Aerodynamic performance of ducted fans for large-scale electric propulsion aircraft under variable operating conditions

Research on both applying similarity criteria to ducted fans and the evolution of their aerodynamic performance under variable operating conditions remains limited, particularly for large-scale electric propulsion aircraft. This study numerically investigates the aerodynamic performance evolution of ducted fans in large-scale electric propulsion aircraft under variable operating conditions, with a focus on parametric dependencies involving true airspeed (TAS), rotational speed (RS), and tip clearance size. The results show that the total thrust exhibits a quadratic dependence on RS and a linear reduction with increasing TAS, demonstrating robust parametric correlations. As TAS increases, the leading edge gage pressure transitions from negative to positive, shifting the force on the duct from thrust to drag. Increasing the relative airflow velocity at the duct inlet through inlet shaping or boundary layer control may help sustain higher total thrust levels at elevated TAS. Increasing tip clearance from 0.5% to 1.5% chord length reduces total thrust by up to 10 N, while higher RS amplifies tip leakage losses through enhanced secondary flows that bypass the blade work regions. Additionally, a similarity criterion for ducted fans is derived and validated. A deeper understanding of the aerodynamic characteristics and similarity criteria for ducted fans under variable operating conditions, which is obtained from the present work, could facilitate accelerated design and engineering applications of electric propulsion systems utilizing ducted fans.