Effects of air-side freestream turbulence on the development of air–liquid surface waves

Takagaki, Naohisa; Suzuki, Naoya; Takahata, S.; Kumamaru, Hiroshige

doi:10.1007/s00348-020-02977-9

Cited by 3 publications

(2 citation statements)

References 43 publications

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“…Toba 1972;Holthuijsen 2007). The significant waves are defined as the waves whose heights are the largest one-thirds among all individual waves, and the individual waves are identified using the zero-up crossing method (Pierson 1954;Takagaki et al 2020). Here, H s and L s are the average wave height and wavelength of the significant waves, respectively.…”

Section: Effect On Wave Growthmentioning

confidence: 99%

Effects of surface tension reduction on wind-wave growth and air–water scalar transfer

et al. 2023

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Effects of surface tension reduction on wind-wave growth are investigated using direct numerical simulations of air–water two-phase turbulent flows. The incompressible Navier–Stokes equations for air and water sides are solved using an arbitrary Lagrangian–Eulerian method with boundary-fitted moving grids. The wave growth of finite-amplitude and non-breaking gravity–capillary waves, whose wavelength is less than 0.07 m, is simulated for two cases of different surface tensions under a low-wind-speed condition of several metres per second. The results show that significant wave height for the smaller surface tension case increases faster than that for the larger surface tension case. Energy fluxes for gravity and capillary wave scales reveal that when the surface tension is reduced, the energy transfer from the significant gravity waves to capillary waves decreases, and the significant waves accumulate more energy supplied by wind. This results in faster wave growth for the smaller surface tension case. The effect on the scalar transfer across the air–water interface is also investigated. The results show that the scalar transfer coefficient on the water side decreases due to the surface tension reduction. The decrease is caused by suppression of turbulence in the water side. In order to support the conjecture, the surface tension effect is compared with laboratory experiments in a small wind-wave tank.

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Section: Effect On Wave Growthmentioning

confidence: 99%

Effects of surface tension reduction on wind-wave growth and air–water scalar transfer

et al. 2023

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“…Additional experiments were performed using a wind-wave tank at Kindai University with a glass test section 6.5 m long, 0.3 m wide, and 0.8 m high (Fig. 1c) (e.g., Takagaki et al, 2020). The water depth D was set at 0.49 m. A Pitot tube (Okano Works, LK-0) and differential manometers (Delta Ohm HD402T) were used to measure the mean wind velocity.…”

Section: Artificial Current Experiments At Kindai Universitymentioning

confidence: 99%

Effects of current on wind waves in strong winds

et al. 2020

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Abstract. It is important to investigate the effects of current on wind waves, called the Doppler shift, at both normal and extremely high wind speeds. Three different types of wind-wave tanks along with a fan and pump are used to demonstrate wind waves and currents in laboratories at Kyoto University, Japan, Kindai University, Japan, and the Institute of Applied Physics, Russian Academy of Sciences, Russia. Profiles of the wind and current velocities and the water-level fluctuation are measured. The wave frequency, wavelength, and phase velocity of the significant waves are calculated, and the water velocities at the water surface and in the bulk of the water are also estimated by the current distribution. The study investigated 27 cases with measurements of winds, waves, and currents at wind speeds ranging from 7 to 67 m s−1. At normal wind speeds under 30 m s−1, wave frequency, wavelength, and phase velocity depend on wind speed and fetch. The effect of the Doppler shift is confirmed at normal wind speeds; i.e., the significant waves are accelerated by the surface current. The phase velocity can be represented as the sum of the surface current and artificial phase velocity, which is estimated by the dispersion relation of the deepwater waves. At extremely high wind speeds over 30 m s−1, a similar Doppler shift is observed as under the conditions of normal wind speeds. This suggests that the Doppler shift is an adequate model for representing the acceleration of wind waves by current, not only for wind waves at normal wind speeds but also for those with intensive breaking at extremely high wind speeds. A weakly nonlinear model of surface waves at a shear flow is developed. It is shown that it describes dispersion properties well not only for small-amplitude waves but also strongly nonlinear and even breaking waves, which are typical for extreme wind conditions (over 30 m s−1).

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Large-eddy simulation of the effects of a tower structure on wind velocity and drag coefficient

Michioka

2024

Asian J. Atmos. Environ

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A large-eddy simulation was implemented for the flow around a cylindrical observation tower to investigate the effects of the tower structure on wind speed and drag coefficient. The mean wind velocity accelerates above the tower because flow separation occurs at the leading edge of the top of the tower. The drag coefficient is strongly linked to the Reynolds shear stress. Above the tower, the Reynolds shear stresses change from negative to positive within the recirculation zone and return to a negative value in the latter half of the tower because of the steep velocity gradients near the top of the tower. The change in the Reynolds shear stress results in an inaccurate drag coefficient. When one anemometer is used, a location at over 10 m above the top of the tower is suitable for measuring the drag coefficient accurately. When two anemometers are used, the Reynolds shear stress can be measured more accurately. Although the effects of the tower on the drag coefficient are not entirely removed, the use of two anemometers is a promising approach to estimate the drag coefficient in a tower. Graphical Abstract

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Effects of air-side freestream turbulence on the development of air–liquid surface waves

Cited by 3 publications

References 43 publications

Effects of surface tension reduction on wind-wave growth and air–water scalar transfer

Effects of surface tension reduction on wind-wave growth and air–water scalar transfer

Effects of current on wind waves in strong winds

Large-eddy simulation of the effects of a tower structure on wind velocity and drag coefficient

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