Rotorcraft Aeromechanical Analysis Using A Nonlinear Unsteady Aerodynamic Model

A unified, two-dimensional, time domain model has been developed for calculating unsteady nonlinear aerodynamic forces throughout the rotor fight envelope, including compressible and separated flows. The model is conceptually and computationally separated into three parts: (1) a linear, attached flow solution, (2) a nonlinear, separated flow solution and (3) a dynamic stall solution. It has been validated against test data for the HH02 airfoil undergoing unsteady forcing, including dynamic stall. The process dynamics of each model constituent are expressed as equivalent continuous time state space subsystems which augment the system state equations. The model is incorporated into a finite element rotor dynamics code and demonstrates the importance of nonlinear aerodynamic effects when the rotor is highly loaded or operating at high advance ratio.