In this paper, the effect of compressibility on stall behavior of NACA0012 airfoil at a Reynolds number of 3.98x106 is studied using the OpenFOAM package. Large Eddy Simulation (LES) turbulence model is used to simulate flow at high angle of attack in near-stall or stall condition. Different grid sizes have been examined and the suitable mesh whose CL and CD are close to the experimental data had been presented. It is observed that at an angle of attack of 18◦ and Mach number of 0.2, the compressibility does not have a major effects and incompressible simulation gives more accurate results, whereas at a flow field with Mach number of 0.25 the compressible simulation is necessary. The influence of vortexes formation, movement and separation is investigated on the lift, drag and wall pressure coefficients. It is shown that these vortexes cause the pressure distribution to have a fluctuating behavior on the upper surface of the airfoil. This behavior causes the airfoil to be unstable and has serious implications in term of achievable performance at stall condition.

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