Developing a Digital Twin Framework for Wind Tunnel Testing: Validation of Turbulent Inflow and Airfoil Load Applications

Mishra, Rishabh; Guilmineau, Emmanuel; Neunaber, Ingrid; Braud, Caroline

doi:https://doi.org/10.5194/wes-2023-70

Preprints

https://doi.org/10.5194/wes-2023-70

Preprints

11 Jul 2023

| 11 Jul 2023

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

Developing a Digital Twin Framework for Wind Tunnel Testing: Validation of Turbulent Inflow and Airfoil Load Applications

Rishabh Mishra, Emmanuel Guilmineau, Ingrid Neunaber, and Caroline Braud

Abstract. Wind energy systems, such as horizontal-axis wind turbines and vertical-axis wind turbines, operate within the turbulent atmospheric boundary layer, where turbulence significantly impacts their efficiency. Therefore, it is crucial to investigate the impact of turbulent inflow on the aerodynamic performance at the rotor blade scale. As field investigations are challenging, in this work, we present a framework where we combine wind tunnel measurements in turbulent flow with a digital twin of the experimental setup. For this, first, the decay of the turbulent inflow needs to be described and simulated correctly. Here, we use Reynolds-Averaged Navier-Stokes (RANS) simulations with k −ω turbulence models, where a suitable turbulence length scale is required as an inlet boundary condition. While the integral length scale is often chosen without a theoretical basis, this study derives that the Taylor micro-scale is the correct choice for simulating regular grid generated turbulence: the temporal decay of turbulent kinetic energy (TKE) is shown to depend on the initial value of the Taylor micro-scale by solving the differential equations given by Speziale and Bernard in 1992. Further, the spatial decay of TKE and its dependence on the Taylor micro-scale at the inlet boundary are derived. With this theoretical understanding, RANS simulations with k − ω turbulence models are conducted using the Taylor micro-scale and the TKE obtained from grid experiments as the inlet boundary condition. Second, the results are validated with excellent agreement with the TKE evolution downstream of a grid obtained through hot-wire measurements in the wind tunnel. Third, the study further introduces an airfoil in both the experimental and the numerical setting where 3d simulations are performed. A very good match between force coefficients, obtained in experiments and in the digital twin, is found. In conclusion, this study demonstrates that the Taylor micro-scale is the appropriate turbulence length scale to be used as the boundary condition and initial condition to simulate the evolution of TKE for regular grid generated turbulent flows. Additionally, the digital twin of the wind tunnel can accurately replicate the force coefficients obtained in the physical wind tunnel.

Received: 27 Jun 2023 – Discussion started: 11 Jul 2023

Download & links

Rishabh Mishra et al.

Status: open (extended)

Post a comment Subscribe to comment alert

RC1: 'Comment on wes-2023-70', Anonymous Referee #1, 02 Aug 2023 reply

The manuscript discusses the use of a digital twin to perform wind turbine and airfoil tests in wind tunnels with turbulent inflows. Hot-wire anemometry is first used to characterize grid-generated turbulence in the wind tunnel. Pressure and force sensors are then applied to record the pressure, drag and lift coefficients of an airfoil under different angles of attack at a chord-based Reynolds number of 2.0x10^5. On the other hand, RANS simulations at the same Reynolds number are used to capture the kinetic energy decay of the grid-generated flows and the different coefficients within the airfoil. Good agreement is found between all quantities, provided that the Taylor microscale is used in the RANS simulations as the length scale required to simulate the grid-generated turbulent flow.
I find the thematic of this manuscript within the scope of the journal. Furthermore, it is well written and organized, with a theoretical discussion and numerical results that are of interest for the wind energy community. Nevertheless, before recommending publication the authors should assess the following points:
- Several arguments used to deduce equations 23 and 27 rely on the presence of a fully developed grid-generated turbulent flow, that is only found far downstream the grid. The range studied here (x<30M, with the airfoil placed at x~20M) may present some differences in terms of the approximations made in equations 10, 13 and 20. While the authors refer to a previous publication from the group, these points should be addressed in the present manuscript.
- Related to my previous point, several papers discuss the decay of kinetic energy in terms of invariants (Sinhuber et al, PRL 2015; Krogstad and Davidson JFM 2009), and also the role of the integral length scale on such models. Furthermore, the power laws predicted contain a virtual origin that is not present in the theoretical discussion of the present work. First, these approaches should be mentioned at the section ‘Brief theoretical description of decaying grid turbulence’. Second, they should be at least addressed when figure 4 is presented. Have the authors tried to compare their data with them? Are the decay exponents near the ones predicted in such papers?
- Presenting figure 4 in logarithmic scale (or using an inset for that) would help to assess the quality of the power-law adjustment. Also, if I understand correctly, the theoretical curve has no fitting parameters? If that is the case, it should be made more explicit on the text as it is a relevant result.
- To properly address the relevance of the Taylor scale on the RANS models, a more systematic study with several grids (producing different values of integral and Taylor scales) should be performed. The present study is an interesting contribution pointing towards the relevance of the Taylor scale in RANS modelling, but gives no conclusive proof. I consider that the conclusions should emphasize this point.
- The accuracy of the numerical simulation in the estimation of different coefficients is discussed in terms of the experimental results but not compared with other numerical works/schemes. I suggest that the authors discuss other works from the literature when presenting figures 16 to 22. Also, those figures should have error bars added.
- I also suggest that figures 11 to 15 are merged onto a single one.

Reply

Citation: https://doi.org/10.5194/wes-2023-70-RC1

Rishabh Mishra et al.

Viewed

Total article views: 465 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	BibTeX	EndNote
384	67	14	465	7	6

HTML: 384
PDF: 67
XML: 14
Total: 465
BibTeX: 7
EndNote: 6

Views and downloads (calculated since 11 Jul 2023)

Month	HTML	PDF	XML	Total
Jul 2023	158	30	8	196
Aug 2023	151	21	5	177
Sep 2023	75	16	1	92

Cumulative views and downloads (calculated since 11 Jul 2023)

Month	HTML	PDF	XML	Total
Jul 2023	158	30	8	196
Aug 2023	151	21	5	177
Sep 2023	75	16	1	92

Viewed (geographical distribution)

Total article views: 440 (including HTML, PDF, and XML) Thereof 440 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 22 Sep 2023

Short summary

In this study, we investigated how turbulence affects wind turbines by studying the aerodynamics of a 2d blade section derived from a real wind turbine. Using wind tunnel measurements and simulations, we found the correct method to simulate turbulence and accurately replicated experimental results. This improves our understanding of wind turbine performance.


Total:	0
HTML:	0
PDF:	0
XML:	0