| 29 Oct 2025
Turbulence Distortion Matters in Predicting Inflow Turbulence Noise of Future Wind Turbines
Abstract. This study examines the role of turbulence distortion in predicting inflow turbulence (IT) noise generation from large wind turbines via Amiet's theory. Two subsequent distortion mechanisms are investigated: (i) the streamtube expansion in the rotor induction zone and (ii) the interaction with the surface of thick blade profiles. Large-eddy simulations reveal that the turbulence spectra, which reflect distortion effects, remain largely unaffected by rotor induction within the frequency range relevant for noise generation. As for the other mechanism, the distortion of the turbulence approaching a blade leading edge is modeled with a simplified closed-form solution of Goldstein’s Rapid Distortion Theory. This vorticity-deflection-based model is extended here beyond the high-frequency approximation and integrated into an analytical Amiet-based IT noise tool. Applications to representative test cases show that while distortion effects are minimal for current turbine sizes, they become relevant for future configurations featuring larger rotor sizes and thicker airfoils. The developed model reveals that IT noise levels do not necessarily scale with rotor size, but are shaped by spectral changes induced by the blade geometry, operational parameters, and inflow conditions. This model offers a physically consistent, computationally efficient framework for aeroacoustic assessment of next-generation wind turbine design.
This article is providing a correction to the well-known Amiet model for inflow turbulence (IT) noise. This correction accounts for the deformation of the turbulent flowfield due to the thickness of the airfoil. It generalizes the Rapid Distortion Theory by including also large structures. It is also investigated if the atmospheric flow axial flow expansion does have an effect on the turbulent characteristics.
The article is clearly and well written. The mathematical derivations are well described.
Nevertheless, the reviewer notices a few inconsistencies and details that should be corrected, but do not compromise the pertinence of the article and validity of the results and conclusions.
One is related to the terminology used to describe the change in slope for the turbulence spectra. It is formulated in p.5 and p.16 that the slope (e.g. of -5/3) is "reduced", when the reviewer would rather in both case that the slope is increased. The reviewer assumes here that the authors mean that the coefficient of the logarithmic slope is increased. It is possibly a matter of taste about how to formulate this information.
The length scale of 312 m appears quite large to the reviewer. At which altitude is it evaluated?
There exist an inconsistency in Fig.3. Fig.3(f) is a zoom-in of Fig.3(c), however in 3(c) the model results overestimate the measurements in the frequency range 40-100 Hz, while it is the opposite in 3(f).
p.14, l.325: It is not clear to the reviewer why it can be concluded that the turbulence is isotropic.
p.16, l.360: A Blade-Passage-Frequency of 0.45Hz is consistent with 9 RPM. However, in Fig. 7, the first spectral peak is located at 0.9Hz... which is inconsistent.
Furthermore, in Fig.7 the slope "decrease" above, say, 0.1 Hz, which corresponds to the mesh cut-off frequency in Fig.4, is not clearly explained. In the reviewer's opinion, the low resolution upstream of the refined mesh zone contains large scale turbulence. During the time period for the turbulent flow to reach the measurement point, e.g. at -0.25D, smaller structures don't have the time to develop through the energy cascade of turbulence, which could explain the lower energy level (above 0.1Hz) than expected.
The reviewer is not familiar with the RDT equations and their derivation. However, the argument that the second order Lagrangian derivative disappear from Eq. 19 to give Eq. 29 is not clear for the reviewer.
The phrasing in p.23, l. 498-500 is not clear. The distortion length is first defined as the/a (?) circle radius. Then, it is defined by the "length between the LE radius and half of the max. thickness" which doesn't make sense as it does not describe a length per se... or does the reviewer misunderstand?
p.23, l.507: The spectra are plotted for a position in the vicinity of the LE, but it is not specifically defined.
All in all, this is an interesting paper that should be published without major revision. The small inconsistencies and details mentioned above should be addressed though.