Large-eddy simulation of gusty wind turbulence over a travelling wave

Abstract

Wind gustiness in the marine atmospheric boundary layer affects significantly the dynamics of air–sea interaction. To understand the impacts of wind gust events, we perform large-eddy simulation of wind turbulence over a travelling wave to investigate the response of the wind field to an impulsive wind speed increase or decrease. It is found that the turbulence fluctuations and the terms in the turbulent kinetic energy budget equation have a delayed response to the change in the mean flow, while the response of the wave-coherent motions is quasi-stationary. The wave-coherent motions are investigated quantitatively through comparison with a viscous curvilinear model developed by Cao et al. (J. Fluid Mech., vol. 901, 2020, A27) and Cao & Shen (J. Fluid Mech., vol. 919, 2021, A38). We observe an asymmetric hysteresis between the growing wind and the decaying wind in the evolution of the form drag and the viscous drag. We find further that the variation of the wave growth rate during the wind gust is related closely to the contribution from the out-of-phase component of the vertical velocity. Our discoveries provide evidence for the necessity of improving non-equilibrium turbulence and wind input modelling to account for the wind gustiness effect in future studies.

A Dynamic Large-Scale Driving-Force to Control the Targeted Wind Speed in Large Eddy Simulations above Ocean Waves

“…However, there is no physical reason for this assumption (c.f. [59,62,65]), since the largescale conditions could well vary in scales much larger than the computational domain.…”

“…[46]). A pioneer LES over wavy surfaces was proposed in [47], and was followed by the developments of [48][49][50][51][52][53][54][55][56][57][58][59], with a recent review of the state-of-the-art methodology presented in [60]. The DNS model presented in Sullivan et al [38] was adapted in [48][49][50], into the LES model (from the NCAR, USA) employed herein.…”

“…To study large-scale dynamics, atmospheric LES approaches use these physics to drive the flow in the numerical domain [48,60]. To avoid having to model the entire ABL and above, a homogeneous longitudinal pressure gradient (∂P /∂x) is widely used in micro-scale studies to drive the flow instead [47,[49][50][51][52][53][54][55][56][57]59]. In this case, unlike in reality, the flow travels along the pressure gradient direction as in a wind tunnel.…”

“…In previous studies of wind-wave interactions by LES, the large-scale driving force (here ∂P /∂x) was usually prescribed as a constant [47][48][49][50][51][52][53][54][55][56][57]60]. As an exception, an arbitrary time-varying force was recently employed to simulate a wind gust event [59]. Over land, however, a few applications considered transient large-scale forcing terms in LES (c.f.…”