The manuscript in question presents simulation results and analysis regarding the performance of standard k-omega-squared torque turbine torque controllers in non-flat terrain. Although by itself an interesting and relevant topic worthy of publication in WES, I believe the manuscript has some significant shortcomings that would need to be addressed before it can be published here. All comments can be found in the PDF attached, but my main concerns are reiterated below:

• The paper is generally poorly written. Some sentences are hard to understand or do not flow naturally. The structure of the paper does not always make sense and should be reconsidered. The introduction is missing big chunks of information that are relevant for the paper. I strongly suggest having a professional editor or at minimum a native English speaker with writing experience take a look at the manuscript before resubmitting. 
• The authors generously self-cite previous work, but fail to point out what specifically this manuscript adds with respect to previous publications. I have not read all the previous publications in full, but I've read enough to know that there is significant overlap between those papers and this manuscript. To address this, the authors should include a more descriptive paragraph on previous research in the introduction, followed by a summation of contributions unique to this work.
• A lot of the methodological choices and modeling simplifications are not or not well explained or justified. This includes but is not necessarily limited to: the choice of the terrain, the choice of the surface roughness, the choice of the turbine location, the choice of the controller used, the choice of the turbine model. Flow results from the RANS simulations, which are the heart of the manuscript, are almost completely omitted, making it very hard for readers to assess what is happening to the flow around the hill, with and without a turbine.
• From the introduction, I was made to understand that the main contribution of this manuscript was that it investigates how suboptimal control affects power performance of turbines in non-flat terrain. The authors cite different studies investigating complex terrain, and note that suboptimal control might influence the findings of these studies. However, in the manuscript, they fail to quantify the exact influence of a sub-optimally tuned controller on the total power production of a turbine on or near a hill. Furthermore, they fail to implement potentially simple improvements to the controller, to verify that the power production can actually be increased on non-flat terrain.

Despite these shortcomings, I believe this manuscript still has the potential to be published in WES. Apart from improving the presentation quality, this would also require a significant rewrite to emphasize the value of the manuscript with respect to previous work, as well as additional simulations to assess the true influence of sub-optimal or uncalibrated control on wind turbine power production in non-flat terrain. Ideally, the manuscript would also propose a solution to this challenge (perhaps as simple as a recalibration of the optimal TSR), including simulations showing the potential benefit of this solution. 

Review of ‘Wind turbine performance and control in complex terrain.’

This article addresses an important topic on optimal control of wind turbines in complex terrain. The authors perform RANS simulations with turbine control to investigate the effect of flow field acceleration on rotor aerodynamic performance. The subject is of interest to the wind energy community. However, there are several aspects that need to be addressed before the article can be published.

1. The results appear to be very terrain-specific. What general lessons can one draw from the study apart from the fact that turbine control is terrain dependent?
2. How are the turbine positions chosen? I understand that it is natural to place a turbine at the hilltop, but why at the foot of the hill? If the wind speed changes by 180°, the turbine placed at the foot of the hill will be in its wake. What happens then? I think the choice of turbine locations should be justified.
3. While discussing Figure 3(a), the authors mention that the turbine at the foot of the hill produces ‘slightly more’ power than that in flat terrain. However, visually, I cannot see any difference between the two curves. If indeed there is a very small improvement, is it higher than any uncertainty in the quantification of power from simulations?
4. The authors discuss in detail what leads to the sub-optimal performance of turbines on a hill. However, they do not demonstrate any control strategy that could lead to a better turbine performance in a non-uniform background flow.
5. There are many grammatical and typographical errors, especially in the abstract and introduction. In general, the writing quality can be improved.