Study of the nonlinear lift coefficient of the symmetrical airfoil at low reynolds number near the 0o angle of attack
对称翼型低雷诺数小攻角升力系数非线性现象研究

The nonlinear effect of the lift coefficient of the symmetrical airfoil near the 0$^{\circ}$ angle of attack occurs at low Reynolds number. It may be disadvantageous for control. The 3rd order Roe scheme developed by Rogers was used to solve the unsteady incompressible Navier-Stokes equations, in the temporal direction the 2nd order two-step method was accepted, to numerically simulate the flowfield laminar separation vortex structure and the lift coefficient of the symmetrical airfoil SD8020 at low Reynolds number ($Re=40\,000$, 100\,000) at different angle of attack. The correctness of the simulation was proved by comparing the present CFD results with the experiment. Through the analysis and study to the time-averaged result of the numerical simulations, the new trailing-edge laminar separation bubble model for the airfoil near the 0$^{\circ}$ angle of attack was described in this paper, which is different from the classical laminar separation bubble model both in the inner structure and the development with the angle of attack. And this model was used to study and explain the mechanisms of nonlinear effect of the lift coefficient of the symmetrical airfoil at low Reynolds number at low angle of attack.