Numerical Experiments of Atmospheric Boundary Layer flows:interplay between distributed drag elements and buoyancy effects

• Main Author: Sharma, Varun
• Format: Text
• Language: English
• Published: Lausanne, EPFL 2018
• Subjects: Antarc*; Antarctica
• Online Access: http://infoscience.epfl.ch/record/253069; https://doi.org/10.5075/epfl-thesis-8409; https://infoscience.epfl.ch/record/253069/files/EPFL_TH8409.pdf

Anthropogenic emissions of greenhouse gases due to human activity is causing global warming and inducing climate change. A major implication of global warming is the decreasing ice mass in the polar regions resulting in sea-level rise. It is now known that sublimation of drifting and blowing snow is one of the dominant terms of the mass balance of Antarctica. There are various efforts underway to curtail greenhouse gas emissions and mitigate the impact of global warming. One of the most promising solutions involves using non-polluting renewable sources of electricity. Global wind energy estimates have been shown to be far in excess of current and projected energy requirements. From a fluid dynamics perspective, turbulence in the lowest region of the atmosphere, known as the Atmospheric boundary layer (ABL) exerts significant control on both wind energy extraction systems as well as drifting and blowing snow particles, both of which can be considered as distributed drag elements that act as a sink of momentum. The first part of the thesis is concerned with large-eddy simulations (LES) of the turbulent, time-varying ABL with an immersed wind farm. First, a new time-adaptive wind turbine model for LES is introduced that enables the wind turbines to yaw and realign with the incoming wind vector, similar to real wind turbines. The performance of the new model is tested with in a neutrally-stratified ABL forced with a time varying geostrophic wind as well as a synthetic time-changing thermal ABL. Next, the effect of extensive terrestrial wind farms on the spatio-temporal structure of the diurnally-evolving ABL is explored. It is shown that extensive wind farms substantially perturb the vertical structure of the stable boundary layer and the dynamics of the `morning' transition. The effect of these perturbations on the potential power output of an extensive wind farm output is also analysed. Finally, flow characteristics through finite-sized wind farms and the influence of the wind-farm configuration on modulating this ...