The manuscript presents a sensitivity analysis of different CFD model fidelities and parameters to simulate VIV of a wind turbine blade under forced motion. The results obtained with two CFD models (EllipSys3D, Ansys CFX) and 5 turbulence models are compared for both low and high inclination angles. VIV is a topic of increasing interest for wind turbine blades of increasing lengths and different modelling approaches exist in the literature. As such, the present work is of relevance to the field. The methodology is also scientifically sound. The main outcome of the paper is that URANS is not suitable for simulating VIV of blades with low inclination angles.

Although the work is interesting and relevant, the main weakness of the manuscript is that the scope of the work, and discussion of the results, is rather limited for a paper on its own. Also, the choices made in the work are not always justified.

I suggest addressing the following comments/suggestions in the revisions of the manuscript.

- The present approach of prescribing the VIV motion is justified based on previous work using a similar setup. However, in this work, it is also shown that some of the previous work was using insufficient spatial resolution to properly resolve the flow phenomena and associated effective power. Can these work still support the idea that forced motion is realistic enough?

- Line 141: no checks for orthogonality, why is that?

- The mesh sizes used is both codes are different. This is briefly described in Sec 1.4. However, it’s still not fully clear why the first cell size is larger with CFX whilst it is mentioned that its numerical schemes are of lower accuracy. Please explain in more details. In Sec 2.1.2, it is mentioned that a limit of 5 inner iterations is used for CFX. This is also smaller than with the other code. This is not justified nor explained.

- Line 234 mentions the numerical damping in loosely coupled FSI. Can the authors further quantify this, based on this work or previous work?

- The figure legends (e.g. Fig 7) mention case names such as P100I30. This only becomes clear later in the manuscript (i.e. at the start of Section 2.2.1). It would be beneficial to introduce this naming in the text or in a table at an earlier stage in the manuscript.

- In Sec 2.1.2, the setups are presented but the results shown in Fig 8 are not really discussed. The EllipSys3D results are also not monotonically converging with decreasing time step. This deserves further explanation.

Minor changes.

- Line 76: add reference at end of sentence.

- Line 90 of 18m/s --> up to 18m/s?

- Line 155: unfinished sentence

- Line 255: low5 (typo)

The article describes forced motion simulations of a clamped wind turbine blade for two different inflow conditions and with two different computational fluid dynamics codes. Several turbulence models, grid resolutions and time step sizes are investigated, with analysis of the aerodynamic power on the blade. The article is thus a sensitivity study using existing codes, but provides interesting guidelines for vortex-induced vibration simulations of wind turbine blades.

• Line 69-70: The forced motion (or forced response) method has also been used extensively for gas turbines, with references going back at least 20 years. It would be good to mention that this type of method only works well if the fluid does not modify the vibration frequency significantly compared to in-vacuum, so typically only for air and gasses.
• Line 117: The time discretization scheme for EllipSys3D seems to be missing.
• Line 127-139: The grid deformation technique is described in some detail, but the text is still vague and I would not be able to reproduce the results based on this text. Can references be added? The tuning of the parameters is not documented.
• Line 159: Why is the first cell height 10x larger for CFX than for EllipSys3D? The flow conditions are the same and similar turbulence models are applied.
• Line 207: How many periods (n) were used to calculate the total aerodynamic power? How does this quantity change as a function of the number of periods? Were the first periods omitted from the averaging?
• Line 276-278: The effect of the convergence tolerance is mentioned, but not clearly described. Show in a table the effect of the tolerance on the result.
• Line 282: The result of a time step size study is preferably a time-varying quantity, instead of a time-average.
• Line 292: Figure 9 is not mentioned in the text.
• Line 294: The text indicates as if the small scale vortices are shed directly from the blade, while they typically develop in the wake. Please clarify whether these small scale vortices are present already very close to the blade (so shed by the blade) or whether they develop in the wake, from larger vortices that become unstable (so develop rather than shed).
• Line 317: Figure 13 is not mentioned in the text.

Minor comments:

• Line 38: vortex => Vortex
• Line 123: surface.The => surface. The
• Caption Figure 3: clarity => clarity.
• Line 128: exploring => exploiting
• Line 155: Incomplete sentence
• Line 208: force => spanwise force density
• Line 222: F_STRUC is only defined further, below Equation (7). Furthermore, this symbol F was previously used for force density, so confusing to use it also as dissipation factor.
• Line 228: 5 => (5)
• Line 242: SAS,SBES => SAS, SBES
• Line 255: low5 => low
• Line 316: U_0 was used for amplitude, now A_tip, so maybe use U_0,tip.