Large-eddy simulation of wind farms with parameterization of wind turbines is emerging as a powerful tool for improving the performance and lowering the maintenance cost of existing wind farms and assessing potential sites for installation. As a result, Sandia National Laboratories (SNL) is working with the University of Minnesota (UMN) St. Anthony Falls Laboratory to document and prepare the university’s offshore version of the Virtual Wind Simulator (VWiS) code for release.
VWiS is a state-of-the-art, large-eddy code that is capable of simulating atmospheric turbulence interacting with wind farms in both land-based and offshore environments. The code uses the Curvilinear Immersed Boundary method to simulate flow around geometrically complex moving bodies. For wind farm applications, it can either resolve turbine geometrical details or choose from several predefined turbine rotor modeling approaches.
The code has an advanced two-phase flow module based on the level set method that allows simulation of coupled free-surface flows with water waves, winds, and 6-degree-of-freedom (DOF) fluid-structure interaction (FSI) of floating structures. Computational science obtains valuable information by isolating specific elements of a problem or structure and studying their response to real-world forces; however, nature does not operate in such a “vacuum.” Waves can act on a floating turbine structure in one way while the wind impacts it with a different set of loads. These loads can occasionally cancel each other out, but more often can have an additive or magnifying effect. The improved 6-DOF FSI capabilities offered by VWiS can effectively explore these complex, coupled interactions, whereas previous models, because they implemented simplified assumptions, could not capture these interactions.
VWiS can also incorporate the effects of broadband ocean waves via a multiple-scale coupling approach. Figure 1 highlights these complex interactions; a 6-DOF FSI simulation of a floating turbine under real-life ocean waves is shown in Figure 1 (left) with the structural response of the turbine in heave and pitch displayed in Figure 1 (right).
The code is planned for release in September 2015 and will include a detailed manual with several test cases. SNL has been working with UMN to ensure that the test cases are user-friendly and well documented, in addition to reviewing the manual. As an example, one test case is the free-heave decay test of a horizontal cylinder, which validates the coupled FSI algorithm. A figure of the water entry of the cylinder moving with prescribed velocity is shown in Figure 2 (left). An example of a wedge impinging on the free surface is shown on the right.
Read more about the research conducted by SNL and UMN in:
Large-eddy simulation of turbulent flow past wind turbines/farms: the Virtual Wind Simulator (VWiS)