Abstract: Wind energy has the capacity to become a disruptive renewable energy technology that can dominate the world’s electric energy production portfolio. Realizing this goal, however, necessitates broadening the focus of research from the individual turbine to integrated, interconnected multi-turbine wind parks.  In this talk I will discuss the challenges and opportunities for high-fidelity modeling as a powerful tool for enabling wind-farm optimization and will introduce the University of Minnesota Virtual Wind Simulator (VWiS), a high-fidelity, multi-resolution, fluid-structure interaction computational framework for carrying out large-eddy simulation of atmospheric turbulence past land-based and offshore wind-farms in arbitrarily complex terrains. I will present new insights into the large-scale dynamics of axial turbine wakes gained by high-fidelity simulations resolving all geometrical details of the turbine.  The simulations reveal that the counter-rotating (relative to the turbine) hub vortex can undergo spiral vortex breakdown in the near wake.  The slowly precessing spiral hub vortex intercepts and energizes the top-tip shear layer at approximately 2-3 rotor diameter downwind providing the mechanism for augmenting the extent and intensity of the wake meandering region in the far wake.  I will demonstrate the inherent inability of the widely used today actuator line parameterization of wind turbines to capture this complex near/far wake interaction and underscore the need for developing improved reduced-order models of turbine blades in order to enable accurate and efficient simulations of multi-turbine wind farms. Bio: Fotis Sotiropoulos is the James L. Record Professor of Civil Engineering and the director of the St. Anthony Falls Laboratory at the University of Minnesota, Twin Cities. He is also the director of the DOE-funded University of Minnesota EOLOS Wind Energy Research consortium.  Sotiropoulos received a BS in Mechanical Engineering from the National Technical University of Athens in 1987, a MS in Aerospace Engineering from the Penn State University in 1989, and a PhD in Aerospace Engineering from the University of Cincinnati in 1991.  His research is aimed at developing computational techniques, which take advantage of high-performance supercomputers, to tackle a wide range of interdisciplinary fluid mechanics problems in renewable energy, environmental, biological, and cardiovascular applications.  Sotiropoulos has authored and co-authored over 130 peer reviewed journal papers and book chapters.  His research is sponsored by NSF, DOE, Sandia National Laboratories, and the private industry.  Sotiropoulos is a fellow of the American Physical Society (APS), he has won twice the APS Division of Fluid Dynamics Gallery of Fluid Motion (2009, 2011), and is a recipient of a Career award from the US National Science Foundation. He is also a 2014 distinguished lecturer of the Mortimer and Raymond Sackler Institute of Advanced Studies at Tel Aviv University and is serving on the editorial boards of the ASCE Journal of Hydraulic Engineering, the ASME Journal of Biomechanical Engineering, the International Journal of Heat and Fluid Flow, and Computers and Fluids Host: Prof. Igor Mezic