High-fidelity numerical simulation of the flow field around a NACA-0012 aerofoil from the laminar separation bubble to a full stall |
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Authors: | Eltayeb ElJack |
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Affiliation: | 1. Aeronautical Engineering Department, King Abdulaziz University, Jeddah, Saudi Arabia;2. Mechanical Engineering Department, University of Khartoum, Khartoum, Sudaneljack@kau.edu.sa |
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Abstract: | In the present work, large eddy simulations of the flow field around a NACA-0012 aerofoil near stall conditions are performed at a Reynolds number of 5 × 104, Mach number of 0.4, and at various angles of attack. The results show the following: at relatively low angles of attack, the bubble is present and intact; at moderate angles of attack, the laminar separation bubble bursts and generates a global low-frequency flow oscillation; and at relatively high angles of attack, the laminar separation bubble becomes an open bubble that leads the aerofoil into a full stall. Time histories of the aerodynamic coefficients showed that the low-frequency oscillation phenomenon and its associated physics are indeed captured in the simulations. The aerodynamic coefficients compared to previous and recent experimental data with acceptable accuracy. Spectral analysis identified a dominant low-frequency mode featuring the periodic separation and reattachment of the flow field. At angles of attack α ≤ 9.3°, the low-frequency mode featured bubble shedding rather than bubble bursting and reformation. The underlying mechanism behind the quasi-periodic self-sustained low-frequency flow oscillation is discussed in detail. |
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Keywords: | Low-frequency flow oscillation short bubble long bubble bubble bursting flow separation laminar separation transition to turbulence leading-edge separation trailing-edge shedding turbulent reattachment |
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