Novel Insights Gained by Numerical Simulations and Field Experiments
Fotis Sotiropoulos, Ph.D.
SUNY Distinguished Professor and Dean
College of Engineering and Applied Sciences
Stony Brook University
Sidney & Marian Green Classroom (3550 MEK)
Abstract: The fundamental structure of coherent vortices in the wake of a N-bladed axial-flow wind turbine rotor has largely been shaped by the basic N+1 vortex model by Jukowski: N spiral tip vortices of circulation Γ and a counter-rotating hub vortex of strength -NΓ. Recent high-fidelity large-eddy simulations (LES) coupled with laboratory and field scale experiments, however, have dramatically expanded this basic understanding and yielded new insights into the rich dynamics of wind turbine wakes and the impact of near-wake phenomena to far wake meandering. The hub vortex has been shown to undergo spiral vortex breakdown undergoing low frequency oscillations and lateral expansion ultimately interacting with the turbine tip shear layer and energizing the intensity of wake meandering several rotor diameters downwind (Kang et al., J. Fluid Mech. 2014). Large-scale snow PIV and LES of utility scale turbines have further uncovered a previously unknown centrifugal instability mode of the turbine tip shear layer, which manifests itself in the form of a second set of spiral vortices with vorticity of opposite sign relative to the spiral tip vortices (Yang et al., J. Fluid Mech. 2016). Standard actuator disk or line models widely used today to parameterize wind turbines in wind farm simulations are not able to capture such phenomena and especially the instability of the hub vortex. To mitigate this major shortcoming, we have developed a new class of actuator surface models that incorporate the turbine nacelle and are able to capture the correct coherent dynamics of the near wake and their impact on far wake meandering (Yang and Sotiropoulos, Wind Energy, 2018). I will present this new class of models, demonstrate their improved predictive capabilities, and discuss implications for large scale simulations of real life wind and tidal energy farms. I will also present a new computational framework that paves the way for high-fidelity simulations of offshore floating wind farms coupling atmospheric turbulence with broadband ocean waves and 6 degree-of-freedom floating platform and turbine dynamics (Calderer et al., J. Comp. Physics, 2018).
- Bio: Fotis Sotiropoulos serves as Dean of the College of Engineering and Applied Sciences and SUNY Distinguished Professor of Civil Engineering at Stony Brook University. Before joining Stony Brook University, he was the James L. Record Professor of Civil Engineering; Director of the St. Anthony Falls Laboratory; and Director of the EOLOS wind energy research consortium at the University of Minnesota, Twin Cities (2006-2015). Prior to that, he was on the faculty of the School of Civil and Environmental Engineering at the Georgia Institute of Technology, with a joint appointment in the G. W. Woodruff School of Mechanical Engineering (1995-2005). His research focuses on simulation-based engineering science for tackling complex, societally relevant fluid mechanics problems in energy, environment and human health applications. He has authored over 190 peer reviewed journal papers and book chapters, has an H-index of 52, and his research results have been featured on the cover of several prestigious journals. He is the 2017 recipient of the Hunter Rouse Hydraulic Engineering Award from the American Society of Civil Engineers, a Fellow of the American Physical Society (APS), and a recipient of a Career Award from the National Science Foundation. He has twice won the APS Division of Fluid Dynamics Gallery of Fluid Motion (2009, 2011), is a 2014 distinguished lecturer of the Mortimer and Raymond Sackler Institute of Advanced Studies at Tel Aviv University and is serving or has served on the editorial boards of several journals.