Shedding vortex characteristics analysis of NACA 0012 airfoil at low Reynolds numbers

In this paper, the vortex shedding characteristics been numerically simulated for Re = 1 × 104 by computational fluid dynamics (CFD), which caused by flow separation of NACA0012 airfoil. What is more, the variation of vortex shedding structure and the corresponding frequency characteristics of vortex shedding at different angles of attack are studied. The results reveal that with the increase of the angle of attack, the flow state around the airfoil will change from steady state to unsteady state, the vortex structure of the suction surface will become more and more complex with the increase of the angle of attack. In the periodic wake vortex shedding flow field, according analysis of the vortex structure and vortex shedding frequency, the vortex shedding will show 2S (Single) mode (8°∼15°) - chaotic state (16°∼18°) - 2S (Single) model (19°)- quasi periodic flow (20°∼24°) with the increase of angle of attack for α>7°. The rising section and falling section of airfoil lift and drag coefficient curves correspond to the vortex shedding and formation respectively. The frequency spectrum corresponding to the lift coefficient can be used to analyze the characteristics of vortex shedding from the perspective of frequency domain. With the increase of the angle of attack, the stability of flow field decreases, and the Strouhal number of vortex shedding frequency decreases basically. The order of the Strouhal number in different flow field states is 2S mode > quasi periodic flow > chaotic state. Among them, most of the Strouhal number corresponding to 2S mode fluctuate around 0.2, and the Strouhal number corresponding to chaotic state and quasi periodic flow fluctuate around 0.02 and 0.07 respectively