Large eddy simulation of non-stationary highly turbulent hurricane boundary layer winds

Abstract

Recent extreme tropical cyclones have caused extensive damage to critical civil infrastructure globally. To better capture the unique hurricane wind characteristics, a large eddy simulation (LES) hurricane boundary layer (HBL) model is developed by considering the variation of meso-scale kinematic and thermodynamic conditions. An asymmetric model is adopted to obtain the gradient wind velocity using the National Hurricane Center data. The meso-scale thermal conditions are obtained by extracting the hourly air temperature and relative humidity profiles from the ERA5 reanalysis output. Measurements recorded at the Aransas County airport during Hurricane Harvey and at the City of Naples during Irma are used to validate the developed LES model. Research results show that the simulated 10-min average wind speed and direction are consistent with the observations. The developed model can well predict the high wind turbulence intensity, which is around 20 % in Hurricane Harvey and 26 % in Hurricane Irma. The 3-s gust wind speeds reach 62.4 m/s at 10-m elevation during Hurricane Harvey and 53.5 m/s at 15-m elevation during Hurricane Irma, close to the field observed data of 61.3 and 54.2 m/s, respectively. The simulated 3-s gust factors are close to the observation except at some moments with significant variations because of the poorly understood physical phenomena. The simulated wind spectrum in longitudinal and lateral directions agrees well with the observed results. In addition, the vertical profiles of averaged wind speed and inflow angle agree with dropsonde observations. The maximum supergradient wind speed height decreases as it approaches the hurricane center. In summary, the developed LES-based HBL model can capture the main characteristics of hurricane structure and turbulence characteristics and is applicable for modeling civil infrastructure exposed to hurricanes.