The physical planning, spacing and location of individual turbines are important factors in the design of wind farms to increase their efficiency and decrease any kind of negative turbulence and wake effects. It is well know that wind turbine aerodynamics can create significant turbulence and downstream wakes. These turbine-induced turbulence losses subsequently encountered by downstream wind turbines can be due to two different phenomenon. The first is from the operational, power-producing rotating blades of upstream wind turbines that agitate the subsequent downstream wind, often in a cork-screw like manner, thus generating a downstream wake. These wake effects from turbines not optimally located within a wind farm can be significant. The electricity generated from any downstream turbines impacted by these dynamically operating upstream turbines will be reduced, as will be the profits of the wind farm. The second is from turbine-induced turbulence/wake losses of non-rotating wind turbines, which are not operational and not generating power. These stationary, non-operating turbines in this condition are from either temporarily scheduled maintenance or servicing shutdown (which is typically required by the turbine manufacturer after certain specified operational hours). Or they are rendered non-functional due to other longer-term operational problems that have forced the wind farm operator to take those turbines out of service.   

Interestingly, however, the study of downstream turbulence and wake effects of non-operational wind turbines is not well documented, and infrequently discussed in the literature. Though non-operational turbines may be on only a temporary maintenance or service shutdown, their subsequent wakes are of a different nature and duration than those of operational wind turbine wakes. Computational Fluid Dynamics (CFD) is a foundational analytical tool used to help predict and describe both boundary layer behavior and the resulting downstream turbulence for both upstream turbines and the impacted downstream turbines. In this work, the authors, using CFD, focus on studying the downstream turbulence and wakes of non-operational Horizontal Axis Wind Turbines (HAWTs) to understand their nature and intensity.

For this analysis a flow field was constructed using an unstructured grid mesh of a typical fixed, non-rotating, three-blade HAWT that was designed using SolidWorks. The rotor elevation was defined at 80 meters, with a blade length of 40 meters. Various wind velocities were studied up to a typical utility-scale wind turbine “Cut-Off” speed of 25 meters per second. Navier-Stokes equations were solved for incompressible flow to assess downstream turbulence using a three-dimensional unsteady state SST k-ω (two equation) turbulence model within ANSYS Fluent (SIMPLE solution method). Two different non-rotating blade positions with respect to angle of attack (α) were studied, with one configuration at a 4 degree angle of attack, and one with a “feathered blade” into the wind (thus minimizing turbulence around the blade). Pressures and velocities for distances of 100 meters in front of the non-operating wind turbine and 700 meters downstream from the wind turbine were studied. The authors review how such conditions can impact the CFD downstream output results.


A Computational Fluid Dynamics Analysis of Turbulence and Wakes of Horizontal Axis Wind Turbines During Non-Operational Time Periods

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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