Computational fluid dynamics has been utilized to investigate the effect of transition on a pitching airfoil. Since the SST transition model has indicated high potential in predicting the transition in aerodynamic applications, it has been selected as the closure model to the URANS equations. The 2D NACA0012 airfoil hinged at the quarter chord point prescribe to sinusoidal pitching motion was used. The motivation of the study is the lack of information in determining the occurrence of the flow transition on the airfoil under unsteady conditions and the range of Reynolds number at which this phenomenon should be expected. In the first step, the results are validated against an experimental study at Reynolds number of 50000 at which transition happens. Then based on a novel observation, the effect of Reynolds number on the aerodynamic characteristics of a pitching airfoil undergoing transition has been studied. As the Reynods number rises toward the fully turbulent flow, the aerodynamic forces follow the input (sinusoidal angle of attack) more and become more sinusoidal, whereas the lower Reynolds number results in nonlinear behaviour of aerodynamic forces. It is shown that beyond Re ≈ 40 × 10~4 flow can be considered almost fully turbulent whereas bellow Re ≈ 20 × 10~4 transition effects are significant. Furthermore, the flow near the trailing edge of the airfoil was studied in detail to address any deviation from Kutta condition under transition conditions which can be a benchmark to enhance numerical methods such as UVLM to be able to predict the frequency response of a moving airfoil in the transition region.
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