Unsteady Nonlinear 2D Lift Model Based on Steady Coefficients

This study introduces an improved modeling framework for predicting unsteady aerodynamic loads on wing sections undergoing pitching motion. The objective is to enhance accuracy across both attached and separated flow regimes using steady wind-tunnel measurements as a foundation. Classical thin-airfoil theory and the Wagner indicial function are refined by replacing the theoretical 2π lift-curve slope with experimentally derived nonlinear static values, resulting in markedly better agreement with independently measured unsteady loads. An additional modification to the delay term in Wagner’s function is applied to account for boundary-layer separation, enabling a more accurate representation of lift buildup and decay during separation. The resulting formulation retains the simplicity of classical unsteady aerodynamic models while substantially improving predictive performance using Wagner’s indicial function. Comparative evaluation shows that the modified Wagner model provides a favorable balance of accuracy, robustness, and computational efficiency, offering a practical low-order tool for aeroelastic and flight-dynamics applications requiring reliable time-domain load predictions. The two-dimensional formulation also establishes a foundation for an efficient three-dimensional model currently in development.