Accurate laminar-turbulent prediction is very much important to understand the complete performance characteristics of any airfoil which operates at low and medium Reynolds number. In this article, a numerical study has been performed over two different thick airfoils operating at low Reynolds number using k-ω SST, k-kl-ω and Spalart-Allmaras (SA) RANS models. The unsteady two dimensional (2D) simulations are performed over NACA 0021 and NACA 65-021 at Re 120,000 for a range of angle of attacks. The performances of these models are assessed through aerodynamic lift, drag and pressure coefficients. To obtain better comparison, the simulated results are compared with the experimental measurements and XFOIL results as well. In this present study, it is found that the k-kl-ω transition model is capable of predicting correct lift, drag coefficient and separation bubble as reported in experiments. At high angles of attack, this model fails to predict performance variables accurately. The SA and SST models are fail to predict laminar separation bubble. However, At high angle of attack, SA model shows better predictions compared to k-kl-ω and k-ω SST models.

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