Wind Tunnel Modelling and Computational Fluid Dynamics Simulation of Wind Flow Over 3-D Hills

Abstract

The knowledge of wind flow over hills is essential for siting wind turbines, assessing aviation safety, designing structures, and predicting wind damage of crops in mountainous regions. The current knowledge is mainly based on field measurements, wind tunnel experiments and numerical simulation of three-dimensional isolated hills with moderate slopes without flow separation. However, most of the hills in natural environment are with steep slopes and cause flow separation on hill slopes. The flow separation significantly influences speed and turbulence of wind flow thus is an important flow phenomenon in the flow field near mountains. This study aims to investigate how flow separation modifies wind speed and turbulence intensities near 3-D isolated hills using wind tunnel experiments and computational fluid dynamic (CFD) simulations. Five isolated 3-D hills with generic shapes and an aspect ratio (A) (i.e., the ratio between characteristic hill length scale in longitudinal and lateral directions) of 1, 2, 3, 1/2, and 1/3 were manufactured as stepped models in a length scale of 1:500 and were tested in a boundary layer wind tunnel. The maximum hill slope of hills with A = 1, 2, and 3 was 15o and A = 1/2 and 1/3 were 28o and 38o, respectively. The three-component mean wind speeds and turbulence intensities were recorded at various heights over hills using a Cobra probe (TFI® series 100). The wind flow near 3-D hills was modeled in CFD simulation using Reynolds-Averaged Navier Stokes (RANS) equations with a k-ε turbulence closure model.