Large and detached eddy simulation of separated flow over 3D hill geometries with surface roughness to mimic flows over complex terrains

etc15 Tracking Number 468

With the push to making wind power a significant contributor to the energy portfolio in the U.S. and Europe, there is considerable effort to deploy the currently available peta-scale computational resources to assess and improve well known simulation techniques, such as the large eddy simulation (LES) and detached eddy simulation (DES) techniques, to model the complex flows in wind farms, taken as a whole, as opposed to individual wind turbines. Simulating turbulent flows in wind farms, consisting of arrays of wind turbines, begins with the modeling and simulation of the atmospheric boundary layer (ABL) over complex terrain that is characterized by regions of separated flow with a high degree of turbulence anisotropy. Over the years there has been considerable work on applying LES and Reynolds Averaged Navier--Stokes (RANS) simulations over terrain geometries, such as the Askervein Hill, to understand turbulence closure models for flow over complex terrain. Such studies, however, have had limited success due to difficulties associated with the closure models in the near wall region of the flow. At the same time, turbulence simulations over \emph{canonical} geometries, such as the periodic and axisymmetric hills, have been shown to compare well with data obtained from laboratory scale experiments, where the inflow turbulence and boundary conditions are better characterized and defined respectively. In an effort to extend these canonical flows to be more representative of flows over complex terrain, this paper aims to present results of large and detached eddy simulations of separated flow over three dimensional hill geometries with roughness parametrization, with the objective of developing better closure models for flow over complex terrain.