Effects of atmospheric thermal stratification on wake aerodynamics of a regenerative wind farm unit

Li, YuanTso; Sciacchitano, Andrea; Yu, Wei

doi:10.5194/wes-2026-116

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https://doi.org/10.5194/wes-2026-116

Preprints

08 Jul 2026

| 08 Jul 2026

Status: this preprint is currently under review for the journal WES.

Effects of atmospheric thermal stratification on wake aerodynamics of a regenerative wind farm unit

YuanTso Li, Andrea Sciacchitano, and Wei Yu

Abstract. The effects of atmospheric thermal stratification on the wake aerodynamics of an isolated unit of a regenerative wind farm unit (RGWF), referred to as a multi-rotor system with lifting device (MRSL), are investigated using precursor-based large-eddy simulations. MRSL is a wind-energy harvesting system designed to realize the concept of RGWF. The core principle of RGWF is to generate large-scale streamwise vortices that enhance the vertical entrainment of kinetic energy, thereby promoting wake recovery and mitigating wake-induced power losses in wind farms. The effectiveness of the RGWF concept has previously been demonstrated under simplified inflow conditions. The present work extends the assessment to realistic atmospheric boundary layers with different thermal stratifications. The results show that, although atmospheric thermal stratification modifies wake dynamics, the beneficial effects of the RGWF concept remain significant under convective (CBL), neutral (NBL), and stable (SBL) atmospheric boundary-layer conditions. In particular, MRSL's wakes recover substantially faster than those of conventional counterparts (i.e., those without lifting devices) across all investigated conditions, further supporting the potential of this technology.

Received: 28 Jun 2026 – Discussion started: 08 Jul 2026

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YuanTso Li, Andrea Sciacchitano, and Wei Yu

Status: final response (author comments only)

RC1:
'Comment on wes-2026-116', Anonymous Referee #1, 06 Aug 2026
The authors analysed the behaviour of multi-rotor systems with lifting devices (MRSLs) under different atmospheric stability conditions using high-fidelity LES simulations. The impact on system performance and wake recovery was evaluated. The Reviewer finds the topic and research activity interesting and worthy of investigation. The methodology is adequate for the stated purpose and applied consistently throughout the study. The results are presented clearly.
A few minor comments to further improve the quality of the manuscript:
Introduction: MRSL appears to be a specific design within the broader family of RGWFs, which can employ different flow mechanisms to enhance wake recovery. This distinction should be made clearer throughout the manuscript;

Introduction: Beyond the use of lifting devices, the multi-rotor configuration itself is a non-conventional design choice. Please briefly explain in the introduction why this design is preferred over a conventional wind farm layout;

Methodology: Neglecting Coriolis effects is a relevant simplification, particularly for the stratified flow case. Do the authors expect this to affect their findings? Please add a brief discussion of this point to the manuscript.
Citation: https://doi.org/10.5194/wes-2026-116-RC1
RC2:
'Comment on wes-2026-116', Anonymous Referee #2, 01 Sep 2026
The manuscript covers LES of multi-rotor systems with lifting devices (MRSLs) under various thermal stratifications, conducted with SOWFA-6. While the practical effectiveness of such devices is questionable but beyond the scope of this review, the manuscript is excellent, the results are presented exceptionally clearly, the approach is logical and easy to follow, and there is not even a single typo. I particularly enjoyed the figures, with consistent color schemes across the various cases and clear and properly-sized Latex-like fonts. I only have two minor requests and a few comments.
Minor requests
Looking at Fig. 6, especially for the stable case, there appears to be a significant negative deficit, i.e., an acceleration of the flow, which reaches the lower part of the "rotor" starting at 6D in the DW case. This is quite interesting because it would imply a hidden benefit for downstream devices with down washing. However, when I looked at Fig. 15, somehow this advantage is not there or is washed out with the variable Xi. I think that the reason might be the limits of the y-integration in Eq. 12. Extending the calculation to 5D laterally is excessive because the available power that truly matters is just that going through the rotor. The reasoning that "wind direction changes continuously in a wind farm" is not really applicable in this case because the wind direction did not change at all in these simulations. Plus, again, even if the wind direction changes, the MRSL would always face the wind, thus only the lateral extent of +/- 0.5D matters. I kindly request that you re-evaluate Eq. 12 and Fig. 15 using a more realistic range of +/- 0.5D for the the y-integration. I suspect that the DW case will appear more appealing this way. This modification will affect Table 2 also.

Similarly, I suspect that the benefits of the UW case might be over-estimated by considering such a high vertical extent in the integrals in Eqs. 9: why go as high as 3D? For the practical purposes of generating power, again, only the vertical extent of the rotor matters. Who cares if there is a high wind speed deficit above the farm? (I mean for power generation only purposes; obviously it matters for boundary layer alterations). I would prefer to see results in Fig. 7 that are limited to 1D in the vertical (thus integrate from 0 to 1D in Eqs. 9 instead of 0-3D).

Comments
Why are the three cases starting at 0.3 in Fig. 7 (middle)?

Why does the wake center first rise and then drop in the DW case, and vice versa in the UW case, in Fig. 7 (right)?

Proper definition of added TI noted in Eq. 11, well done.
Citation: https://doi.org/10.5194/wes-2026-116-RC2

YuanTso Li, Andrea Sciacchitano, and Wei Yu

Data sets

Supplementary materials for "Effects of atmospheric thermal stratification on wake aerodynamics of a regenerative wind farm unit" Y. Li et al. https://data.4tu.nl/private_datasets/01fX1E2Q7uLAwvMA-vXFbZ808m9_N9-jS-ydqGOUznk

YuanTso Li, Andrea Sciacchitano, and Wei Yu

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Short summary

We investigate the regenerative wind farming (RGWF) concept under realistic atmospheric conditions using large-eddy simulations. The effects of convective, neutral, and stable atmospheric boundary layers on the wake of a multi-rotor system with lifting devices (MRSL, the unit of RGWF) are examined. The results show that RGWF concept remains effective across all stability regimes, demonstrating its robustness and providing guidance for its future design and deployment.


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