the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Numerical Investigation of Regenerative Wind Farms Featuring Enhanced Vertical Energy Entrainment
Abstract. Numerical simulations of wind farms consisting of innovative wind energy harvesting systems are conducted. The novel wind harvesting system is designed to generate strong lift (vertical force) with lifting-devices. It is demonstrated that the tip-vortices generated by these lifting-devices can substantially enhance wake recovery rates by altering the vertical entrainment process. Specifically, the wake recovery of the novel systems is based on vertical advection processes instead of turbulent mixing. Additionally, the novel wind energy harvesting systems are hypothesized to be feasible without requiring significant technological advancements, as they could be implemented as Multi-Rotor Systems with Lifting-devices (MRSLs), where the lifting-devices consist of large airfoil structures. Wind farms with these novel wind harvesting systems, namely MRSLs, are termed regenerative wind farm, inspired by the concept that the upstream MRSLs actively entrain energy for the downstream ones. With the concept of regenerative wind farming, much higher wind farm capacity factors are anticipated. Specifically, the results indicate that the wind farm efficiencies can be nearly doubled by replacing traditional wind turbines with MRSLs under the tested conditions, and this disruptive advancement can potentially lead to a profound reduction in the cost of future renewable energy.
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RC1: 'Comment on wes-2024-124', Anonymous Referee #1, 13 Nov 2024
This paper presents a novel idea which aims to increase the AEP in a wind farm, by forcing the advection of the atmospheric wind into the wake to reenergise the incoming flow for the next wind power generator. This paper presents preliminary RANS simulations using actuator elements to represent the wind turbines.
 While I have doubts that this type of system would be largely deployed in the future (due to structural integrity, robustness, reliability and control), the concept is original and it's worth doing this thought experiment.The paper is globally well written and relatively easy to follow, despite some convoluted turns of phrase. The simulation results are interesting and seem possible to be reproduced as the settings and the code are apparently available.
I have mostly one main concern and one point that troubled me.1. My main concern is the possible large blockage of such a system. When I look at figure 1, I see quite a lot of projected surface compared with more conventional wind turbines. I would imagine that not all the flow would pass through the system and would rather deviate and go around the system. If the flow deflects, it means that there is a smaller mass flow rate through the system, so less energy can be extracted. Could the authors confirm that in their RANS model, the flow deflection is correctly modelled? For example there are assumptions to define uelels and uelein. May this assumption impact the mass flow passing through the system?
2. The point that troubled me is the terminology with "upward-lifting" and "downward lifting". To me, it seems the upward wind in the wake is due to a downward lift (for example in figure 3, the suction side of the airfoil points downward, so the lift is directed downwards, but it would create an upward wind). This does not impact the results of the paper, but I was doubting if I understood the concept correctly. Could the authors confirm or correct my thoughts and better explain and define this concept in the paper?I have a couple of other minor remarks:
3. Why did the authors choose this airfoil for the lifting devices?
4. A Turbulence Intensity of 8% seems fair, but it could be much higher in the reality. As it is mentioned the Turbulent Kinetic Energy plays a minor role, I would interested to know whether the conclusions still hold with a higher TI (such as 20%).
5. Similarly, the difference of results between the different turbulence models seem quite large. Could the authors precise what could be the reasons for such a large difference between the k-omega and k-epsilon models?Citation: https://doi.org/10.5194/wes-2024-124-RC1 -
RC2: 'Comment on wes-2024-124', Anonymous Referee #2, 14 Nov 2024
The article describes a multi-rotor wind energy system with static lifting devices, aimed to increase the momentum entrainment and mitigate wake losses.
The paper is structured well, and the methodology is mostly clearly presented. Perhaps the paper could be shortened by not spelling out every well known concept, for example the RANS equation system with k-omega turbulence model (eqs. 1-4).Some general remarks below.
It is not clear how the MRSL appears in the modeling grid. The name indicates several rotors, but Figure 4 indicates one (square) rotor with the diameter D=300m, and 186m hub-height.Â
Nothing is said about the system integrity and loads on the structure. How does such a system turn into the wind? It could also be assumed that it is fixed and suitable for uni-directional wind climate. In this is the case, please state. While this device appears entirely conceptual and will highly unlikely ever be used at scale, it is however attractive to find an engineering way to capture some of the potential to double the energy density in large wind farms (e.g. Table 4). Have you perhaps tried to add the 5th wing at the lower edge of the system? What about if the wings are installed separate from the multi-rotor structure?
There are many acronyms in the article, but downward-lifting and upward-lifting are for some reason spelled in full over 100 times. Suggest using DL and UL instead.
Citation: https://doi.org/10.5194/wes-2024-124-RC2
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