Design Variable Effects and Flow Characteristics of High-Altitude Contra-Rotating Propellers for Long-Endurance UAVs

To enhance the propulsion efficiency of near-space high-altitude unmanned aerial vehicle under low-density conditions and to gain a deeper understanding of the aerodynamic characteristics of contra-rotating propellers under complex interference, this study focuses on a high-altitude contra-rotating propeller propulsion system. A systematic investigation is conducted on the influence of design variables and flow characteristics. Considering the distinctive features of high-altitude environments, including low Reynolds numbers, high induced velocity ratios, and strong mutual interference between front and rear rotors, a numerical simulation method for contra-rotating propellers is established. The aerodynamic performance and typical flow structures are analyzed and compared with conventional propeller configurations to elucidate the aerodynamic advantages of contra-rotating propellers. Furthermore, key design variables such as axial distance, pitch angles of the front and rear propellers, and rotational speed matching are systematically examined to assess their effects on aerodynamic characteristics. Comparative analysis of axial velocity distributions reveals the interaction mechanisms between front and rear rotors under different parameter combinations and identifies the dominant factors influencing aerodynamic performance. The results indicate that rational matching of geometric parameters between front and rear rotors can effectively mitigate adverse interference, optimize wake structures, and improve the overall aerodynamic performance of contra-rotating propellers at high altitudes. These findings provide theoretical guidance and engineering references for the aerodynamic design and parameter selection of high-altitude contra-rotating propeller systems.