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In order to eliminate the nonlinear aerodynamic behaviour of a symmetric airfoil within the low angles of attack at low Reynolds number, this paper establishes a low Reynolds number airfoil optimization design procedure based on Gaussian process regression model and NSGA-II multi-objective genetic algorithm coupled with RANS numerical method. Then this paper carries out the airfoil optimization design with the average cruise factor in the range of small angle of attack of multiple states as the objective function. The results show that the optimized airfoil exhibits pronounced geometric bump and effectively alters the position and type of the laminar separation bubble. The aerodynamic characteristics of the airfoil are significantly improved, and the nonlinear phenomenon of the lift coefficient within the small angle of attack range at Re=4×104 basically disappears. Further analysis reveals that the bump of the optimized airfoil enhances the convective influence of the wall, which enhances the resistance of the incoming flow to the upward pressure gradient, thus improving the airfoil aerodynamic characteristics. [ABSTRACT FROM AUTHOR]

The effect of surface local vibration excitation on the aerodynamic characteristics of SD8020 airfoil under small angles of attack is studied by numerical simulation at Re=4×104. The influence of vibration frequency and amplitude on the flow characteristics of airfoil is studied from time averaged and unsteady aspects. The results show that local vibration at 2° and 3° can effectively affect flow field, promote the transformation of the laminar separation bubble structure and improve the aerodynamic performance of the airfoil. It is found that the effects of vibration frequency on aerodynamic characteristics and flow field structure of airfoil are similar under different angles of attack. When f=32 Hz, the improvement of aerodynamic characteristic is the most effective. With the increase of the vibration amplitude, the separation bubble structure span becomes smaller and moves towards the leading edge. The further unsteady analysis shows that the evolution process of unsteady vortex presents the similar mode under the same control strategy. And pressure pulsation frequency at chordal position is consistent with the vibration excitation frequency. It can be found that the unsteady characteristics of the flow field are dominated by the vibration excitation under this research condition. [ABSTRACT FROM AUTHOR]

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