CFD Modeling of Non-Neutral Atmospheric Boundary Layer Conditions

Tilman Koblitz

Research output: Book/ReportPh.D. thesisResearch

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For wind resource assessment, the wind industry is increasingly relying on Computational Fluid Dynamics models that focus on modeling the airflow in a neutrally stratified surface-layer. Physical processes like the Coriolis force, buoyancy forces and heat transport, that are important to the atmospheric boundary-layer, are mostly ignored so far. In order to decrease the uncertainty of wind resource assessment, the present work focuses on atmospheric flows that include atmospheric stability and the Coriolis effect. Within the present work a RANS model framework is developed and implemented into the DTU Wind Energy flow solver EllipSys3D. The high Reynolds number flows considered in this work are based on the solution of the Reynolds-Averaged Navier-Stokes equations. Together with a two-equation closure method the flow within the whole boundary-layer can be computed at a much lower computational cost than e.g. using large-eddy simulations.
The developed ABL model is successfully validated using a range of different test cases with increasing complexity. Data from several large scale field campaigns, wind tunnel experiments, and previous numerical simulations is presented and compared against model results. A method is developed how to simulate the time-dependant non-neutral ABL flow over complex terrain: a precursor simulation is used to specify unsteady inlet boundary conditions on complex terrain domains. The advantage of the developed RANS model framework is its general applicability. All implementations in the ABL model are tuning free, and except for standard site specific input parameters, no additional model coefficients need to be specified before the simulation. In summary the results show that the implemented modifications are applicable and reproduce the main flow characteristics of neutral and non-neutral ABL flow. The developed ABL model significantly improves the predicted flow fields over both flat and complex terrain, when compared against neutral models and measurements.
Original languageEnglish
PublisherDTU Wind Energy
Number of pages104
ISBN (Electronic)978-87-92896-49-0
Publication statusPublished - 2013
SeriesDTU Wind Energy PhD


  • DTU Wind Energy PhD-0019(EN)
  • DTU Wind Energy PhD-0019

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