Dynamic stall is a phenomenon that frequently occurs inside the offshore wind turbine blades. The unsteadiness within the flow leads to an alternative increase in the angle of attack to a higher value than the static stall condition and as a consequence, a dynamic stall occurs. In this paper, the airfoil is simulated in the oscillating case with different oscillatory frequencies in order to observe the dynamic stall. Then entropy generation rate is considered as a criterion in the analysis of this mechanism and also a tool for accurate designing. The simulations have been done in a 2D unsteady state flow field. The hysteresis charts show that S822 and SD7062 airfoils, which have a delay in flow separation, have almost lower drag coefficient compared with S809 airfoil. In this study, using entropy generation rate contours, the relation between different phenomenon and irreversibility or losses have been determined. The drag coefficient, separation, dynamic stall, and effective work have been calculated with considering entropy generation criteria for the airfoils in the practical condition. By focusing on the entropy generation in a transient stall condition, could be a strong tool to design accurate and offshore wind turbines with lower losses in near future.