A comparative study on aerodynamic performance and noise characteristics of two kinds of long-eared owl wing models

摘要

The camber line, chord length and thickness of the airfoil are important factors affecting the aerodynamic performance and noise characteristics of the blade. In this research, the long-eared owl wing as bionic prototype and two bionic blades were constructed by using bionic reconstruction method. The one named bionic blade A is based on the long-eared owl wing, which is reconstructed according to section theory and fitting formula of the measured long-eared owl wing. The other is the three-dimensional stretched cross-sectional bionic blade B. To compare the aerodynamic performance and noise characteristics of two bionic blades, the LES method coupled with FW-H equation was adopted to simulate the flow fields and the corresponding sound fields numerically at low Reynolds number condition. The results show that the lift coefficient for the bionic blade B is larger than that for the bionic blade A when the angle of attack is in the range of 0 degrees - 30 degrees. The pressure curve of bionic blade B indicates that the pressure generated from the suction side makes a greater contribution to lift force than the pressure side, especially at the leading edge. The location of the separation bubble moves from the trailing edge to the leading edge in the suction side of the blade at alpha = 15 degrees. The size of vortex shedding near the surface of the bionic blade A is smaller than the bionic blade B at alpha = 0 degrees and it's caused by the deeply concaved lower surface near the wing root probably. The range of the separation bubble acts as the main influence on the noise generation. Compared with the bionic blade B, the aerodynamic noise generated by the blade A is lower and the minimum value of sound pressure level is even 12.88 dB on the y-direction. That means the special construction of the natural long-eared owl wing could suppress the unsteady pressure fluctuation on the blade surface efficiently to decrease the aerodynamic noise.