scholarly journals On the measurement of stability parameter over complex mountainous terrain

2021 ◽  
Author(s):  
Elena Cantero ◽  
Javier Sanz ◽  
Fernando Borbón ◽  
Daniel Paredes ◽  
Almudena García
Keyword(s):  
Richardson Number ◽  
Wind Farm ◽  
Sonic Anemometer ◽  
Atmospheric Stability ◽  
Test Site ◽  
Theoretical Background ◽  
Energy Yield ◽  
Bulk Richardson Number ◽  
Energy Applications ◽  
Two Temperature

Abstract. Atmospheric stability has a significant effect on wind shear and turbulence intensity, and these variables, in turn, have a direct impact on wind power production and loads on wind turbines. It is therefore important to know how to characterize atmospheric stability in order to make better energy yield estimation in a wind farm. Based on research grade meteorological mast at Alaiz (CENER's Test Site in Navarre, Spain) named MP5, this work compares and evaluates different instrument set-ups and methodologies for stability characterization. The Obukhov parameter ζ = z/L, which can be measured locally with the use of a sonic anemometer, and bulk Richardson number have been studied. The methods are examined considering their theoretical background, implementation complexity, instrumentation requirements, and practical use in connection with wind energy applications. Bulk Richardson number, which is based on one height wind speed measurement and two temperature measurements, is sometimes calculated using values from any two temperature levels without taking into account that one of the measurements would be representative of surface conditions. With the data available in MP5, it will be shown how this approximation is not correct to obtain an adequate stability characterization.

Evaluation of methods for estimating atmospheric stability at two coastal sites

2018 ◽  
Vol 42 (6) ◽  
pp. 561-575 ◽  
Author(s):  
Lars Morten Bardal ◽  
Anja Eide Onstad ◽  
Lars Roar Sætran ◽  
John Amund Lund
Keyword(s):  
Surface Layer ◽  
Richardson Number ◽  
Atmospheric Stability ◽  
Stability Conditions ◽  
Bulk Richardson Number ◽  
Wind Speed Profile ◽  
Flux Measurements ◽  
Vertical Wind Speed ◽  
Stability Measurements ◽  
Evaluation Of Methods

Understanding the atmospheric stability conditions is important in order to obtain accurate estimates of the vertical wind speed profile. This work compares and evaluates common methods for estimation of atmospheric stability using standard meteorological mast observations. Atmospheric stability distributions from three different met-masts located at two coastal sites are calculated and compared. The atmospheric stability parameter, L is estimated using the bulk Richardson number, the surface-layer Richardson number, and calculated directly from eddy covariance flux measurements. The resulting distributions vary depending on which method is used. The atmospheric stability measurements from two masts located 3 km apart in similar terrain are compared directly. The highest correlation is found for the surface-layer Richardson number method. This method it also less sensitive to variation of measurement heights than the bulk Richardson number method.

scholarly journals 3-D shear-layer model for the simulation of multiple wind turbine wakes: description and first assessment

2017 ◽  
Vol 2 (2) ◽  
pp. 569-586 ◽  
Author(s):  
Davide Trabucchi ◽  
Lukas Vollmer ◽  
Martin Kühn
Keyword(s):  
Wind Turbine ◽  
Shear Layer ◽  
Wind Farm ◽  
Wind Farms ◽  
Theoretical Background ◽  
Offshore Wind ◽  
Energy Yield ◽  
Main Concern ◽  
Layer Model ◽  
New Model

Abstract. The number of turbines installed in offshore wind farms has strongly increased in the last years and at the same time the need for more precise estimations of the wind farm efficiency too. In this sense, the interaction between wakes has become a relevant aspect for the definition of a wind farm layout, for the assessment of its annual energy yield and for the evaluation of wind turbine fatigue loads. For this reason, accurate models for multiple overlapping wakes are a main concern of the wind energy community. Existing engineering models can only simulate single wakes, which are superimposed when they are interacting in a wind farm. This method is a practical solution, but it is not fully supported by a physical background. The limitation to single wakes is given by the assumption that the wake is axisymmetric. As an alternative, we propose a new shear-layer model that is based on the existing engineering wake models but is extended to also simulate non-axisymmetric wakes. In this paper, we present the theoretical background of the model and four application cases. We evaluate the new model for the simulation of single and multiple wakes using large-eddy simulations as reference. In particular, we report the improvements of the new model predictions in comparison to a sum-of-squares superposition approach for the simulation of three interacting wakes. The lower deviation from the reference considering single and multiple wakes encourages the further development of the model and promises a successful application for the simulation of wind farm flows.

scholarly journals Comparison of Length Scale Parameterization Methodologies

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 89
Author(s):  
Faruk Tuna ◽  
Ferhat Bingöl
Keyword(s):  
Wind Shear ◽  
Richardson Number ◽  
Atmospheric Stability ◽  
The Other ◽  
Length Scale ◽  
Bulk Richardson Number ◽  
Obukhov Length ◽  
Average Value ◽  
Flux Profile

Atmospheric stability has been studied for decades. There are several methodologies that evolved over the years. In this study, a special experimental meteorological mast that has been erected to a complex site has been used to calculate dimensionless Obukhov length ( ζ = z L ) , dimensionless momentum ( φ m ), and heat coefficients ( φ h ). The results are compared with the ones from average value approaches: Richardson number, flux-profile (F-P) relations, and wind shear exponent methods. The results show that the estimated ζ values, using the bulk Richardson number, get along well with the reference ζ within the neutral and stable regimes. F-P relations and wind shear exponent methods result in the best agreement for stable and neutral regimes. Nevertheless, average oriented methods are not reliable for the other regimes.

scholarly journals An intercomparison of mesoscale models at simple sites for wind energy applications

2017 ◽  
Vol 2 (1) ◽  
pp. 211-228 ◽  
Author(s):  
Bjarke T. Olsen ◽  
Andrea N. Hahmann ◽  
Anna Maria Sempreviva ◽  
Jake Badger ◽  
Hans E. Jørgensen
Keyword(s):  
Wind Speed ◽  
Wind Energy ◽  
Wind Farm ◽  
Weather Prediction ◽  
Atmospheric Stability ◽  
Resource Assessment ◽  
Offshore Wind ◽  
Grid Spacing ◽  
Energy Applications ◽  
Wind Resource

Abstract. Understanding uncertainties in wind resource assessment associated with the use of the output from numerical weather prediction (NWP) models is important for wind energy applications. A better understanding of the sources of error reduces risk and lowers costs. Here, an intercomparison of the output from 25 NWP models is presented for three sites in northern Europe characterized by simple terrain. The models are evaluated using a number of statistical properties relevant to wind energy and verified with observations. On average the models have small wind speed biases offshore and aloft (< 4 %) and larger biases closer to the surface over land (> 7 %). A similar pattern is detected for the inter-model spread. Strongly stable and strongly unstable atmospheric stability conditions are associated with larger wind speed errors. Strong indications are found that using a grid spacing larger than 3 km decreases the accuracy of the models, but we found no evidence that using a grid spacing smaller than 3 km is necessary for these simple sites. Applying the models to a simple wind energy offshore wind farm highlights the importance of capturing the correct distributions of wind speed and direction.

scholarly journals Estimating the wake deflection downstream of a wind turbine in different atmospheric stabilities: an LES study

2016 ◽  
Vol 1 (2) ◽  
pp. 129-141 ◽  
Author(s):  
Lukas Vollmer ◽  
Gerald Steinfeld ◽  
Detlev Heinemann ◽  
Martin Kühn
Keyword(s):  
Wind Turbines ◽  
Wind Farm ◽  
Atmospheric Stability ◽  
Wind Farms ◽  
Stability Control ◽  
Energy Yield ◽  
Multiple Sources ◽  
Ambient Wind ◽  
Precise Knowledge ◽  
Temporal Averaging

Abstract. An intentional yaw misalignment of wind turbines is currently discussed as one possibility to increase the overall energy yield of wind farms. The idea behind this control is to decrease wake losses of downstream turbines by altering the wake trajectory of the controlled upwind turbines. For an application of such an operational control, precise knowledge about the inflow wind conditions, the magnitude of wake deflection by a yawed turbine and the propagation of the wake is crucial. The dependency of the wake deflection on the ambient wind conditions as well as the uncertainty of its trajectory are not sufficiently covered in current wind farm control models. In this study we analyze multiple sources that contribute to the uncertainty of the estimation of the wake deflection downstream of yawed wind turbines in different ambient wind conditions. We find that the wake shapes and the magnitude of deflection differ in the three evaluated atmospheric boundary layers of neutral, stable and unstable thermal stability. Uncertainty in the wake deflection estimation increases for smaller temporal averaging intervals. We also consider the choice of the method to define the wake center as a source of uncertainty as it modifies the result. The variance of the wake deflection estimation increases with decreasing atmospheric stability. Control of the wake position in a highly convective environment is therefore not recommended.

scholarly journals 3D Shear layer simulation model for the mutual interaction of wind turbine wakes: Description and first assessment

2017 ◽  
Author(s):  
Davide Trabucchi ◽  
Lukas Vollmer ◽  
Martin Kühn
Keyword(s):  
Wind Turbine ◽  
Shear Layer ◽  
Wind Farm ◽  
Wind Farms ◽  
Theoretical Background ◽  
Offshore Wind ◽  
Energy Yield ◽  
Main Concern ◽  
Offshore Wind Farms ◽  
New Model

Abstract. The number of turbines installed in offshore wind farms has strongly increased in the last years and at the same time the need for more precise estimation of the wind farm efficiency. In this sense, the interaction between wakes has become a relevant aspect for the definition of a wind farm layout, for the assessment of its annual energy yield and for the evaluation of wind turbine fatigue loads. For this reason, accurate models for multiple wakes are a main concern of the wind energy community. Existing engineering models can only simulate single wakes which are superimposed when they are interacting in a wind farm. This method is a practical solution, but it is not fully supported by a physical background. The limitation to single wakes is given by the assumption that the wake is axisymmetric. As alternative, we propose a new shear layer model which is based on the existing engineering wake models, but is extended to simulate also non-axisymmetric wakes. In this paper, we present the theoretical background of the model and two application cases. First, we proved that for axisymmetric wakes the new model is equivalent to a commonly used engineering model. Then, we evaluated the improvements of the new model for the simulation of multiple wakes using large eddy simulations as reference. In particular, we report the improvements of the new model in comparison to a sum-of-squares superposition approach for the simulation of three interacting wakes. The remarkable lower deviation from the reference in terms of rotor equivalent wind speed considering two and three interacting wakes encourages the further development of the model, and promises a successful application for the simulation of wind farms.

scholarly journals Estimating the wake deflection downstream of a wind turbine in different atmospheric stabilities: An LES study

2016 ◽  
Author(s):  
Lukas Vollmer ◽  
Gerald Steinfeld ◽  
Detlev Heinemann ◽  
Martin Kühn
Keyword(s):  
Wind Turbines ◽  
Wind Farm ◽  
Atmospheric Stability ◽  
Wind Farms ◽  
Energy Yield ◽  
Multiple Sources ◽  
Atmospheric Boundary Layers ◽  
Ambient Wind ◽  
Precise Knowledge ◽  
Temporal Averaging

Abstract. An intentional yaw misalignment of wind turbines is currently discussed as one possibility to increase the overall energy yield of wind farms. The idea behind this control is to decrease wake losses of downstream turbines by altering the wake trajectory of the controlled upwind turbines. For an application of such an operational control, precise knowledge about the wind conditions, the magnitude of wake deflection by a yawed turbine and the propagation of the wake is crucial. The dependency of the wake deflection on the ambient wind conditions as well as the uncertainty of its trajectory are not sufficiently covered in current wind farm control models. In this study we analyze multiple sources that contribute to the uncertainty of the estimation of the wake deflection downstream of yawed wind turbines in different ambient wind conditions. We find that the wake shapes and the magnitude of deflection differ in the three evaluated atmospheric boundary layers of neutral, stable and unstable thermal stability. Uncertainty to the wake deflection estimation increases for smaller temporal averaging intervals. We also consider the choice of the method to define the wake center as an uncertainty as it modifies the result. The variance of the wake deflection estimation increases with decreasing atmospheric stability. A control of the wake position in a highly convective environment is therefore not recommended.

scholarly journals Spatiotemporal Correlations in the Power Output of Wind Farms: On the Impact of Atmospheric Stability

Energies ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1486 ◽  
Author(s):  
Nicolas Tobin ◽  
Adam Lavely ◽  
Sven Schmitz ◽  
Leonardo P. Chamorro
Keyword(s):  
Power Output ◽  
Wind Farm ◽  
Statistical Significance ◽  
Atmospheric Stability ◽  
Wind Farms ◽  
Temporal Correlations ◽  
Theoretical Predictions ◽  
Power Variance ◽  
Ambient Turbulence ◽  
The Impact

The dependence of temporal correlations in the power output of wind-turbine pairs on atmospheric stability is explored using theoretical arguments and wind-farm large-eddy simulations. For this purpose, a range of five distinct stability regimes, ranging from weakly stable to moderately convective, were investigated with the same aligned wind-farm layout used among simulations. The coherence spectrum between turbine pairs in each simulation was compared to theoretical predictions. We found with high statistical significance (p < 0.01) that higher levels of atmospheric instability lead to higher coherence between turbines, with wake motions reducing correlations up to 40%. This is attributed to higher dominance of atmospheric motions over wakes in strongly unstable flows. Good agreement resulted with the use of an empirical model for wake-added turbulence to predict the variation of turbine power coherence with ambient turbulence intensity (R 2 = 0.82), though other empirical relations may be applicable. It was shown that improperly accounting for turbine–turbine correlations can substantially impact power variance estimates on the order of a factor of 4.

Sign in / Sign up

Export Citation Format

Share Document