Wind Turbine Boundary Layers Near the Hub

2006 ◽  
Author(s):  
Pasquale Sforza
Keyword(s):  
Wind Turbine ◽  
Boundary Layers

scholarly journals The impact of stable atmospheric boundary layers on wind-turbine wakes within offshore wind farms

2015 ◽  
Vol 144 ◽  
pp. 146-153 ◽  
Author(s):  
Martin Dörenkämper ◽  
Björn Witha ◽  
Gerald Steinfeld ◽  
Detlev Heinemann ◽  
Martin Kühn
Keyword(s):  
Wind Turbine ◽  
Boundary Layers ◽  
Wind Farms ◽  
Offshore Wind ◽  
Atmospheric Boundary Layers ◽  
Offshore Wind Farms ◽  
The Impact

Space–time VMS method for flow computations with slip interfaces (ST-SI)

2015 ◽  
Vol 25 (12) ◽  
pp. 2377-2406 ◽  
Author(s):  
Kenji Takizawa ◽  
Tayfun E. Tezduyar ◽  
Hiroki Mochizuki ◽  
Hitoshi Hattori ◽  
Sen Mei ◽  
...  
Keyword(s):  
High Resolution ◽  
Wind Turbine ◽  
Boundary Layers ◽  
Vertical Axis ◽  
3D Models ◽  
Space Time ◽  
Arbitrary Lagrangian Eulerian ◽  
Vertical Axis Wind Turbine ◽  
Starting Point ◽  
Sliding Interfaces

We present the space–time variational multiscale (ST-VMS) method for flow computations with slip interfaces (ST-SI). The method is intended for fluid–structure interaction (FSI) analysis where one or more of the subdomains contain spinning structures, such as the rotor of a wind turbine, and the subdomains are covered by meshes that do not match at the interface and have slip between them. The mesh covering a subdomain with the spinning structure spins with it, thus maintaining the high-resolution representation of the boundary layers near the structure. The starting point in the development of the method is the version of the arbitrary Lagrangian–Eulerian VMS (ALE-VMS) method designed for computations with "sliding interfaces". Interface terms similar to those in the ALE-VMS version are added to the ST-VMS formulation to account for the compatibility conditions for the velocity and stress. In addition to having a high-resolution representation of the boundary layers, because the ST framework allows NURBS functions in temporal representation of the structure motion, we have exact representation of the circular paths associated with the spinning. The ST-SI method includes versions for cases where the SI is between fluid and solid domains with weakly-imposed Dirichlet conditions for the fluid and for cases where the SI is between a thin porous structure and the fluid on its two sides. Test computations with 2D and 3D models of a vertical-axis wind turbine show the effectiveness of the ST-SI method.

scholarly journals On the Wind Turbine Wake and Forest Terrain Interaction

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7204
Author(s):  
Shyuan Cheng ◽  
Mahmoud Elgendi ◽  
Fanghan Lu ◽  
Leonardo P. Chamorro
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Boundary Layers ◽  
Wind Turbines ◽  
Quadrant Analysis ◽  
Optimized Design ◽  
Incoming Flow ◽  
High Background ◽  
Forest Density ◽  
Turbine Wake

Future wind power developments may be located in complex topographic and harsh environments; forests are one type of complex terrain that offers untapped potential for wind energy. A detailed analysis of the unsteady interaction between wind turbines and the distinct boundary layers from those terrains is necessary to ensure optimized design, operation, and life span of wind turbines and wind farms. Here, laboratory experiments were carried to explore the interaction between the wake of a horizontal-axis model wind turbine and the boundary layer flow over forest-like canopies and the modulation of forest density in the turbulent exchange. The case of the turbine in a canonical boundary layer is included for selected comparison. The experiments were performed in a wind tunnel fully covered with tree models of height H/zhub≈0.36, where zhub is the turbine hub height, which were placed in a staggered pattern sharing streamwise and transverse spacing of Δx/dc=1.3 and 2.7, where dc is the mean crown diameter of the trees. Particle image velocimetry is used to characterize the incoming flow and three fields of view in the turbine wake within x/dT∈(2,7) and covering the vertical extent of the wake. The results show a significant modulation of the forest-like canopies on the wake statistics relative to a case without forest canopies. Forest density did not induce dominant effects on the bulk features of the wake; however, a faster flow recovery, particularly in the intermediate wake, occurred with the case with less dense forest. Decomposition of the kinematic shear stress using a hyperbolic hole in the quadrant analysis reveals a substantial effect sufficiently away from the canopy top with sweep-dominated events that differentiate from ejection-dominated observed in canonical boundary layers. The comparatively high background turbulence induced by the forest reduced the modulation of the rotor in the wake; the quadrant fraction distribution in the intermediate wake exhibited similar features of the associated incoming flow.

scholarly journals Evaluation of tilt control for wind-turbine arrays in the atmospheric boundary layer

2021 ◽  
Vol 6 (3) ◽  
pp. 663-675
Author(s):  
Carlo Cossu
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Turbine ◽  
Boundary Layers ◽  
High Speed ◽  
Large Scale ◽  
Passive Control ◽  
Vertical Wind Shear ◽  
Large Power ◽  
Turbine Arrays

Abstract. Wake redirection is a promising approach designed to mitigate turbine–wake interactions which have a negative impact on the performance and lifetime of wind farms. It has recently been found that substantial power gains can be obtained by tilting the rotors of spanwise-periodic wind-turbine arrays. Rotor tilt is associated with the generation of coherent streamwise vortices which deflect wakes towards the ground and, by exploiting the vertical wind shear, replace them with higher-momentum fluid (high-speed streaks). The objective of this work is to evaluate power gains that can be obtained by tilting rotors in spanwise-periodic wind-turbine arrays immersed in the atmospheric boundary layer and, in particular, to analyze the influence of the rotor size on power gains in the case where the turbines emerge from the atmospheric surface layer. We show that, for the case of wind-aligned arrays, large power gains can be obtained for positive tilt angles of the order of 30∘. Power gains are substantially enhanced by operating tilted-rotor turbines at thrust coefficients higher than in the reference configuration. These power gains initially increase with the rotor size reaching a maximum for rotor diameters of the order of 3.6 boundary layer momentum thicknesses (for the considered cases) and decrease for larger sizes. Maximum power gains are obtained for wind-turbine spanwise spacings which are very similar to those of large-scale and very-large-scale streaky motions which are naturally amplified in turbulent boundary layers. These results are all congruent with the findings of previous investigations of passive control of canonical boundary layers for drag-reduction applications where high-speed streaks replaced wakes of spanwise-periodic rows of wall-mounted roughness elements.

scholarly journals Hybrid RANS/LES Turbulence Model Applied to a Transitional Unsteady Boundary Layer on Wind Turbine Airfoil

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 128
Author(s):  
Di Zhang ◽  
Daniel R. Cadel ◽  
Eric G. Paterson ◽  
K. Todd Lowe
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Wind Turbine ◽  
Boundary Layers ◽  
Turbulence Model ◽  
Model Problem ◽  
Local Flow ◽  
Flow Angle ◽  
Eddy Simulation ◽  
Large Eddy

A hybrid Reynolds-averaged Navier Stokes/large-eddy simulation (RANS/LES) turbulence model integrated with a transition formulation is developed and tested on a surrogate model problem through a joint experimental and computational fluid dynamic approach. The model problem consists of a circular cylinder for generating coherent unsteadiness and a downstream airfoil in the cylinder wake. The cylinder flow is subcritical, with a Reynolds number of 64,000 based upon the cylinder diameter. The quantitative dynamics of vortex shedding and Reynolds stresses in the cylinder near wake are well captured, owing to the turbulence-resolving large eddy simulation mode that was activated in the wake. The hybrid model switched between RANS and LES modes outside the boundary layers, as expected. According to the experimental and simulation results, the airfoil encountered local flow angle variations up to ±50°. Further analysis through a phase-averaging technique found phase lags in the airfoil boundary layer along the chordwise locations, and both the phase-averaged and mean velocity profiles collapsed into the Law-of-the-wall in the range of 0 < y + < 50 . The features of high blade-loading fluctuations due to unsteadiness and transitional boundary layers are of interest in the aerodynamic studies of full-scale wind turbine blades, making the current model problem a comprehensive benchmark case for future model development and validation.

Anisotropy stress invariants of thermally stratified wind turbine array boundary layers using large eddy simulations

2018 ◽  
Vol 10 (1) ◽  
pp. 013301 ◽  
Author(s):  
Naseem Ali ◽  
Nicholas Hamilton ◽  
Gerard Cortina ◽  
Marc Calaf ◽  
Raúl Bayoán Cal
Keyword(s):  
Wind Turbine ◽  
Boundary Layers ◽  
Large Eddy Simulations ◽  
Large Eddy
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