Large-eddy simulations are performed to investigate the dynamic response of a natural laminar flow airfoil undergoing harmonic small-amplitude pitch oscillations at a chord based Reynolds number of $R{e}_c=750,000$. Large changes in the transition location as well as trailing-edge separation are observed throughout the pitch cycles, which leads to a nonlinear response of the aerodynamic forces. Despite the highly nonlinear nature of the flow, the evolution of the boundary layer over the airfoil can be modeled by using a simple phase-lag concept, which suggests a quasi-steady evolution of the boundary layer. A simple empirical model is developed based on this phase-lag assumption, which fits very well with the measured experimental data and identifies the primary source of non-linearities in the unsteady aerodynamic forces.

进行大涡模拟以研究自然层流翼型在基于弦的雷诺数的基础上经历谐波小振幅俯仰振荡的动力响应。 $\mathrm{[R}{Ë}_C=750，000$。在整个俯仰周期中观察到过渡位置的大变化以及后缘分离，这导致了空气动力的非线性响应。尽管流动具有高度非线性的性质，但可以通过使用简单的相位滞后概念对翼型上边界层的演化进行建模，这表明边界层的准稳态演化。基于该相位滞后假设，开发了一个简单的经验模型，该模型非常适合所测得的实验数据，并确定了非恒定气动动力中非线性的主要来源。