid dynamics (CFD). The test results show that the thrust is increased at lower wind speed compared with 0 m/s. Specifically, it increased by 8.1% at 2 m/s and 8.8% at 4 m/s, respectively. It is interesting to note that the increased power consumption caused by the interference of horizontal wind at a higher rotor speed leads to a decrease in power loading (PL). Additionally, the thrust increased with a higher PL at low speed, where the PL achieved the maximum for the wind of 2.5 m/s and obtained a better aerodynamic performance. Compared with traditional octorotor UAVs and eight equivalent isolated rotors, the orthogonal octorotor UAV has also been proven to obtain good wind resistance. Simulation results show that the increase in wind speed and rotor speed will make the flow field more complex and the airflow interference between rotors more intense, which leads to changes in rotor thrust and power consumption.