Comments are given in document attached

The authors have implemented an Actuator Cylinder Model for Vertical Axis Wind Turbines (VAWTs) in the CFD framework OpenFOAM.  An extensive validation has been performed on different test cases available in literature, for which numerical and experimental data are available. Both single- and multi-turbine configurations have been considered, highlighting the performance of the proposed tool in wind farm assessment.

The reviewer believes that the topic and the activity is very interesting and worthy of investigation, although not very innovative in the adopted methodology. The study is extensive and the authors have investigated a wide variety of machine design and farm configurations. Notwithstanding this, the presentation of the paper needs to be improved.  Important details about the approach used throughout the paper are missing. Some specific considerations:

• The abstract is too long and general, failing in highlighting the value of the authors’ work.
• The introduction fails in highlighting the novelty of the authors' work. It is unclear why the proposed method should be preferred to other approaches available in the literature. On top of that, the latter are presented in a confusing way. More references should be added.
• From the Reviewer point of view, it would be more effective to merge sections 2 and 3 into section 4, in order to have a more compact overview of the proposed AC model.
• In section 4, where the AC-RANS model is presented, many information is missing. In particular, the algorithms used for the sampling of the inflow velocity from the CFD field and for the insertion of the volume forces into the grid should be clarified.
• No information about the model numerical set-up (mesh, numerical methods, number of iterations, convergence criterion) are provided. Has a mesh sensitivity been performed?
• No information about the AC model formulation is available. How was the polar data used for the simulations obtained? Are any aerodynamic models such as dynamic stall or flow curvature included?
• In the Reviewer's view, it would be nice to split the results in two different section, one for the single-turbine cases and one for the multi-turbine ones.
• Line 52: How come the ALM cannot be used for multi-turbine simulations?
• Line 61: Is there a quantitative definition for low-solidity?
• Figures 3 and 4 should be splitted in 3 sub-figures to improve readibility
• Section 5.3: Was flow curvature considered somehow? In the Reviewer experience, neglecting such effect for relevant chord-to-radius ratios such as the one considered (c/R=0.2) might introduce a notable error in the results, especially if the static stall angle values were used for tuning as in this case.
• Figure 13: it would be nice to add an arrow with the wind direction
• Figure 14: the legend is not easy to locate, it is suggested to add a frame to it
• Line 272: typo, "dessert" is written instead of "desert"

Based on the aforementioned comments, the reviewer recommends the publication of this paper after the major revisions suggested has been performed.