基于动网格法的翼型启动过程数值模拟

Numerical Simulation of the Airfoil Start-Up Procedure Baced on Dynamic Mesh Method

采用动网格法对NACA4421翼型以15°攻角启动过程进行了数值模拟。计算给出了启动过程中尾缘启动涡的生成、脱落与绕翼型环流充分发展的瞬态流场及气动力特性变化曲线,并对升力数据进行了拟合。计算结果表明,启动瞬间,上翼面最大负压和上下翼面最大压强差均出现在翼型后半段,随后逐渐向前缘移动,最终稳定在前缘点附近。下翼面最大正压点和上下翼面压差随弦向位置的最大变化率则始终维持在前缘点附近。加速过程中,整个翼型受到的升力近似于瞬时速度的二次幂指数的规律变化。加速段结束后,翼型转入匀速运动的瞬间出现升力小幅下降的现象,之后逐渐回升至稳定升力。

A start-up procedure of an NACA 4421 airfoil at an angle of attack of 15° was studied numerically using the dynamic mesh method. The generation and moving-down of the starting vortex and the development of the circulating flow around the airfoil in the instantaneous flow field were presented together with the development of the aerodynamic force. Also, the lift force data was fitted. The results of computations showed that at the initial start-up moment, both the maximum negative pressure on the lower surface and the maximum pressure difference between the lower surface and the upper surface appeared at the back section of the airfoil, and then gradually moved forward as the airfoil speeds up and reached the point nearby the leading point of the airfoil in the end. During the whole start-up procedure, the maximum positive pressure on the lower surface and the maximum pressure difference changing rate along the chord both maintained their position nearby the leading point of the airfoil, while the lift force on the airfoil changed approximately as a quadratic equation of the instantaneous velocity. At the moment of transformation from the speeding up stage to the uniform motion stage, the lift force declined suddenly in a small range, and then gradually increased to the normal level.