Modeling of wind turbine wakes under thermally-stratified atmospheric boundary layer

El‐Askary, W. A.; Sakr, I.M.; Abdelsalam, Ali M.; Abuhegazy, Mohamed

doi:10.1016/j.jweia.2016.11.001

Cited by 30 publications

(15 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…El-Askary et al [14] are investigated, and the models are hereafter referred to as the AM, Laan and El-Askary models, respectively. The TKE source term S ε,ABL is added in the Laan model and its modified model (the proposed model) to keep flow homogeneity under stable conditions.…”

Section: Turbulence Modelingmentioning

confidence: 99%

“…In the AM model and the El-Askary model, S k,ABL = 0. For stable cases, C ε3 is set to -2.9 in the AM model [15] and set to 1 in the El-Askary model [14].…”

Section: Turbulence Modelingmentioning

confidence: 99%

“…Besides field measurements and wind tunnel experiments of wind turbine wakes under non-neutral conditions, numerical models based on the computational fluid dynamics (CFD) have also been used to investigate the effect of atmospheric stability on the wind turbine wakes [1,[9][10][11][12][13][14] .High-fidelity large eddy simulations with the actuator line model (AL-LES) [9,10] or the actuator disk model (AD-LES) [1,11] are commonly used to study the structure and dynamics of wind turbine wakes in varying stability cases. This is mainly because that the LES approaches allow to capture the near wake structure, resolve the interactions of tip vortices with large-scale eddies of the ambient flow and wake meandering.…”

Section: Introductionmentioning

confidence: 99%

“…In Prospathopoulos et al [13], an additional buoyancy production based on the Richardson number Ri was added to the turbulent kinetic energy equation to model wind turbine wakes under stable conditions. El-Askary et al [14] further used this model and additionally applied a dissipation source term to investigate the wake behavior at different atmospheric stability conditions.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Monin-Obukhov Similarity Theory for Modeling of Wind Turbine Wakes under Atmospheric Stable Conditions: Breakdown and Modifications

Han

Liu

et al. 2019

Preprint

View full text Add to dashboard Cite

Monin-Obukhov similarity theory (MOST) overestimates wind shear in some atmospheric stable conditions, i.e. Richardson number $R_f<0.25$. The overestimated wind shear that leads to an under-predicted friction wind speed and a lower ambient turbulence intensity for a given hub-height reference wind speed and a given roughness length, could influence wake modeling of a wind turbine. This work investigates the side effects of the breakdown of MOST on wake modeling under stable conditions and makes some modifications to the flow similarity functions to eliminate these side effects. Based on a field measurement in a wind farm, we firstly show that MOST predicts a larger wind shear for the atmospheric stability parameter $\zeta>0.1$ and proposes new flow similarity functions without constraining $R_f$ to limit the overestimated wind shear by MOST. Next, different turbulence models based on MOST and a modified one based on the new similarity functions are investigated through numerical simulations. These turbulence models are combined with the actuator disk model (AD) and Reynolds-averaged Navier–Stokes equations (RANS) to model wind turbine wakes under stable conditions. As compared to measurements, numerical results show that turbulence models based on MOST result in larger wake deficits and slower wake recovery rate with a square root of the mean-squared-error (RSME) of wake deficit in the range of 0.07-0.18. This overestimated wake effect is improved by applying the new similarity functions and the RSME of wake deficit is averagely reduced by 0.05. Finally, we check the role of the under-predicted turbulence intensity playing in the larger wake deficit predicted by models based MOST. Additional numerical simulations using the modified turbulence model are carried out, in which the roughness length is reduced to impose a hub-height ambient turbulence intensity equivalent to the MOST case. Simulation results show that reducing turbulence intensity enhances wake effects, however, it cannot reproduce the large wake deficit predicted by models based on MOST, which suggests that the overestimated wake effect by MOST could be also related to the overestimated wind shear.

show abstract

Section: Turbulence Modelingmentioning

confidence: 99%

“…In the AM model and the El-Askary model, S k,ABL = 0. For stable cases, C ε3 is set to -2.9 in the AM model [15] and set to 1 in the El-Askary model [14].…”

Section: Turbulence Modelingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Monin-Obukhov Similarity Theory for Modeling of Wind Turbine Wakes under Atmospheric Stable Conditions: Breakdown and Modifications

Han

Liu

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…also used Equation (14), but set the parameter to be 0.37 for calculating the wind turbine wakes. Since then, this value (C 4ε = 0.37) has begun to use for wind turbine simulation in ABL [50] or thermally-stratified ABL [51], the wake of tidal turbine was also studied by using this constant [52]. However, the influence of the blade on the inflow is not uniform, owing to the blade which is combined with different shapes of airfoil.…”

Section: Turbulence Model Source Termmentioning

confidence: 99%

Actuator Disc Approach of Wind Turbine Wake Simulation Considering Balance of Turbulence Kinetic Energy

et al. 2018

View full text Add to dashboard Cite

The operation of the wind turbines downstream is affected by the wake of the wind turbines upstream. Wind turbine wake flow is investigated by applying the actuator disc (AD) method. The modified k-ε turbulence model is proposed by using both the turbulent kinetic energy source term and the dissipation rate source term to improve the standard k-ε turbulence model for coordinating the generation and the dissipation of the turbulent kinetic energy. The dissipation rate parameter C 4ε that obeys a parabolic distribution is used, based on theoretical analysis. The force distributed on the AD is also used instead of a constant, as used in the classical AD method. The simulation results were consistent with the measurements that correspond to different kinds of wind turbines and conditions. The nacelle and the inflow turbulence intensity have great influences on accurately simulating the wake, so it is necessary to imitate the rotor along with the nacelle and accurately measure the inflow turbulence intensity. been continually developing [11]. The engineering "wake model" was established earlier and has a simple structure and short calculation time. The most famous Jensen model, which is also the basic model of the commonly used commercial wind resources software WAsP, was proposed to evaluate the wind turbine wakes on flat terrain [12]. The eddy viscosity model appeared as another analytical wind turbine wakes model and was used in the commercial wind resources software WindFarmer belonging to the Garrad Hassan company [13]. These models are based on assumptions of the flow behavior, such as axisymmetry and self-similarity. They work fast and are suitable for engineering applications, but they cannot predict wake accurately. The blade model can be constructed directly in the flow field and used to precisely calculate the load of the wind turbine and other aspects related to wind turbine performance [14]. Qian Y.R. used this method to predict the air-load with different wind speeds under yaw conditions [15]. However, this method needs more grids around the blade and a lot of computing resources; therefore, it does not apply to multiple wind turbines or wind farm scales. The actuator line model simplifies the blade into a line which is rotated as the blade, then constructs a functional relationship between the aerodynamic data of the blade's local section airfoil and body force, so that it can simulate the interaction between the blade and the inflow [16]. The actuator line model, combined with the large eddy simulation (LES) method, was used to investigate the near wake region and explain the reason why the velocity deficit and turbulence intensity increase nearby the rotor [17]. Storey R.C. coupled the model with multi-physics method in order to research the wind turbine performance under transient conditions [18]. The actuator line model also can demonstrate the wake of the wind turbine over complex terrain and reduce the cost of wind farm simulation to a certain extent [19], but it still takes a lot of computing res...

show abstract

Large eddy simulations of wind turbine wakes in typical complex topographies

Liu

Ishihara

2020

Wind Energy

View full text Add to dashboard Cite

There is a need to clarify the coupling characteristics of terrain-induced wind fields and wind turbine-induced wake in wind farm micrositing. However, research investigating the effect of hill shape on this interaction is lacking. In addition, during the optimization of the layout of the turbines over topographies, the flow behind the turbines should be predicted in a fast way. After obtaining the wake flow of the turbine mounted on flat terrain and the flow over the topographies, there are mainly two superposition methods to predict the turbine wake flow over the topographies.One is to add the wind deficit following the location with a vertical distance of the hub height (D-line). The other is to add the wind deficit following the streamline starting from the turbine center (B-line). It remains unknown to what extent these two superposition methods can be adopted. Therefore, the effects of hill shape, wind turbine size, and turbine location are investigated. When the wind deficit, obtained from modeling the wake flow of the turbine mounted on flat terrain, is superposed following B-line, the results are overall better than those when following D-line.

show abstract

Modeling of wind turbine wakes under thermally-stratified atmospheric boundary layer

Cited by 30 publications

References 25 publications

Monin-Obukhov Similarity Theory for Modeling of Wind Turbine Wakes under Atmospheric Stable Conditions: Breakdown and Modifications

Monin-Obukhov Similarity Theory for Modeling of Wind Turbine Wakes under Atmospheric Stable Conditions: Breakdown and Modifications

Actuator Disc Approach of Wind Turbine Wake Simulation Considering Balance of Turbulence Kinetic Energy

Large eddy simulations of wind turbine wakes in typical complex topographies

Contact Info

Product

Resources

About