Investigation on improving efficiency of high-altitude propeller with tandem configuration

For airships and unmanned aerial vehicles at an altitude above 20km, it’s very difficult to improve the efficiency of propellers due to the physics of low Reynolds number flow. Based on conventional configuration of propellers, this paper further explores a new propeller configuration, tandem configuration, to achieve higher aerodynamic efficiency. Reynolds averaged Navier-Stokes (RANS) flow solver is used to simulate the flow around the propeller. Some key parameters for tandem configuration, including the distance between the front and back propellers, scale factors and stagger angle et al., are investigated to obtain the effect on the performance of propeller. Furthermore, the flow feature of the tandem propeller, including the front and the rear blades, is studied through the slip velocity and vorticity. The results show that compared to the conventional configuration, the propeller with tandem configuration can increase the efficiency by 2 percent or more; larger distance between the front and back propellers is in favor of higher efficiency of the propeller with tandem configuration; the front propeller always has higher efficiency than the rear one. As for the scale factor, there is an optimum value existing to enable the maximum efficiency; the stagger angle between the front and back propellers has little influence on the efficiency.