Discussion on “Entropy generation analysis of S825, S822, and SD7062 offshore wind turbine airfoil geometries” by Mamouri, A. R., Khoshnevis, A. B. and Lakzian, E

This discussion is based on the paper by Mamouri et al. (2019) (hereafter identified as “the original authors” or “the original paper”). The original authors employed computational fluid dynamics to calculate the flow field around several wind turbine airfoils, and combined this with an evaluation of the entropy generation to estimate the second law efficiency. It came to our attention that the equations used to estimate the entropy generation, and in particular the term that is used to estimate the entropy generated by turbulent fluctuations, are incorrect. In addition, the original authors claim that one of the main contributions of their work is the identification of a relation between entropy generation and drag, probably ignoring that the same relation has been known and used by several authors in the past, and examples can be found from at least 60 years ago.