the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Dec 2024
Brief communication: A note on the variance of wind speed and turbulence intensity
Abstract. This note addresses the issue that several papers in the peer-reviewed literature of wind energy applications have used an incorrect equation that equals the variance of wind speed (σ2U) to the sum of the variances of the wind components. This incorrect equation is often used to calculate turbulent intensity (TI), which, as a consequence, is often incorrectly estimated too. While exact analytical equations do not exist, here two approximate analytical equations are derived for σ2U and TI, both functions of the variances of the wind components. Both formulations are validated with samples from a prior field campaign and perform satisfactorily.
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Status: open (until 09 Jan 2025)
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RC1: 'Comment on wes-2024-159', Anonymous Referee #1, 12 Dec 2024
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This paper deals with the difference between the variance of the wind component along the mean wind vector and the variance of the length of the wind vector, also called the wind speed. It is well known that those quantities are under most circumstances (i.e. not too high turbulence intensity) almost equal (e.g. L.. Kristensen 1998, JTech, vol 5, p6). The transverse component enters only the speed variance to second order in the turbulence intensity (see eq 8 in the mentioned paper). These observations do not change if the coordinate system is not aligned with the wind.
The other subject paper is an apparent mistake in the literature. The author states that the variance of the wind speed is sometimes mistakingly said to be equal to the sum of the variances of the two horizontal components. This is obviously wrong, as the author clearly states, but I’m am unaware of these mistakes in the literature. The author does not provide evidence for these mistakes, which makes the need for this paper limited. The author might be wary to point out mistakes in specific papers, but this is unfortunately what has to be done in order to advance science. You cannot leave it to the readers to find documentation for this possible mistake in the literature.
I therefore think, that the paper is not suited for publication in Wind Energy Science. The problem in the literature has to be documented. Once the issue is confirmed with a thorough list of papers containing this mistake, and thus proving its relevance, the paper should be made more succinct, as there are no substantially new derivations.
Citation: https://doi.org/10.5194/wes-2024-159-RC1 -
AC1: 'Reply on RC1', Cristina Archer, 16 Dec 2024
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See attached PDF
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AC1: 'Reply on RC1', Cristina Archer, 16 Dec 2024
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