|I believe the authors have improved the manuscript and. I previously inquired about the accuracy and validation of the simulations, and I believe that this has not been fully addressed yet. As indicated in my previous report, it is understandable when simulations and experiments do not fully agree. Based on the provided answers that seems to be the case as turbulence intensity levels are not accurately reproduced (a difference of 5 to 10 percentage points in atmospheric turbulence at the location of interest is significant). I think this should be more clearly discussed in abstract and conclusion, instead of just stating there that all agrees very well. Now the discussion of differences between experiments and simulations is somewhat limited and mainly presented in section 4.2. |
Below some additional thoughts on this aspect.
For comparison to the experiments and validation of the results, table 3, section 4.2, is particularly relevant. Can you please double-check/confirm that the presented differences in turbulence intensity are indeed in percentage points (with a percentage point being the unit for the arithmetic difference of two percentages. For example, moving up from 40 per cent to 44 per cent is an increase of 4 percentage points.) For the FLOWer domain, the difference in turbulence intensity is 5 to 10 percentage points at the turbine location, which is very significantly different given general atmospheric turbulence levels.
This difference between experiments and simulations seems to relate to the transition from the Ewind solution at the entrance of the FLOWer domain from a Mann modelled turbulence spectrum to a flow that accurately captures atmospheric turbulence. In figure 16, you indicate that the flow discontinuity at the entrance of the FLOWer domain is related to this. This seems to indicate that the flow needs to transition from the Mann modelled spectrum, which can require significant space. I find the answer in the response document is clearer than what is added to the manuscript.
In the conclusion (see, for example, line 570), it is now stated that turbulence is captured well without discussing these aspects. However, a more balanced discussion addressing the aspects indicated above seems warranted. I.e. it should be clear from the abstract and conclusion that the Mann spectrum is used at the interface between FLOWer and Ewind and that this could have limitations.
Some specific points
* Table 2: the naming of "empty" and "terrain" is perhaps not ideal.
* Table 3: It would be helpful also to present the absolute values and not just the difference. This would make it easier to assess statements like the one on 336. "At mast 20, both the horizontal wind speed WS and the wind direction WD fit very well over the entire mast height, indicating that the vertical wind shear is met." --> with the information at hand, the shear (or difference in shear cannot be determined).
* line 359: "It can be concluded that the DDES of the complex terrain in Perdigão with FLOWer … ". In table 3, it is now indicated that the difference in Turbulence intensity is 5 to 10 percentage points. Given that turbulence intensity can affect the loading on turbines, this is important to discuss, see also above.
* Figures 14, 18, 20, 21, 22, and 24 could be normalized to account for the different inflow strengths of the different cases as given in table 4.
* line 570: "Both mean velocities and turbulence up to 1Hz are realistically captured at the turbine position." --> See discussions above. The difference in TI is 5 to 10 percentage points at the turbine location in the FLOWER simulation. This is significant and requires a more balanced discussion to explain this to the reader.
* line 573: "The characteristics of the turbine wake can be compared with lidar measurements, for example, and are well represented in the simulation." --> Where is this comparison of the measured and simulated wake presented (sorry in case I missed this).
* Several figure captions: D from mast 20 --> As "D" is typically used for turbine diameter, it is not ideal to use its abbreviation for "distance."
* Figure 9 caption "WS" in between brackets
* Figure 10a at the top ==> should this be with and without turbine instead of "terrain - empty"?
* 3.2 "Unsteady terrain simulation" ==> The terrain itself is not unsteady.
* line 158: "following the literature mentioned in Sect. 1.1." --> can these references be specified? Many studies are cited in 1.1
* line 166: "a pre-run with an increased time step ( 70 t) is utilized." --> Can you give a reference to this procedure? It would seem that this makes your timestep too large to satisfy CFL conditions.
* line 185: "BL cells with reduced resolution". The use of "reduced resolution is confusing; use, for example ", cells with smaller vertical extent."
* Double-check for spelling/grammar