Indicial Aerodynamic Model for Flutter Assessment in Axial Flight Considering Blade Airfoil, Rotor Inflow and Wake Periodicity

Abstract

The complete physics of the complex flow field around a rotor is obtained by the application of high-fidelity methods and hence, this is the preferred approach to find the optimal design for aerodynamic and acoustic performance. In comparison, the approach based on indicial aerodynamics ranks as low-fidelity, but offers an efficient and robust method allowing an easy model setup with fast access to basic aeroelastic phenomena at an early design stage. To include both methods in the rotor assessment, an aerodynamic multi-fidelity approach around the same dynamic rotor model is the objective. Hereby, used numerical methods for the low-fidelity approach comprise multibody dynamics together with an unsteady aerodynamic model based on Wagner's function and related enhancements for the general motion of an airfoil section considering heave and pitch motion as well as dynamic rotor inflow and wake periodicity. Since the aerodynamic model is state based, numerical solutions are available from time domain and linearization. The results from linearization allow the assessment of frequency placement and damping of the isolated rotor system.