CFD simulation of wind flow over natural complex terrain: Case study with validation by field measurements for Ria de Ferrol, Galicia, Spain

Accurate and reliable Computational Fluid Dynamics (CFD) simulations of wind flow over natural complex terrain are important for a wide range of applications including dispersion of pollutants, wind energy resource assessment and ship manoeuvring in channels and near harbours. In the past 50 years, a very large number of CFD studies of wind flow over hills have been performed. However, a detailed review of the literature shows a lack of CFD studies including validation by field measurements for natural complex terrain beyond the case of isolated hills. Therefore, this paper presents a CFD study with field measurement validation for natural complex terrain that consists of an irregular succession of hills and valleys surrounding a narrow entrance channel. The aim of the study is twofold: (1) to evaluate the accuracy of 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations with a revised k-ε model for calculating mean wind-velocity patterns over this type of natural complex terrain; and (2) to provide mean velocity data that can be used as input for real-time ship manoeuvring simulations to evaluate accessing the LNG terminal with larger LNG carriers. The irregular hilly terrain is expected to yield complex wind environmental conditions in the channel and complex forces on the LNG carriers. The study focuses on high wind speed conditions, for which the atmospheric boundary layer exhibits neutral stratification. The simulations are performed with 3D steady RANS and the realisable k-ε model for 12 wind directions. Special attention is given to surface roughness parameterisation and specification. The simulation results of mean wind speed and wind direction are generally within 10-20% of the corresponding measurement values. The results show that for wind directions 60° and 90°, the funnelling effect leads to an increase of wind speed in the channel compared to the wind speed over open sea. For other wind directions, the topography leads to a reduction of the wind speed in the channel, but also to strong wind speed gradients along the channel axis, which are important for ship manoeuvring. The study shows that for the present application, the 3D steady RANS approach with the realisable k-ε model can provide an accurate assessment of the complex mean wind-flow patterns and the funnelling effect by the natural complex topography on the wind.