# SKM 2023 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 5: Fluid Physics: Turbulence and Convection

### DY 5.5: Vortrag

### Montag, 27. März 2023, 10:45–11:00, MOL 213

Offshore wind: Evidence for two-dimensional turbulence and role of sea horizon — •So-Kumneth Sim^{1}, Joachim Peinke^{2}, and Philipp Maass^{1} — ^{1}Fachbereich Physik, Universität Osnabrück, Germany — ^{2}Insitut für Physik & ForWind, Universität Oldenburg, Germany

We analyze offshore wind speeds with a time resolution of one second over a period of 20 months [1].
Wind speed power spectra show a scaling behavior that is governed by three- and two-dimensional turbulence [2].
The latter is observed for frequencies lower than a crossover frequency f_{2D}.
An analysis of the third moment (third-order structure function) of wind speed fluctuations provides strong evidence of this transition to two-dimensional turbulence [3].
We argue that f_{2D}∼ v/d, where v is the mean wind speed and d the distance between the measurement device and the sea horizon.
For the regime of two-dimensional turbulence, two scaling regimes are predicted, which originate from an inverse energy and an enstrophy cascade.
Our results indicate that the scaling due to the inverse energy cascade occurs at low frequencies and is followed by the scaling of the enstrophy cascade at higher frequencies.
This in agreement with the theoretical prediction but contrary to earlier observations.

[1] S.-K. Sim, J. Peinke, P. Maass, arXiv:2203.07685 (2022).

[2] X. Larsén, S. Larsen, E. Petersen, Boundary-Layer Meteorol. 159,

[2] 349 (2016).

[3] R. Cerbus, P. Chakraborty, Phys. Fluids 299, 111110 (2017).