A Rotor Blade Unsteady Airload Model with Dynamic Stall

摘要

An unsteady airload model appropriate for rotorcraft analysis is still a challenge. Especially in the field of rotorcraft flight simulation, unsteady and dynamic stall has long been overlooked. This paper describes a nonlinear unsteady airloads model based on a combination of unsteady thin airfoil theory and the ONERA dynamic stall equations. In the linear range, a rigorous and unique theoretical approach based on unsteady airfoil theory is applied. While there is a lack of tools for extremely complicated rotor dynamic stall, a semi-empirical model is used in a manner consistent with linear unsteady airfoil modeling. A finite state formulation is applied to facilitate combining this model with finite state representations of inflow and a modal representation of blade elasticity. This approach is then used in FLIGHTLAB to predict airfoil oscillating loads, the isolated rotor loads, and the fully coupled rotor/fuselage stability and dynamic response in free flight. The results are correlated with airfoil measured data and compared with results from quasi-steady airloads to assess the effect of unsteady airload on flight simulation.