CgWind is a new, high-ﬁdelity simulation tool designed to meet the modeling requirements of advanced wind energy resources. These new resources, targeting 20% of the US electrical supply by 2030, require the development of larger and lighter wind turbines as well as more accurate estimates for the performance of turbines in realistic terrain and atmospheric conditions.
To model such systems, CgWind couples large eddy simulation (LES) models, based on the incompressible Navier-Stokes equations, with moving grid techniques that resolve the ﬂow near the turbine blades. Both LES and detached eddy simulation methods will be available in CgWind. In particular, CgWind is incorporating nonlinear LES models that capture anisotropy at the sub-grid-scale and are well-suited for atmospheric boundary layer ﬂows. The new modeling framework enables the use of advanced numerical methods to design and predict the performance of individual wind turbines and large-scale wind parks.
CgWind’s technology exploits the composite grid approach, which leverages the computational beneﬁts of overlapping, structured grids to represent complex geometry. These grids are ideal for the high-order accurate compact discretizations used by CgWind as well as the matrix-free geometric multi-grid algorithm that enables large-scale, high-resolution computations with realistic geometry. The composite grid approach, also known as overlapping or Chimera grids, provides a natural and efﬁcient mechanism for modeling bodies in relative motion. Each turbine blade and tower is meshed independently with high-quality, structured grids and assembled automatically into a collection of overlapping grids. When the geometry moves (e.g., the blades rotate or deform), the new configuration undergoes local regridding, which is orders of magnitude faster than the global remeshing methods used in many unstructured mesh approaches.