Discussion on "Performance analysis of Wells turbine blades using the entropy generation minimization method" by Shehata, A. S., Saqr, K. M., Xiao, Q., Shahadeh, M. F. and Day, A.

This paper presents a critical appraisal of the paper “Performance analysis of Wells turbine blades using the entropy generation minimization method” by Shehata, A. S., Saqr, K. M., Xiao, Q., Shahadeh, M. F. and Day, A., published in Renewable Energy, volume 86, pp. 1123–1133. The discussion focuses in particular on five aspects of the work being critiqued: the set-up of the numerical experiment, the similarity of the problem studied with the large existing literature on oscillating airfoils, the estimation of entropy generation through the numerical solution of the Navier-Stokes equations, the equivalence between entropy and drag, and finally a comparison of the results presented with existing literature. From this appraisal, it is concluded that the problem studied is not representative of a Wells turbine and that the article contains a number of fundamental errors that lead to incorrect results. These mistakes would have been evident had the results been analyzed critically and compared to the existing literature on the subject. If the results had been presented in non-dimensional form, as best practice recommends, they would have been more readily comparable to those in existing literature and important discrepancies might not have been obscured.