Experimental and Numerical Modelling of Flow over Complex Terrain: The Bolund Hill

Abstract

In the wind-energy sector, wind-power forecasting, turbine siting, and turbinedesign selection are all highly dependent on a precise evaluation of atmospheric wind conditions. On-site measurements provide reliable data; however, in complex terrain and at the scale of a wind farm, local measurements may be insufficient for a detailed site description. On highly variable terrain, numerical models are commonly used but still constitute a challenge regarding simulation and interpretation. We propose a joint state-of-the-art study of two approaches to modelling atmospheric flow over the Bolund hill: a wind-tunnel test and a large-eddy simulation (LES). The approach has the particularity of describing both methods in parallel in order to highlight their similarities and differences. The work provides a first detailed comparison between field measurements, wind-tunnel experiments and numerical simulations. The systematic and quantitative approach used for the comparison contributes to a better understanding of the strengths and weaknesses of each model and, therefore, to their enhancement. Despite fundamental modelling differences, both techniques result in only a 5 % difference in the mean wind speed and 15 % in the turbulent kinetic energy (TKE). The joint comparison makes it possible to identify the most difficult features to model: the near-ground flow and the wake of the hill. When compared to field data, both models reach 11 % error for the mean wind speed, which is close to the best performance reported in the literature. For the TKE, a great improvement is found using the LES model compared to previous studies (20 % error). Wind-tunnel results are in the low range of error when compared B Boris Conan 123 B. Conan et al.to experiments reported previously (40 % error). This comparison highlights the potential of such approaches and gives directions for the improvement of complex flow modelling.

Effect of Reynolds number and inflow parameters on mean and turbulent flow over complex topography

“…Studies of the wind flow over Bolund Hill include the original field campaign , follow-up lidar measurements of the escarpment wake (Lange et al, 2016a), computational and physical modelling of the hill as a part of the blind comparison test , wind tunnel modelling (Yeow et al, 2015), LES modelling (Diebold et al, 2013), and wind tunnel and LES modelling (Conan et al, 2016). During the field campaign, measurements were taken via 35 anemometers on 10 masts, positioned along two main incoming flow directions referred to as line A (239 • ) and line B (270 • ).…”

“…These include wind tunnel and water channel experiments from the blind comparison , wind tunnel PIV and three-component hot-wire (3CHW) tests conducted by Yeow et al (2015) on a 1 : 115 scale at two Reynolds numbers (4.15 × 10 4 and 8.21 × 10 4 ), and wind tunnel PIV modelling conducted by Conan et al (2016) on a 1 : 500 scale and Re = 2.1 × 10 4 . Benchmarking the WindEEE Cobra probe and PIV and the BLWTL Cobra probe results from the present experiment against these data sets provides some validation of the present experimental procedure and also serves as an initial point of discussion on the differences between conducting the same experiment on three scales, i.e.…”

Sound propagation through the wake flow of a hilltop wind turbine—A numerical study

“…The growing demand for wind energy gave rise to more detailed investigations of the airflow over hills, its impact on the wind energy potential, and consequences to the wake flow. Comprehensive surveys of this kind were the Askervein Hill Project in 1982/1983 and the Bolund Experiment in 2007/2008. A further field experiment was planned within the NEWA project and conducted in 2017 near Perdigão/Portugal.…”

“…potential, and consequences to the wake flow. Comprehensive surveys of this kind were the Askervein Hill Project 21 in 1982/1983 and the Bolund Experiment 22,23 in 2007/2008. A further field experiment was planned within the NEWA project 24 and conducted in 2017 near Perdigão/Portugal.…”

Wind Turbine Control Based on Computational Fluid Dynamics (CFD) and Its Economic Effects

“…One technical issue which needs to be resolved in the near future in the field of wind power generation is to establish a numerical wind synopsis prediction technique which allows 1) accurate assessment of the local wind synopsis for wind turbines and 2) identification of local wind risks (terrain-induced turbulence) to wind turbines [1][2][3][4][5][6][7][8] .…”