Numerical study of nonlinearity of unsteady aerodynamics for NLR7301 profile

Details of unsteady aerodynamics for a two dimensional NLR7301 airfoil with flap were numerically investigated by a Navier-Stokes code in the transonic regime. Unsteady aerodynamic coefficients such as lift and pitching moment show nonlinear aspects in a small amplitude range of forced excitation modes. The pressure distribution of the supersonic region on the upper surface is very sensitive to the incidence angle, which yields the nonlinearity of the unsteady aerodynamics in a small amplitude range of pitching motion. The behaviour of reattachment of the boundary layer behind the shock wave also affects the nonlinearity. Shock wave motions were also examined. Linearized lift and pitching moment coefficients for each amplitude were applied to the Eigenvalue analysis for the flutter boundary. Time domain flutter simulations were also carried out and the result showed that the amplitude of the limit cycle oscillation could be explained by the flutter boundary of the Eigenvalue analysis.