Whirl Flutter Analysis of Counter-Rotating Propeller Rotors with complex geometrical flexible blades under arbitrary inflow direction

Aero-engines with Contra-rotating propeller rotors (CROR) aero-engine face significant whirl flutter risks, necessitating accurate instability analysis that considers flow velocity distributions and blade flexibility. To address this, a 3D blade element momentum (BEM) method incorporating arbitrary inflow direction and blade-row interactions was established to calculate propeller-plane flow velocities. Its accuracy and efficiency are validated by CFD comparisons and scaled CROR load tests. Next, a flexible blade model was developed using beam elements, validated via 3D finite-element simulation and modal testing, and subsequently used to construct a time-variant CROR structural model incorporating rotational effects. Building on propeller-plane flow velocities, transient aerodynamic loads that account for blade–rotor motion are obtained and integrated into the CROR structural model, forming a fully aeroelastic dynamic model. Stability and responses are then computed. The results show that aerodynamic loads weaken damping and trigger two instability modes: rotor whirl flutter and blade stall flutter. Key factors such as operation conditions, blade flexibility, and inflow direction significantly influence aerodynamic loads and the system’s effective stiffness and damping, thereby shifting stability boundaries and steady responses. The integrated aeroelastic framework offers a comprehensive engineering-oriented tool for predicting boundaries and responses and for guiding the design of support stiffness and blade flexibility in CROR systems.