Hover performance and smoke flow field study of key configuration parameters for staggered rotor systems

The staggered rotor system is a potential power system layout for compact multi-rotor aircraft designed for urban air mobility. Deeply revealing the aerodynamic interaction mechanism between rotors under the influence of key configuration parameters is crucial for the refined aerodynamic design of such aircraft. Therefore, this study experimentally measured the effects of parameters such as rotor speed, rotation direction, axial spacing (H/R), and radial spacing (L/R) on hover performance. Furthermore, by integrating smoke flow visualization technology, the transient flow field structures under different rotation directions and radial spacings were captured, with a focus on exploring their correlation mechanisms with hover performance. The results indicate that, within the experimental parameter range, radial spacing is the dominant parameter affecting the degree of aerodynamic interaction between rotors. The influence of rotation direction and axial spacing is secondary and exhibits a coupling effect with radial spacing, while the influence of rotor speed is minimal. A high correlation exists between the transient flow field structure and hover performance. At small radial spacings, the high immersion of the lower rotor in the downwash of the upper rotor causes a thrust loss of ∼50% for co-rotating and 30% for counter-rotating configurations. As L/R increases, the flow field structure stabilizes, and thrust recovers. In addition, by comparing rotation directions, it was found that the wake contraction rate shows a proportional relationship with rotor thrust loss. This study can provide a reference basis for the aerodynamic layout design and optimization of compact multi-rotor aircraft.