Discussion on “Review of CFD studies on axial-flow self-rectifying turbines for OWC wave energy conversion” by Cui, Y., Liu, Z., Zhang, X. and Xu, C.

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This discussion is based on the paper by Cui et al. (2019) (hereafter identified as “the original authors” or “the original paper”). The original authors present a review on the application of CFD in the analysis of self-rectifying turbines for OWC wave energy conversion devices. We feel that this review is incomplete, as it overlooks a number of papers published in recent years that gave a new explanation for a phenomenon largely studied in the last two decades and discussed in the original paper: the hysteresis in Wells turbine performance. In addition, the original authors, in their conclusions, envisage a larger use of CFD in the coming years, especially for the unsteady analysis of the chamber-turbine interaction, probably ignoring that several CFD studies focusing on this aspect have already been published. In fact, it is through three-dimensional time-dependent CFD studies of the unsteady interaction between chamber and turbine that the explanation of the cause of the hysteresis was found. The objective of this discussion is to clarify two important aspects: the chamber-turbine interaction and the turbine hysteresis, that in our opinion were not correctly analyzed in the original review paper by Cui et al.