the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Aug 2023
Inclusion of the subgrid wake effect between turbines in the wind farm parameterization of WRF
Wei Liu
Xuefeng Yang
Shengli Chen
Shaokun Deng
Peining Yu
Jiuxing Xing
Abstract. Wind farms, as an important renewable energy source to combat climate change, have had explosive development in recent years. Assessing impacts of wind farms on atmospheric and marine environments requires an accurate parameterization of wind farms in atmospheric models. The current wind farm parameterization scheme (Fitch et al. 2012) in WRF plays an important role in the study of impacts of wind farms. The scheme, however, has some shortfalls, e.g., does not consider the wind wake behind turbines inside a grid cell. In this research, the Fitch scheme in WRF is modified by inclusion of the wake effect of wind turbines. Based on an engineering wake model of a turbine, a wake superposition coefficient and an angle correction coefficient are proposed. A solution model for the inflow wind speed is established to obtain the angle correction coefficient. Other coefficients in the engineering wake model are calculated based on the CFD results. These coefficients are added in the WRF to improve the wind farm parameterization, and sensitivity experiments are conducted. Model results show that the new improved scheme significantly increases wind energy, output power and turbulent kinetic energy in the wind farm area compared with the original scheme. Sensitivity experiments also reveal that, with enlarged model grid size and shortened turbine spacing, the subgrid wake effect becomes more significant, and the new scheme shows more advantages.
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Wei Liu et al.
Status: final response (author comments only)
- RC1: 'Comment on gmd-2023-174', Anonymous Referee #1, 18 Sep 2023
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RC2: 'Comment on gmd-2023-174', Anonymous Referee #2, 16 Nov 2023
Here the authors try to include subgrid wake effects in the Fitch scheme, which is the WRF’s default wind farm parametrization. The manuscript is at this state and stage very weak both in its conceptualization, its presentation, and its results, and therefore, I cannot suggest its publication. I became very worried about this work, so I stopped reading it after I saw the authors even carried out sensitivity experiments as well! So, my review goes until Section 4.1. I apologize but my opinion is that this manuscript needs major surgery before it can be submitted again to a proper journal as GMD. Unfortunately, I have to recommend its rejection, but I encourage the authors to revise it thoroughly. Also, I strongly recommend sending this paper to a English grammar office since the language can be also largely improved; it is not much about misspellings but about the way to write science per se.
Major comments:
- CFD: already in the abstract you mentioned that the coefficients will be derived from CFD results, but you do not say anything about what do you mean by CFD here. Moreover, you do not mention what CFD tool you used later in the manuscript. CFD can be anything; it can even be WRF itself! Since it is an important part of your study, the “CFD” should be properly described, is it LES, RANS, uRANS? What is the turbine model in it? How is turbulence model? Etc.
- Section 3.1: As mentioned in point 1 there is no description of the so-called CFD model. But also important is that from the text, it sounds as if the subgrid model you end up using is based on Eqn. (4), which is determined by the coefficients you estimate based on your specific CFD precomputations. This reads as if the layout of the wind farm or the turbine itself is different from that you used in your CFD precomputations, then these coefficients in Eqn. (4) will also differ (or are they generic?). Then, this ends up not being a generic wind farm parameterization anymore because (I guess) you did not simulate all possible layouts within a grid cell or all types of turbines.
- In order to understand the results shown in Fig. 11, information about the wind direction within the 3 days of simulation is needed. From Fig. 10 we only have a snapshot and it hints as the northeasterly sector is the one dominant but direction can change quickly during these three days.
- Also related to point 3 above: It is difficult to understand what do you mean by wind energy in Figure 11 and the text around it in page 16? Do you mean the amount of energy that you could extract from the wind? If so, then it should not depend on the wind farm parametrization but only on the wind climatology without the wind farm (basically you should have run a simulation without then wind farm). However, you have two different results for the two types of parametrization so I guess this is the energy extracted within the 3 days but then the units should be in MW h/day or similar. The numbers you provide in Page 16 are all very strange. What does 1.44x1013 mean? Or 8.54x1012? There is no “absorption of wind energy in the wind farm region” How can you know that the error is reduced (line 353), how could you know it was being overestimated? The text in lines 348-357 is just way too weird.
- Figure 12 and text around: Also a very strange plot and description. I guess you do not mean 70 MW in the colorbar but GW? But most importantly, is this power output at a particular time? I mean is this the instantaneous power output or some kind of average power output within the 3 days. Further, the number is strange as your maximum power output should be 76800 MW but you have numbers of 11639 and 5703 MW, so about 10% of the rater power of this mega hyper wind farm.
- And perhaps more importantly: if I understood correctly the new parametrization (Fitch and subgrid model) results in larger energy yield than the original one (Fitch only). If the Fitch scheme is basically the same, the effect of the subgrid model should be to lower the energy yield as you are accounting for the effect of wakes within the grid cell. So I do not really understand why is your new scheme yielding more energy.
Specific comments:
- Line 20: “These coefficients are added in the WRF”; I guess you mean that they were added in a new implementation of the Fitch scheme, which is coupled within the WRF modelling system.
- Line 21: “Sensitivity experiments”; here you need to say of what? Spatial resolution, PBL schemes? What kind of sensitivity?
- Line 25: “shows more advantages” compared to what?
- Line 35: replace “achieving a rapid development period
- Line 59: full stop after meters and then start a new sentence with “Numerical”
- Line 76: delete “technology” after “LES”
- Line 78: replace “LES simulation of wind farm is processed by the” by “LES is combined with”
- Lines 80-83: these two sentences referring to the work of Elshafei et al. (2021) has nothing to do with your work
- At the end of the introduction, you introduce the different sections of your work but not all of them
- (1)—(3) are wrong as these are not those implemented in the original Fitch scheme
- (4) and some others: you use the dot product to represent multiplication sometimes. You should not. This is the dot product between two vectors and a coefficient is not a vector
- Line 148: Replace “which is related to the roughness” by “which can be related to the roughness”
- Line 160: “Eq. (2.5)” there is no such an equation, so do you mean Eq. (5)?
- Line 286: “two-turbine wake experiment” which one? Did you introduce it before?
- Lines 311 and 312: Do you mean “Implementation”?
- Line 339: what is “the kind of speed”?
- Lines 339-341: please rephrased. What do you mean by conducive?
- 11: Is this for the innermost domain? If so please state this in the caption
- 12: what are the units of the turbulent kinetic energy?
Citation: https://doi.org/10.5194/gmd-2023-174-RC2
Wei Liu et al.
Wei Liu et al.
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