Invited talk: Laboratory Studies of Wind Turbines – High Reynolds Number Aerodynamics

Wind turbines and wind farms present unique challenges, fluid mechanically, as they combine extremely high Reynolds numbers with additional time scales imposed by the rotation and three-dimensional effects. This implies that resolved numerical solutions are too computationally expensive and investigations in conventional wind tunnels are impossible due to the flow speeds and rotational rates needed in order to satisfy the dynamic similarity requirements. At Princeton, we achieve the conditions a large wind turbine experiences, experimentally, by compressing the air around a model-scale turbine up to 238 bar. This yields conditions similar to those experienced by a field-sized turbine using a model that is only 20cm in diameter. Using pressure enables tests at high Reynolds numbers but at low velocities, which implies that realistic non-dimensional frequencies can be tested even with such a small model. The power output and forces are investigated over an unprecedented range of Reynolds numbers, and it is shown that aerodynamic scale-effects persist at higher Reynolds numbers than previously believed, and that the boundary layer state is critical for turbine performance.

Marcus Hultmark is associate professor in the Department of Mechanical and Aerospace Engineering at Princeton University and director of the Princeton Gas Dynamics Laboratory.  His research interests include a variety of problems related to fluid mechanics, with focus on problems involving turbulence, such as heat and mass transfer as well as drag reduction and wind energy. Experimental studies are combined with theoretical work, and an important part of his research program is the development and evaluation of new sensing techniques to investigate these phenomena with high accuracy and resolution.  He was awarded the 2016 Air Force Young Investigator award, the 2017 NSF Career award and in 2017 he received the Nobuhide Kasagi Award. He received his M.Sc. degree from Chalmers University in 2007 and his Ph.D. from Princeton University in 2011.